CoordinatorLayout.Behavior

CoordinatorLayout我们可以将它理解为一个超级Fragment,它的布局方式是一层一层叠上去，而且它可以组织子View之间的协作。组织协作的方式需要使用最重要的对象Behavior

Behavior是CoordinatorLayout实现子View之间交互的插件，它可以实现用户的一个或多个交互行为，它们可能包括拖拽、滑动、或者其他一些手势。

我们在使用CoordinatorLayout的时候，在NestedScrollView的xml属性中总是能看到

app:layout_behavior="@string/appbar_scrolling_view_behavior"

。NestedScrollView要想与AppBarLayout有联动，那么NestedScrollView作为直接的子View,就必须设置这个behavior，当然这个behavior谷歌已经给默认设置好了。

常用的方法（暂不介绍嵌套滑动）

1 .

onLayoutChild

可以用于子View视图布局的更改，修改behavior默认设置子View的行为。需要调用

parent.onLayoutChild

/**
*
* @param parent CoordinatorLayout
* @param child   子View
* @param layoutDirection  ViewCompat.LAYOUT_DIRECTION_LTR(水平布局从左到右)
*                         ViewCompat.LAYOUT_DIRECTION_RTL(水平布局从右到左)
* @return  false表示不改变，true改变View的视图
*/
@Override
public boolean onLayoutChild(CoordinatorLayout parent, ImageView child, int layoutDirection) {
return super.onLayoutChild(parent, child, layoutDirection);
}

2 .

layoutDependsOn

View的依赖关系在这里设置

/**
* 表示是否给应用Behavior的View指定一个依赖的布局，一般当依赖的View布局发生变化时
* 不管被被依赖View的顺序怎样，被依赖的View也会重新布局
* @param parent CoordinatorLayout
* @param child 绑定behavior 的View
* @param dependency   依赖的view
* @return 如果child是依赖的指定的View 返回true,否则返回false
*/
@Override
public boolean layoutDependsOn(CoordinatorLayout parent, View child, View dependency) {
return super.layoutDependsOn(parent, child, dependency);
}

3 .

onDependentViewChanged

/**
* 当依赖的视图状态位置、大小发生变化时，就会调用这个方法
* @param parent
* @param child
* @param dependency
* @return
*/
@Override
public boolean onDependentViewChanged(CoordinatorLayout parent, View child, View dependency) {
return super.onDependentViewChanged(parent, child, dependency);
}

只是介绍这几个方法，可能我们还不太清楚，所以直接做几个练习，就能看到效果了。

我这里不准备做练习了，练习可以自己试，我这里要简单说一说源码里面这几个方法怎么调用的（我的水平只能简单说一说/(ㄒoㄒ)/~~）

我们一般会在XML中直接定义Behavior,我们在代码中来看看这个Behavior是怎么解析的。

LayoutParams(Context context, AttributeSet attrs) {
super(context, attrs);

...省略代码

final TypedArray a = context.obtainStyledAttributes(attrs,
R.styleable.CoordinatorLayout_LayoutParams);

...省略代码

//通过检测app:behavior="xxx",获取路径。所以在定义behavior的时候，一定要写有
//两个参数的构造方法
mBehaviorResolved = a.hasValue(
R.styleable.CoordinatorLayout_LayoutParams_layout_behavior);
if (mBehaviorResolved) {
mBehavior = parseBehavior(context, attrs, a.getString(
R.styleable.CoordinatorLayout_LayoutParams_layout_behavior));
}

a.recycle();
}

static Behavior parseBehavior(Context context, AttributeSet attrs, String name) {
if (TextUtils.isEmpty(name)) {
return null;
}

final String fullName;
if (name.startsWith(".")) {
//相对路径
fullName = context.getPackageName() + name;
} else if (name.indexOf('.') >= 0) {
//全限定名
fullName = name;
} else {
// Assume stock behavior in this package (if we have one)
fullName = !TextUtils.isEmpty(WIDGET_PACKAGE_NAME)
? (WIDGET_PACKAGE_NAME + '.' + name)
: name;
}

try {
Map<String, Constructor<Behavior>> constructors = sConstructors.get();
if (constructors == null) {
constructors = new HashMap<>();
sConstructors.set(constructors);
}
Constructor<Behavior> c = constructors.get(fullName);
//通过反射来新建实例
if (c == null) {
final Class<Behavior> clazz = (Class<Behavior>) Class.forName(fullName, true,
context.getClassLoader());
c = clazz.getConstructor(CONSTRUCTOR_PARAMS);
c.setAccessible(true);
constructors.put(fullName, c);
}
return c.newInstance(context, attrs);
} catch (Exception e) {
throw new RuntimeException("Could not inflate Behavior subclass " + fullName, e);
}
}

在xml里面写的话，是在inflate的时候对Behavior赋值的

以注解方式写的话，是在onMeasure内赋值的。（后面会说为什么）

为View配置了Behavior，那么我们接着来看View之间是怎么依赖的。首先在

LayoutParams

中有关依赖的代码如下:

boolean
4000
dependsOn(CoordinatorLayout parent, View child, View dependency) {
return dependency == mAnchorDirectChild|| (mBehavior != null && mBehavior.layoutDependsOn(parent, child, dependency));
}

返回两种结果，满足一种就是依赖的关系。一种是设置anchor ，另一种就是View的Behavior对另一个View有依赖。

如何处理这种依赖关系呢？既然Behavior能够监测另一个View的变化状况，那么肯定会有重新测量等操作。所以我们来看下面的代码

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
prepareChildren();
ensurePreDrawListener();
...省略代码
}

点进去

prepareChildren();

方法，看看里面写了什么…

private final List<View> mDependencySortedChildren = new ArrayList<View>();

//根据依赖关系对child进行排序
private void prepareChildren() {
mDependencySortedChildren.clear();
for (int i = 0, count = getChildCount(); i < count; i++) {
final View child = getChildAt(i);
final LayoutParams lp = getResolvedLayoutParams(child);
lp.findAnchorView(this, child);

mDependencySortedChildren.add(child);
}
//排序，按依赖关系排序，被依赖的View排在前面，保证被依赖的View先被测量绘制
selectionSort(mDependencySortedChildren, mLayoutDependencyComparator);
}

可以看到

mDependencySortedChildren

这个集合按照依赖关系将View存储了起来，至于为什么要排序，这个有性能上的考虑。

getResolvedLayoutParams(child)

这里有判断和解析注解的：

LayoutParams getResolvedLayoutParams(View child) {
final LayoutParams result = (LayoutParams) child.getLayoutParams();
//XML中如果定义了Behavior,那么result.mBehaviorResolved = true;
if (!result.mBehaviorResolved) {
Class<?> childClass = child.getClass();
DefaultBehavior defaultBehavior = null;
while (childClass != null &&
(defaultBehavior = childClass.getAnnotation(DefaultBehavior.class)) == null) {
childClass = childClass.getSuperclass();
}
if (defaultBehavior != null) {
try {
result.setBehavior(defaultBehavior.value().newInstance());
} catch (Exception e) {
Log.e(TAG, "Default behavior class " + defaultBehavior.value().getName() +
" could not be instantiated. Did you forget a default constructor?", e);
}
}
result.mBehaviorResolved = true;
}
return result;
}

依赖的集合也有了，那么接下来，就要添加各种监听了，监听绘制过程，监听View的层级变化了，所以在

ensurePreDrawListener

方法中先判断是否存在依赖关系，如果存在，直接注册相关的监听。

//添加或者删除绘制前的监听器
void ensurePreDrawListener() {
boolean hasDependencies = false;
final int childCount = getChildCount();
//判断下CoordinatorLayout的子view是否存在依赖关系
//如果存在的话就hasDependencies为true
for (int i = 0; i < childCount; i++) {
final View child = getChildAt(i);
if (hasDependencies(child)) {
hasDependencies = true;
break;
}
}

if (hasDependencies != mNeedsPreDrawListener) {
if (hasDependencies) {
addPreDrawListener();
} else {
removePreDrawListener();
}
}
}

...省略代码

void addPreDrawListener() {
if (mIsAttachedToWindow) {
// Add the listener
if (mOnPreDrawListener == null) {
mOnPreDrawListener = new OnPreDrawListener();
}
final ViewTreeObserver vto = getViewTreeObserver();
//在重绘之前，我们在onPreDraw里调用了dispatchOnDependentViewChanged方法
vto.addOnPreDrawListener(mOnPreDrawListener);
}

// Record that we need the listener regardless of whether or not we're attached.
// We'll add the real listener when we become attached.
mNeedsPreDrawListener = true;
}
...省略代码

class OnPreDrawListener implements ViewTreeObserver.OnPreDrawListener {
@Override
public boolean onPreDraw() {
dispatchOnDependentViewChanged(false);
return true;
}
}

ViewTreeObserver 是用来注册一个观察者来监听视图树，当视图树的布局、焦点、绘制、滚动等发生改变时，ViewTreeObserver都会收到通知。ViewTreeObserver不能被实例化，可以调用View.getViewTreeObserver()来获得。

dispatchOnDependentViewChanged

方法是核心的方法，它会遍历根据依赖关系排序好的子View集合，找到位置改变了的View，或者有锚定目标的View,并回调依赖这个View的Behavior的onDependentViewChanged方法

void dispatchOnDependentViewChanged(final boolean fromNestedScroll) {
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();

// 检查View设置了Anchor，然后处理
for (int j = 0; j < i; j++) {
final View checkChild = mDependencySortedChildren.get(j);

if (lp.mAnchorDirectChild == checkChild) {
//调整child，让孩子到正确的锚视图位置
offsetChildToAnchor(child, layoutDirection);
}
}

// Did it change? if not continue
final Rect oldRect = mTempRect1;
final Rect newRect = mTempRect2;
getLastChildRect(child, oldRect);
getChildRect(child, true, newRect);
//比较前后两次的位置信息
if (oldRect.equals(newRect)) {
continue;
}
//记录newRect到LayoutParams里
recordLastChildRect(child, newRect);

// 找到依赖当前View的Behavior来进行回调
for (int j = i + 1; j < childCount; j++) {
final View checkChild = mDependencySortedChildren.get(j);
final LayoutParams checkLp = (LayoutParams) checkChild.getLayoutParams();
final Behavior b = checkLp.getBehavior();

if (b != null && b.layoutDependsOn(this, checkChild, child)) {
if (!fromNestedScroll && checkLp.getChangedAfterNestedScroll()) {
// If this is not from a nested scroll and we have already been changed
// from a nested scroll, skip the dispatch and reset the flag
checkLp.resetChangedAfterNestedScroll();
continue;
}

final boolean handled = b.onDependentViewChanged(this, checkChild, child);

if (fromNestedScroll) {
// If this is from a nested scroll, set the flag so that we may skip
// any resulting onPreDraw dispatch (if needed)
checkLp.setChangedAfterNestedScroll(handled);
}
}
}
}
}

监听提供依赖的View的添加和移除，

HierarchyChangeListener

在View的添加和移除都会回调

private class HierarchyChangeListener implements OnHierarchyChangeListener {
...
@Override
public void onChildViewRemoved(View parent, View child) {
dispatchDependentViewRemoved(child);
...
}
}

然后回调给

Behavior#onDependentViewRemoved

void dispatchDependentViewRemoved(View view) {
final int childCount = mDependencySortedChildren.size();
boolean viewSeen = false;
for (int i = 0; i < childCount; i++) {
final View child = mDependencySortedChildren.get(i);
if (child == view) {
// 判断后续位置的View是否依赖当前View并回调
viewSeen = true;
continue;
}
if (viewSeen) {
CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams)child.getLayoutParams();
CoordinatorLayout.Behavior b = lp.getBehavior();
if (b != null && lp.dependsOn(this, child, view)) {
b.onDependentViewRemoved(this, child, view);
}
}
}
}

这样Behavior中关于依赖的关系就是这个样子了。

下面我们写一个简单的demo来测试一下，上面的方法。简单暴力，直接贴代码，也没有什么好讲的。

XML

<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"
tools:ignore="RtlHardcoded">

<android.support.design.widget.AppBarLayout
android:id="@+id/main.appbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

e666
<android.support.design.widget.CollapsingToolbarLayout
android:id="@+id/main.collapsing"
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_scrollFlags="scroll|exitUntilCollapsed|snap">

<ImageView
android:id="@+id/main.imageview.placeholder"
android:layout_width="match_parent"
android:layout_height="300dp"
android:scaleType="fitXY"
android:src="@drawable/huo"
android:tint="#11000000"
app:layout_collapseMode="parallax"
app:layout_collapseParallaxMultiplier="0.9"
android:contentDescription=""
tools:ignore="ContentDescription" />

<FrameLayout
android:id="@+id/main.framelayout.title"
android:layout_width="match_parent"
android:layout_height="100dp"
android:layout_gravity="bottom|center_horizontal"
android:background="@color/primary"
android:orientation="vertical"
app:layout_collapseMode="parallax"
app:layout_collapseParallaxMultiplier="0.3">

<LinearLayout
android:id="@+id/main.linearlayout.title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:orientation="vertical"
tools:ignore="UselessParent">

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:gravity="bottom|center"
android:text="@string/quila_name"
android:textColor="@android:color/white"
android:textSize="30sp" />

<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:layout_marginTop="4dp"
android:text="@string/quila_tagline"
android:textColor="@android:color/white" />

</LinearLayout>
</FrameLayout>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>

<android.support.v4.widget.NestedScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scrollbars="none"
app:layout_behavior="@string/appbar_scrolling_view_behavior">

<android.support.v7.widget.CardView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin="8dp"
app:cardElevation="8dp"
app:contentPadding="16dp">

<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:lineSpacingExtra="8dp"
android:text="@string/lorem"
android:textSize="18sp" />
</android.support.v7.widget.CardView>

</android.support.v4.widget.NestedScrollView>

<android.support.v7.widget.Toolbar
android:id="@+id/main.toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="@color/primary"
app:layout_anchor="@id/main.framelayout.title"
app:theme="@style/ThemeOverlay.AppCompat.Dark"
app:title="">

<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent">

<TextView
android:id="@+id/main.textview.title"
android:layout_width="wrap_content"
android:layout_centerInParent="true"
android:layout_height="wrap_content"
android:text="@string/quila_name2"
android:textColor="@android:color/white"
android:textSize="20sp" />

</RelativeLayout>
</android.support.v7.widget.Toolbar>

<ImageView
android:layout_width="@dimen/image_width"
android:layout_height="@dimen/image_width"
android:layout_gravity="center"
app:layout_behavior="myapplication.ImageCameraBehavior"
android:src="@drawable/ic_perm_camera_mic_black_48dp"/>
<ImageView
android:layout_width="@dimen/image_width"
android:layout_height="@dimen/image_width"
android:layout_gravity="center"
app:layout_behavior="myapplication.ImageHomeBehavior"
android:src="@drawable/ic_home_black_48dp"/>

</android.support.design.widget.CoordinatorLayout>

这里请注意ToolBar设置了锚定于上面的FrameLayout

主要是让两个ImageView有交互，所以我找了两张图片。然后先设置

ImageCameraBehavior

@SuppressWarnings("unused")
public class ImageCameraBehavior extends CoordinatorLayout.Behavior<ImageView> {

private final static String TAG = "kim";
private Context mContext;
private int toolBarYPosition;
private int currentImageX;
private int finalYPosition = 150;
private float changeBehaviorPoint;
private float childX;
private int imageHeight;

public ImageCameraBehavior(Context context, AttributeSet attrs) {
mContext = context;
}

@Override
public boolean layoutDependsOn(CoordinatorLayout parent, ImageView child, View dependency) {
return dependency instanceof Toolbar;
}

@Override
public boolean onDependentViewChanged(CoordinatorLayout parent, ImageView child, View dependency) {
InitProperties(child, dependency);

final int maxScrollDistance = toolBarYPosition;
//展开的百分比，初始是1.
float expandedPercentageFactor = dependency.getY() / maxScrollDistance;
if (expandedPercentageFactor < changeBehaviorPoint) {
//折叠的百分比
float heightFactor = (changeBehaviorPoint - expandedPercentageFactor) / changeBehaviorPoint;
//这里直接设置150硬编码，为了方便，实际开发请从dimens中获取
float distanceXToSubtract = ((currentImageX - 150) * heightFactor) + (child.getWidth() / 2);

float distanceYToSubtract = (toolBarYPosition)
* (1f - expandedPercentageFactor);

float iX = currentImageX - distanceXToSubtract;
float iY = toolBarYPosition - distanceYToSubtract;
Log.e(TAG, "ix=" + iX + "iy=" + iY);
child.setX(iX);
child.setY(iY);

float heightToSubtract = ((imageHeight - 200) * heightFactor);
CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams) child.getLayoutParams();
lp.width = (int) (imageHeight - heightToSubtract);
lp.height = (int) (imageHeight - heightToSubtract);
child.setLayoutParams(lp);

} else {

float distanceYToSubtract = ((toolBarYPosition)
* (1f - expandedPercentageFactor));

child.setX(currentImageX);
child.setY(toolBarYPosition - distanceYToSubtract);
CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams) child.getLayoutParams();
lp.width = imageHeight;
lp.height = imageHeight;
child.setLayoutParams(lp);
}
return true;
}
//初始化需要用到的参数
private void InitProperties(ImageView child, View dependency) {

if (toolBarYPosition == 0)
toolBarYPosition = (int) dependency.getY();
//        Log.e(TAG, "toolBarYPosition=" + toolBarYPosition);
if (currentImageX == 0)
currentImageX = (int) (child.getX() + child.getWidth());
//        Log.e(TAG, "currentImageX=" + currentImageX);
if (finalYPosition == 0)
finalYPosition = dependency.getHeight();//ToolBar高度
//        Log.e(TAG, "mFinalYPosition=" + finalYPosition);

if (imageHeight == 0) {
imageHeight = child.getHeight();
}
//设定一个阈值，滑动到设定的阈值范围之后，开始移动变化
if (changeBehaviorPoint == 0)
changeBehaviorPoint = child.getHeight() / (2f * (toolBarYPosition - finalYPosition));

}

}

代码比较好理解，就是一些移动与计算。另一个ImageView的Behavior也和这个差不多，就不贴了。而且这里面在计算上还有一些问题，没有时间去搞了。

那么看一眼效果图吧：



最近看到项目组的大佬们在重构代码，马上就要上线的项目，还要大改架构，真是不明白这是在干啥。之前用了1年半的时间，解决了将近4k个问题了，这样一搞，可能要重来一遍了。。。。。

幸亏和我没啥关系，大爷的。O(∩_∩)O