I have the following layout:
<android.support.design.widget.CoordinatorLayout
android:id="@+id/rootLayout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.design.widget.AppBarLayout
android:id="@+id/appBarLayout"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<android.support.design.widget.CollapsingToolbarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
app:layout_scrollFlags="scroll|exitUntilCollapsed|snap">
<ImageView
android:layout_width="match_parent"
android:layout_height="160dp"
app:layout_collapseMode="parallax" />
<android.support.v7.widget.Toolbar
android:layout_width="match_parent"
android:layout_height="52dp"
app:layout_collapseMode="pin" />
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
<android.support.v4.widget.NestedScrollView
android:id="@+id/nestedScrollView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fillViewport="true"
app:layout_behavior="com.example.CardViewBehavior">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content">
<FrameLayout
android:id="@+id/fixedBanner"
android:layout_width="match_parent"
android:layout_height="wrap_content">
</FrameLayout>
<FrameLayout
android:id="@+id/card1"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<!-- random content -->
</FrameLayout>
<FrameLayout
android:id="@+id/card2"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</FrameLayout>
</LinearLayout>
</android.support.v4.widget.NestedScrollView>
</layout>
When scrolling down (finger goes upwards) from fixedBanner or card1, the appBarLayout collapses first, then nestedScrollView scrolls down. However, if scrolling down from recyclerView, recyclerView starts scrolling. I want nestedScrollView to scroll down first before recyclerView.
I have tried using a custom CardViewBehavior set on nestedScrollView which overrides onNestedPreScroll to consume scroll deltas if appBarLayout is not fully collapsed and there is still range to scroll in nestedScrollView.
However, if I swipe fast enough on recyclerView, recyclerView starts flinging before nestedScrollView has fully scrolled to bottom. I tried overriding onNestedPreFling and onNestedFling in CardViewBehavior, but it seems those two methods were never called when RecyclerView starts flinging by itself.
How can I ensure that nestedScrollView scrolls to bottom before recyclerView starts scrolling?
Thanks @Henry, I have successfully recreate the behaviour from the article you mentioned by @AlexLockwood in kotlin. I've dealing with this problem for two days, the other answers usually suggest using WRAP_CONTENT attribute and basically defeat the purpose of RecyclerView as the View is not being recycled anymore. I'm providing the code below just in case this may help someone in the future.
class NestedScrollLayout(
context: Context,
attrs: AttributeSet?
) : NestedScrollView(context, attrs),
NestedScrollingParent3 {
private var parentHelper = NestedScrollingParentHelper(this)
override fun onStartNestedScroll(child: View, target: View, axes: Int, type: Int): Boolean {
return (axes and ViewCompat.SCROLL_AXIS_VERTICAL) != 0
}
override fun onNestedScrollAccepted(child: View, target: View, axes: Int, type: Int) {
parentHelper.onNestedScrollAccepted(child, target, axes)
startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL, type)
}
override fun onNestedPreScroll(target: View, dx: Int, dy: Int, consumed: IntArray, type: Int) {
if(target is RecyclerView) {
if ((dy < 0 && isRvScrolledToTop(target)) || (dy > 0 && !isNsvScrolledToBottom(this))) {
scrollBy(0, dy)
consumed[1] = dy
return
}
}
dispatchNestedPreScroll(dx, dy, consumed, null, type)
}
override fun onNestedScroll(
target: View,
dxConsumed: Int,
dyConsumed: Int,
dxUnconsumed: Int,
dyUnconsumed: Int,
type: Int
) {
val oldScrollY = scrollY
scrollBy(0, dyUnconsumed)
val mConsumed = scrollY - oldScrollY
val mUnconsumed = dyUnconsumed - mConsumed
dispatchNestedScroll(0, mConsumed, 0, mUnconsumed, null, type)
}
override fun onStopNestedScroll(target: View, type: Int) {
parentHelper.onStopNestedScroll(target, type)
stopNestedScroll(type)
}
override fun onStartNestedScroll(child: View, target: View, axes: Int): Boolean {
Log.println(Log.ASSERT, "NestedScrollLayout:onStartNestedScroll", "Requested")
return onStartNestedScroll(child, target, axes, ViewCompat.TYPE_TOUCH)
}
override fun onNestedScrollAccepted(child: View, target: View, axes: Int) {
onNestedScrollAccepted(child, target, axes, ViewCompat.TYPE_TOUCH)
}
override fun onNestedPreScroll(target: View, dx: Int, dy: Int, consumed: IntArray) {
onNestedPreScroll(target, dx, dy, consumed, ViewCompat.TYPE_TOUCH)
}
override fun onNestedScroll(
target: View,
dxConsumed: Int,
dyConsumed: Int,
dxUnconsumed: Int,
dyUnconsumed: Int
) {
onNestedScroll(
target,
dxConsumed,
dyConsumed,
dxUnconsumed,
dyUnconsumed,
ViewCompat.TYPE_TOUCH
)
}
override fun onStopNestedScroll(target: View) {
onStopNestedScroll(target, ViewCompat.TYPE_TOUCH)
}
override fun getNestedScrollAxes(): Int {
return parentHelper.nestedScrollAxes
}
companion object {
private fun isNsvScrolledToBottom(nsv: NestedScrollView): Boolean {
return !nsv.canScrollVertically(1)
}
private fun isRvScrolledToTop(rv: RecyclerView): Boolean {
rv.layoutManager?.let { lm ->
return when (lm) {
is LinearLayoutManager -> {
lm.findViewByPosition(0)?.top == 0 && lm.findFirstVisibleItemPosition() == 0
}
is GridLayoutManager -> {
lm.findViewByPosition(0)?.top == 0 && lm.findFirstVisibleItemPosition() == 0
}
is StaggeredGridLayoutManager -> {
lm.findViewByPosition(0)?.top == 0 && lm.findFirstVisibleItemPositions(
intArrayOf(0)
)[0] == 0
}
else -> lm.findViewByPosition(0)?.top == 0
}
}
return false
}
}
}
Then we can use NestedScrollLayout as follows:
<com.organization.appname.NestedScrollLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
...
<androidx.recyclerview.widget.RecyclerView
android:layout_width="match_parent"
android:layout_height="400dp" />
...
</com.organization.appname.NestedScrollLayout>