/** * Sets the data behind this ListView. * * The adapter passed to this method may be wrapped by a {@link WrapperListAdapter}, * depending on the ListView features currently in use. For instance, adding * headers and/or footers will cause the adapter to be wrapped. * * @param adapter The ListAdapter which is responsible for maintaining the * data backing this list and for producing a view to represent an * item in that data set. * * @see #getAdapter() */ @Override public void setAdapter(ListAdapter adapter) { if (mAdapter != null && mDataSetObserver != null) { mAdapter.unregisterDataSetObserver(mDataSetObserver);//移除了与当前listview的adapter绑定数据集观察者DataSetObserver } resetList();//重置listview，主要是清除所有的view，改变header、footer的状态 mRecycler.clear(); //清除掉RecycleBin对象mRecycler中所有缓存的view，RecycleBin后面着重介绍，主要是关系到Listview中item的重用机制，它是AbsListview的一个内部类 if (mHeaderViewInfos.size() > 0|| mFooterViewInfos.size() > 0) { //判断是否有headerview和footview mAdapter = new HeaderViewListAdapter(mHeaderViewInfos, mFooterViewInfos, adapter); } else { mAdapter = adapter; } mOldSelectedPosition = INVALID_POSITION; mOldSelectedRowId = INVALID_ROW_ID; // AbsListView#setAdapter will update choice mode states. super.setAdapter(adapter); if (mAdapter != null) { mAreAllItemsSelectable = mAdapter.areAllItemsEnabled(); mOldItemCount = mItemCount; mItemCount = mAdapter.getCount(); checkFocus(); mDataSetObserver = new AdapterDataSetObserver(); //注册headerview的观察者 mAdapter.registerDataSetObserver(mDataSetObserver);//在RecycleBin对象mRecycler记录下item类型的数量 mRecycler.setViewTypeCount(mAdapter.getViewTypeCount()); int position; if (mStackFromBottom) { position = lookForSelectablePosition(mItemCount - 1, false); } else { position = lookForSelectablePosition(0, true); } setSelectedPositionInt(position);//AdapterView中的方法，记录当前的position setNextSelectedPositionInt(position);//AdapterView中的方法，记录下一个position if (mItemCount == 0) { // Nothing selected checkSelectionChanged(); } } else { mAreAllItemsSelectable = true; checkFocus(); // Nothing selected checkSelectionChanged(); } requestLayout(); } /** * Obtain the view and add it to our list of children. The view can be made * fresh, converted from an unused view, or used as is if it was in the * recycle bin. * * @param position Logical position in the list * @param y Top or bottom edge of the view to add * @param flow If flow is true, align top edge to y. If false, align bottom * edge to y. * @param childrenLeft Left edge where children should be positioned * @param selected Is this position selected? * @return View that was added */ private View makeAndAddView(int position, int y, boolean flow, int childrenLeft, boolean selected) { View child; if (!mDataChanged) { // Try to use an existing view for this position child = mRecycler.getActiveView(position); //首先是从已经回收的的view中重新激活 if (child != null) { if (ViewDebug.TRACE_RECYCLER) { ViewDebug.trace(child, ViewDebug.RecyclerTraceType.RECYCLE_FROM_ACTIVE_HEAP, position, getChildCount()); } // Found it -- we're using an existing child // This just needs to be positioned setupChild(child, position, y, flow, childrenLeft, selected, true); return child; } } //下面是listview中获取重用view的机制 // Make a new view for this position, or convert an unused view if possible child = obtainView(position, mIsScrap); // This needs to be positioned and measured setupChild(child, position, y, flow, childrenLeft, selected, mIsScrap[0]); return child; } /** * Get a view and have it show the data associated with the specified * position. This is called when we have already discovered that the view is * not available for reuse in the recycle bin. The only choices left are * converting an old view or making a new one. * * @param position The position to display * @param isScrap Array of at least 1 boolean, the first entry will become true if * the returned view was taken from the scrap heap, false if otherwise. * * @return A view displaying the data associated with the specified position */ View obtainView(int position, boolean[] isScrap) { isScrap[0] = false; View scrapView; scrapView = mRecycler.getScrapView(position); //首先是从回收站进行检查，找到相应位置的被回收的 View child; if (scrapView != null) { if (ViewDebug.TRACE_RECYCLER) { ViewDebug.trace(scrapView, ViewDebug.RecyclerTraceType.RECYCLE_FROM_SCRAP_HEAP, position, -1); } child = mAdapter.getView(position, scrapView, this); if (ViewDebug.TRACE_RECYCLER) { ViewDebug.trace(child, ViewDebug.RecyclerTraceType.BIND_VIEW, position, getChildCount()); } if (child != scrapView) { //如果重用的view和adapter获得的view是不一样的，将scrapView进行回收 mRecycler.addScrapView(scrapView, position); if (mCacheColorHint != 0) { child.setDrawingCacheBackgroundColor(mCacheColorHint); } if (ViewDebug.TRACE_RECYCLER) { ViewDebug.trace(scrapView, ViewDebug.RecyclerTraceType.MOVE_TO_SCRAP_HEAP, position, -1); } } else { isScrap[0] = true; //如果重用的view和adapter获得的view是一样的，将isScrap[0]值为true，否则默认为false child.dispatchFinishTemporaryDetach(); } } else { child = mAdapter.getView(position, null, this); //当getview中为null的时候会在getview的方法中进行新建这个view if (mCacheColorHint != 0) { child.setDrawingCacheBackgroundColor(mCacheColorHint); } if (ViewDebug.TRACE_RECYCLER) { ViewDebug.trace(child, ViewDebug.RecyclerTraceType.NEW_VIEW, position, getChildCount()); } } return child; }
