深入剖析：Android中RelativeLayout源代码大揭秘

Relativelayout是Android中的一种布局方式，它基于父容器中的其他视图来确定自身的位置。下面是Relativelayout的源代码： ```java public class RelativeLayout extends ViewGroup { private static final String TAG = "RelativeLayout"; public RelativeLayout(Context context) { super(context); init(); } public RelativeLayout(Context context, AttributeSet attrs) { super(context, attrs); init(); } public RelativeLayout(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); init(); } private void init() { setChildrenDrawingOrderEnabled(true); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { final int count = getChildCount(); int totalWidth = 0; int totalHeight = 0; int top = 0; int left = 0; int right = 0; int bottom = 0; int usedWidth = 0; int usedHeight = 0; final int specMode = MeasureSpec.getMode(widthMeasureSpec); final int specSize = MeasureSpec.getSize(widthMeasureSpec); final int specModeHeight = MeasureSpec.getMode(heightMeasureSpec); final int specSizeHeight = MeasureSpec.getSize(heightMeasureSpec); for (int i = 0; i < count; i++) { View child = getChildAt(i); measureChild(child, widthMeasureSpec, heightMeasureSpec); if (specMode == MeasureSpec.AT_MOST && specSize < child.getMeasuredWidth()) { throw new IllegalStateException("The total width of all child views under RelativeLayout exceeds the parent width"); } if (specModeHeight == MeasureSpec.AT_MOST && specSizeHeight < child.getMeasuredHeight()) { throw new IllegalStateException("The total height of all child views under RelativeLayout exceeds the parent height"); } int childWidth = child.getMeasuredWidth(); int childHeight = child.getMeasuredHeight(); int childLeft; int childTop; if (child.getLayoutParams() instanceof RelativeLayout.LayoutParams) { RelativeLayout.LayoutParams layoutParams = (RelativeLayout.LayoutParams) child.getLayoutParams(); childLeft = layoutParams.leftMargin + left; childTop = layoutParams.topMargin + top; int childWidthSpec = MeasureSpec.makeMeasureSpec(specSize - usedWidth, MeasureSpec.EXACTLY); int childHeightSpec = MeasureSpec.makeMeasureSpec(specSizeHeight - usedHeight, MeasureSpec.EXACTLY); child.measure(childWidthSpec, childHeightSpec); childLeft += layoutParams.leftMargin; childTop += layoutParams.topMargin; childWidth = child.getMeasuredWidth(); childHeight = child.getMeasuredHeight(); } else { childLeft = left; childTop = top; child.measure(widthMeasureSpec, heightMeasureSpec); } if (childLeft < left) { left = childLeft; } if (childTop < top) { top = childTop; } if (childLeft + childWidth > right) { right = childLeft + childWidth; } if (childTop + childHeight > bottom) { bottom = childTop + childHeight; } usedWidth += childWidth; usedHeight += childHeight; } setMeasuredDimension(specMode == MeasureSpec.EXACTLY ? specSize : Math.max(specSize, usedWidth), specModeHeight == MeasureSpec.EXACTLY ? specSizeHeight : Math.max(specSizeHeight, usedHeight)); } @Override protected void onLayout(boolean changed, int l, int t, int r, int b) { final int count = getChildCount(); for (int i = 0; i < count; i++) { View child = getChildAt(i); if (child.getVisibility() == GONE) { continue; } int childLeft; int childTop; if (child.getLayoutParams() instanceof RelativeLayout.LayoutParams) { RelativeLayout.LayoutParams layoutParams = (RelativeLayout.LayoutParams) child.getLayoutParams(); childLeft = layoutParams.leftMargin + left; childTop = layoutParams.topMargin + top; } else { childLeft = left; childTop = top; } child.layout(childLeft, childTop, childLeft + child.getMeasuredWidth(), childTop + child.getMeasuredHeight()); } } @Override protected boolean checkLayoutParams(ViewGroup.LayoutParams p) { return p instanceof RelativeLayout.LayoutParams; } @Override protected ViewGroup.LayoutParams generateDefaultLayoutParams() { return new RelativeLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT); } @Override protected ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) { return new RelativeLayout.LayoutParams(p); } @Override protected void onLayoutChildren(List<Animator> layoutChild animators) { // do nothing. } } ``` 这段代码定义了Relativelayout的构造函数、初始化方法、测量方法和布局方法。在测量方法中，它遍历所有的子视图，为每个子视图分配宽度和高度，然后根据子视图的位置和大小来调整父视图的大小。在布局方法中，它同样遍历所有的子视图，为每个子视图设置位置。 ######[AI写代码神器 | 1096点数解答 | 2023-11-08 00:27:00]