当单行 Snackbar 被刷掉时，FAB 没有动画

Question

我有一个支持FloatingActionButton 的CoordinatorLayout，我想在其中显示一个Snackbar..

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

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        ...
    </RelativeLayout>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab_add_field"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="end|bottom"
        android:layout_margin="@dimen/margin_default"
        android:layout_marginBottom="@dimen/profile_floating_margin_bottom"
        android:layout_marginRight="@dimen/profile_floating_margin_right"
        android:clickable="true"
        android:src="@drawable/icon_plus"
        app:backgroundTint="@color/brand_green"
        app:borderWidth="0dp"
        app:elevation="@dimen/fac_icon_elevation"/>
</android.support.design.widget.CoordinatorLayout>

现在我正在展示这样的 Snackbar

Snackbar.make(mRootView, "Something went wrong", Snackbar.LENGHT_SHORT)
        .show();

当它显示时，FAB 向上滑动，当它（在 LENGHT_SHORT 之后）消失时，FAB 向下滑动，一切正常。

但是，如果我将 Snackbar 滑开，FAB 会向下移动而没有幻灯片动画。它只是闪烁到它的初始位置。

有趣的是，如果 Snackbar 有两条线（无论它是否有动作）并且被滑开，FAB 会以通常的滑动动画正确地动画回到它的位置。

这是android.support.design.widget.CoordinatorLayout 中的错误吗？ 或android.support.design.widget.FloatingActionButton？有什么解决方法吗？

Answer 1

不使用基于Matteo Destro's post 的ValueAnimator 的Kotlin 解决方案：

class SnackBarAwareBehavior : CoordinatorLayout.Behavior<View> {

    companion object {
        private const val DURATION = 180
    }

    constructor() : super() {}

    constructor(context: Context, attrs: AttributeSet) : super(context, attrs) {}

    override fun layoutDependsOn(
        parent: CoordinatorLayout,
        child: View,
        dependency: View
    ): Boolean {
        return dependency is Snackbar.SnackbarLayout
    }

    override fun onDependentViewChanged(
        parent: CoordinatorLayout,
        child: View,
        dependency: View
    ): Boolean {
        if (dependency.visibility == View.VISIBLE) {
            moveChildUp(child, dependency.height + dependency.marginBottom)
            return true
        }
        return false
    }

    override fun onDependentViewRemoved(parent: CoordinatorLayout, child: View, dependency: View) {
        moveChildToInitialPosition(child)
    }

    private fun moveChildUp(child: View, translation: Int) {
        child.animate()
            .translationY((-translation).toFloat())
            .setInterpolator(DecelerateInterpolator())
            .setDuration(DURATION.toLong())
            .start()
    }

    private fun moveChildToInitialPosition(child: View) {
        child.animate()
            .translationY(0f)
            .setInterpolator(AccelerateInterpolator())
            .setDuration(DURATION.toLong())
            .start()
    }
}

Answer 2

我最近遇到了同样的问题，我最终为 FAB 创建了一个自定义布局行为类，以便在轻扫小吃栏时执行动画。

创建这个类：

public class SnackbarAwareBehavior extends CoordinatorLayout.Behavior<View> {

    private static final int ANIMATION_DURATION = 180;

    public SnackbarAwareBehavior() {
        super();
    }

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

    @Override
    public boolean layoutDependsOn(@NonNull CoordinatorLayout parent, @NonNull View child, @NonNull View dependency) {
        return dependency instanceof Snackbar.SnackbarLayout;
    }

    @Override
    public boolean onDependentViewChanged(@NonNull CoordinatorLayout parent, @NonNull View child, @NonNull View dependency) {
        if (dependency.getVisibility() == View.VISIBLE) {
            // Change the translation of the FAB only if the snackbar is visible
            child.setTranslationY(dependency.getTranslationY() - getTranslationYBottom(dependency));
            return true;
        }
        return false;
    }

    @Override
    public void onDependentViewRemoved(@NonNull CoordinatorLayout parent, @NonNull View child, @NonNull View dependency) {
        if (dependency.getVisibility() == View.VISIBLE) {
            child.setTranslationY(0f);
        } else {
            // Execute the animation only if the snackbar has been swiped away, i.e. when it's not visible
            ValueAnimator animator = new ValueAnimator();
            animator.setFloatValues(child.getTranslationY(), 0f);
            animator.setInterpolator(FAST_OUT_SLOW_IN_INTERPOLATOR);
            animator.setDuration(ANIMATION_DURATION);
            animator.addUpdateListener(animation -> child.setTranslationY((float) animation.getAnimatedValue()));
            animator.start();
        }
    }

    private int getTranslationYBottom(View view) {
        // Get the translation position of the snackbar when it's hidden.
        // Method taken from BaseTransientBottomBar.Behavior class.
        int translationY = view.getHeight();
        ViewGroup.LayoutParams layoutParams = view.getLayoutParams();
        if (layoutParams instanceof ViewGroup.MarginLayoutParams) {
            translationY += ((ViewGroup.MarginLayoutParams) layoutParams).bottomMargin;
        }
        return translationY;
    }

}

然后在你的布局中：

 <android.support.design.widget.FloatingActionButton
      ...
      app:layout_behavior="your.package.SnackbarAwareBehavior">