Android API：自定义ViewGroup

 无论是出于项目功能需求还是出于界面美观，或者是因为项目中对控件进行封装等，自定义View在我们开发中是非常常见的， Android官方DEMO中也提供了自定义View的例子，今天学习的是自定义ViewGroup.

public class CustomLayout extends ViewGroup {    /** 子控件离左边的距离 */    private int mLeftWidth;    /** 子控件离左边的距离 */    private int mRightWidth;    /** 计算子控件容器的范围 */    private final Rect mTmpContainerRect = new Rect();    /** 计算子控件的范围 */    private final Rect mTmpChildRect = new Rect();    /*     * View的三个构造函数     */    public CustomLayout(Context context) {        super(context);    }    public CustomLayout(Context context, AttributeSet attrs) {        this(context, attrs, 0);    }    public CustomLayout(Context context, AttributeSet attrs, int defStyle) {        super(context, attrs, defStyle);    }    /**     * 任何不滚动的布局管理器都应该像这样重写该方法     */    @Override    public boolean shouldDelayChildPressedState() {        return false;    }    /**     * 测量（子）控件大小     */    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        // 子控件数量        int count = getChildCount();        mLeftWidth = 0;        mRightWidth = 0;        // 设置最大高度，最大宽度及状态        int maxHeight = 0;        int maxWidth = 0;        int childState = 0;        // 遍历所有子控件，分别进行测量        for (int i = 0; i < count; i++) {            final View child = getChildAt(i);            if (child.getVisibility() != GONE) {                // 测量子控件：某一个子view宽及高,                // 内部加上了viewGroup的padding值、margin值和传入的宽高widthUsed、heightUsed                measureChildWithMargins(child, widthMeasureSpec, 0,                        heightMeasureSpec, 0);                // 通过LayoutParams来设置大小                final LayoutParams lp = (LayoutParams) child.getLayoutParams();                if (lp.position == LayoutParams.POSITION_LEFT) {                    mLeftWidth += Math.max(maxWidth, child.getMeasuredWidth()                            + lp.leftMargin + lp.rightMargin);                } else if (lp.position == LayoutParams.POSITION_RIGHT) {                    mRightWidth += Math.max(maxWidth, child.getMeasuredWidth()                            + lp.leftMargin + lp.rightMargin);                } else {                    maxWidth = Math.max(maxWidth, child.getMeasuredWidth()                            + lp.leftMargin + lp.rightMargin);                }                maxHeight = Math.max(maxHeight, child.getMeasuredHeight()                        + lp.topMargin + lp.bottomMargin);                childState = combineMeasuredStates(childState,                        child.getMeasuredState());            }        }        // 总宽度是内部所有子视图的宽度加上其他约束的宽度        maxWidth += mLeftWidth + mRightWidth;        // 检查默认的最小高度和最小宽度，取最大值        maxHeight = Math.max(maxHeight, getSuggestedMinimumHeight());        maxWidth = Math.max(maxWidth, getSuggestedMinimumWidth());        // 设置最终的尺寸        setMeasuredDimension(                resolveSizeAndState(maxWidth, widthMeasureSpec, childState),                resolveSizeAndState(maxHeight, heightMeasureSpec,                        childState << MEASURED_HEIGHT_STATE_SHIFT));    }    /**     * 设置子控件在ViewGroup中的位置     */    @Override    protected void onLayout(boolean changed, int left, int top, int right,            int bottom) {        final int count = getChildCount();        // 视图在布局中放置的左右外边        int leftPos = getPaddingLeft();        int rightPos = right - left - getPaddingRight();        // 视图流内部的中心区域        final int middleLeft = leftPos + mLeftWidth;        final int middleRight = rightPos - mRightWidth;        // 所操作的布局的顶边和底边        final int parentTop = getPaddingTop();        final int parentBottom = bottom - top - getPaddingBottom();        for (int i = 0; i < count; i++) {            final View child = getChildAt(i);            if (child.getVisibility() != GONE) {                final LayoutParams lp = (LayoutParams) child.getLayoutParams();                // 测量宽度和测量高度                final int width = child.getMeasuredWidth();                final int height = child.getMeasuredHeight();                // 计算正在放置子视图的窗体                if (lp.position == LayoutParams.POSITION_LEFT) {                    mTmpContainerRect.left = leftPos + lp.leftMargin;                    mTmpContainerRect.right = leftPos + width + lp.rightMargin;                    leftPos = mTmpContainerRect.right;                } else if (lp.position == LayoutParams.POSITION_RIGHT) {                    mTmpContainerRect.right = rightPos - lp.rightMargin;                    mTmpContainerRect.left = rightPos - width - lp.leftMargin;                    rightPos = mTmpContainerRect.left;                } else {                    mTmpContainerRect.left = middleLeft + lp.leftMargin;                    mTmpContainerRect.right = middleRight - lp.rightMargin;                }                mTmpContainerRect.top = parentTop + lp.topMargin;                mTmpContainerRect.bottom = parentBottom - lp.bottomMargin;                // //通过子视图的重心值和尺寸决定其在容器内的最终布局                Gravity.apply(lp.gravity, width, height, mTmpContainerRect,                        mTmpChildRect);                // 放置子视图                child.layout(mTmpChildRect.left, mTmpChildRect.top,                        mTmpChildRect.right, mTmpChildRect.bottom);            }        }    }    /**     * 下面的实现部分是针对每个子视图的布局参数的，如果你不需要这些（比如说你写了一个布局管理器）不需要混合放置子视图，那么你可以删除这部分     */    // ----------------------------------------------------------------------    /**     * 要自定义ViewGroup支持子控件的layout_margin参数，     * 则自定义的ViewGroup类必须重载generateLayoutParams     * ()函数，并且在该函数中返回一个ViewGroup.MarginLayoutParams派生类对象，这样才能使用margin参数。     */    @Override    public LayoutParams generateLayoutParams(AttributeSet attrs) {        return new CustomLayout.LayoutParams(getContext(), attrs);    }    // 返回一组默认布局参数。没有设置布局参数执行addview（View）时，这些参数被请求时返回null，并抛出一个异常。    @Override    protected LayoutParams generateDefaultLayoutParams() {        return new LayoutParams(LayoutParams.MATCH_PARENT,                LayoutParams.MATCH_PARENT);    }    @Override    protected ViewGroup.LayoutParams generateLayoutParams(            ViewGroup.LayoutParams p) {        return new LayoutParams(p);    }    @Override    protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {        return p instanceof LayoutParams;    }    /**     * 自定义子控件的LayoutParams     */    public static class LayoutParams extends MarginLayoutParams {        // 设置居中方式        public int gravity = Gravity.TOP | Gravity.START;        public static int POSITION_MIDDLE = 0;        public static int POSITION_LEFT = 1;        public static int POSITION_RIGHT = 2;        public int position = POSITION_MIDDLE;        public LayoutParams(Context c, AttributeSet attrs) {            super(c, attrs);            // 获取定义在XML中的自定义属性            TypedArray a = c.obtainStyledAttributes(attrs,                    R.styleable.CustomLayoutLP);            gravity = a.getInt(                    R.styleable.CustomLayoutLP_android_layout_gravity, gravity);            position = a.getInt(R.styleable.CustomLayoutLP_layout_position,                    position);            a.recycle();        }        public LayoutParams(int width, int height) {            super(width, height);        }        public LayoutParams(ViewGroup.LayoutParams source) {            super(source);        }    }}

 把定义好的ViewGroup当作我们通常使用的诸如LinearLayout等控件一样使用就可以啦。

更多API代码：https://github.com/ldm520/ANDROID_API_DEMOS等Android官方API开源代码。