Android View 源码解析(一) - setContentView
Android View 源码解析(二) - LayoutInflater
Android View 源码解析(三) - View的绘制过程
Android View 源码解析(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
1.将内部View根据纵向关系和横向关系排序
2.初始化相关变量
3.遍历水平关系的View
4.遍历竖直关系的View
5.baseline计算
6.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<Node> 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<Node, DependencyGraph> 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<Node> 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<Node> findRoots(int[] rulesFilter) {
//keyNodes为nodelist
final SparseArray<Node> keyNodes = mKeyNodes;
final ArrayList<Node> 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<Node> 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, -2<sup>31</sup>.
*/
//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
【附录】
资料图
需要资料的朋友可以加入Android架构交流QQ群聊：513088520
点击链接加入群聊【Android移动架构总群】：加入群聊
获取免费学习视频，学习大纲另外还有像高级UI、性能优化、架构师课程、NDK、混合式开发（ReactNative+Weex）等Android高阶开发资料免费分享。
网友评论