ViewGroup代码示例 Android开发技术

   有关Android的ViewGroup的使用例子比较少，早期的Android Home中使用到了这个ViewGroup相对于GridView来说ViewGroup更为灵活，下面是Android中一段经典的示例代码

  public class FitCenterFrameLayout extends ViewGroup {
    public FitCenterFrameLayout(Context context) {
        super(context);
    }

    public FitCenterFrameLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  //修改尺寸
        final int width = resolveSize(getSuggestedMinimumWidth(), widthMeasureSpec);
        final int height = resolveSize(getSuggestedMinimumHeight(), heightMeasureSpec);
        setMeasuredDimension(width, height);

        int childWidthSpec = MeasureSpec.makeMeasureSpec(width, MeasureSpec.UNSPECIFIED);
        int childHeightSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.UNSPECIFIED);

        int childCount = getChildCount();
        for (int i = 0; i < childCount; i++) {
            getChildAt(i).measure(childWidthSpec, childHeightSpec);
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        final int childCount = getChildCount();

        final int parentLeft = getPaddingLeft();
        final int parentTop = getPaddingTop();
        final int parentRight = r – l – getPaddingRight();
        final int parentBottom = b – t – getPaddingBottom();

        final int parentWidth = parentRight – parentLeft;
        final int parentHeight = parentBottom – parentTop;

        int unpaddedWidth, unpaddedHeight, parentUnpaddedWidth, parentUnpaddedHeight;
        int childPaddingLeft, childPaddingTop, childPaddingRight, childPaddingBottom;

        for (int i = 0; i < childCount; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() == GONE) {
                continue;
            }

            childPaddingLeft = child.getPaddingLeft();
            childPaddingTop = child.getPaddingTop();
            childPaddingRight = child.getPaddingRight();
            childPaddingBottom = child.getPaddingBottom();

            unpaddedWidth = child.getMeasuredWidth() – childPaddingLeft – childPaddingRight;
            unpaddedHeight = child.getMeasuredHeight() – childPaddingTop – childPaddingBottom;

            parentUnpaddedWidth = parentWidth – childPaddingLeft – childPaddingRight;
            parentUnpaddedHeight = parentHeight – childPaddingTop – childPaddingBottom;

            if (parentUnpaddedWidth * unpaddedHeight > parentUnpaddedHeight * unpaddedWidth) {
                 final int scaledChildWidth = unpaddedWidth * parentUnpaddedHeight
                        / unpaddedHeight + childPaddingLeft + childPaddingRight;
                child.layout(
                        parentLeft + (parentWidth – scaledChildWidth) / 2,
                        parentTop,
                        parentRight – (parentWidth – scaledChildWidth) / 2,
                        parentBottom);
            } else {
                 final int scaledChildHeight = unpaddedHeight * parentUnpaddedWidth
                        / unpaddedWidth + childPaddingTop + childPaddingBottom;
                child.layout(
                        parentLeft,
                        parentTop + (parentHeight – scaledChildHeight) / 2,
                        parentRight,
                        parentTop + (parentHeight + scaledChildHeight) / 2);
            }
        }
    }
}