如何仅在 Scrollview/Recyclerview 的底部添加淡入淡出边缘？

Question

我用于requiresFadingEdge=true在底部添加淡入淡出效果，但问题是它也在顶部显示淡入淡出效果？如何在向下滚动时禁用顶部的淡入淡出效果？

我在底部附上了屏幕截图。

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:background="@color/grey">
  <android.support.v7.widget.RecyclerView
        android:id="@+id/list_recyclerview"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="?attr/actionBarSize"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:spanCount="2"
        tools:itemCount="14"
        tools:layoutManager="android.support.v7.widget.GridLayoutManager"
        tools:listitem="@layout/layout_thermal_grid" />

 <View
        android:layout_width="match_parent"
        android:layout_height="@dimen/pad_150dp"
        android:layout_alignParentBottom="true"
        android:requiresFadingEdge="vertical"
        android:layout_marginBottom="@dimen/pad_50dp"
        android:fadeScrollbars="true"
        android:fadingEdgeLength="@dimen/pad_120dp"></View>


</RelativeLayout>

Answer 1

你可以使用这样的东西：

class BottomFadingEdgeScrollView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = 0
) : RecyclerView(context, attrs, defStyleAttr) {

    override fun getTopFadingEdgeStrength() = 0f
}

然后在你的布局文件中：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:background="@color/grey">

  <your.package.with.custom.widgets.BottomFadingEdgeScrollView
        android:id="@+id/list_recyclerview"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="?attr/actionBarSize"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:spanCount="2"
        tools:itemCount="14"
        tools:layoutManager="android.support.v7.widget.GridLayoutManager"
        tools:listitem="@layout/layout_thermal_grid" 

        android:fadingEdgeLength="@dimen/pad_120dp"
        android:requiresFadingEdge="vertical" />
</RelativeLayout>