I have a layout in which it has parallax effect. So this are the elements in it -
AppBarLayout
CollapsingToolbarLayout inside AppBarLayout
Toolbar inside CollapsingToolbarLayout
RecyclerView
All this views are within CoordinatorLayout. Now I require to find out what is the first completely visible item of RecyclerView. Normally I used following logic to get it -
int firstVisibleItem = ((LinearLayoutManager) recyclerView.getLayoutManager()).findFirstCompletelyVisibleItemPosition();
But here I am getting lots of 1 when even 0th position is not completely visible.
getChildAt begins at the first visible position, not at the position of the adapter.
Here is the resulting code.
int firstVisiblePosition = layoutManager.findFirstVisibleItemPosition();
View v = layoutManager.getChildAt(0);
if (firstVisiblePosition > 0 && v != null) {
int offsetTop = v.getTop();
chatAdapter.notifyDataSetChanged();
if (firstVisiblePosition - 1 >= 0 && chatAdapter.getItemCount() > 0) {
layoutManager.scrollToPositionWithOffset(firstVisiblePosition - 1, offsetTop);
}
}
I found it myself. As I am using AppBarLayout, I need to check it out whether particular view is available on screen at that particular scroll or not.
I did is:
#Override
public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
View v = recyclerView.getLayoutManager().getChildAt(1);
int offset = 0;
if (v != null) {
offset = v.getTop();
}
if ((verticalOffset * -1) >= offset) {
layoutBuy.setVisibility(View.GONE);
} else {
layoutBuy.setVisibility(View.VISIBLE);
}
}
I used recyclerView.getLayoutManager().getChildAt(1); because I wanted to work around with that particular position which is 1.
Since, vertical offset becomes minus values while scrolling I multiplied it by -1. Then just checked whether offset and top of the view which I am looking for is same or not.
Thus while using parallax effect in a screen and at that same time one needs to check which view is visible in RecyclerView, needs the logic as mentioned above.
Related
I am new to android and hence RV and I am trying to achieve the layout where the first and last card are not centered and instead show more of the cards after and before them. Maybe at In this case I can see 16dp for the second cards and same thing for the penultimate card which makes the first and last card not centered.
But 8dp each for the rest of the cards so the intermediate cards appear centered. Maybe using itemDecoration somehow for the 2nd and the penultimate card somehow.
I was able to achieve showing parts of next and prev cards by following what is suggested here, but that only centers all the cards uniformly :
How to show part of next/previous card RecyclerView
I tried overriding getItemOffsets but it gets triggered everytime I scroll to the first or the last card and moves the 2nd and 2nd to last card incorrectly
and also doesn't center them correctly when I scroll to them.
public static class MyItemDecoration extends RecyclerView.ItemDecoration {
#Override
public void getItemOffsets(#NonNull Rect outRect, #NonNull View view, #NonNull RecyclerView parent, #NonNull RecyclerView.State state) {
super.getItemOffsets(outRect, view, parent, state);
final int itemPosition = parent.getChildAdapterPosition(view);
if (itemPosition == RecyclerView.NO_POSITION) {
return;
}
final int itemCount = state.getItemCount();
if (itemCount > 0 && itemPosition == 1) {
outRect.left -= 16;
outRect.right -= 16;
}
else if (itemCount > 0 && itemPosition == itemCount - 1) {
outRect.left += 16;
outRect.right += 16;
}
}
}
RV Setup
SnapHelper snapHelper = new PagerSnapHelper();
RecyclerView rv = getBinding().rv;
rv.setOnFlingListener(null);
snapHelper.attachToRecyclerView(rv);
PagerSnapHelper centers the RecyclerView items including the decorations, so, unless the decoration widths are balanced, they won't always be centered. This may be what you are seeing.
Try the following for the decoration. This code applies the full-width decoration to the start of the first item and the end of the last item; otherwise, a half decoration width is used. By setting up the decorations this way, you are centering items that have balanced left and right decorations.
DividerItemDecoration decoration =
new DividerItemDecoration(getApplicationContext(), HORIZONTAL) {
private int mDecorationWidth = (int) (getResources().getDisplayMetrics().density * 8);
#Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
RecyclerView.State state) {
final int pos = parent.getChildAdapterPosition(view);
if (pos == RecyclerView.NO_POSITION) {
return;
}
if (pos == 0) {
outRect.set(mDecorationWidth, 0, mDecorationWidth / 2, 0);
} else if (pos == parent.getAdapter().getItemCount() - 1) {
outRect.set(mDecorationWidth / 2, 0, mDecorationWidth, 0);
} else {
outRect.set(mDecorationWidth / 2, 0, mDecorationWidth / 2, 0);
}
}
};
Here is a video showing the results with gray vertical dividers.
If you already have the decorations working to your satisfaction, you can override calculateDistanceToFinalSnap() in PagerSnapHelper to center all views except the first and last view as follows. See calculatedistancetofinalsnap(). Once the PageSnapHelper identifies a target view to snap to, calculatedistancetofinalsnap() is called to determine how many pixels to move to perform the snap. Here, we are moving just enough pixels to center the view (without decorations) in the RecyclerView. PageSnapHelper does the right thing for the first and last items, so we just call the super for these.
PagerSnapHelper pagerSnapHelper = new PagerSnapHelper() {
#Override
public int[] calculateDistanceToFinalSnap(#NonNull RecyclerView.LayoutManager layoutManager,
#NonNull View targetView) {
LinearLayoutManager lm = (LinearLayoutManager) layoutManager;
int pos = mRecycler.getChildAdapterPosition(targetView);
// If first or last view, the default implementation works.
if (pos == 0 || pos == lm.getItemCount() - 1) {
return super.calculateDistanceToFinalSnap(layoutManager, targetView);
}
// Force centering in the view without its decorations.
// targetCenter is the location of the center of the view we want to center.
int targetCenter = targetView.getLeft() + targetView.getWidth() / 2;
// Distance is the number of pixels to move the target so that its center
// lines up with the center of the RecyclerView (mRecycler.getWidth() / 2)
int distance = targetCenter - mRecycler.getWidth() / 2;
return new int[]{distance, 0};
}
};
Either way will work.
I have a vertically scrolling RecyclerView with horizontally scrolling inner RecyclerViews just like this.
With this implementation, users can scroll each horizontal recyclerview synchronously. However, when a user scroll vertically to the parent recyclerView, a new horizontal recyclerview which has just attached on window doesn't display on same scroll x position. This is normal. Because it has just created.
So, I had tried to scroll to the scrolled position before it was displayed. Just like this:
Note: this is in adapter of the parent recyclerview whose orientation is vertical.
#Override
public void onViewAttachedToWindow(RecyclerView.ViewHolder holder) {
super.onViewAttachedToWindow(holder);
CellColumnViewHolder viewHolder = (CellColumnViewHolder) holder;
if (m_nXPosition != 0) {
// this doesn't work properly
viewHolder.m_jRecyclerView.scrollBy(m_nXPosition, 0);
}
}
As you can see, scrollBy doesn't effect for row 10, row 11, row 12 and row 13 After that, I debugged the code to be able find out find out what's happening. When I set scroll position using scrollBy, childCount() return zero for row 10, row 11, row 12 and row 13 So they don't scroll. But why ? and Why others work ?
How can I fix this ?
Is onViewAttachedToWindow right place to scroll new attached recyclervViews ?
Note: I have also test scrollToPosition(), it doesn't get any problem like this. But I can't use it at my case. Because users can scroll to the any x position which may not the exact position. So I need to set scroll position using x value instead of the position.
Edit: You can check The source code
I found a solution that is use scrollToPositionWithOffset method instead using scrollBy. Even if both of two scroll another position, they have really different work process in back side.
For example: if you try to use scrollBy to scroll any pixel position and your recyclerView had not been set any adapter which means there is no any data to display and so it has no any items yet, then scrollBy doesn't work. RecyclerView uses its layoutManager's scrollBy method. So in my case, I am using LinearLayoutManager to the horizontal recyclerViews.
Lets see what it's doing :
int scrollBy(int dy, RecyclerView.Recycler recycler, RecyclerView.State state) {
if (getChildCount() == 0 || dy == 0) {
return 0;
}
mLayoutState.mRecycle = true;
ensureLayoutState();
final int layoutDirection = dy > 0 ? LayoutState.LAYOUT_END : LayoutState.LAYOUT_START;
final int absDy = Math.abs(dy);
updateLayoutState(layoutDirection, absDy, true, state);
final int consumed = mLayoutState.mScrollingOffset
+ fill(recycler, mLayoutState, state, false);
if (consumed < 0) {
if (DEBUG) {
Log.d(TAG, "Don't have any more elements to scroll");
}
return 0;
}
final int scrolled = absDy > consumed ? layoutDirection * consumed : dy;
mOrientationHelper.offsetChildren(-scrolled);
if (DEBUG) {
Log.d(TAG, "scroll req: " + dy + " scrolled: " + scrolled);
}
mLayoutState.mLastScrollDelta = scrolled;
return scrolled;
}
As you can see scrollBy ignores the scroll intentions if there is no any child at that time.
if (getChildCount() == 0 || dy == 0) {
return 0;
}
On the other hand scrollToPosition can work perfectly even if there is no any set data yet.
According to the Pro RecyclerView slide, the below sample works perfectly. However you can not do that with scrollBy.
void onCreate(SavedInstanceState state) {
....
mRecyclerView.scrollToPosition(selectedPosition);
mRecyclerView.setAdapter(myAdapter);
}
As a result, I have changed little thing to use scrollToPositionWithOffset().
Before this implementation I was calculating the exact scroll x position as a pixel.
After that, when the scroll came idle state, calculating the first complete visible position to the first parameter of the scrollToPositionWithOffset().
For second parameter which is the offset, I am getting the value using view.getLeft() function which helps to get left position of this view relative to its parent.
And it works perfectly!!
I want to find out the position or ids related to a ListView's items: only those ones which are completely visible on the screen.
Using listview.getFirstVisibleposition and listview.getLastVisibleposition takes partial list items into account.
I followed a little bit similar approach as suggested by Rich, to suit my requirement which was to fetch completely visible items on screen when List View is scrolled every time.
This is what i did
public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
//Loop to get tids of all completely visible List View's item scrolled on screen
for (int listItemIndex = 0; listItemIndex <= getListView().getLastVisiblePosition() - getListView().getFirstVisiblePosition(); listItemIndex++) {
View listItem = getListView().getChildAt(listItemIndex);
TextView tvNewPostLabel = (TextView) listItem.findViewById(R.id.tvNewPostLabel);
if (tvNewPostLabel != null && tvNewPostLabel.getVisibility() == View.VISIBLE) {
int listTid = (int) tvNewPostLabel.getTag();
if (listItem.getBottom() < getListView().getHeight()) {//If List View's item is not partially visible
listItemTids.add(listTid);
}
}
}
}
I have not tried this, but here are the pieces of the framework that I believe will get you to what you're looking for (at least this is what I'd try first)
As you've stated, you should get the last visible position from the list view using ListView.getLastVisiblePosition()
You can then access the View representing this position using ListView.getChildAt(position)
You now have a reference to the view, which you can call a combination of View.getLocationOnScreen(location) and View.getHeight()
Also call View.getLocationOnScreen(location) and View.getHeight() on the ListView. y + height of the View should be less than or equal to y + height of the ListView if it is fully visible.
Is there a way that I can makle sure a given item in an android listview is entirely visible?
I'd like to be able to programmatically scroll to a specific item, like when I press a button for example.
ListView.setSelection() will scroll the list so that the desired item is within the viewport.
Try it:
public static void ensureVisible(ListView listView, int pos)
{
if (listView == null)
{
return;
}
if(pos < 0 || pos >= listView.getCount())
{
return;
}
int first = listView.getFirstVisiblePosition();
int last = listView.getLastVisiblePosition();
if (pos < first)
{
listView.setSelection(pos);
return;
}
if (pos >= last)
{
listView.setSelection(1 + pos - (last - first));
return;
}
}
I believe what you are looking for is ListView.setSelectionFromTop() (although I'm a bit late to the party).
Recently I met the same problem, paste my solution here in case someone need it (I was trying to make the entire last visible item visible):
if (mListView != null) {
int firstVisible = mListView.getFirstVisiblePosition()
- mListView.getHeaderViewsCount();
int lastVisible = mListView.getLastVisiblePosition()
- mListView.getHeaderViewsCount();
View child = mListView.getChildAt(lastVisible
- firstVisible);
int offset = child.getTop() + child.getMeasuredHeight()
- mListView.getMeasuredHeight();
if (offset > 0) {
mListView.smoothScrollBy(offset, 200);
}
}
I have a shorter and, in my opinion, better solution to do this : ListView requestChildRectangleOnScreen method is designed for it.
The answer above ensures that the item will be displayed, but sometimes it will be displayed partly (ie. when it is at the bottom of the screen). The code below ensures that the whole item will be displayed and that the view will scroll only the necessary zone :
private void ensureVisible(ListView parent, View view) {
Rect rect = new Rect(view.getLeft(), view.getTop(), view.getRight(), view.getBottom());
parent.requestChildRectangleOnScreen(view, rect, false);
}
Is there a way that I can makle sure a given item in an android listview is entirely visible?
I'd like to be able to programmatically scroll to a specific item, like when I press a button for example.
ListView.setSelection() will scroll the list so that the desired item is within the viewport.
Try it:
public static void ensureVisible(ListView listView, int pos)
{
if (listView == null)
{
return;
}
if(pos < 0 || pos >= listView.getCount())
{
return;
}
int first = listView.getFirstVisiblePosition();
int last = listView.getLastVisiblePosition();
if (pos < first)
{
listView.setSelection(pos);
return;
}
if (pos >= last)
{
listView.setSelection(1 + pos - (last - first));
return;
}
}
I believe what you are looking for is ListView.setSelectionFromTop() (although I'm a bit late to the party).
Recently I met the same problem, paste my solution here in case someone need it (I was trying to make the entire last visible item visible):
if (mListView != null) {
int firstVisible = mListView.getFirstVisiblePosition()
- mListView.getHeaderViewsCount();
int lastVisible = mListView.getLastVisiblePosition()
- mListView.getHeaderViewsCount();
View child = mListView.getChildAt(lastVisible
- firstVisible);
int offset = child.getTop() + child.getMeasuredHeight()
- mListView.getMeasuredHeight();
if (offset > 0) {
mListView.smoothScrollBy(offset, 200);
}
}
I have a shorter and, in my opinion, better solution to do this : ListView requestChildRectangleOnScreen method is designed for it.
The answer above ensures that the item will be displayed, but sometimes it will be displayed partly (ie. when it is at the bottom of the screen). The code below ensures that the whole item will be displayed and that the view will scroll only the necessary zone :
private void ensureVisible(ListView parent, View view) {
Rect rect = new Rect(view.getLeft(), view.getTop(), view.getRight(), view.getBottom());
parent.requestChildRectangleOnScreen(view, rect, false);
}