Behavior是CoordinatorLayout的一个抽象内部类

public abstract static class Behavior<V extends View> {
      public Behavior() {
      }

      public Behavior(Context context, AttributeSet attrs) {
      }
      ...
}

泛型对应的就是监听的view

自定义behavior有两种情况

1.某个view监听另一个view的状态变化，例如大小、位置、显示状态等

• layoutDependsOn 方法
• onDependentViewChanged 方法

2.某个view监听CoordinatorLayout里的滑动状态

• onStartNestedScroll 方法
• onNestedPreScroll 方法

下面定义一个behavior ，实现一个view监控另一个view实现滑动

public class MyBehavior extends CoordinatorLayout.Behavior<View> {

    public MyBehavior(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean layoutDependsOn(CoordinatorLayout parent, View child, View dependency) {
        return super.layoutDependsOn(parent, child, dependency);
    }

    @Override
    public boolean onDependentViewChanged(CoordinatorLayout parent, View child, View dependency) {
        ViewCompat.offsetLeftAndRight();
        return super.onDependentViewChanged(parent, child, dependency);
    }
}

带有两个参数的这个构造必须重载，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。重两个方法layoutDependsOn和onDependentViewChanged，这两个方法的参数都是一样的，第二个参数是我们设置这个Behavior的View，第三个是我们关心的那个View。如何知道关心的哪个呢？layoutDependsOn的返回值决定了一切！

比如一个TextView

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

设置了关心谁，就是在该view状态发生变化时我们的view要做出一些变化

@Override
public boolean onDependentViewChanged(CoordinatorLayout parent, View child, View dependency) {
    child.setX(dependency.getX()+200);
    child.setY(dependency.getY()+200);
    child.setText(dependency.getX()+","+dependency.getY());
    return true;
}

获取两个View的距离顶部值的差，然后让child的位置进行移动

那么xml我么可以这样写

<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:onclick="click"
        android:id="@+id/button"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:background="#57caa1"
        android:gravity="center"
        android:textColor="#fff"
        android:layout_gravity="top|left"
        android:text="啊哈"/>

    <TextView
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:background="#F26D7E"
        android:gravity="center"
        android:textColor="@android:color/white"
        android:layout_gravity="top|right"
        app:layout_behavior="com.emplme.MytBehavior"
        android:text="555666"/>
</android.support.design.widget.CoordinatorLayout>

第二个textView就是我们的view设置了我们自定义的behavior

然后

@Override protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    findViewById(R.id.button).setOnTouchListener(new View.OnTouchListener() {
      @Override public boolean onTouch(View v, MotionEvent event) {
        switch (event.getAction()){

          case MotionEvent.ACTION_MOVE:
            v.setX(event.getRawX()-v.getWidth()/2);
            v.setY(event.getRawY()-v.getHeight()/2);
            break;
        }
        return false;
      }
    });

  }

接下来第二种情况

public class ScrollBehavior extends CoordinatorLayout.Behavior<View> {

    public ScrollBehavior(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, View child, View directTargetChild, View target, int nestedScrollAxes) {
        return super.onStartNestedScroll(coordinatorLayout, child, directTargetChild, target, nestedScrollAxes);
    }

    @Override
    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, View child, View target, int dx, int dy, int[] consumed) {
        super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
    }

    @Override
    public boolean onNestedPreFling(CoordinatorLayout coordinatorLayout, View child, View target, float velocityX, float velocityY) {
        return super.onNestedPreFling(coordinatorLayout, child, target, velocityX, velocityY);
    }
}

onStartNestedScroll返回值表示要不要关心CoordinatorLayout滑动，那个方向的

@Override
public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, View child, View directTargetChild, View target, int nestedScrollAxes) {
    return (nestedScrollAxes & ViewCompat.SCROLL_AXIS_VERTICAL) != 0;
}
当然我们这是Y轴方向的

onNestedPreScroll关于滑动的处理

@Override
public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, View child, View target, int dx, int dy, int[] consumed) {
    super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
    int leftScrolled = target.getScrollY();
    child.setScrollY(leftScrolled);
}

列子如下：

public class ScrollAwareFABBehavior extends CoordinatorLayout.Behavior<View> {

    private static final Interpolator INTERPOLATOR = new FastOutSlowInInterpolator();
    private boolean mIsAnimatingOut = false;

    public ScrollAwareFABBehavior(Context context, AttributeSet attrs) {
        super();
    }


    @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;

    }

    @Override
    public void onNestedPreScroll(@NonNull CoordinatorLayout coordinatorLayout, @NonNull View child, @NonNull View target, int dx, int dy, @NonNull int[] consumed, int type) {
        super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed, type);

        if (dy>0 && !this.mIsAnimatingOut && child.getVisibility() == View.VISIBLE) {
            animateOut(child);
        } else if (dy < 0 && child.getVisibility() != View.VISIBLE) {
            animateIn(child);
        }
    }

    private void animateOut(final View button) {

        ViewCompat.animate(button).translationY(button.getHeight() + getMarginBottom(button)).setInterpolator(INTERPOLATOR).withLayer()
                .setListener(new ViewPropertyAnimatorListener() {
                    @Override
                    public void onAnimationStart(View view) {
                        ScrollAwareFABBehavior.this.mIsAnimatingOut = true;
                    }

                    @Override
                    public void onAnimationEnd(View view) {
                        ScrollAwareFABBehavior.this.mIsAnimatingOut = false;
                        view.setVisibility(View.INVISIBLE);
                    }

                    @Override
                    public void onAnimationCancel(View view) {
                        ScrollAwareFABBehavior.this.mIsAnimatingOut = false;
                    }
                }).start();
    }

    private void animateIn(View button) {
        button.setVisibility(View.VISIBLE);
        ViewCompat.animate(button).translationY(0)
                .setInterpolator(INTERPOLATOR).withLayer().setListener(null)
                .start();
    }

    private int getMarginBottom(View v) {
        int marginBottom = 0;
        final ViewGroup.LayoutParams layoutParams = v.getLayoutParams();
        if (layoutParams instanceof ViewGroup.MarginLayoutParams) {
            marginBottom = ((ViewGroup.MarginLayoutParams) layoutParams).bottomMargin;
        }
        return marginBottom;
    }

}

结尾在放上一些自定义behavior的炫酷效果

CoordinatorLayout 自定义Behavior并不难，由简到难手把手带你撸三款
CoordinatorLayout与滚动的处理--基础
自定义CoordinatorLayout的Behavior实现知乎和简书快速返回效果
CoordinatorLayout高级用法-自定义Behavior