[英]How to disable overscroll effect on RecyclerView ONLY when you can't scroll anyway ?
有时,用户已经可以看到 recyclerView 的所有项目。
在这种情况下,用户看到过度滚动效果并不重要,因为实际滚动并看到更多项目是不可能的。
我知道为了禁用 RecyclerView 的过度滚动效果,我可以使用:
recyclerView.setOverScrollMode(View.OVER_SCROLL_NEVER);
但我不知道什么时候触发这个,反正滚动是不可能的。
我如何确定所有项目都是完全可见的并且用户不能真正滚动?
如果它有助于假设任何事情,我总是将 LinearLayoutManager(垂直和水平)用于 RecyclerView。
<android.support.v7.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:overScrollMode="never"/>
只需在 XML 中添加android:overScrollMode="never"
你可以试试OVER_SCROLL_IF_CONTENT_SCROLLS
。 根据文档
仅当内容大到足以有意义地滚动时,才允许用户过度滚动此视图,前提是它是可以滚动的视图。
或者您可以检查是否有足够的项目来触发滚动并启用/禁用过度滚动模式,具体取决于它。 例如
boolean notAllVisible = layoutManager.findLastCompletelyVisibleItemPosition() < adapter.getItemCount() - 1;
if (notAllVisible) {
recyclerView.setOverScrollMode(allVisible ? View.OVER_SCROLL_NEVER);
}
由于android:overScrollMode="ifContentScrolls"
不适用于RecyclerView
(请参阅https://issuetracker.google.com/issues/37076456 ),我找到了一些想与您分享的解决方法:
class MyRecyclerView @JvmOverloads constructor(
context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
) : RecyclerView(context, attrs, defStyleAttr) {
override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
super.onLayout(changed, l, t, r, b)
val canScrollVertical = computeVerticalScrollRange() > height
overScrollMode = if (canScrollVertical) OVER_SCROLL_ALWAYS else OVER_SCROLL_NEVER
}
}
你可以尝试这样的事情:
totalItemCount = linearLayoutManager.getItemCount();
firstVisibleItem = linearLayoutManager.findFirstCompletelyVisibleItemPosition()
lastVisibleItem = linearLayoutManager.findLastCompletelyVisibleItemPosition();
if(firstVisibleItem == 0 && lastVisibleItem -1 == totalItemCount){
// trigger the overscroll effect
}
您可以将其添加到您添加到RecyclerView
上的OnScrollListener
的onScrolled()
中。
更长的解决方法,基于这里(解决这个问题),处理更多的情况,但仍然是一个解决方法:
/**a temporary workaround to make RecyclerView handle android:overScrollMode="ifContentScrolls" */
class NoOverScrollWhenNotNeededRecyclerView : RecyclerView {
private var enableOverflowModeOverriding: Boolean? = null
private var isOverFlowModeChangingAccordingToSize = false
constructor(context: Context) : super(context)
constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)
constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr)
override fun setOverScrollMode(overScrollMode: Int) {
if (!isOverFlowModeChangingAccordingToSize)
enableOverflowModeOverriding = overScrollMode == View.OVER_SCROLL_IF_CONTENT_SCROLLS
else isOverFlowModeChangingAccordingToSize = false
super.setOverScrollMode(overScrollMode)
}
override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
super.onLayout(changed, l, t, r, b)
if (enableOverflowModeOverriding == null)
enableOverflowModeOverriding = overScrollMode == View.OVER_SCROLL_IF_CONTENT_SCROLLS
if (enableOverflowModeOverriding == true) {
val canScrollVertical = computeVerticalScrollRange() > height
val canScrollHorizontally = computeHorizontalScrollRange() > width
isOverFlowModeChangingAccordingToSize = true
overScrollMode = if (canScrollVertical || canScrollHorizontally) OVER_SCROLL_ALWAYS else OVER_SCROLL_NEVER
}
}
}
编写自定义RecyclerView.OnScrollListener()
以使用overScrollMode
/**
* Workaround because [View.OVER_SCROLL_IF_CONTENT_SCROLLS] not working properly.
*
* [showHeader]/[showFooter] - for customization, if need show only specific scroll edge.
*/
class RecyclerOverScrollListener(
private val showHeader: Boolean = true,
private val showFooter: Boolean = true
) : RecyclerView.OnScrollListener() {
override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
super.onScrolled(recyclerView, dx, dy)
val lm = recyclerView.layoutManager as? LinearLayoutManager ?: return
val isFirstVisible = lm.findFirstCompletelyVisibleItemPosition() == 0
val isLastVisible = lm.findLastCompletelyVisibleItemPosition() == lm.itemCount - 1
val allVisible = isFirstVisible && isLastVisible
recyclerView.overScrollMode = if (allVisible) {
View.OVER_SCROLL_NEVER
} else {
val showHeaderEdge = showHeader && isFirstVisible && !isLastVisible
val showFooterEdge = showFooter && !isFirstVisible && isLastVisible
if (showHeader && showFooter || showHeaderEdge || showFooterEdge) {
View.OVER_SCROLL_ALWAYS
} else {
View.OVER_SCROLL_NEVER
}
}
}
}
如何实现RecyclerView
:
recyclerView.addOnScrollListener(RecyclerOverScrollListener(showFooter = false))
也不要忘记在 styles 中指定边缘颜色:
<item name="android:colorEdgeEffect">@color/yourRippleColor</item>
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