主页：http://cherylgood.cn/20170302/51

官网描述为：CoordinatorLayout是一个增强版的FrameLayout（继承自ViewGroup）

用途：

1、作为应用的顶层视图。

2、作为一个可以指定子View之间相互作用的容器，通过给CoordinatorLayout的子View指定CoordinatorLayout.Behavior 来定义子view之间的相互作用。（你可以想象成：CoordinatorLayout相当于在两个View之间充当中介,这样子的好处就是两个view之间的耦合度降低了，只需要跟coordinatorLayout打交到即可，而CoordinatorLayout.Behavior 相当于两个view之间的协议，即通过怎样的规则来约束双方的行为。）

设计概念：

1. CoordinatorLayout：CoordinatorLayout 作为最顶层视图，将负责管理所有的子view，使其内部的子View彼此间产生一种联系。这个联系通过Behavior来实现（包括了滑动状态的处理以及View状态的处理）。
2. AppBarLayout：AppBarLayout 继承自限性布局，作为增强版的线性布局，他增加了对滑动手势的处理。
3. Behavior：Behavior 是google新提出的，能够让你以非侵入式的方式去处理目标View和其他View的交互行为。Behavior需要设置在触发事件（比如滚动）的view上，且这个View必须是CoordinatorLayout的第一层级下的子view，否则没有效果，因为Behavior的初始化是在CoordinatorLayout的LayoutParams中通过反射完成的。
   Behavior实例化方式：1、通过app:layout_behavior声明 ；2、在你的自定义View类上添加@DefaultBehavior(MyBehavior.class)；
4. Behavior只是个接口，其调用是由NestedScrollingParent与NestedScrollingChild接口负责调用。

接下来我们通过阅读部分源码进行学习：

首先，我们从两个view是如何通过coordinatorlayout产生关联来入手；看代码

LayoutParams(Context context, AttributeSet attrs) {super(context, attrs);final TypedArray a = context.obtainStyledAttributes(attrs,R.styleable.CoordinatorLayout_Layout);this.gravity = a.getInteger(R.styleable.CoordinatorLayout_Layout_android_layout_gravity,Gravity.NO_GRAVITY);mAnchorId = a.getResourceId(R.styleable.CoordinatorLayout_Layout_layout_anchor,View.NO_ID);this.anchorGravity = a.getInteger(R.styleable.CoordinatorLayout_Layout_layout_anchorGravity,Gravity.NO_GRAVITY);this.keyline = a.getInteger(R.styleable.CoordinatorLayout_Layout_layout_keyline,-1);insetEdge = a.getInt(R.styleable.CoordinatorLayout_Layout_layout_insetEdge, 0);dodgeInsetEdges = a.getInt(R.styleable.CoordinatorLayout_Layout_layout_dodgeInsetEdges, 0);mBehaviorResolved = a.hasValue(R.styleable.CoordinatorLayout_Layout_layout_behavior);if (mBehaviorResolved) {mBehavior = parseBehavior(context, attrs, a.getString(R.styleable.CoordinatorLayout_Layout_layout_behavior));}a.recycle();if (mBehavior != null) {// If we have a Behavior, dispatch that it has been attachedmBehavior.onAttachedToLayoutParams(this);}}

从

mBehaviorResolved = a.hasValue(R.styleable.CoordinatorLayout_Layout_layout_behavior);
if (mBehaviorResolved) {mBehavior = parseBehavior(context, attrs, a.getString(R.styleable.CoordinatorLayout_Layout_layout_behavior));
}

这几句我们可以看到。
mBehaviorResolved 是个boolean 变量，如果

R.styleable.CoordinatorLayout_Layout_layout_behavior CoordinatorLayout的

layout_behavior这个字段设置有值，
1、mBehaviorResolved = true -》调用parseBehavior方法，将所需参数传入通过java的反射技术返回一个Behavior实例。

static Behavior parseBehavior(Context context, AttributeSet attrs, String name) {if (TextUtils.isEmpty(name)) {return null;}final String fullName;if (name.startsWith(".")) {// Relative to the app package. Prepend the app package name.fullName = context.getPackageName() + name;} else if (name.indexOf('.') >= 0) {// Fully qualified package name.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> constructors = sConstructors.get();if (constructors == null) {constructors = new HashMap<>();sConstructors.set(constructors);}Constructor c = constructors.get(fullName);if (c == null) {final Class clazz = (Class) 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);}}

通过这一段我们可以知道，最后是通过调用Behavior的参数为(context,attrs)的构造函数进行实例化。
实例化出Behavior之后我们会调用behavior的onAttachedToLayoutParams方法 将LayoutParams的实例对象传进去mBehavior.onAttachedToLayoutParams(this);

mBehavior.onAttachedToLayoutParams是一个当LayoutParams被实例化后的回调方法。通过这里，我们的

CoordinatorLayout就能够跟用layout_behavior标识的子View产生联系。当子View发生变化时，CoordinatorLayout又是如何处理的的，请看下面代码：

final void onChildViewsChanged(@DispatchChangeEvent final int type) {final int layoutDirection = ViewCompat.getLayoutDirection(this);final int childCount = mDependencySortedChildren.size();final Rect inset = acquireTempRect();final Rect drawRect = acquireTempRect();final Rect lastDrawRect = acquireTempRect();for (int i = 0; i < childCount; i++) {final View child = mDependencySortedChildren.get(i);final LayoutParams lp = (LayoutParams) child.getLayoutParams();if (type == EVENT_PRE_DRAW && child.getVisibility() == View.GONE) {// Do not try to update GONE child views in pre draw updates.continue;}// Check child views before for anchorfor (int j = 0; j < i; j++) {final View checkChild = mDependencySortedChildren.get(j);if (lp.mAnchorDirectChild == checkChild) {offsetChildToAnchor(child, layoutDirection);}}// Get the current draw rect of the viewgetChildRect(child, true, drawRect);// Accumulate inset sizesif (lp.insetEdge != Gravity.NO_GRAVITY && !drawRect.isEmpty()) {final int absInsetEdge = GravityCompat.getAbsoluteGravity(lp.insetEdge, layoutDirection);switch (absInsetEdge & Gravity.VERTICAL_GRAVITY_MASK) {case Gravity.TOP:inset.top = Math.max(inset.top, drawRect.bottom);break;case Gravity.BOTTOM:inset.bottom = Math.max(inset.bottom, getHeight() - drawRect.top);break;}switch (absInsetEdge & Gravity.HORIZONTAL_GRAVITY_MASK) {case Gravity.LEFT:inset.left = Math.max(inset.left, drawRect.right);break;case Gravity.RIGHT:inset.right = Math.max(inset.right, getWidth() - drawRect.left);break;}}// Dodge inset edges if necessaryif (lp.dodgeInsetEdges != Gravity.NO_GRAVITY && child.getVisibility() == View.VISIBLE) {offsetChildByInset(child, inset, layoutDirection);}if (type == EVENT_PRE_DRAW) {// Did it change? if not continuegetLastChildRect(child, lastDrawRect);if (lastDrawRect.equals(drawRect)) {continue;}recordLastChildRect(child, drawRect);}// Update any behavior-dependent views for the changefor (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 (type == EVENT_PRE_DRAW && checkLp.getChangedAfterNestedScroll()) {// If this is from a pre-draw and we have already been changed// from a nested scroll, skip the dispatch and reset the flagcheckLp.resetChangedAfterNestedScroll();continue;}final boolean handled;switch (type) {case EVENT_VIEW_REMOVED:// EVENT_VIEW_REMOVED means that we need to dispatch// onDependentViewRemoved() insteadb.onDependentViewRemoved(this, checkChild, child);handled = true;break;default:// Otherwise we dispatch onDependentViewChanged()handled = b.onDependentViewChanged(this, checkChild, child);break;}if (type == EVENT_NESTED_SCROLL) {// If this is from a nested scroll, set the flag so that we may skip// any resulting onPreDraw dispatch (if needed)checkLp.setChangedAfterNestedScroll(handled);}}}}releaseTempRect(inset);releaseTempRect(drawRect);releaseTempRect(lastDrawRect);}

我们可以看到文档说明，大概意思是当子view发生变化会调用该方法。该方法会遍历所有的子view，
然后调用如下代码，layoutDependsOn（）这个方法是做什么的呢？我们接下来看下该方法。

if (b != null && b.layoutDependsOn(this, checkChild, child)) {if (type == EVENT_PRE_DRAW && checkLp.getChangedAfterNestedScroll()) {// If this is from a pre-draw and we have already been changed// from a nested scroll, skip the dispatch and reset the flagcheckLp.resetChangedAfterNestedScroll();continue;}final boolean handled;switch (type) {case EVENT_VIEW_REMOVED:// EVENT_VIEW_REMOVED means that we need to dispatch// onDependentViewRemoved() insteadb.onDependentViewRemoved(this, checkChild, child);handled = true;break;default:// Otherwise we dispatch onDependentViewChanged()handled = b.onDependentViewChanged(this, checkChild, child);break;}if (type == EVENT_NESTED_SCROLL) {// If this is from a nested scroll, set the flag so that we may skip// any resulting onPreDraw dispatch (if needed)checkLp.setChangedAfterNestedScroll(handled);}}

/*** Determine whether the supplied child view has another specific sibling view as a* layout dependency.**

This method will be called at least once in response to a layout request. If it * returns true for a given child and dependency view pair, the parent CoordinatorLayout * will:

*

1. *
2. Always lay out this child after the dependent child is laid out, regardless * of child order.
3. *
4. Call {@link #onDependentViewChanged} when the dependency view's layout or * position changes.
5. *

** @param parent the parent view of the given child* @param child the child view to test* @param dependency the proposed dependency of child* @return true if child's layout depends on the proposed dependency's layout,*         false otherwise** @see #onDependentViewChanged(CoordinatorLayout, android.view.View, android.view.View)*/public boolean layoutDependsOn(CoordinatorLayout parent, V child, View dependency) {return false;}

这个方法，大概意思是如果我们返回true，说明当前发生变化的子view发生变化时。也就是该方法决定我们用

layout_behavior标识的view是否应该做出相应的变化。默认返回false，该方法需要我们在创建自己的Behavior时重写。
当返回true的话，可以看到会调用

b.onDependentViewRemoved(this, checkChild, child);

handled = b.onDependentViewChanged(this, checkChild, child);为了更好理解这两句代码，我们举个例子，假设有ViewA和ViewB ，当ViewB发生移动时，ViewA要向反方向移动。
1、当ViewB被移除时会调用

b.onDependentViewRemoved(this, checkChild, child);
2、当ViewB发生变化时，会调用

handled = b.onDependentViewChanged(this, checkChild, child);
那么我们就可以在

b.onDependentViewChanged里面写我们的功能代码了。通过以上的分析，希望能帮到大家对CoordinatorLayout的协作调用过程有一些些的帮助。

http://cherylgood.cn/20170302/55