android - 自定义 CoordinatorLayout 行为

Question

这是我的布局:

<android.support.design.widget.CoordinatorLayout
   android:id="@+id/coordinator_layout"
   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">

<include layout="@layout/view_product_details"/>  // This contains a NestedScrollView

<LinearLayout android:id="@+id/indicator"
              android:layout_width="match_parent"
              android:layout_height="wrap_content"
              android:layout_gravity="right|bottom"
              android:layout_marginBottom="16dp"
              android:gravity="right|bottom"
              android:orientation="horizontal"
              app:layout_behavior="utils.CustomBehavior">

            // Some views.. 
</LinearLayout>

我希望当用户打开 Activity 时显示指示器布局，但当用户向下滚动时它应该隐藏。
当用户滚动回页面顶部时，我希望它再次显示。

所以我写了一个自定义行为类:

public class CustomBehavior extends CoordinatorLayout.Behavior {

private int totalY;

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

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

@Override
public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, View child, View directTargetChild, View target, int nestedScrollAxes) {
    return nestedScrollAxes == ViewCompat.SCROLL_AXIS_VERTICAL || 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);

    totalY += dyConsumed;

    Log.d("Scroll", "Total Y : " + totalY);

    LinearLayout fabMenu = (LinearLayout) child;
    FloatingActionButton wishListButton = (FloatingActionButton) fabMenu.findViewById(R.id.fab_wishlist);
    FloatingActionButton collectionButton = (FloatingActionButton) fabMenu.findViewById(R.id.fab_collection);
    FloatingActionButton tastedButton = (FloatingActionButton) fabMenu.findViewById(R.id.fab_tasted_list);

    if (totalY > 10) {
        wishListButton.hide(true);
        collectionButton.hide(true);
        tastedButton.hide(true);
    } else if (totalY < 10) {
        wishListButton.show(true);
        collectionButton.show(true);
        tastedButton.show(true);
    }
}
}

但是总Y值的加减不靠谱。
如何检测到用户已到达 NestedScrollView 的顶部？

或者有更好的方法来实现这样的事情吗？ 谢谢!

Answer 1

查看以下内容是否有帮助 - 在 onNestedScroll() 中:

使用

 if (target instanceof NestedScrollView) {
        final NestedScrollView nestedScrollView = (NestedScrollView) target;
        totalY = nestedScrollView.getScrollY();     
 }

代替

totalY += dyConsumed;