深入了解ListView（3） — 一天一点源码

总述

了解AdapterView以及AbsListView之后，再看ListView中功能的具体实现。

前言

/** * A view that shows items in a vertically scrolling list. The items * come from the {@link ListAdapter} associated with this view. * * <p>See the <a href="{@docRoot}guide/topics/ui/layout/listview.html">List View</a> * guide.</p> * * @attr ref android.R.styleable#ListView_entries * @attr ref android.R.styleable#ListView_divider * @attr ref android.R.styleable#ListView_dividerHeight * @attr ref android.R.styleable#ListView_headerDividersEnabled * @attr ref android.R.styleable#ListView_footerDividersEnabled */

这是一个将子视图显示在垂直的滚动的列表中的视图。这些子视图来自于ListAdapter的关联视图。

方法

    public class FixedViewInfo {        /** The view to add to the list */        public View view;        /** The data backing the view. This is returned from {@link ListAdapter#getItem(int)}. */        public Object data;        /** <code>true</code> if the fixed view should be selectable in the list */        public boolean isSelectable;}    private void removeFixedViewInfo(View v, ArrayList<FixedViewInfo> where) {        int len = where.size();        for (int i = 0; i < len; ++i) {            FixedViewInfo info = where.get(i);            if (info.view == v) {                where.remove(i);                break;            }        }    }

这是一个内部类，该类表示该列表(listView)中的一个固定视图。
view表示添加到list中的视图；
data表示这个视图绑定的数据；
isSelectable表示这个固定视图是否可选中。

removeFixedViewInfo方法实现的是对固定视图的移除。

    public ListView(Context context) {        this(context, null);    }    public ListView(Context context, AttributeSet attrs) {        this(context, attrs, R.attr.listViewStyle);    }    public ListView(Context context, AttributeSet attrs, int defStyleAttr) {        this(context, attrs, defStyleAttr, 0);    }    public ListView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {        super(context, attrs, defStyleAttr, defStyleRes);        final TypedArray a = context.obtainStyledAttributes(                attrs, R.styleable.ListView, defStyleAttr, defStyleRes);        final CharSequence[] entries = a.getTextArray(R.styleable.ListView_entries);        if (entries != null) {            setAdapter(new ArrayAdapter<>(context, R.layout.simple_list_item_1, entries));        }        final Drawable d = a.getDrawable(R.styleable.ListView_divider);        if (d != null) {            // Use an implicit divider height which may be explicitly            // overridden by android:dividerHeight further down.            setDivider(d);        }        final Drawable osHeader = a.getDrawable(R.styleable.ListView_overScrollHeader);        if (osHeader != null) {            setOverscrollHeader(osHeader);        }        final Drawable osFooter = a.getDrawable(R.styleable.ListView_overScrollFooter);        if (osFooter != null) {            setOverscrollFooter(osFooter);        }        // Use an explicit divider height, if specified.        if (a.hasValueOrEmpty(R.styleable.ListView_dividerHeight)) {            final int dividerHeight = a.getDimensionPixelSize(                    R.styleable.ListView_dividerHeight, 0);            if (dividerHeight != 0) {                setDividerHeight(dividerHeight);            }        }        mHeaderDividersEnabled = a.getBoolean(R.styleable.ListView_headerDividersEnabled, true);        mFooterDividersEnabled = a.getBoolean(R.styleable.ListView_footerDividersEnabled, true);        a.recycle();    }

ListView的四个构造函数，初始化构造ListView的一些参数。

    public int getMaxScrollAmount() {        return (int) (MAX_SCROLL_FACTOR * (mBottom - mTop));    }

获得最大滑动参数。

    private void adjustViewsUpOrDown() {        final int childCount = getChildCount();        int delta;        if (childCount > 0) {            View child;            if (!mStackFromBottom) {                // Uh-oh -- we came up short. Slide all views up to make them                // align with the top                child = getChildAt(0);                delta = child.getTop() - mListPadding.top;                if (mFirstPosition != 0) {                    // It's OK to have some space above the first item if it is                    // part of the vertical spacing                    delta -= mDividerHeight;                }                if (delta < 0) {                    // We only are looking to see if we are too low, not too high                    delta = 0;                }            } else {                // we are too high, slide all views down to align with bottom                child = getChildAt(childCount - 1);                delta = child.getBottom() - (getHeight() - mListPadding.bottom);                if (mFirstPosition + childCount < mItemCount) {                    // It's OK to have some space below the last item if it is                    // part of the vertical spacing                    delta += mDividerHeight;                }                if (delta > 0) {                    delta = 0;                }            }            if (delta != 0) {                offsetChildrenTopAndBottom(-delta);            }        }    }

调整上下边界，确认ListView的上下界，确保ListView处于正确的位置。

    public void addHeaderView(View v, Object data, boolean isSelectable) {        final FixedViewInfo info = new FixedViewInfo();        info.view = v;        info.data = data;        info.isSelectable = isSelectable;        mHeaderViewInfos.add(info);        mAreAllItemsSelectable &= isSelectable;        // Wrap the adapter if it wasn't already wrapped.        if (mAdapter != null) {            if (!(mAdapter instanceof HeaderViewListAdapter)) {                wrapHeaderListAdapterInternal();            }            // In the case of re-adding a header view, or adding one later on,            // we need to notify the observer.            if (mDataSetObserver != null) {                mDataSetObserver.onChanged();            }        }    }    public void addHeaderView(View v) {        addHeaderView(v, null, true);    }

添加一个头视图。必须在设置适配器之前添加。
此外还有removeHeader(View v)方法移除头视图。
removeHeader方法中调用的是removeFixedViewInfo(View v, ArrayList where)方法，进行对固定视图的移除。

    public void addFooterView(View v, Object data, boolean isSelectable) {        final FixedViewInfo info = new FixedViewInfo();        info.view = v;        info.data = data;        info.isSelectable = isSelectable;        mFooterViewInfos.add(info);        mAreAllItemsSelectable &= isSelectable;        // Wrap the adapter if it wasn't already wrapped.        if (mAdapter != null) {            if (!(mAdapter instanceof HeaderViewListAdapter)) {                wrapHeaderListAdapterInternal();            }            // In the case of re-adding a footer view, or adding one later on,            // we need to notify the observer.            if (mDataSetObserver != null) {                mDataSetObserver.onChanged();            }        }}    public void addFooterView(View v) {        addFooterView(v, null, true);}public boolean removeFooterView(View v) {…}

添加足视图和移除足视图。同样只能在设置adapter之前调用。

    private void clearRecycledState(ArrayList<FixedViewInfo> infos) {        if (infos != null) {            final int count = infos.size();            for (int i = 0; i < count; i++) {                final View child = infos.get(i).view;                final LayoutParams p = (LayoutParams) child.getLayoutParams();                if (p != null) {                    p.recycledHeaderFooter = false;                }            }        }    }

清除回收状态。在resetList()中调用。（该方法为ListView重写的AbsListView中的方法，当列表为空时调用，用于清除列表中所有视图）

    private boolean showingTopFadingEdge() {        final int listTop = mScrollY + mListPadding.top;        return (mFirstPosition > 0) || (getChildAt(0).getTop() > listTop);    }    private boolean showingBottomFadingEdge() {        final int childCount = getChildCount();        final int bottomOfBottomChild = getChildAt(childCount - 1).getBottom();        final int lastVisiblePosition = mFirstPosition + childCount - 1;        final int listBottom = mScrollY + getHeight() - mListPadding.bottom;        return (lastVisiblePosition < mItemCount - 1)                         || (bottomOfBottomChild < listBottom);    }

显示顶部边缘；显示底部边缘。

    private View fillDown(int pos, int nextTop) {        View selectedView = null;        int end = (mBottom - mTop);        if ((mGroupFlags & CLIP_TO_PADDING_MASK) == CLIP_TO_PADDING_MASK) {            end -= mListPadding.bottom;        }        while (nextTop < end && pos < mItemCount) {            // is this the selected item?            boolean selected = pos == mSelectedPosition;            View child = makeAndAddView(pos, nextTop, true, mListPadding.left, selected);            nextTop = child.getBottom() + mDividerHeight;            if (selected) {                selectedView = child;            }            pos++;        }        setVisibleRangeHint(mFirstPosition, mFirstPosition + getChildCount() - 1);        return selectedView;    }

在指定位置向下填充列表，返回的是我们在绘制过程被中选中的视图。

    private View fillUp(int pos, int nextBottom) {        View selectedView = null;        int end = 0;        if ((mGroupFlags & CLIP_TO_PADDING_MASK) == CLIP_TO_PADDING_MASK) {            end = mListPadding.top;        }        while (nextBottom > end && pos >= 0) {            // is this the selected item?            boolean selected = pos == mSelectedPosition;            View child = makeAndAddView(pos, nextBottom, false, mListPadding.left, selected);            nextBottom = child.getTop() - mDividerHeight;            if (selected) {                selectedView = child;            }            pos--;        }        mFirstPosition = pos + 1;        setVisibleRangeHint(mFirstPosition, mFirstPosition + getChildCount() - 1);        return selectedView;    }

在指定位置向上填充列表，返回的是我们在绘制过程被中选中的视图。
此外还有fillFromTop从顶部开始填充，fillFromMiddle从屏幕中部开始填充。
fillAboveAndBelow(View sel, int position)，如果被选中的视图已经被放置了，将填充该视图以下的可见区域。

    private View fillFromSelection(int selectedTop, int childrenTop, int childrenBottom) {        int fadingEdgeLength = getVerticalFadingEdgeLength();        final int selectedPosition = mSelectedPosition;        View sel;        final int topSelectionPixel = getTopSelectionPixel(childrenTop, fadingEdgeLength,                selectedPosition);        final int bottomSelectionPixel = getBottomSelectionPixel(childrenBottom, fadingEdgeLength,                selectedPosition);        sel = makeAndAddView(selectedPosition, selectedTop, true, mListPadding.left, true);        // Some of the newly selected item extends below the bottom of the list        if (sel.getBottom() > bottomSelectionPixel) {            // Find space available above the selection into which we can scroll            // upwards            final int spaceAbove = sel.getTop() - topSelectionPixel;            // Find space required to bring the bottom of the selected item            // fully into view            final int spaceBelow = sel.getBottom() - bottomSelectionPixel;            final int offset = Math.min(spaceAbove, spaceBelow);            // Now offset the selected item to get it into view            sel.offsetTopAndBottom(-offset);        } else if (sel.getTop() < topSelectionPixel) {            // Find space required to bring the top of the selected item fully            // into view            final int spaceAbove = topSelectionPixel - sel.getTop();            // Find space available below the selection into which we can scroll            // downwards            final int spaceBelow = bottomSelectionPixel - sel.getBottom();            final int offset = Math.min(spaceAbove, spaceBelow);            // Offset the selected item to get it into view            sel.offsetTopAndBottom(offset);        }        // Fill in views above and below        fillAboveAndBelow(sel, selectedPosition);        if (!mStackFromBottom) {            correctTooHigh(getChildCount());        } else {            correctTooLow(getChildCount());        }        return sel;    }

fillFromSelection(int selectedTop, int childrenTop, int childrenBottom) 根据新选择的特定位置填充网格。可以移动位置，使其不与已褪色的边缘相交。然后将网格向上和向下填充。

    private int getBottomSelectionPixel(int childrenBottom, int fadingEdgeLength,            int selectedPosition) {        int bottomSelectionPixel = childrenBottom;        if (selectedPosition != mItemCount - 1) {            bottomSelectionPixel -= fadingEdgeLength;        }        return bottomSelectionPixel;    }    private int getTopSelectionPixel(int childrenTop, int fadingEdgeLength, int selectedPosition) {        // first pixel we can draw the selection into        int topSelectionPixel = childrenTop;        if (selectedPosition > 0) {            topSelectionPixel += fadingEdgeLength;        }        return topSelectionPixel;    }

得到通过计算获得的底部（顶部）绘制位置。

    private View moveSelection(View oldSel, View newSel, int delta, int childrenTop,            int childrenBottom) {        int fadingEdgeLength = getVerticalFadingEdgeLength();        final int selectedPosition = mSelectedPosition;        View sel;        final int topSelectionPixel = getTopSelectionPixel(childrenTop, fadingEdgeLength,                selectedPosition);        final int bottomSelectionPixel = getBottomSelectionPixel(childrenTop, fadingEdgeLength,                selectedPosition);        if (delta > 0) {            /*             * Case 1: Scrolling down.             */            /*             *     Before           After             *    |       |        |       |             *    +-------+        +-------+             *    |   A   |        |   A   |             *    |   1   |   =>   +-------+             *    +-------+        |   B   |             *    |   B   |        |   2   |             *    +-------+        +-------+             *    |       |        |       |             *             *    Try to keep the top of the previously selected item where it was.             *    oldSel = A             *    sel = B             */            // Put oldSel (A) where it belongs            oldSel = makeAndAddView(selectedPosition - 1, oldSel.getTop(), true,                    mListPadding.left, false);            final int dividerHeight = mDividerHeight;            // Now put the new selection (B) below that            sel = makeAndAddView(selectedPosition, oldSel.getBottom() + dividerHeight, true,                    mListPadding.left, true);            // Some of the newly selected item extends below the bottom of the list            if (sel.getBottom() > bottomSelectionPixel) {                // Find space available above the selection into which we can scroll upwards                int spaceAbove = sel.getTop() - topSelectionPixel;                // Find space required to bring the bottom of the selected item fully into view                int spaceBelow = sel.getBottom() - bottomSelectionPixel;                // Don't scroll more than half the height of the list                int halfVerticalSpace = (childrenBottom - childrenTop) / 2;                int offset = Math.min(spaceAbove, spaceBelow);                offset = Math.min(offset, halfVerticalSpace);                // We placed oldSel, so offset that item                oldSel.offsetTopAndBottom(-offset);                // Now offset the selected item to get it into view                sel.offsetTopAndBottom(-offset);            }            // Fill in views above and below            if (!mStackFromBottom) {                fillUp(mSelectedPosition - 2, sel.getTop() - dividerHeight);                adjustViewsUpOrDown();                fillDown(mSelectedPosition + 1, sel.getBottom() + dividerHeight);            } else {                fillDown(mSelectedPosition + 1, sel.getBottom() + dividerHeight);                adjustViewsUpOrDown();                fillUp(mSelectedPosition - 2, sel.getTop() - dividerHeight);            }        } else if (delta < 0) {            /*             * Case 2: Scrolling up.             */            /*             *     Before           After             *    |       |        |       |             *    +-------+        +-------+             *    |   A   |        |   A   |             *    +-------+   =>   |   1   |             *    |   B   |        +-------+             *    |   2   |        |   B   |             *    +-------+        +-------+             *    |       |        |       |             *             *    Try to keep the top of the item about to become selected where it was.             *    newSel = A             *    olSel = B             */            if (newSel != null) {                // Try to position the top of newSel (A) where it was before it was selected                sel = makeAndAddView(selectedPosition, newSel.getTop(), true, mListPadding.left,                        true);            } else {                // If (A) was not on screen and so did not have a view, position                // it above the oldSel (B)                sel = makeAndAddView(selectedPosition, oldSel.getTop(), false, mListPadding.left,                        true);            }            // Some of the newly selected item extends above the top of the list            if (sel.getTop() < topSelectionPixel) {                // Find space required to bring the top of the selected item fully into view                int spaceAbove = topSelectionPixel - sel.getTop();               // Find space available below the selection into which we can scroll downwards                int spaceBelow = bottomSelectionPixel - sel.getBottom();                // Don't scroll more than half the height of the list                int halfVerticalSpace = (childrenBottom - childrenTop) / 2;                int offset = Math.min(spaceAbove, spaceBelow);                offset = Math.min(offset, halfVerticalSpace);                // Offset the selected item to get it into view                sel.offsetTopAndBottom(offset);            }            // Fill in views above and below            fillAboveAndBelow(sel, selectedPosition);        } else {            int oldTop = oldSel.getTop();            /*             * Case 3: Staying still             */            sel = makeAndAddView(selectedPosition, oldTop, true, mListPadding.left, true);            // We're staying still...            if (oldTop < childrenTop) {                // ... but the top of the old selection was off screen.                // (This can happen if the data changes size out from under us)                int newBottom = sel.getBottom();                if (newBottom < childrenTop + 20) {                    // Not enough visible -- bring it onscreen                    sel.offsetTopAndBottom(childrenTop - sel.getTop());                }            }            // Fill in views above and below            fillAboveAndBelow(sel, selectedPosition);        }        return sel;    }

根据向上或者向下滑动，根据新的被选择的视图填充列表。

    private class FocusSelector implements Runnable {        // the selector is waiting to set selection on the list view        private static final int STATE_SET_SELECTION = 1;        // the selector set the selection on the list view, waiting for a layoutChildren pass        private static final int STATE_WAIT_FOR_LAYOUT = 2;        // the selector's selection has been honored and it is waiting to request focus on the        // target child.        private static final int STATE_REQUEST_FOCUS = 3;        private int mAction;        private int mPosition;        private int mPositionTop;        FocusSelector setupForSetSelection(int position, int top) {            mPosition = position;            mPositionTop = top;            mAction = STATE_SET_SELECTION;            return this;        }        public void run() {            if (mAction == STATE_SET_SELECTION) {                setSelectionFromTop(mPosition, mPositionTop);                mAction = STATE_WAIT_FOR_LAYOUT;            } else if (mAction == STATE_REQUEST_FOCUS) {                final int childIndex = mPosition - mFirstPosition;                final View child = getChildAt(childIndex);                if (child != null) {                    child.requestFocus();                }                mAction = -1;            }        }        @Nullable Runnable setupFocusIfValid(int position) {            if (mAction != STATE_WAIT_FOR_LAYOUT || position != mPosition) {                return null;            }            mAction = STATE_REQUEST_FOCUS;            return this;        }        void onLayoutComplete() {            if (mAction == STATE_WAIT_FOR_LAYOUT) {                mAction = -1;            }        }    }

一个内部类，定义了一个焦点选择器。

   private void measureScrapChild(View child, int position, int widthMeasureSpec, int heightHint) {        LayoutParams p = (LayoutParams) child.getLayoutParams();        if (p == null) {            p = (AbsListView.LayoutParams) generateDefaultLayoutParams();            child.setLayoutParams(p);        }        p.viewType = mAdapter.getItemViewType(position);        p.isEnabled = mAdapter.isEnabled(position);        p.forceAdd = true;        final int childWidthSpec = ViewGroup.getChildMeasureSpec(widthMeasureSpec,                mListPadding.left + mListPadding.right, p.width);        final int lpHeight = p.height;        final int childHeightSpec;        if (lpHeight > 0) {            childHeightSpec = MeasureSpec.makeMeasureSpec(lpHeight, MeasureSpec.EXACTLY);        } else {            childHeightSpec = MeasureSpec.makeSafeMeasureSpec(heightHint, MeasureSpec.UNSPECIFIED);        }        child.measure(childWidthSpec, childHeightSpec);        // Since this view was measured directly aginst the parent measure        // spec, we must measure it again before reuse.        child.forceLayout();    }

测量失效的子视图。

    private View fillSpecific(int position, int top) {        boolean tempIsSelected = position == mSelectedPosition;        View temp = makeAndAddView(position, top, true, mListPadding.left, tempIsSelected);        // Possibly changed again in fillUp if we add rows above this one.        mFirstPosition = position;        View above;        View below;        final int dividerHeight = mDividerHeight;        if (!mStackFromBottom) {            above = fillUp(position - 1, temp.getTop() - dividerHeight);            // This will correct for the top of the first view not touching the top of the list            adjustViewsUpOrDown();            below = fillDown(position + 1, temp.getBottom() + dividerHeight);            int childCount = getChildCount();            if (childCount > 0) {                correctTooHigh(childCount);            }        } else {            below = fillDown(position + 1, temp.getBottom() + dividerHeight);            // This will correct for the bottom of the last view not touching the bottom of the list            adjustViewsUpOrDown();            above = fillUp(position - 1, temp.getTop() - dividerHeight);            int childCount = getChildCount();            if (childCount > 0) {                 correctTooLow(childCount);            }        }        if (tempIsSelected) {            return temp;        } else if (above != null) {            return above;        } else {            return below;        }    }

填充一个具体的子视图到屏幕具体的位置上。

    private void correctTooHigh(int childCount) {        // First see if the last item is visible. If it is not, it is OK for the        // top of the list to be pushed up.        int lastPosition = mFirstPosition + childCount - 1;        if (lastPosition == mItemCount - 1 && childCount > 0) {            // Get the last child ...            final View lastChild = getChildAt(childCount - 1);            // ... and its bottom edge            final int lastBottom = lastChild.getBottom();            // This is bottom of our drawable area            final int end = (mBottom - mTop) - mListPadding.bottom;            // This is how far the bottom edge of the last view is from the bottom of the            // drawable area            int bottomOffset = end - lastBottom;            View firstChild = getChildAt(0);            final int firstTop = firstChild.getTop();            // Make sure we are 1) Too high, and 2) Either there are more rows above the            // first row or the first row is scrolled off the top of the drawable area            if (bottomOffset > 0 && (mFirstPosition > 0 || firstTop < mListPadding.top))  {                if (mFirstPosition == 0) {                    // Don't pull the top too far down                    bottomOffset = Math.min(bottomOffset, mListPadding.top - firstTop);                }                // Move everything down                offsetChildrenTopAndBottom(bottomOffset);                if (mFirstPosition > 0) {                    // Fill the gap that was opened above mFirstPosition with more rows, if                    // possible                    fillUp(mFirstPosition - 1, firstChild.getTop() - mDividerHeight);                    // Close up the remaining gap                    adjustViewsUpOrDown();                }            }        }    }

检测是否将底部滑动太高(当没有这个需求是)，即触底反弹。当回复正常底部显示时，将所有视图正确的显示。还有一个correctTooLow(int childCount)检测是否将底部拖的过低。

@Overrideprotected void layoutChildren() {…}

重写了AbsListView的layoutChildren方法。将子布局填充了进去，并实现了listView的回收等。

    private void removeUnusedFixedViews(@Nullable List<FixedViewInfo> infoList) {        if (infoList == null) {            return;        }        for (int i = infoList.size() - 1; i >= 0; i--) {            final FixedViewInfo fixedViewInfo = infoList.get(i);            final View view = fixedViewInfo.view;            final LayoutParams lp = (LayoutParams) view.getLayoutParams();            if (view.getParent() == null && lp != null && lp.recycledHeaderFooter) {                removeDetachedView(view, false);                lp.recycledHeaderFooter = false;            }        }    }

移除不被使用的固定视图。当头视图/足视图没有像其他视图一样已失效或缓存，但他们确实接触了与这个ViewGroup的绑定(当前listView)时，在布局被操作后调用此方法对其移除。

    private View makeAndAddView(int position, int y, boolean flow, int childrenLeft,            boolean selected) {        if (!mDataChanged) {            // Try to use an existing view for this position.            final View activeView = mRecycler.getActiveView(position);            if (activeView != null) {                // Found it. We're reusing an existing child, so it just needs                // to be positioned like a scrap view.                setupChild(activeView, position, y, flow, childrenLeft, selected, true);                return activeView;            }        }        // Make a new view for this position, or convert an unused view if        // possible.        final View child = obtainView(position, mIsScrap);        // This needs to be positioned and measured.        setupChild(child, position, y, flow, childrenLeft, selected, mIsScrap[0]);        return child;    }

创建一个视图对象，并将其添加到我们list的子布局中。这个视图可以是新建的，也可以是不被使用的视图转换的，以及在回收站中的视图的复用。

    private void setupChild(View child, int position, int y, boolean flowDown, int childrenLeft,            boolean selected, boolean isAttachedToWindow) {        Trace.traceBegin(Trace.TRACE_TAG_VIEW, "setupListItem");        final boolean isSelected = selected && shouldShowSelector();        final boolean updateChildSelected = isSelected != child.isSelected();        final int mode = mTouchMode;        final boolean isPressed = mode > TOUCH_MODE_DOWN && mode < TOUCH_MODE_SCROLL                && mMotionPosition == position;        final boolean updateChildPressed = isPressed != child.isPressed();        final boolean needToMeasure = !isAttachedToWindow || updateChildSelected                || child.isLayoutRequested();        // Respect layout params that are already in the view. Otherwise make        // some up...        AbsListView.LayoutParams p = (AbsListView.LayoutParams) child.getLayoutParams();        if (p == null) {            p = (AbsListView.LayoutParams) generateDefaultLayoutParams();        }        p.viewType = mAdapter.getItemViewType(position);        p.isEnabled = mAdapter.isEnabled(position);        // Set up view state before attaching the view, since we may need to        // rely on the jumpDrawablesToCurrentState() call that occurs as part        // of view attachment.        if (updateChildSelected) {            child.setSelected(isSelected);        }        if (updateChildPressed) {            child.setPressed(isPressed);        }        if (mChoiceMode != CHOICE_MODE_NONE && mCheckStates != null) {            if (child instanceof Checkable) {                ((Checkable) child).setChecked(mCheckStates.get(position));            } else if (getContext().getApplicationInfo().targetSdkVersion                    >= android.os.Build.VERSION_CODES.HONEYCOMB) {                child.setActivated(mCheckStates.get(position));            }        }        if ((isAttachedToWindow && !p.forceAdd) || (p.recycledHeaderFooter                && p.viewType == AdapterView.ITEM_VIEW_TYPE_HEADER_OR_FOOTER)) {            attachViewToParent(child, flowDown ? -1 : 0, p);            // If the view was previously attached for a different position,            // then manually jump the drawables.            if (isAttachedToWindow                    && (((AbsListView.LayoutParams) child.getLayoutParams()).scrappedFromPosition)                            != position) {                child.jumpDrawablesToCurrentState();            }        } else {            p.forceAdd = false;            if (p.viewType == AdapterView.ITEM_VIEW_TYPE_HEADER_OR_FOOTER) {                p.recycledHeaderFooter = true;            }            addViewInLayout(child, flowDown ? -1 : 0, p, true);            // add view in layout will reset the RTL properties. We have to re-resolve them            child.resolveRtlPropertiesIfNeeded();        }        if (needToMeasure) {            final int childWidthSpec = ViewGroup.getChildMeasureSpec(mWidthMeasureSpec,                    mListPadding.left + mListPadding.right, p.width);            final int lpHeight = p.height;            final int childHeightSpec;            if (lpHeight > 0) {                childHeightSpec = MeasureSpec.makeMeasureSpec(lpHeight, MeasureSpec.EXACTLY);            } else {                childHeightSpec = MeasureSpec.makeSafeMeasureSpec(getMeasuredHeight(),                        MeasureSpec.UNSPECIFIED);            }            child.measure(childWidthSpec, childHeightSpec);        } else {            cleanupLayoutState(child);        }        final int w = child.getMeasuredWidth();        final int h = child.getMeasuredHeight();        final int childTop = flowDown ? y : y - h;        if (needToMeasure) {            final int childRight = childrenLeft + w;            final int childBottom = childTop + h;            child.layout(childrenLeft, childTop, childRight, childBottom);        } else {            child.offsetLeftAndRight(childrenLeft - child.getLeft());            child.offsetTopAndBottom(childTop - child.getTop());        }        if (mCachingStarted && !child.isDrawingCacheEnabled()) {            child.setDrawingCacheEnabled(true);        }        Trace.traceEnd(Trace.TRACE_TAG_VIEW);    }

添加一个视图作为子视图，确认其已经被测量(如果要求)，以及其具体位置。

    int lookForSelectablePositionAfter(int current, int position, boolean lookDown) {        final ListAdapter adapter = mAdapter;        if (adapter == null || isInTouchMode()) {            return INVALID_POSITION;        }        // First check after the starting position in the specified direction.        final int after = lookForSelectablePosition(position, lookDown);        if (after != INVALID_POSITION) {            return after;        }        // Then check between the starting position and the current position.        final int count = adapter.getCount();        current = MathUtils.constrain(current, -1, count - 1);        if (lookDown) {            position = Math.min(position - 1, count - 1);            while ((position > current) && !adapter.isEnabled(position)) {                position--;            }            if (position <= current) {                return INVALID_POSITION;            }        } else {            position = Math.max(0, position + 1);            while ((position < current) && !adapter.isEnabled(position)) {                position++;            }            if (position >= current) {                return INVALID_POSITION;            }        }        return position;    }

找到一个可以点击的位置。如果从起始位置的一个确定的方向上没有可点击的位置，就从起始位置相反的方向查找到当前位置。

    public void setSelectionAfterHeaderView() {        final int count = getHeaderViewsCount();        if (count > 0) {            mNextSelectedPosition = 0;            return;        }        if (mAdapter != null) {            setSelection(count);        } else {            mNextSelectedPosition = count;            mLayoutMode = LAYOUT_SET_SELECTION;        }    }````给头视图后的，列表的第一个条目设置可选状态。<div class="se-preview-section-delimiter"></div>

private boolean commonKey(int keyCode, int count, KeyEvent event) {    if (mAdapter == null || !isAttachedToWindow()) {        return false;    }    if (mDataChanged) {        layoutChildren();    }    boolean handled = false;    int action = event.getAction();    if (KeyEvent.isConfirmKey(keyCode)            && event.hasNoModifiers() && action != KeyEvent.ACTION_UP) {        handled = resurrectSelectionIfNeeded();        if (!handled && event.getRepeatCount() == 0 && getChildCount() > 0) {            keyPressed();            handled = true;        }    }

判断键状态，并重写android.view.KeyEvent.Callback的onKeyDown、onKeyUp和onKeyMultiple将键的状态进行返回。(接口回调)<div class="se-preview-section-delimiter"></div>

boolean pageScroll(int direction) {    final int nextPage;    final boolean down;    if (direction == FOCUS_UP) {        nextPage = Math.max(0, mSelectedPosition - getChildCount() - 1);        down = false;    } else if (direction == FOCUS_DOWN) {        nextPage = Math.min(mItemCount - 1, mSelectedPosition + getChildCount() - 1);        down = true;    } else {        return false;    }    if (nextPage >= 0) {        final int position = lookForSelectablePositionAfter(mSelectedPosition, nextPage, down);        if (position >= 0) {            mLayoutMode = LAYOUT_SPECIFIC;            mSpecificTop = mPaddingTop + getVerticalFadingEdgeLength();            if (down && (position > (mItemCount - getChildCount()))) {                mLayoutMode = LAYOUT_FORCE_BOTTOM;            }            if (!down && (position < getChildCount())) {                mLayoutMode = LAYOUT_FORCE_TOP;            }            setSelectionInt(position);            invokeOnItemScrollListener();            if (!awakenScrollBars()) {                invalidate();            }            return true;        }    }    return false;}

需要传入一个int类型的方向，将屏幕上的子视图向这个方向滑动。<div class="se-preview-section-delimiter"></div>

boolean fullScroll(int direction) {    boolean moved = false;    if (direction == FOCUS_UP) {        if (mSelectedPosition != 0) {            final int position = lookForSelectablePositionAfter(mSelectedPosition, 0, true);            if (position >= 0) {                mLayoutMode = LAYOUT_FORCE_TOP;                setSelectionInt(position);                invokeOnItemScrollListener();            }            moved = true;        }    } else if (direction == FOCUS_DOWN) {        final int lastItem = (mItemCount - 1);        if (mSelectedPosition < lastItem) {            final int position = lookForSelectablePositionAfter(                    mSelectedPosition, lastItem, false);            if (position >= 0) {                mLayoutMode = LAYOUT_FORCE_BOTTOM;                setSelectionInt(position);                invokeOnItemScrollListener();            }            moved = true;        }    }    if (moved && !awakenScrollBars()) {        awakenScrollBars();        invalidate();    }    return moved;}

传入一个int类型的方向，移动到第一个或者最后一个子视图位置。<div class="se-preview-section-delimiter"></div>

private boolean handleHorizontalFocusWithinListItem(int direction) {    if (direction != View.FOCUS_LEFT && direction != View.FOCUS_RIGHT)  {        throw new IllegalArgumentException("direction must be one of"                + " {View.FOCUS_LEFT, View.FOCUS_RIGHT}");    }    final int numChildren = getChildCount();    if (mItemsCanFocus && numChildren > 0 && mSelectedPosition != INVALID_POSITION) {        final View selectedView = getSelectedView();        if (selectedView != null && selectedView.hasFocus() &&                selectedView instanceof ViewGroup) {            final View currentFocus = selectedView.findFocus();            final View nextFocus = FocusFinder.getInstance().findNextFocus(                    (ViewGroup) selectedView, currentFocus, direction);            if (nextFocus != null) {                // do the math to get interesting rect in next focus' coordinates                Rect focusedRect = mTempRect;                if (currentFocus != null) {                    currentFocus.getFocusedRect(focusedRect);                    offsetDescendantRectToMyCoords(currentFocus, focusedRect);                    offsetRectIntoDescendantCoords(nextFocus, focusedRect);                } else {                    focusedRect = null;                }                if (nextFocus.requestFocus(direction, focusedRect)) {                    return true;                }            }            // we are blocking the key from being handled (by returning true)            // if the global result is going to be some other view within this            // list.  this is to acheive the overall goal of having            // horizontal d-pad navigation remain in the current item.            final View globalNextFocus = FocusFinder.getInstance().findNextFocus(                    (ViewGroup) getRootView(), currentFocus, direction);            if (globalNextFocus != null) {                return isViewAncestorOf(globalNextFocus, this);            }        }    }    return false;}

避免横向使子视图被选中的状态发生改变。<div class="se-preview-section-delimiter"></div>

boolean arrowScroll(int direction) {    try {        mInLayout = true;        final boolean handled = arrowScrollImpl(direction);        if (handled) {            playSoundEffect(SoundEffectConstants.getContantForFocusDirection(direction));        }        return handled;    } finally {        mInLayout = false;    }}

滑动到上一个或者下一个子视图，根据传入的direction确定方向。<div class="se-preview-section-delimiter"></div>

private final int nextSelectedPositionForDirection(        View selectedView, int selectedPos, int direction) {    int nextSelected;    if (direction == View.FOCUS_DOWN) {        final int listBottom = getHeight() - mListPadding.bottom;        if (selectedView != null && selectedView.getBottom() <= listBottom) {            nextSelected = selectedPos != INVALID_POSITION && selectedPos >= mFirstPosition ?                    selectedPos + 1 :                    mFirstPosition;        } else {            return INVALID_POSITION;        }    } else {        final int listTop = mListPadding.top;        if (selectedView != null && selectedView.getTop() >= listTop) {            final int lastPos = mFirstPosition + getChildCount() - 1;            nextSelected = selectedPos != INVALID_POSITION && selectedPos <= lastPos ?                    selectedPos - 1 :                    lastPos;        } else {            return INVALID_POSITION;        }    }    if (nextSelected < 0 || nextSelected >= mAdapter.getCount()) {        return INVALID_POSITION;    }    return lookForSelectablePosition(nextSelected, direction == View.FOCUS_DOWN);}/** * Handle an arrow scroll going up or down.  Take into account whether items are selectable, * whether there are focusable items etc. * * @param direction Either {@link android.view.View#FOCUS_UP} or {@link android.view.View#FOCUS_DOWN}. * @return Whether any scrolling, selection or focus change occured. */private boolean arrowScrollImpl(int direction) {    if (getChildCount() <= 0) {        return false;    }    View selectedView = getSelectedView();    int selectedPos = mSelectedPosition;    int nextSelectedPosition = nextSelectedPositionForDirection(selectedView, selectedPos, direction);    int amountToScroll = amountToScroll(direction, nextSelectedPosition);    // if we are moving focus, we may OVERRIDE the default behavior    final ArrowScrollFocusResult focusResult = mItemsCanFocus ? arrowScrollFocused(direction) : null;    if (focusResult != null) {        nextSelectedPosition = focusResult.getSelectedPosition();        amountToScroll = focusResult.getAmountToScroll();    }    boolean needToRedraw = focusResult != null;    if (nextSelectedPosition != INVALID_POSITION) {        handleNewSelectionChange(selectedView, direction, nextSelectedPosition, focusResult != null);        setSelectedPositionInt(nextSelectedPosition);        setNextSelectedPositionInt(nextSelectedPosition);        selectedView = getSelectedView();        selectedPos = nextSelectedPosition;        if (mItemsCanFocus && focusResult == null) {            // there was no new view found to take focus, make sure we            // don't leave focus with the old selection            final View focused = getFocusedChild();            if (focused != null) {                focused.clearFocus();            }        }        needToRedraw = true;        checkSelectionChanged();    }    if (amountToScroll > 0) {        scrollListItemsBy((direction == View.FOCUS_UP) ? amountToScroll : -amountToScroll);        needToRedraw = true;    }    // if we didn't find a new focusable, make sure any existing focused    // item that was panned off screen gives up focus.    if (mItemsCanFocus && (focusResult == null)            && selectedView != null && selectedView.hasFocus()) {        final View focused = selectedView.findFocus();        if (focused != null) {            if (!isViewAncestorOf(focused, this) || distanceToView(focused) > 0) {                focused.clearFocus();            }        }    }    // if  the current selection is panned off, we need to remove the selection    if (nextSelectedPosition == INVALID_POSITION && selectedView != null            && !isViewAncestorOf(selectedView, this)) {        selectedView = null;        hideSelector();        // but we don't want to set the ressurect position (that would make subsequent        // unhandled key events bring back the item we just scrolled off!)        mResurrectToPosition = INVALID_POSITION;    }    if (needToRedraw) {        if (selectedView != null) {            positionSelectorLikeFocus(selectedPos, selectedView);            mSelectedTop = selectedView.getTop();        }        if (!awakenScrollBars()) {            invalidate();        }        invokeOnItemScrollListener();        return true;    }    return false;}

这两个方法是对移动一个位置的实现，将子视图的所有属性状态也进行传递。<div class="se-preview-section-delimiter"></div>

private void handleNewSelectionChange(View selectedView, int direction, int newSelectedPosition,        boolean newFocusAssigned) {    if (newSelectedPosition == INVALID_POSITION) {        throw new IllegalArgumentException("newSelectedPosition needs to be valid");    }    // whether or not we are moving down or up, we want to preserve the    // top of whatever view is on top:    // - moving down: the view that had selection    // - moving up: the view that is getting selection    View topView;    View bottomView;    int topViewIndex, bottomViewIndex;    boolean topSelected = false;    final int selectedIndex = mSelectedPosition - mFirstPosition;    final int nextSelectedIndex = newSelectedPosition - mFirstPosition;    if (direction == View.FOCUS_UP) {        topViewIndex = nextSelectedIndex;        bottomViewIndex = selectedIndex;        topView = getChildAt(topViewIndex);        bottomView = selectedView;        topSelected = true;    } else {        topViewIndex = selectedIndex;        bottomViewIndex = nextSelectedIndex;        topView = selectedView;        bottomView = getChildAt(bottomViewIndex);    }    final int numChildren = getChildCount();    // start with top view: is it changing size?    if (topView != null) {        topView.setSelected(!newFocusAssigned && topSelected);        measureAndAdjustDown(topView, topViewIndex, numChildren);    }    // is the bottom view changing size?    if (bottomView != null) {        bottomView.setSelected(!newFocusAssigned && !topSelected);        measureAndAdjustDown(bottomView, bottomViewIndex, numChildren);    }}

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当选择的视图改变时，可能造成视图大小的改变。如果造成了大小的改变，我们需要取消一些视图的显示，然后重新绘制适当的布局。