前沿
Behavior是Android新出的Design库里新增的布局概念。Behavior只有是CoordinatorLayout的直接子View才有意义。可以为任何View添加一个Behavior。Behavior是一系列回调。让你有机会以非侵入的为View添加动态的依赖布局，和处理父布局(CoordinatorLayout)滑动手势的机会。
一、 某个View需要监听另一个View的状态（比如：位置、大小、显示状体）
一个View监听另一个View，只需要在自定义Behavior重写：layoutDependsOn/onDependentViewChanged方法
自定义Behavior
public class CustomBehavior extends CoordinatorLayout.Behavior {
public CustomBehavior(Context context, AttributeSet attrs) {
super(context, attrs);
}
/**
* 用来决定需要监听哪些控件或者容器的状态（1.知道监听谁；2.什么状态改变）
* CoordinatorLayout parent ，父容器
* View child, 子控件---需要监听dependency这个view的视图们---观察者
* View dependency，你要监听的那个View
*/
@Override
public boolean layoutDependsOn(CoordinatorLayout parent, View child, View dependency) {
//还可以根据ID或者TAG来判断是哪一个TextView
return dependency instanceof TextView || super.layoutDependsOn(parent, child, dependency);
}
/**
* 当被监听的view发生改变的时候回调
* 可以在此方法里面做一些响应的联动动画等效果。
*/
@Override
public boolean onDependentViewChanged(CoordinatorLayout parent, View child, View dependency) {
//获取被监听的view的状态---垂直方向位置
int offset = dependency.getTop() - child.getTop();
//让child进行平移
ViewCompat.offsetTopAndBottom(child, offset);
child.animate().rotation(child.getTop()*90);
return true;
}
}
xml文件
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/tv1"
android:tag="tv1"
android:layout_width="80dp"
android:layout_height="80dp"
android:background="#ff0"
android:layout_gravity="left|top"
android:text="被观察--dependent" />
<ImageView
app:layout_behavior="com.example.mycustombehavior.CustomBehavior"
android:layout_width="80dp"
android:layout_height="80dp"
android:layout_gravity="right|top"
android:background="#f00"
android:src="@mipmap/ic_launcher"
android:text="观察者" />
</android.support.design.widget.CoordinatorLayout>
MainActivity中设置一个控件的点击事件
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.tv1).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
ViewCompat.offsetTopAndBottom(v, 10);
}
});
}
效果图：
tips:
1、自定义Behavior一定要重写构造方法不然就会报错（因为在CoordinatorLayout里利用反射去获取这个Behavior的时候就是拿的这个构造。）
2、layoutDependsOn(parent,child,dependency) ： 用来决定需要监听哪些控件或者容器的状态，parent父容器；child子控件也是观察者；dependency监听的View也是被观察者
3、onDependentViewChanged(parent,child,dependecy) ： 当被监听的View发生改变的时候回调，可以在此方法里面做一些相应的联动效果
二、某个View需要监听CoordinatorLayout里面所有控件的滑动状态。
某个View需要监听CoordinatorLayout里面所有控件的滑动效果需要重写：onStartNestedScroll/onNestedScroll，或则onNestedPreScroll方法，
==注意==：能被CoordinatorLayout捕获到的滑动状态的控件只有：recyclerView/NestScrollView/ViewPager
自定义Behavior
public class SyncScrollBehavior extends CoordinatorLayout.Behavior<View>{
public SyncScrollBehavior(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
public boolean onStartNestedScroll(@NonNull CoordinatorLayout coordinatorLayout, @NonNull View child, @NonNull View directTargetChild, @NonNull View target, int axes) {
return (axes == ViewCompat.SCROLL_AXIS_VERTICAL) || super.onStartNestedScroll(coordinatorLayout, child, directTargetChild, target, axes);
}
@Override
public void onNestedPreScroll(@NonNull CoordinatorLayout coordinatorLayout, @NonNull View child, @NonNull View target, int dx, int dy, @NonNull int[] consumed) {
int scrollY = target.getScrollY();
child.setScrollY(scrollY);
super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
}
/*@Override
public boolean onNestedFling(@NonNull CoordinatorLayout coordinatorLayout, @NonNull View child, @NonNull View target, float velocityX, float velocityY, boolean consumed) {
// 快速滑动的惯性移动（松开手指后还会有滑动效果）
((NestedScrollView)child).fling((int) velocityY);
return super.onNestedFling(coordinatorLayout, child, target, velocityX, velocityY, consumed);
}*/
}
xml文件
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<android.support.v4.widget.NestedScrollView
android:layout_width="80dp"
android:layout_height="match_parent"
android:layout_gravity="left" >
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:layout_width="80dp"
android:layout_height="180dp"
android:layout_gravity="left|top"
android:background="#ff0"
android:text="被观察--dependent" />
<TextView
android:layout_width="80dp"
android:layout_height="180dp"
android:layout_gravity="left|top"
android:background="#ff0"
android:text="被观察--dependent" />
...
</LinearLayout>
</android.support.v4.widget.NestedScrollView>
<android.support.v4.widget.NestedScrollView
android:layout_width="80dp"
android:layout_height="match_parent"
app:layout_behavior="com.example.mycustombehavior2.SyncScrollBehavior"
android:layout_gravity="right" >
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:layout_width="80dp"
android:layout_height="180dp"
android:layout_gravity="left|top"
android:background="#ff0"
android:text="被观察--dependent" />
<TextView
android:layout_width="80dp"
android:layout_height="180dp"
android:layout_gravity="left|top"
android:background="#ff0"
android:text="被观察--dependent" />
...
</LinearLayout>
</android.support.v4.widget.NestedScrollView>
</android.support.design.widget.CoordinatorLayout>
以上代码有点问题，就是当快速滑动的时候会出现错位，原因是惯性引起。
如下图：
有问题
所以解决问题有两种:
① 、需要在onNestedFling方法调用RecyclerView的fling方法（上面自定义Behavior里的注释的代码）
②、上面代码自定义Behavio的两个方法都是过时的，因此使用不是过时的就可以了
public class SyncScrollBehavior extends CoordinatorLayout.Behavior{
public SyncScrollBehavior(Context context, AttributeSet attrs) {
super(context, attrs);
}
@Override
public boolean onStartNestedScroll(@NonNull CoordinatorLayout coordinatorLayout,
@NonNull View child, @NonNull View directTargetChild, @NonNull View target, int axes, int type) {
return (axes == ViewCompat.SCROLL_AXIS_VERTICAL) || super.onStartNestedScroll(coordinatorLayout, child, directTargetChild, target, axes, type);
}
@Override
public void onNestedPreScroll(@NonNull CoordinatorLayout coordinatorLayout, @NonNull View child, @NonNull View target, int dx, int dy, @NonNull int[] consumed, int type) {
int scrollY = target.getScrollY();
child.setScrollY(scrollY);
super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed, type);
}
}
最终效果：
完美图
三、Behavior源码分析
在CoordinatorLayout源码parseBehavior函数中，此函数是在初始化CoordinatorLayout.LayoutParams的时候调用
public static class LayoutParams extends ViewGroup.MarginLayoutParams {
Behavior mBehavior;
...
LayoutParams(Context context, AttributeSet attrs) {
super(context, attrs);
final TypedArray a = context.obtainStyledAttributes(attrs,
R.styleable.CoordinatorLayout_LayoutParams);
...
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 (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);
...
}
其中CONSTRUCTOR_PARAMS
static final Class<?>[] CONSTRUCTOR_PARAMS = new Class<?>[] {
Context.class,
AttributeSet.class
};
由此可见必须要在子类中重写构造方法
根据上面文中的一和二来查看源码.
首先一中的layoutDependsOn和onDependentViewChanged是在CoordinatorLayout类onChildViewsChanged方法中进行调用
final void onChildViewsChanged(@DispatchChangeEvent final int type) {
......
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;
}
......
// Update any behavior-dependent views for the change
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 (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 flag
checkLp.resetChangedAfterNestedScroll();
continue;
}
final boolean handled;
switch (type) {
case EVENT_VIEW_REMOVED:
// EVENT_VIEW_REMOVED means that we need to dispatch
// onDependentViewRemoved() instead
b.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);
}
}
}
}
...
}
从源码中看出当Child为GONE时将不会执行后面的onDependenViewChanged等方法
通过查看onChildViewsChanged方法的调用的源头可以看出最终也是由onNestedPreScroll和onNestedScroll调用
@Override
public void onNestedScroll(View target, int dxConsumed, int dyConsumed,
int dxUnconsumed, int dyUnconsumed) {
final int childCount = getChildCount();
boolean accepted = false;
for (int i = 0; i < childCount; i++) {
final View view = getChildAt(i);
if (view.getVisibility() == GONE) {//如果为GONE则跳过
// If the child is GONE, skip...
continue;
}
final LayoutParams lp = (LayoutParams) view.getLayoutParams();
if (!lp.isNestedScrollAccepted()) {
continue;
}
final Behavior viewBehavior = lp.getBehavior();
if (viewBehavior != null) {
viewBehavior.onNestedScroll(this, view, target, dxConsumed, dyConsumed,
dxUnconsumed, dyUnconsumed);
accepted = true;//当调用了Behavior的onNestedScroll方法也将会调用onChildViewChanged方法
}
}
if (accepted) {
onChildViewsChanged(EVENT_NESTED_SCROLL);//调用了上面提到的onChildViewChanged方法进而调用layoutDependsOn和onDependentViewChanged
}
}
当时onStartNestedScroll方法并没有调用，当然这也和在onStartNestedScroll方法进行判断滑动View是竖直还是水平有关
@Override
public boolean onStartNestedScroll(View child, View target, int nestedScrollAxes) {
boolean handled = false;
final int childCount = getChildCount();
for (int i = 0; i < childCount; i++) {
final View view = getChildAt(i);
if (view.getVisibility() == View.GONE) {
// If it's GONE, don't dispatch
continue;
}
final LayoutParams lp = (LayoutParams) view.getLayoutParams();
final Behavior viewBehavior = lp.getBehavior();
if (viewBehavior != null) {
final boolean accepted = viewBehavior.onStartNestedScroll(this, view, child, target,
nestedScrollAxes);
handled |= accepted;
lp.acceptNestedScroll(accepted);
} else {
lp.acceptNestedScroll(false);
}
}
return handled;
}
至此简易的源码介绍结束
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