自定义Behavior（二）

上次讲了自定义Behavior的child监听dependency的状态变化，这次就接着说child监听实现了NestedScrollingChild的接口的dependency的滑动状态。 需要重写两个方法

@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 onNestedScroll(CoordinatorLayout coordinatorLayout, View child, View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed) { super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed); }

先来看onStartNestedScroll，这个方法表明我们在这次滑动中关心的方向，如果是X轴，则return nestedScrollAxes == ViewCompat.SCROLL_AXIS_HORIZONTAL;若是关心Y轴方向的滑动，return nestedScrollAxes == ViewCompat.SCROLL_AXIS_VERTICAL即可。

onNestedScroll这个方法才是我们关注的重点，coordinatorLayout这个参数就不说了，child是指设置了这个Behavior的coordinatorLayout的子View，target则是前面提到的实现了NestedScrollingChild的接口的dependency。dxConsumed、dyConsumed是指x、y轴方向上target消费的像素值，简单来说，就是滚动的距离，至于后面两个参数，百度了，也看了源码的注释，还是不太明白，翻译过来字面意思就是：不被目标自身的滚动操作所消耗的垂直、水平像素，而是用户要求的(本来以为是调用scrollto之类方法产生的，试过了发现不是)。

说完这么多屁话，看个例子 先上效果图 仔细看还是和之前的有点区别，在上滑和下滑时，隐藏显示FloatingActionButton和BottomBar。

XML

<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.design.widget.AppBarLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar" app:elevation="0dp"> <TextView android:layout_width="match_parent" android:layout_height="50dp" android:gravity="center" android:text="topBar" app:layout_scrollFlags="scroll|enterAlways" /> </android.support.design.widget.AppBarLayout> <android.support.v4.widget.NestedScrollView android:layout_width="match_parent" android:layout_height="match_parent" android:scrollbars="none" app:behavior_overlapTop="30dp" app:layout_behavior="@string/appbar_scrolling_view_behavior"> <include layout="@layout/layout_main" /> </android.support.v4.widget.NestedScrollView> <TextView android:layout_width="match_parent" android:layout_height="50dp" android:layout_gravity="bottom" android:background="@color/colorPrimary" android:gravity="center" android:text="bottomBar" app:layout_behavior=".BottomScrollBehavior" /> <android.support.design.widget.FloatingActionButton android:layout_width="50dp" android:layout_height="50dp" android:layout_gravity="bottom|right" android:layout_marginBottom="70dp" android:layout_marginRight="20dp" android:src="@mipmap/ic_launcher_round" app:elevation="5dp" app:layout_behavior=".ScrollingBehavior" /> </android.support.design.widget.CoordinatorLayout>

也和上一篇的相似，唯一的区别就是BottomBar和FloatingActionButton的Behavior换了 再看自定义的Behavior

ScrollingBehavior

public class ScrollingBehavior extends CoordinatorLayout.Behavior<FloatingActionButton> { //是否正在执行动画的标示符 private boolean isAnimator; public ScrollingBehavior(Context context, AttributeSet attrs) { super(context, attrs); } @Override public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, FloatingActionButton child, View directTargetChild, View target, int nestedScrollAxes) { return nestedScrollAxes == ViewCompat.SCROLL_AXIS_VERTICAL; } @Override public void onNestedScroll(CoordinatorLayout coordinatorLayout, FloatingActionButton child, View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed) { if ((dyConsumed > 0 || dyUnconsumed > 0) && !isAnimator && child.getVisibility() == View.VISIBLE) { hideAnimator(child); } else if ((dyConsumed < 0 || dyUnconsumed < 0) && !isAnimator && child.getVisibility() != View.VISIBLE) { showAnimator(child); } } private void showAnimator(View view) { view.setVisibility(View.VISIBLE); ViewCompat.animate(view) .scaleX(1.0f) .scaleY(1.0f) .alpha(1.0f) .setDuration(800) .setListener(new ViewPropertyAnimatorListener() { @Override public void onAnimationStart(View view) { isAnimator = true; } @Override public void onAnimationEnd(View view) { isAnimator = false; } @Override public void onAnimationCancel(View view) { isAnimator = false; } }) .start(); } private void hideAnimator(View view) { ViewCompat.animate(view) .scaleX(0) .scaleY(0) .alpha(0) .setDuration(800) .setListener(new ViewPropertyAnimatorListener() { @Override public void onAnimationStart(View view) { isAnimator = true; } @Override public void onAnimationEnd(View view) { isAnimator = false; view.setVisibility(View.INVISIBLE); } @Override public void onAnimationCancel(View view) { isAnimator = false; } }) .start(); } }

BottomScrollBehavior

public class BottomScrollBehavior extends CoordinatorLayout.Behavior<View> { private boolean isAnimator; public BottomScrollBehavior(Context context, AttributeSet attrs) { super(context, attrs); } @Override public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, View child, View directTargetChild, View target, int nestedScrollAxes) { return nestedScrollAxes == ViewCompat.SCROLL_AXIS_VERTICAL; } @Override public void onNestedScroll(CoordinatorLayout coordinatorLayout, View child, View target, int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed) { if ((dyConsumed > 0 || dyUnconsumed > 0) && !isAnimator && child.getTranslationY() == 0) { hideAnimator(child); } else if ((dyConsumed < 0 || dyUnconsumed < 0) && !isAnimator && child.getTranslationY() == child.getHeight()) { showAnimator(child); } super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed); } private void showAnimator(View view) { ViewCompat.animate(view) .translationY(0) .setDuration(800) .setListener(new ViewPropertyAnimatorListener() { @Override public void onAnimationStart(View view) { isAnimator = true; } @Override public void onAnimationEnd(View view) { isAnimator = false; } @Override public void onAnimationCancel(View view) { isAnimator = false; } }) .start(); } private void hideAnimator(View view) { ViewCompat.animate(view) .translationY(view.getHeight()) .setDuration(800) .setListener(new ViewPropertyAnimatorListener() { @Override public void onAnimationStart(View view) { isAnimator = true; } @Override public void onAnimationEnd(View view) { isAnimator = false; } @Override public void onAnimationCancel(View view) { isAnimator = false; } }) .start(); } }