Android中Fab(FloatingActionButton)实现上下滑动的渐变效果

前言

Promoted Actions是指一种操作按钮，它不是放在actionbar中，而是直接在可见的UI布局中（当然这里的UI指的是setContentView所管辖的范围）。因此它更容易在代码中被获取到（试想如果你要在actionbar中获取一个菜单按钮是不是很难？），Promoted Actions往往主要用于一个界面的主要操作，比如在email的邮件列表界面，promoted action可以用于接受一个新邮件。promoted action在外观上其实就是一个悬浮按钮，更常见的是漂浮在界面上的圆形按钮，一般我直接将promoted action称作悬浮按钮，英文名称Float Action Button 简称（FAB，不是FBI哈）。

系统自带的 Fab 也会随着页面上下滚动,但是淡出或者进入的效果太不自然。

这里记录一个小知识点,Fab 随着页面的 RecyclerView 上下滚动而渐变的动画效果。

包含 Fab 控件的布局如下:

实现的 Java 代码如下:

public class ScrollAwareFABBehavior extends FloatingActionButton.Behavior {
 private static final Interpolator INTERPOLATOR = new FastOutSlowInInterpolator();
 private boolean mIsAnimatingOut = false;

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

 @Override
 public boolean onStartNestedScroll(final CoordinatorLayout coordinatorLayout, final FloatingActionButton child,
     final View directTargetChild, final View target, final int nestedScrollAxes) {
 // Ensure we react to vertical scrolling
 return nestedScrollAxes == ViewCompat.SCROLL_AXIS_VERTICAL
  || super.onStartNestedScroll(coordinatorLayout, child, directTargetChild, target, nestedScrollAxes);
 }

 @Override
 public void onNestedScroll(final CoordinatorLayout coordinatorLayout, final FloatingActionButton child,
    final View target, final int dxConsumed, final int dyConsumed,
    final int dxUnconsumed, final int dyUnconsumed) {
 super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dyConsumed, dxUnconsumed, dyUnconsumed);
 if (dyConsumed > 0 && !this.mIsAnimatingOut && child.getVisibility() == View.VISIBLE) {
  // User scrolled down and the FAB is currently visible -> hide the FAB
  animateOut(child);
 } else if (dyConsumed < 0 && child.getVisibility() != View.VISIBLE) {
  // User scrolled up and the FAB is currently not visible -> show the FAB
  animateIn(child);
 }
 }

 // Same animation that FloatingActionButton.Behavior uses to hide the FAB when the AppBarLayout exits
 private void animateOut(final FloatingActionButton button) {
 if (Build.VERSION.SDK_INT >= 14) {
  ViewCompat.animate(button).scaleX(0.0F).scaleY(0.0F).alpha(0.0F).setInterpolator(INTERPOLATOR).withLayer()
   .setListener(new ViewPropertyAnimatorListener() {
   public void onAnimationStart(View view) {
    ScrollAwareFABBehavior.this.mIsAnimatingOut = true;
   }

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

   public void onAnimationEnd(View view) {
    ScrollAwareFABBehavior.this.mIsAnimatingOut = false;
    view.setVisibility(View.GONE);
   }
   }).start();
 } else {
  Animation anim = AnimationUtils.loadAnimation(button.getContext(), R.anim.fab_out);
  anim.setInterpolator(INTERPOLATOR);
  anim.setDuration(200L);
  anim.setAnimationListener(new Animation.AnimationListener() {
  public void onAnimationStart(Animation animation) {
   ScrollAwareFABBehavior.this.mIsAnimatingOut = true;
  }

  public void onAnimationEnd(Animation animation) {
   ScrollAwareFABBehavior.this.mIsAnimatingOut = false;
   button.setVisibility(View.GONE);
  }

  @Override
  public void onAnimationRepeat(final Animation animation) {
  }
  });
  button.startAnimation(anim);
 }
 }

 // Same animation that FloatingActionButton.Behavior uses to show the FAB when the AppBarLayout enters
 private void animateIn(FloatingActionButton button) {
 button.setVisibility(View.VISIBLE);
 if (Build.VERSION.SDK_INT >= 14) {
  ViewCompat.animate(button).scaleX(1.0F).scaleY(1.0F).alpha(1.0F)
   .setInterpolator(INTERPOLATOR).withLayer().setListener(null)
   .start();
 } else {
  Animation anim = AnimationUtils.loadAnimation(button.getContext(), R.anim.fab_in);
  anim.setDuration(200L);
  anim.setInterpolator(INTERPOLATOR);
  button.startAnimation(anim);
 }
 }
}

fab_in.xml 文件如下(fab_out.xml 同理),当然要改变淡出或者进入的样式,一般修改这里的 XML 文件就可以了 :

大致效果就像上面。

总结

好了，以上就是这篇文章的全部内容了，希望本文的内容对各位Android开发者们能带来一定的帮助，如果有疑问大家可以留言交流。