Android(安卓)View 相关源码分析之五 RelativeLayout 源码分析
16lz
2021-12-04
Android View 相关源码分析之一 从setContentView说起
Android View 相关源码分析之二 继LayoutInflater来说
Android View 相关源码分析之三 View的绘制过程
Android View 相关源码分析之四 LinearLayout源码分析
RelativeLayout 源码分析
继承自ViewGroup 没有重载onDraw方法 内部子View又是相对 只要计算出View的坐标 layout过程同样简单
measure过程
主要过程
- 将内部View根据纵向关系和横向关系排序
- 初始化相关变量
- 遍历水平关系的View
- 遍历竖直关系的View
- baseline计算
- 宽度和高度修正
1 将内部View根据纵向关系和横向关系排序
layout_toRightOf 为横向关系 layout_below为纵向关系
//首先会根据mDirtyHierarchy的值判断是否需要将子View重新排序 if (mDirtyHierarchy) { mDirtyHierarchy = false; sortChildren(); }相关调用方法
//mDirtyHierarchy的值只有在requestLayout方法下被更新 public void requestLayout() { super.requestLayout(); mDirtyHierarchy = true; } //sortChildren()方法对横向纵向关系的view的数组进行非空判断 用DependencyGraph进行判断 private void sortChildren() { final int count = getChildCount(); if (mSortedVerticalChildren == null || mSortedVerticalChildren.length != count) { mSortedVerticalChildren = new View[count]; } if (mSortedHorizontalChildren == null || mSortedHorizontalChildren.length != count) { mSortedHorizontalChildren = new View[count]; } final DependencyGraph graph = mGraph; graph.clear(); for (int i = 0; i < count; i++) { graph.add(getChildAt(i)); } graph.getSortedViews(mSortedVerticalChildren, RULES_VERTICAL); graph.getSortedViews(mSortedHorizontalChildren, RULES_HORIZONTAL); }DependencyGraph的相关方法
private static class DependencyGraph { ... /** * Adds a view to the graph. * * @param view The view to be added as a node to the graph. */ void add(View view) { //因为是图 根据view生成一个节点 final int id = view.getId(); final Node node = Node.acquire(view); //如果是有效的id 则将该节点添加到List中 if (id != View.NO_ID) { mKeyNodes.put(id, node); } mNodes.add(node); } /** * Builds a sorted list of views. The sorting order depends on the dependencies * between the view. For instance, if view C needs view A to be processed first * and view A needs view B to be processed first, the dependency graph * is: B -> A -> C. The sorted array will contain views B, A and C in this order. * * @param sorted The sorted list of views. The length of this array must * be equal to getChildCount(). * @param rules The list of rules to take into account. */ void getSortedViews(View[] sorted, int... rules) { //当前View找不到其它的可依赖的View时 作为root节点 final ArrayDeque roots = findRoots(rules); int index = 0; Node node; //读取root的下一个node while ((node = roots.pollLast()) != null) { final View view = node.view; final int key = view.getId(); //将符合规则的View加到 sorted中 sorted[index++] = view; final ArrayMap dependents = node.dependents; //dependents 依赖该node的node (A C依赖B 则B的dependents中存A C) final int count = dependents.size(); //遍历所有依赖自己的node for (int i = 0; i < count; i++) { final Node dependent = dependents.keyAt(i); //dependencies 是被依赖的的node的规则和node(A 依赖 B D 则dependencies存有B D ) final SparseArray dependencies = dependent.dependencies; //移除当前node和dependencies的依赖关系 dependencies.remove(key); //如果解除依赖后没有其它依赖 则将该node也视为rootNode if (dependencies.size() == 0) { roots.add(dependent); } } } if (index < sorted.length) { throw new IllegalStateException("Circular dependencies cannot exist in RelativeLayout"); } } ...} eg: A依赖B B依赖C 首先存入C 因为不依赖任何其它的
/** * Finds the roots of the graph. A root is a node with no dependency and * with [0..n] dependents. * * @param rulesFilter The list of rules to consider when building the * dependencies * * @return A list of node, each being a root of the graph */ private ArrayDeque findRoots(int[] rulesFilter) { //keyNodes为nodelist final SparseArray keyNodes = mKeyNodes; final ArrayList nodes = mNodes; final int count = nodes.size(); //初始化依赖该node的node和该node依赖的node相关参数 for (int i = 0; i < count; i++) { final Node node = nodes.get(i); node.dependents.clear(); node.dependencies.clear(); } //遍历所有node 存入当前view和他所依赖的关系 for (int i = 0; i < count; i++) { final Node node = nodes.get(i); final LayoutParams layoutParams = (LayoutParams) node.view.getLayoutParams(); //取出当前View所有的依赖关系 final int[] rules = layoutParams.mRules; final int rulesCount = rulesFilter.length; //遍历当前View所有的 for (int j = 0; j < rulesCount; j++) { //rule对应被依赖view的id final int rule = rules[rulesFilter[j]]; if (rule > 0) { //找到被依赖的node final Node dependency = keyNodes.get(rule); //跳过空view和本身 if (dependency == null || dependency == node) { continue; } //添加依赖被依赖的node dependency.dependents.put(node, this); node.dependencies.put(rule, dependency); } } } final ArrayDeque roots = mRoots; roots.clear(); // 再次遍历 如果该node的依赖关系为0 即该view不依赖任何view 则视为rootView for (int i = 0; i < count; i++) { final Node node = nodes.get(i); if (node.dependencies.size() == 0) roots.addLast(node); } return roots; } 2 初始化相关变量
int myWidth = -1; int myHeight = -1; int width = 0; int height = 0; final int widthMode = MeasureSpec.getMode(widthMeasureSpec); final int heightMode = MeasureSpec.getMode(heightMeasureSpec); final int widthSize = MeasureSpec.getSize(widthMeasureSpec); final int heightSize = MeasureSpec.getSize(heightMeasureSpec); // 如果不是UNSPECIFIED模式 则将widthSize赋值于myWidth if (widthMode != MeasureSpec.UNSPECIFIED) { myWidth = widthSize; } // 如果不是UNSPECIFIED模式 则将heightSize赋值于myHeight if (heightMode != MeasureSpec.UNSPECIFIED) { myHeight = heightSize; } //如果是EXACTLY模式 则将myWidth和myHeight记录 if (widthMode == MeasureSpec.EXACTLY) { width = myWidth; } if (heightMode == MeasureSpec.EXACTLY) { height = myHeight; } View ignore = null; //判断是否为Start 和 top 确定左上角坐标 int gravity = mGravity & Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK; final boolean horizontalGravity = gravity != Gravity.START && gravity != 0; gravity = mGravity & Gravity.VERTICAL_GRAVITY_MASK; final boolean verticalGravity = gravity != Gravity.TOP && gravity != 0; int left = Integer.MAX_VALUE; int top = Integer.MAX_VALUE; int right = Integer.MIN_VALUE; int bottom = Integer.MIN_VALUE; boolean offsetHorizontalAxis = false; boolean offsetVerticalAxis = false; // 记录ignore的view if ((horizontalGravity || verticalGravity) && mIgnoreGravity != View.NO_ID) { ignore = findViewById(mIgnoreGravity); } //宽度个高度是否为warp模式 final boolean isWrapContentWidth = widthMode != MeasureSpec.EXACTLY; final boolean isWrapContentHeight = heightMode != MeasureSpec.EXACTLY; //在计算和分配的子View的坐标的时候 需要用到父VIew的尺寸 但是暂时无法拿到准确值(待完成下面操作) //先使用默认值代替 在计算后 用偏移量更新真是坐标 final int layoutDirection = getLayoutDirection(); if (isLayoutRtl() && myWidth == -1) { myWidth = DEFAULT_WIDTH; }3 遍历水平关系的View
View[] views = mSortedHorizontalChildren; int count = views.length; for (int i = 0; i < count; i++) { View child = views[i]; if (child.getVisibility() != GONE) { LayoutParams params = (LayoutParams) child.getLayoutParams(); //根据方向获得子View中设置的规则 int[] rules = params.getRules(layoutDirection); //将左右方向规则转换为左右的坐标 applyHorizontalSizeRules(params, myWidth, rules); //测算水平方向的子View的尺寸 measureChildHorizontal(child, params, myWidth, myHeight); //确定水平方向子View的位置 if (positionChildHorizontal(child, params, myWidth, isWrapContentWidth)) { offsetHorizontalAxis = true; } } }相关方法
private void applyHorizontalSizeRules(LayoutParams childParams, int myWidth, int[] rules) { RelativeLayout.LayoutParams anchorParams; childParams.mLeft = VALUE_NOT_SET; childParams.mRight = VALUE_NOT_SET; //得到当前子View的layout_toLeftOf属性对应的View anchorParams = getRelatedViewParams(rules, LEFT_OF); if (anchorParams != null) { //如果这个属性存在 则当前子View的右坐标是layout_toLeftOf对应的view的左坐标减去对应view的marginLeft的值和自身marginRight的值 childParams.mRight = anchorParams.mLeft - (anchorParams.leftMargin + childParams.rightMargin); //如果alignWithParent为true alignWithParent取alignWithParentIfMissing //如果layout_toLeftOf的view为空 或者gone 则将RelativeLayout当做被依赖的对象 } else if (childParams.alignWithParent && rules[LEFT_OF] != 0) { //如果父容器RelativeLayout的宽度大于0 //则子View的右坐标为 父RelativeLayout的宽度减去 mPaddingRight 和自身的marginRight if (myWidth >= 0) { childParams.mRight = myWidth - mPaddingRight - childParams.rightMargin; } } //类似的方法 得到左坐标(通过参数RIGHT_OF) anchorParams = getRelatedViewParams(rules, RIGHT_OF); if (anchorParams != null) { childParams.mLeft = anchorParams.mRight + (anchorParams.rightMargin + childParams.leftMargin); } else if (childParams.alignWithParent && rules[RIGHT_OF] != 0) { childParams.mLeft = mPaddingLeft + childParams.leftMargin; } //类似的方法 得到左坐标 (通过参数ALIGN_LEFT) anchorParams = getRelatedViewParams(rules, ALIGN_LEFT); if (anchorParams != null) { childParams.mLeft = anchorParams.mLeft + childParams.leftMargin; } else if (childParams.alignWithParent && rules[ALIGN_LEFT] != 0) { childParams.mLeft = mPaddingLeft + childParams.leftMargin; } //类似的方法 得到右坐标 (通过参数ALIGN_RIGHT) anchorParams = getRelatedViewParams(rules, ALIGN_RIGHT); if (anchorParams != null) { childParams.mRight = anchorParams.mRight - childParams.rightMargin; } else if (childParams.alignWithParent && rules[ALIGN_RIGHT] != 0) { if (myWidth >= 0) { childParams.mRight = myWidth - mPaddingRight - childParams.rightMargin; } } //根据ALIGN_PARENT_LEFT 将自己放到父RelativeLayout的左边 if (0 != rules[ALIGN_PARENT_LEFT]) { childParams.mLeft = mPaddingLeft + childParams.leftMargin; } //根据ALIGN_PARENT_RIGHT 将自己放到父RelativeLayout的右边 if (0 != rules[ALIGN_PARENT_RIGHT]) { if (myWidth >= 0) { childParams.mRight = myWidth - mPaddingRight - childParams.rightMargin; } } }private void measureChildHorizontal(View child, LayoutParams params, int myWidth, int myHeight) { //获得child的宽度MeasureSpec final int childWidthMeasureSpec = getChildMeasureSpec(params.mLeft, params.mRight, params.width, params.leftMargin, params.rightMargin, mPaddingLeft, mPaddingRight, myWidth); final int childHeightMeasureSpec; //在低于4.2的时候 mAllowBrokenMeasureSpecs为true //当myHeight < 0 时 则根据父RelativeLayout设置其MeasureSpec模式 if (myHeight < 0 && !mAllowBrokenMeasureSpecs) { //如果父RelativeLayout的height大于0 则 设置子view的MeasureSpec模式为EXACTLY if (params.height >= 0) { childHeightMeasureSpec = MeasureSpec.makeMeasureSpec( params.height, MeasureSpec.EXACTLY); } else { //反之 如果其小于0 则设置子View的MeasureSpec为UNSPECIFIED childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED); } } else { //当当前myHeight >= 0 //判断当前高度是否与父RelativeLayout高度相同 设置heightMode //根据maxHeight 和heightMode设置子View的MeasureSpec模式 final int maxHeight; if (mMeasureVerticalWithPaddingMargin) { maxHeight = Math.max(0, myHeight - mPaddingTop - mPaddingBottom - params.topMargin - params.bottomMargin); } else { maxHeight = Math.max(0, myHeight); } final int heightMode; if (params.height == LayoutParams.MATCH_PARENT) { heightMode = MeasureSpec.EXACTLY; } else { heightMode = MeasureSpec.AT_MOST; } childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(maxHeight, heightMode); } //获得了子View的WidthMeasureSpec和HeightMeasureSpec //子View可以通过measure方法获取自身的size child.measure(childWidthMeasureSpec, childHeightMeasureSpec);}/** * Get a measure spec that accounts for all of the constraints on this view. * This includes size constraints imposed by the RelativeLayout as well as * the View's desired dimension. * * @param childStart The left or top field of the child's layout params * @param childEnd The right or bottom field of the child's layout params * @param childSize The child's desired size (the width or height field of * the child's layout params) * @param startMargin The left or top margin * @param endMargin The right or bottom margin * @param startPadding mPaddingLeft or mPaddingTop * @param endPadding mPaddingRight or mPaddingBottom * @param mySize The width or height of this view (the RelativeLayout) * @return MeasureSpec for the child */ private int getChildMeasureSpec(int childStart, int childEnd, int childSize, int startMargin, int endMargin, int startPadding, int endPadding, int mySize) { int childSpecMode = 0; int childSpecSize = 0; final boolean isUnspecified = mySize < 0; //如果父RelativeLayout宽度小于0 版本号不小于4.2 if (isUnspecified && !mAllowBrokenMeasureSpecs) { //如果子View的左边距和右边距都不为VALUE_NOT_SET //且右边距坐标大于左边距坐标 则将其差当做宽度赋予View 设置模式为EXACTLY //VALUE_NOT_SET = Integer.MIN_VALUE /** * Constant for the minimum {@code int} value, -231. */ //public static final int MIN_VALUE = 0x80000000; if (childStart != VALUE_NOT_SET && childEnd != VALUE_NOT_SET) { childSpecSize = Math.max(0, childEnd - childStart); childSpecMode = MeasureSpec.EXACTLY; } else if (childSize >= 0) { // 如果childSpecSize >= 0 则赋值于childSpecSize //同样设置模式为EXACTLY childSpecSize = childSize; childSpecMode = MeasureSpec.EXACTLY; } else { // 都不满足则设置模式为UNSPECIFIED childSpecSize = 0; childSpecMode = MeasureSpec.UNSPECIFIED; } return MeasureSpec.makeMeasureSpec(childSpecSize, childSpecMode); } // 计算 开始和结束相关 int tempStart = childStart; int tempEnd = childEnd; //如果没有指定start值 则默认赋予 padding和merage的值 if (tempStart == VALUE_NOT_SET) { tempStart = startPadding + startMargin; } //同上 if (tempEnd == VALUE_NOT_SET) { tempEnd = mySize - endPadding - endMargin; } //指定最大可提供的大小 final int maxAvailable = tempEnd - tempStart; if (childStart != VALUE_NOT_SET && childEnd != VALUE_NOT_SET) { //如果Start和End都是有效值 根据isUnspecified设置specMode为UNSPECIFIED或EXACTLY //并将设置对应的size childSpecMode = isUnspecified ? MeasureSpec.UNSPECIFIED : MeasureSpec.EXACTLY; childSpecSize = Math.max(0, maxAvailable); } else { //反之 判断childSize的相关值 if (childSize >= 0) { //设置模式为EXACTLY //判断maxAvailable和childSize情况 取较大值设置为childSpecSize childSpecMode = MeasureSpec.EXACTLY; if (maxAvailable >= 0) { // We have a maximum size in this dimension. childSpecSize = Math.min(maxAvailable, childSize); } else { // We can grow in this dimension. childSpecSize = childSize; } } else if (childSize == LayoutParams.MATCH_PARENT) { //如果子View是match模式 参照isUnspecified设置相关 childSpecMode = isUnspecified ? MeasureSpec.UNSPECIFIED : MeasureSpec.EXACTLY; childSpecSize = Math.max(0, maxAvailable); } else if (childSize == LayoutParams.WRAP_CONTENT) { //在wrap进行设置 if (maxAvailable >= 0) { // We have a maximum size in this dimension. childSpecMode = MeasureSpec.AT_MOST; childSpecSize = maxAvailable; } else { // We can grow in this dimension. Child can be as big as it // wants. childSpecMode = MeasureSpec.UNSPECIFIED; childSpecSize = 0; } } } return MeasureSpec.makeMeasureSpec(childSpecSize, childSpecMode); }以上 完成了View的第一次测量 确定了View的大小 然后根据大小觉得把子view放在父RelativeLayout中的位置
private boolean positionChildHorizontal(View child, LayoutParams params, int myWidth, boolean wrapContent) { //获取RelativeLayout的布局方向 final int layoutDirection = getLayoutDirection(); int[] rules = params.getRules(layoutDirection); if (params.mLeft == VALUE_NOT_SET && params.mRight != VALUE_NOT_SET) { // 如果右边界有效 左边界无效 根据右边界计算出左边界 params.mLeft = params.mRight - child.getMeasuredWidth(); } else if (params.mLeft != VALUE_NOT_SET && params.mRight == VALUE_NOT_SET) { // 同上反之 params.mRight = params.mLeft + child.getMeasuredWidth(); } else if (params.mLeft == VALUE_NOT_SET && params.mRight == VALUE_NOT_SET) { //都无效的时候 if (rules[CENTER_IN_PARENT] != 0 || rules[CENTER_HORIZONTAL] != 0) { //设置了CENTER_IN_PARENT或者 CENTER_HORIZONTAL的情况下 if (!wrapContent) { //非wrap情况下 //把子View水平中心固定在RelativeLayout的中心 centerHorizontal(child, params, myWidth); } else { //左边距为padding+margin //右边距为左边距加上测量宽度 params.mLeft = mPaddingLeft + params.leftMargin; params.mRight = params.mLeft + child.getMeasuredWidth(); } return true; } else { //RTL右到左 布局方向 //LTR�左到右 布局方向 if (isLayoutRtl()) { params.mRight = myWidth - mPaddingRight- params.rightMargin; params.mLeft = params.mRight - child.getMeasuredWidth(); } else { params.mLeft = mPaddingLeft + params.leftMargin; params.mRight = params.mLeft + child.getMeasuredWidth(); } } } return rules[ALIGN_PARENT_END] != 0; //当为CENTER_IN_PARENT CENTER_HORIZONTAL ALIGN_PARENT_END三种情况之一时返回True}4 遍历竖直关系的View
... for (int i = 0; i < count; i++) { final View child = views[i]; if (child.getVisibility() != GONE) { final LayoutParams params = (LayoutParams) child.getLayoutParams(); //将竖直方向规则转换为坐标 applyVerticalSizeRules(params, myHeight, child.getBaseline()); //测量子View measureChild(child, params, myWidth, myHeight); //确定竖直方向子View的位置 if (positionChildVertical(child, params, myHeight, isWrapContentHeight)) { offsetVerticalAxis = true; } //首先判断是否为wrap模式 if (isWrapContentWidth) { //根据RTL或者LTR和版本进行区分 //Build.VERSION_CODES.KITKAT = 19 //主要对margin进行处理 if (isLayoutRtl()) { if (targetSdkVersion < Build.VERSION_CODES.KITKAT) { width = Math.max(width, myWidth - params.mLeft); } else { width = Math.max(width, myWidth - params.mLeft - params.leftMargin); } } else { if (targetSdkVersion < Build.VERSION_CODES.KITKAT) { width = Math.max(width, params.mRight); } else { width = Math.max(width, params.mRight + params.rightMargin); } } } if (isWrapContentHeight) { if (targetSdkVersion < Build.VERSION_CODES.KITKAT) { height = Math.max(height, params.mBottom); } else { height = Math.max(height, params.mBottom + params.bottomMargin); } } if (child != ignore || verticalGravity) { left = Math.min(left, params.mLeft - params.leftMargin); top = Math.min(top, params.mTop - params.topMargin); } if (child != ignore || horizontalGravity) { right = Math.max(right, params.mRight + params.rightMargin); bottom = Math.max(bottom, params.mBottom + params.bottomMargin); } } }...5 baseline计算
// Use the top-start-most laid out view as the baseline. RTL offsets are// applied later, so we can use the left-most edge as the starting edge. View baselineView = null; LayoutParams baselineParams = null; for (int i = 0; i < count; i++) { final View child = views[i]; if (child.getVisibility() != GONE) { final LayoutParams childParams = (LayoutParams) child.getLayoutParams(); if (baselineView == null || baselineParams == null || compareLayoutPosition(childParams, baselineParams) < 0) { baselineView = child; baselineParams = childParams; } } } mBaselineView = baselineView;6 宽度和高度修正
//如何是wrap模式 if (isWrapContentWidth) { width += mPaddingRight; if (mLayoutParams != null && mLayoutParams.width >= 0) { width = Math.max(width, mLayoutParams.width); } width = Math.max(width, getSuggestedMinimumWidth()); width = resolveSize(width, widthMeasureSpec); //在得到最后的width之后 对依赖RelativeLayout的子View添上偏移量 if (offsetHorizontalAxis) { for (int i = 0; i < count; i++) { final View child = views[i]; if (child.getVisibility() != GONE) { final LayoutParams params = (LayoutParams) child.getLayoutParams(); final int[] rules = params.getRules(layoutDirection); //对CENTER_IN_PARENT或者CENTER_HORIZONTAL的子View重测 if (rules[CENTER_IN_PARENT] != 0 || rules[CENTER_HORIZONTAL] != 0) { centerHorizontal(child, params, width); //对ALIGN_PARENT_RIGHT重测 } else if (rules[ALIGN_PARENT_RIGHT] != 0) { final int childWidth = child.getMeasuredWidth(); params.mLeft = width - mPaddingRight - childWidth; params.mRight = params.mLeft + childWidth; } } } } } //同上 if (isWrapContentHeight) { height += mPaddingBottom; if (mLayoutParams != null && mLayoutParams.height >= 0) { height = Math.max(height, mLayoutParams.height); } height = Math.max(height, getSuggestedMinimumHeight()); height = resolveSize(height, heightMeasureSpec); if (offsetVerticalAxis) { for (int i = 0; i < count; i++) { final View child = views[i]; if (child.getVisibility() != GONE) { final LayoutParams params = (LayoutParams) child.getLayoutParams(); final int[] rules = params.getRules(layoutDirection); if (rules[CENTER_IN_PARENT] != 0 || rules[CENTER_VERTICAL] != 0) { centerVertical(child, params, height); } else if (rules[ALIGN_PARENT_BOTTOM] != 0) { final int childHeight = child.getMeasuredHeight(); params.mTop = height - mPaddingBottom - childHeight; params.mBottom = params.mTop + childHeight; } } } } } //根据gravity再次修正 if (horizontalGravity || verticalGravity) { final Rect selfBounds = mSelfBounds; selfBounds.set(mPaddingLeft, mPaddingTop, width - mPaddingRight, height - mPaddingBottom); final Rect contentBounds = mContentBounds; Gravity.apply(mGravity, right - left, bottom - top, selfBounds, contentBounds, layoutDirection); final int horizontalOffset = contentBounds.left - left; final int verticalOffset = contentBounds.top - top; if (horizontalOffset != 0 || verticalOffset != 0) { for (int i = 0; i < count; i++) { final View child = views[i]; if (child.getVisibility() != GONE && child != ignore) { final LayoutParams params = (LayoutParams) child.getLayoutParams(); if (horizontalGravity) { params.mLeft += horizontalOffset; params.mRight += horizontalOffset; } if (verticalGravity) { params.mTop += verticalOffset; params.mBottom += verticalOffset; } } } } } //如果是RTL(右到左显示)则再次修改 if (isLayoutRtl()) { final int offsetWidth = myWidth - width; for (int i = 0; i < count; i++) { final View child = views[i]; if (child.getVisibility() != GONE) { final LayoutParams params = (LayoutParams) child.getLayoutParams(); params.mLeft -= offsetWidth; params.mRight -= offsetWidth; } } }简单总结
RelativeLayout更加关注子View的left right top bottom值 并且优先级高于width和height
RelativeLayout的layout过程
对于RelativeLayout来的 layout过程更多的根据子View的left right top bottom值来设定位置
protected void onLayout(boolean changed, int l, int t, int r, int b) { // The layout has actually already been performed and the positions // cached. Apply the cached values to the children. final int count = getChildCount(); for (int i = 0; i < count; i++) { View child = getChildAt(i); if (child.getVisibility() != GONE) { RelativeLayout.LayoutParams st = (RelativeLayout.LayoutParams) child.getLayoutParams(); child.layout(st.mLeft, st.mTop, st.mRight, st.mBottom); } } }RelativeLayout的draw过程
RelativeLayout作为ViewGroup的子类 因为其性质原因 没有对draw过程进行修改
以上
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