我将 FloatingActionButton 设置为屏幕底部，我想为按钮设置动画。

• 向下滚动时隐藏
• 向上滚动时显示

就像谷歌在他们的 Google+ app 中实现的一样.

我认为 CoordinatorLayout 和 AppBarLayout 是必需的，但如何实现它以将其与 FloatingActionButton 一起使用？

最佳答案

您可以使用默认的 FloatingActionButton 更改它的 默认 Behavior 使用 app:layout_behavior 属性:

您可以使用如下布局:

 <android.support.design.widget.CoordinatorLayout     
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:id="@+id/main_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
            app:layout_scrollFlags="scroll|enterAlways" />

    </android.support.design.widget.AppBarLayout>

    // Your layout, for example a RecyclerView
    <RecyclerView
         .....
         app:layout_behavior="@string/appbar_scrolling_view_behavior" />

    <android.support.design.widget.FloatingActionButton
            android:id="@+id/fab"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="end|bottom"
            android:layout_margin="@dimen/fab_margin"
            android:src="@drawable/ic_done"      
            app:layout_behavior="com.support.android.designlibdemo.ScrollAwareFABBehavior" />

    </android.support.design.widget.CoordinatorLayout>

使用 app:layout_behavior，您可以定义自己的 Behavior。使用 onStartNestedScroll() 和 onNestedScroll() 方法，您可以与滚动事件进行交互。

您可以使用这样的行为。 可以找到原码here:

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);
        }
    }
}

关于android - 如何像在 Android 的 Google+ 应用程序中一样为 FloatingActionButton 设置动画？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30937028/