本文分析下上篇文章的布局情况。CoordinatorLayout的布局跟普通viewgroup不太一样,behavior会插一手。本篇主要介绍behavior如何影响measure和layout。
上文activity的xml如下
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.fish.behaviordemo.MainActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
android.support.design.widget.AppBarLayout>
<include layout="@layout/content_fab" />
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="@dimen/fab_margin"
android:src="@android:drawable/ic_dialog_email"
app:layout_behavior="com.fish.behaviordemo.fab.MyBehavior" />
android.support.design.widget.CoordinatorLayout>
界面显示效果如下所示
最外层是CoordinatorLayout,里面放了个AppBarLayout、content_fab、FloatingActionButton。我们先不管FloatingActionButton。都说CoordinatorLayout是个super FrameLayout,那这里的布局应该是content_fab叠在AppBarLayout上咯?可是我们看到的是content_fab在AppBarLayout下方,这可不像FrameLayout,难道是被盖住了一部分没看到吗?错了,content_fab的的确却是在AppBarLayout的下方,这是CoordinatorLayout布局的时候定下来的。
我们这里的style如下,这个style的view tree内是没有statusbar的,可参考http://blog.csdn.net/litefish/article/details/52034813
<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
-- Customize your theme here. -->
<item name="colorPrimary">@color/colorPrimary
- "colorPrimaryDark"
>@color/colorPrimaryDark
- "colorAccent">@color/colorAccent
style>
那就有另一个问题了,为何AppBarLayout不在屏幕的顶上,而在statubar的下方。
带着这2个问题,我们来看CoordinatorLayout的布局过程。
问题1:为何AppBarLayout会在statusbar的下方
问题2:为何content_fab在AppBarLayout的下方
behavior是会介入onMeasure和onLayout过程的,我们先把各个子view的behavior找出来
AppBarLayout的behavior是由注解决定的
而content_fab的behavior是什么?content_fab是个RelativeLayout,后文我们称RelativeLayout。
xml内有这么一句话
app:layout_behavior="@string/appbar_scrolling_view_behavior"
@string/appbar_scrolling_view_behavior是什么?
<string name="appbar_scrolling_view_behavior" translatable="false">android.support.design.widget.AppBarLayout$ScrollingViewBehaviorstring>
其实从下面代码可以看出是AppBarLayout.ScrollingViewBehavior
所以此处的CoordinatorLayout的3个子view和behavior如下所示
view | behavior |
---|---|
AppBarLayout | AppBarLayout.Behavior |
RelativeLayout | AppBarLayout.ScrollingViewBehavior |
FloatingActionButton | MyBehavior |
我们不管FloatingActionButton,看AppBarLayout和RelativeLayout,都挺复杂的,下图是累关系图,可以看到都是从ViewOffsetBehavior派生而来的。
再来看AppBarLayout.ScrollingViewBehavior内的代码,可以看到依赖于AppBarLayout,所以这里RelativeLayout依赖于AppBarLayout
//AppBarLayout.ScrollingViewBehavior
@Override
public boolean layoutDependsOn(CoordinatorLayout parent, View child, View dependency) {
// We depend on any AppBarLayouts
return dependency instanceof AppBarLayout;
}
CoordinatorLayout的onMeasure方法如下所示,比较简单,主要流程是,先算出insets的值,然后measure的时候去掉这些insets,在measure 子view的时候,behavior先measure,返回false的话,才轮到view本身measure。
我们知道CoordinatorLayout是userRoot的根节点,所以第一次measure CoordinatorLayout的heightMeasureSpec.size是第一次用1668(1794-126),第二次用1794(1920-126)。上边这些数字都是在我手机上的值,1794是DisplayMetrics的高度值,126是navigatorbar的高度,1920是屏幕高度。
所以下边代码里,onMeasure参数heightMeasureSpec的size第一次是1668,第二次是1794。
下面开始具体分析
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
prepareChildren();
ensurePreDrawListener();
。。。
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
final int widthSize = MeasureSpec.getSize(widthMeasureSpec);
final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
final int heightSize = MeasureSpec.getSize(heightMeasureSpec);
final int widthPadding = paddingLeft + paddingRight;
final int heightPadding = paddingTop + paddingBottom;
...
final int childCount = mDependencySortedChildren.size();
for (int i = 0; i < childCount; i++) {
int childWidthMeasureSpec = widthMeasureSpec;
int childHeightMeasureSpec = heightMeasureSpec;
if (applyInsets && !ViewCompat.getFitsSystemWindows(child)) {
// We're set to handle insets but this child isn't, so we will measure the
// child as if there are no insets
final int horizInsets = mLastInsets.getSystemWindowInsetLeft()
+ mLastInsets.getSystemWindowInsetRight();
//获取vertInsets值,其实这里就是statubar的高度
final int vertInsets = mLastInsets.getSystemWindowInsetTop()
+ mLastInsets.getSystemWindowInsetBottom();
childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(
widthSize - horizInsets, widthMode);
childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(
heightSize - vertInsets, heightMode);
}
final Behavior b = lp.getBehavior();
//behavior先measure,返回false的话,才轮到view本身measure
if (b == null || !b.onMeasureChild(this, child, childWidthMeasureSpec, keylineWidthUsed,
childHeightMeasureSpec, 0)) {
onMeasureChild(child, childWidthMeasureSpec, keylineWidthUsed,
childHeightMeasureSpec, 0);
}
}
。。。
}
final int width = ViewCompat.resolveSizeAndState(widthUsed, widthMeasureSpec,
childState & ViewCompat.MEASURED_STATE_MASK);
final int height = ViewCompat.resolveSizeAndState(heightUsed, heightMeasureSpec,
childState << ViewCompat.MEASURED_HEIGHT_STATE_SHIFT);
setMeasuredDimension(width, height);
}
第一次measure,heightMeasureSpec.size为1668
prepareChildren和ensurePreDrawListener,之前在 这里分析过,不清楚的可以回顾下。
因为子view没有写fitsSystemWindows,所以L20会进去,在L23会算出vertInsets,这里实际就是statubar的高度(63)。然后L29,修改childHeightMeasureSpec.size为1668-63=1605。从这里可以看出在measure的过程中,其实是除掉了statubar的高度,然后走到L35,先交给behavior measure。这里我们主要看下RelativeLayout这个child是如何measure的,RelativeLayout的behavior是AppBarLayout.ScrollingViewBehavior,他没有复写onMeasureChild方法,所以看父类HeaderScrollingViewBehavior。先看L7,只有MATCH_PARENT或WRAP_CONTENT,我们behavior才处理,否则直接返回false,丢给view自己处理,我们这里是MATCH_PARENT,由behavior处理。 然后看L13,找到一个header,这是个view,这个非常重要,是当前view的第一个依赖view(可以称为header),当前view的各种操作都会依赖于header,明显,我们的RelativeLayout的header就是AppBarLayout,再看L28,如果head没有layout过,那直接返回false,意思就是必须在head 布局完成之后,再来measure我们RelativeLayout。这个行为是比较奇怪的,一个view的measure居然依赖另一个view的layout。此时,我们肯定没有layout过,所以直接返回false,然后走上边代码的L39,之后RelativeLayout的measuredHeight变为1605.
第二次measure,先看上文代码,heightMeasureSpec.size为1794,在L28改为1794-63=1731,进入下边代码,此时header还没layout,所以返回false,依然是view自身measure,之后RelativeLayout的measuredHeight变为1794.
上2次measure都在layout之前,是通过view本身来measure的,我们在看看layout之后的measure
第三次measure(这次measure是怎么触发的呢?),此时已经layout过了
先看上文代码,heightMeasureSpec.size为1794,在L29改为1794-63=1731,进入下边代码,此时header已经layout,所以进入L28的if内,重点关注L35,
final int height = availableHeight - header.getMeasuredHeight()
+ getScrollRange(header);
翻一下就是parent的高度-header的measuredHeight+header的滚动范围
这里减掉了一个header.getMeasuredHeight(),加上了getScrollRange(header),后者我们暂时不考虑,此时其实就是减去了AppBarlayout的measuredHeight,在这里就是1731-147=1584,然后调用 CoordinatorLayout.onMeasureChild,最后measure结果就是1584,下边代码返回true。这其实是HeaderScrollingViewBehavior的一个特性,让当前view处于header的下方。
好了,三轮measure下来,最终RelativeLayout的measuredHeight被定为1584
//HeaderScrollingViewBehavior
@Override
public boolean onMeasureChild(CoordinatorLayout parent, View child,
int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec,
int heightUsed) {
final int childLpHeight = child.getLayoutParams().height;
if (childLpHeight == ViewGroup.LayoutParams.MATCH_PARENT
|| childLpHeight == ViewGroup.LayoutParams.WRAP_CONTENT) {
// If the menu's height is set to match_parent/wrap_content then measure it
// with the maximum visible height
final List dependencies = parent.getDependencies(child);
final View header = findFirstDependency(dependencies);
if (header != null) {
if (ViewCompat.getFitsSystemWindows(header)
&& !ViewCompat.getFitsSystemWindows(child)) {
// If the header is fitting system windows then we need to also,
// otherwise we'll get CoL's compatible measuring
ViewCompat.setFitsSystemWindows(child, true);
if (ViewCompat.getFitsSystemWindows(child)) {
// If the set succeeded, trigger a new layout and return true
child.requestLayout();
return true;
}
}
//header未layout,我就不measure
if (ViewCompat.isLaidOut(header)) {
int availableHeight = View.MeasureSpec.getSize(parentHeightMeasureSpec);
if (availableHeight == 0) {
// If the measure spec doesn't specify a size, use the current height
availableHeight = parent.getHeight();
}
final int height = availableHeight - header.getMeasuredHeight()
+ getScrollRange(header);
final int heightMeasureSpec = View.MeasureSpec.makeMeasureSpec(height,
childLpHeight == ViewGroup.LayoutParams.MATCH_PARENT
? View.MeasureSpec.EXACTLY
: View.MeasureSpec.AT_MOST);
// Now measure the scrolling view with the correct height
parent.onMeasureChild(child, parentWidthMeasureSpec,
widthUsed, heightMeasureSpec, heightUsed);
return true;
}
}
}
return false;
}
看下边CoordinatorLayout的onLayout,发现布局的子view的时候,先由behavior处理,behavior未处理成功再交给child处理,跟onMeasure类似。
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
final int layoutDirection = ViewCompat.getLayoutDirection(this);
final int childCount = mDependencySortedChildren.size();
for (int i = 0; i < childCount; i++) {
final View child = mDependencySortedChildren.get(i);
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
final Behavior behavior = lp.getBehavior();
if (behavior == null || !behavior.onLayoutChild(this, child, layoutDirection)) {
onLayoutChild(child, layoutDirection);
}
}
}
我们再来分析,因为RelativeLayout依赖于AppBarLayout,所以在mDependencySortedChildren内,AppBarLayout在前,RelativeLayout在后。
先看如何布局AppBarLayout。
看AppBarLayout.Behavior的onLayoutChild,首先调用了super.onLayoutChild,会调用到ViewOffsetBehavior的onLayoutChild
//AppBarLayout.Behavior
@Override
public boolean onLayoutChild(CoordinatorLayout parent, AppBarLayout abl,
int layoutDirection) {
boolean handled = super.onLayoutChild(parent, abl, layoutDirection);
...
}
再看ViewOffsetBehavior的onLayoutChild,调用layoutChild,然后调用parent.onLayoutChild,parent是谁,CoordinatorLayout
public boolean onLayoutChild(CoordinatorLayout parent, V child, int layoutDirection) {
// First let lay the child out
layoutChild(parent, child, layoutDirection);
if (mViewOffsetHelper == null) {
mViewOffsetHelper = new ViewOffsetHelper(child);
}
mViewOffsetHelper.onViewLayout();
if (mTempTopBottomOffset != 0) {
mViewOffsetHelper.setTopAndBottomOffset(mTempTopBottomOffset);
mTempTopBottomOffset = 0;
}
if (mTempLeftRightOffset != 0) {
mViewOffsetHelper.setLeftAndRightOffset(mTempLeftRightOffset);
mTempLeftRightOffset = 0;
}
return true;
}
protected void layoutChild(CoordinatorLayout parent, V child, int layoutDirection) {
// Let the parent lay it out by default
parent.onLayoutChild(child, layoutDirection);
}
CoordinatorLayout的onLayoutChild一般会调用layoutChild,看完这段代码,就应该能明白问题1。里面有个parent叫Rect,这个Rect代表CoordinatorLayout内部可以放子view的空间,一开始的时候parent的top为0,在L15把statusbar的高度加到top里去,这其实就是为了让AppbarLayout不要和statusbar重叠。在L21根据AppbarLayout的getMeasuredHeight()和parent,算出一个Rect out,用这个Rect来给AppbarLayout布局,out里的top必定是statusbar的高度,在L23 child.layout内AppbarLayout的mTop必然被设置为statusbar的高度,所以问题1解决,核心代码就是layoutChild。注意layoutChild不是针对AppbarLayout,所以任何子view都不可能跑到statubar上。
private void layoutChild(View child, int layoutDirection) {
final LayoutParams lp = (LayoutParams) child.getLayoutParams();
final Rect parent = mTempRect1;
parent.set(getPaddingLeft() + lp.leftMargin,
getPaddingTop() + lp.topMargin,
getWidth() - getPaddingRight() - lp.rightMargin,
getHeight() - getPaddingBottom() - lp.bottomMargin);
if (mLastInsets != null && ViewCompat.getFitsSystemWindows(this)
&& !ViewCompat.getFitsSystemWindows(child)) {
// If we're set to handle insets but this child isn't, then it has been measured as
// if there are no insets. We need to lay it out to match.
parent.left += mLastInsets.getSystemWindowInsetLeft();
//这里把statusbar的高度算进去了
parent.top += mLastInsets.getSystemWindowInsetTop();
parent.right -= mLastInsets.getSystemWindowInsetRight();
parent.bottom -= mLastInsets.getSystemWindowInsetBottom();
}
final Rect out = mTempRect2;
GravityCompat.apply(resolveGravity(lp.gravity), child.getMeasuredWidth(),
child.getMeasuredHeight(), parent, out, layoutDirection);
child.layout(out.left, out.top, out.right, out.bottom);
}
此时,其实相当于给AppBarLayout设置了一个额外的padding,这个值会被记录下来,在onLayoutChild的L8,有mViewOffsetHelper.onViewLayout.由下边代码可知mLayoutTop就记录了这个额外的padding。ViewOffsetHelper内部有mLayoutTop,mOffsetTop。mLayoutTop代表基本top,mOffsetTop代表额外top偏移量,实际view的top为 mLayoutTop+ mOffsetTop。ViewOffsetHelper内的setTopAndBottomOffset的参数offset是一个绝对值,但是view的offsetTopAndBottom的参数offset是一个delta值,mLayoutTop就可以把绝对值转化为delta值。
public void onViewLayout() {
// Now grab the intended top
mLayoutTop = mView.getTop();
mLayoutLeft = mView.getLeft();
// And offset it as needed
updateOffsets();
}
RelativeLayout的behavior是AppBarLayout.ScrollingViewBehavior
和布局AppBarLayout一样,会调用ViewOffsetBehavior的onLayoutChild
ViewOffsetBehavior的onLayoutChild,调用layoutChild,此时layoutChild可不一样了,因为HeaderScrollingViewBehavior复写了。看下边代码可以解决我们的第二个问题,首先寻找依赖的view,我们的RelativeLayout依赖AppBarLayout,然后看L13,这个代码非常关键,available这个Rect设置在AppBarLayout的下方,然后类似的在L20啊,根据getMeasuredHeight()和available计算出out,再用out来layout RelativeLayout。所以RelativeLayout必然在AppBarLayout的下方,这是由它的behavior决定的。HeaderScrollingViewBehavior要求排在首个依赖view(header)的下方
@Override
protected void layoutChild(final CoordinatorLayout parent, final View child,
final int layoutDirection) {
final List dependencies = parent.getDependencies(child);
//寻找依赖
final View header = findFirstDependency(dependencies);
if (header != null) {
final CoordinatorLayout.LayoutParams lp =
(CoordinatorLayout.LayoutParams) child.getLayoutParams();
final Rect available = mTempRect1;
//这个rect在依赖view的下边
available.set(parent.getPaddingLeft() + lp.leftMargin,
header.getBottom() + lp.topMargin,
parent.getWidth() - parent.getPaddingRight() - lp.rightMargin,
parent.getHeight() + header.getBottom()
- parent.getPaddingBottom() - lp.bottomMargin);
final Rect out = mTempRect2;
GravityCompat.apply(resolveGravity(lp.gravity), child.getMeasuredWidth(),
child.getMeasuredHeight(), available, out, layoutDirection);
final int overlap = getOverlapPixelsForOffset(header);
child.layout(out.left, out.top - overlap, out.right, out.bottom - overlap);
mVerticalLayoutGap = out.top - header.getBottom();
} else {
// If we don't have a dependency, let super handle it
super.layoutChild(parent, child, layoutDirection);
mVerticalLayoutGap = 0;
}
}
1、CoordinatorLayout像一个FrameLayout,但是里面的布局受behavior影响,我们可以通过改写behavior来修改布局策略
2、CoordinatorLayout的高度包括statubar,如果CoordinatorLayout的子view没有写fitsSystemWindows,都不可能跑到statubar上,因为measure的时候会除掉statubar,layoutChild的时候也会处理。
3、如果CoordinatorLayout的子view重写了fitsSystemWindows,那么子view的范围会包括statubar
4、HeaderScrollingViewBehavior有个特性,使用此behavior的view 必然排在他的首个依赖view(简称header)的下方,因为复写了layoutChild