Develop Reference

How to fix Scrolling issue of horizontal ViewPager2 and RecyclerView that are inside a vertical RecyclerView?

I have a RecyclerView (say, rootRecyclerView) that can have different kinds of rows depending on some API response. I implemented one of them is a horizontal ViewPager2 and another one is implemented with horizontal RecyclerView (say, childRecyclerView).
The rootRecyclerView swipes vertically whereas the viewPager2 and childRecyclerView swipes horizontally.
The Problem:
When I swipe on the screen, if the swipe is on the the viewPager2 or childRecyclerView, the swipe MUST go perfectly straight horizontally. Otherwise, they won't scroll horizontally; the swipe is taken by the rootRecyclerView and so the you would see vertical movement.
So, this happens because your thumb would move in a curved/circular direction creating movement in both the X axis and Y axis, and the so the rootRecyclerView intercepts the swipe creating this unpleasant user experience.
I did try to solve the issue, such as adding an OnItemTouchListener to the childRecyclerView like this:
private float Y_BUFFER = ViewConfiguration.get(getContext())
.getScaledPagingTouchSlop(); // 10;
private float preX = 0f;
private float preY = 0f;
childRecyclerView.addOnItemTouchListener(new RecyclerView.OnItemTouchListener() {
#Override
public boolean onInterceptTouchEvent(#NonNull RecyclerView rv, #NonNull MotionEvent e) {
if(e.getAction()==MotionEvent.ACTION_DOWN){
childRecyclerView.getParent().requestDisallowInterceptTouchEvent(true);
}
if(e.getAction() == MotionEvent.ACTION_MOVE){
if (Math.abs(e.getX() - preX) > Math.abs(e.getY() - preY)) {
childRecyclerView.getParent().requestDisallowInterceptTouchEvent(true);
} else if (Math.abs(e.getY() - preY) > Y_BUFFER) {
childRecyclerView.getParent().requestDisallowInterceptTouchEvent(false);
}
}
preX = e.getX();
preY = e.getY();
return false;
}
// ... rest of the code
It solves the problem only for the childRecyclerView, but I could not solve it for the ViewPager2.
I have also tried to use GestureDetector as described in this answer link, and some other combinations of code, but I could not make it work.
Could anyone help me?

Okay, so after some research, I came to the conclusion of substituting my ViewPager2 with a recyclerView that will 'behave like' a viewPager :/ .
First I replaced my viewPager2 with a horizontal recyclerView. To make it behave like a viewpager, use SnapHelper.
RecyclerView childRecyclerView2 = findViewById(R.id.previously_viewPager);
// other init like setup layout manager, adapter etc
SnapHelper snapHelper = new PagerSnapHelper();
snapHelper.attachToRecyclerView(replacedRecyclerView); // <-- this makes out rv behave like a viewPager
After that, you have to add an OnItemTouchListener and override onInterceptTouchEvent just like the code segment in my question:
childRecyclerView2.addOnItemTouchListener(new RecyclerView.OnItemTouchListener() {
#Override
public boolean onInterceptTouchEvent(#NonNull RecyclerView rv, #NonNull MotionEvent e) {
// same as the code segment in the question,
//so skipping this part.
//just copy it from my question
}
// ...
}
Optional:
In viewPager2, you can get the current focus with getCurrentItem(), but since we have replaced out viewpager2 with recyclerview, we don't have that method. So, we need to implement our own equivalent version. If you are a Kotlin guy, you can directly jump to the reference 2 and skip this part. Here is the java version if you need, I'll skip the explanation though.
Create SnapHelperExt.java
public class SnapHelperExt {
public SnapHelperExt(){}
public int getSnapPosition(RecyclerView recyclerView, SnapHelper snapHelper){
RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
View snapView = snapHelper.findSnapView(layoutManager);
if (snapView != null) {
return layoutManager.getPosition(snapView);
}else{
return -1;
}
}
}
Next create an interface OnSnapPositionChangeListener as our listener :
public interface OnSnapPositionChangeListener {
void onSnapPositionChange(int position);
}
After that, create SnapOnScrollListener.java:
public class SnapOnScrollListener extends RecyclerView.OnScrollListener {
public enum Behavior {
NOTIFY_ON_SCROLL,
NOTIFY_ON_SCROLL_STATE_IDLE
}
private SnapHelperExt snapHelperExt;
private SnapHelper snapHelper;
private Behavior behavior;
private OnSnapPositionChangeListener onSnapPositionChangeListener;
private int snapPosition = RecyclerView.NO_POSITION;
public SnapOnScrollListener(SnapHelper snapHelper, Behavior behavior, OnSnapPositionChangeListener onSnapPositionChangeListener){
this.snapHelper = snapHelper;
this.behavior = behavior;
this.onSnapPositionChangeListener = onSnapPositionChangeListener;
this.snapHelperExt = new SnapHelperExt();
}
#Override
public void onScrolled(#NonNull RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
if (behavior == Behavior.NOTIFY_ON_SCROLL) {
maybeNotifySnapPositionChange(recyclerView);
}
}
#Override
public void onScrollStateChanged(#NonNull RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
if (behavior == Behavior.NOTIFY_ON_SCROLL_STATE_IDLE
&& newState == RecyclerView.SCROLL_STATE_IDLE) {
maybeNotifySnapPositionChange(recyclerView);
}
}
private void maybeNotifySnapPositionChange(RecyclerView recyclerView){
int prevPosition = this.snapHelperExt.getSnapPosition(recyclerView, snapHelper);
boolean snapPositionIsChanged = (this.snapPosition!=prevPosition);
if(snapPositionIsChanged){
onSnapPositionChangeListener.onSnapPositionChange(prevPosition);
this.snapPosition = prevPosition;
}
}
}
Finally, use it in this way:
SnapOnScrollListener snapOnScrollListener = new SnapOnScrollListener(
snapHelper,
SnapOnScrollListener.Behavior.NOTIFY_ON_SCROLL,
position -> {
Log.e(TAG, "currently focused page no = "+position);
// your code here, do whatever you want
}
);
childRecyclerView2.addOnScrollListener(snapOnScrollListener);
References:
create-viewpager-using-recyclerview
detecting-snap-changes-with-androids-recyclerview

OnClick in one RecyclerView item affects other items

Edit #1: Through debugging I've discovered that the bug 'disappears'. Basically I set a breakpoint and slowly go through steps of checking each multiChoiceItem and the heights of the other RecyclerView child items do not change. Does this mean it is a drawing/timing related issue?
Edit #2: Also, a new find, if I change the height of Child: 6 it changes for Child: 3 and Child: 0
I apologize for the long question. I've checked other answers regarding the same problem and none of them apply. I've tried solving this myself and just couldn't so I would love some help. If there is anything I can do to make this easier to read, please let me know and I'll get right on it!
With the way my code is written, this technically should be impossible to happen but yet here it is.
The Problem: I have an onClickListener() for a TextView within a RecyclerView item. The onClickListener() calls a multiChoiceItem AlertDialog in the container class of the RecyclerAdapter which then calls notifyDataSet(), after completed, with an addOnLayoutChangeListener() at the end which measures the height after the new RecyclerView is drawn.
Notifying that the data set ended then causes the TextView within the RecyclerView item to change to show the text of each Checked item. Then this height is measured in the addOnLayoutChangeListener() and sent to a ViewModel which measures the height of the same position item of three fragments and sets the items height to the max height so they all look the same height.
The Confusing Part: This problem only occurs for one of the three fragments AND the other effected item heights do not match the other two fragments. Which tells me that this is localized to one fragment (which has its own class)
The Code:
The code is long so I reduced it to what I think was important
The ViewHolder
class TextViewViewHolder extends RecyclerView.ViewHolder {
TextView vhTVTextView;
TextView vhTVMainTextView;
CardView vhTVCardView;
TextViewClickedListener vhTextViewClickedListener;
// Gets current position from 'onBindViewHolder'
int vhPosition = 0;
public TextViewViewHolder(View itemView, TextViewClickedListener textViewClickedListener) {
super(itemView);
this.vhTextViewClickedListener = textViewClickedListener;
this.vhTVCardView = itemView.findViewById(R.id.thoughtCard);
this.vhTVTextView = itemView.findViewById(R.id.thoughtNumber);
this.vhTVMainTextView = itemView.findViewById(R.id.textEntry);
/*
When the main TextView is clicked, it calls a function in the container
'FragTextView' which pops up an AlertDialog. It was chosen to do it in the
container instead of here because the Adapter is so adapt the lists data to the view
and the container is what dictates what the lists data actually is.
*/
vhTVMainTextView.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(vhTextViewClickedListener != null) {
vhTextViewClickedListener.onTextViewClicked(vhPosition);
}
}
});
}
}
onBindViewHolder
#Override
public int getItemViewType(int position) {
/*
If mThoughtEntries is not null, then that means we can find the ViewType we are working
with inside of it. Otherwise, we are mDistortions and we must be working on TYPE_TEXTVIEW
*/
if(mThoughtEntries != null) return mThoughtEntries.get(position).getViewType();
else return Constants.TYPE_TEXTVIEW;
}
#Override
public void onBindViewHolder(#NonNull RecyclerView.ViewHolder holder, int position) {
int adapterPosition = holder.getAdapterPosition();
switch (holder.getItemViewType()) {
case Constants.TYPE_EDITTEXT:
EditTextViewHolder editTextViewHolder = (EditTextViewHolder)holder;
// update MyCustomEditTextListener every time we bind a new item
// so that it knows what item in mDataset to update
editTextViewHolder.mMyCustomEditTextListener.setTWPosition(holder.getAdapterPosition());
//Displaying list item to its correct position
editTextViewHolder.vhETTextView.setText(String.valueOf(adapterPosition + 1));
editTextViewHolder.vhETEditText.setText(mThoughtEntries.get(adapterPosition).getThought());
break;
case Constants.TYPE_TEXTVIEW:
TextViewViewHolder textViewViewHolder = (TextViewViewHolder)holder;
// Send current position to viewHolder so when the text listener is called, it knows
// exactly which position of the Distortions list to change
textViewViewHolder.vhPosition = adapterPosition;
//Displaying list item to its correct position
textViewViewHolder.vhTVTextView.setText(String.valueOf(adapterPosition + 1));
textViewViewHolder.vhTVMainTextView.setText(distortionsToString(mDistortions.get(adapterPosition)));
break;
}
}
AlertDialog in Parent
#Override
public void onTextViewClicked(int position) {
//pass the 'context' here
AlertDialog.Builder alertDialog = new AlertDialog.Builder(getContext());
final int recyclerPosition = position;
/*
Turning the distortions into a list of strings and an array of what should, or should
not, be checked.
*/
final String[] distortionStrings = distortionNameToStringArray(mDistortions.get(position));
final boolean[] checkedDistortions = distortionCheckToBooleanArray(mDistortions.get(position));
alertDialog.setMultiChoiceItems(distortionStrings, checkedDistortions,
new DialogInterface.OnMultiChoiceClickListener() {
#Override
public void onClick(DialogInterface dialog, int which, boolean isChecked) {
if (isChecked) {
// If the user checked the item, add it to the selected items
mDistortions.get(recyclerPosition).get(which).setChecked(true);
} else {
// Else, if the item is already in the array, remove it
mDistortions.get(recyclerPosition).get(which).setChecked(false);
}
/*
Because the RecyclerView takes a while to draw, if we call the below function
as we normally we would, it would appear to have no effect because it would
be automatically overwritten when the RecyclerView is drawn. So we call this
onLayout change listener to wait til the view is drawn and then we call
the function
*/
mRecyclerView.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
#Override
public void onLayoutChange(View v, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
mRecyclerView.removeOnLayoutChangeListener(this);
// Send new height to the ViewModel
if(mLayoutManager.findViewByPosition(recyclerPosition) != null) {
// Get view of item measuring
View recyclerChild = mLayoutManager.findViewByPosition(recyclerPosition);
// Get LinearLayout from view
LinearLayout linearLayout = recyclerChild.findViewById(R.id.horizontalLayout);
// This is called to find out how big a view should be. The constraints are to check
// measurement when it is set to 'wrap_content'.
linearLayout.measure(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
// Get height of the specified view
int height = linearLayout.getMeasuredHeight();
// Send to child abstracted class which then calls function from 'SharedEntryFragments'
setViewModelHeight(height, recyclerPosition);
}
}
});
mAdapter.notifyDataSetChanged();
}
});
alertDialog.setPositiveButton("Okay", new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
// DO SOMETHING HERE
dialog.cancel();
}
});
AlertDialog dialog = alertDialog.create();
dialog.show();
}
The function that makes all the fragment item heights equal
I know this part of the code doesn't affect it because where the views that heights are changed are skipped by if(positionalHeight.get(i) != 0) {} So technically...they should never change!
/*
This is the listener that will set all the RecyclerViews childrens heights. It
listens to getTallestLiveHeight() inside of 'SharedEntryFragments.java' and when
a change occurs, this is called
*/
if(getActivity() != null) {
// The container holds the ViewModel so this must make sure getActivity() is not null
mViewModel = ViewModelProviders.of(getActivity()).get(SharedEntryFragments.class);
/*
Creates the observer which updates the UI. The observer takes the
PositionalHeight class as an input. This class keeps track of which index
of the RecyclerView to change and what height it will be changed to.
*/
final Observer<List<Integer>> maxHeight = new Observer<List<Integer>>() {
#Override
public void onChanged(#Nullable final List<Integer> positionalHeight) {
if (positionalHeight != null) {
// Get the index that we are going to change and its height
//int position = positionalHeight.getPosition();
//int height = positionalHeight.getHeight();
/*
We're going to run through each child of mRecyclerView and change
its height accordingly
*/
int listSize = positionalHeight.size();
for(int i = 0; i < listSize; i++) {
// If height reads zero then skip because it will make our view disappear
if(positionalHeight.get(i) != 0) {
// This is the child item that we will be changing
View recyclerChild = mLayoutManager.findViewByPosition(i);
// Ensure that the child exists before continuing
if (recyclerChild != null) {
// We will be changing the CardView's height
// TODO might have to add a check to detect which viewholder
CardView cardView = recyclerChild.findViewById(R.id.thoughtCard);
// Get the LayoutParams first to ensure everything stays the same
ViewGroup.LayoutParams lparams = cardView.getLayoutParams();
// Get and set height
lparams.height = positionalHeight.get(i);
cardView.setLayoutParams(lparams);
}
}
}
}
}
};
mViewModel.getTallestLiveHeight().observe(this, maxHeight);
}
}

I wish I could provide a better answer for other people but this is what I discovered:
For some reason when I call mAdapter.notifyDataSetChanged(); in the AlertDialog function, every third item in the RecyclerView changed to the equaled height. I decided to change it to mAdapter.notifyItemChanged(recyclerPosition); to save on memory and, coincidentally, the bug has disappeared.
If someone could explain why, I will set that as the accepted answer but as of now, this satisfies the question so I will keep it as an answer.

Android onScrolled not called when View is set to GONE

I am trying to hide a RelativeLayout when I scroll up and show it when I scroll down. onScroll works fine and is invoked every time until View is set to GONE.
final RelativeLayout placeHeaderMain = findViewById(R.id.place_header_main);
mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
if (dy > 0) {
// Scrolling up
placeHeaderMain.setVisibility(View.GONE);
} else {
// Scrolling down
placeHeaderMain.setVisibility(View.VISIBLE);
}
}
});
I want my listener to continue working after setting the View to Gone in order to make it Visible when scrolled down.
Thanks in advance.

Are there enough items to be scrolled?
That code above won't be triggered if dy == 0. It could be not enough items to make the scroll and it will return dy equal to 0, father more it won't to call onScroll(...)
What dy do you have when RelativeLayout has hidden?
Try to check that method below:
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
}

Try to set the view to INVISIBLE and not to GONE. when you set any view to View.GONE he is invisible and it doesn't take any space inside your layout , but when you set a view to View.INVISIBLE like before he will be invisible but unlike View.GONE your view still takes up space inside the layout.

RecyclerView get height of first visible item

How can i calculate the height of the first visible item in my recyclerview ?
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
switch (newState) {
case RecyclerView.SCROLL_STATE_IDLE:
Log.d("scroll_stop","The RecyclerView is not scrolling : ");
View firstItemView = mGLM.findViewByPosition(mGLM.findFirstVisibleItemPosition());
View mVizibleView= mPlm.findViewByPosition(mGLM.findFirstVisibleItemPosition());
}
});
But this give me the full height of the view

Taking the Size of any RecyclerView Item is pointless, If you getHeight() or getWidth() of any item it's just gonna give a Null Error and your app is gonna crash.
What you can do, Is to Use your ViewHolder from recyclerView Adapter and First set a Specific Height to any Item you want and Then use that Height somewhere Else.
Look at the Code Below, Maybe helps:
class myViewHolder extends RecyclerView.ViewHolder {
RemaltiveLayout itemLayout;
public myViewHolder(View itemView) {
super(itemView);
itemLayout = (RemaltiveLayout) itemView.findViewById(R.id.myItemLayout);
itemLayout.getLayoutParams().height = res.getDimensionPixelSize(R.dimen.height_value);
}
You should be able to use item at a specific location position as well
This is not gonna work with Width though, cause items are always being stretched to fill columns of layoutManager

Steps to get first item height:
Get the layout manager from the recyclerview reference in onScrolled()
Get the first the visible item position using layoutManager.findFirstVisibleItemPosition()
If fist visible item position is 0 then get the 0th child height layoutManager.getChildAt(0)
Sample code:
RecyclerView.OnScrollListener scrollListener = new RecyclerView.OnScrollListener() {
#Override
public void onScrolled(#NonNull RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
if (layoutManager != null) {
int child0Height = 0;
int currentFirstVisibleItem = layoutManager.findFirstVisibleItemPosition();
if (currentFirstVisibleItem == 0) {
final View childAt0 = layoutManager.getChildAt(0);
if (childAt0 != null) {
child0Height = childAt0.getHeight();
}
}
}
}
};

RecyclerView not calling onScrolled at the bottom

I'm trying to create a RecyclerView with pagination and I have a problem with showing progress bar when I try to scroll down being already at the very end of the list. There's a callback RecyclerView.OnScrollListener which has a method onScrolled for handling scroll events, but it's not working when no actual scrolling has happened.
There's onScrollStateChanged method that works when I try to scroll down from the bottom, but my logic requires me to know direction of the gesture (up/down), so this method is not helpfull in my situation.
I currently trying to do it somewhat like this (which is obviously not working):
recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
fetchDataFromServer();
}
});
EDIT: I tried to detect if the end is reached in onScrolled and it kinda worked, but sometimes when I try to fetch the data from the server I don't receive anything, so after such a request I'm still at the end of the list and I want to scroll down to try to update the list again, but I can't since onScrolled is not getting called.
Any ideas on how to fix that? Is there another callback that I can use?

I guess to show progress at the end of the recyclerview, you just need to make sure that end has been reached.
This is how it goes -
private int visibleThreshold = 1; // trigger just one item before the end
private int lastVisibleItem, totalItemCount;
mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
#Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
}
#Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
totalItemCount = mLayoutManager.getItemCount();
lastVisibleItem = mLayoutManager.findLastVisibleItemPosition();
if (totalItemCount <= (lastVisibleItem + visibleThreshold) {
// ... end has been reached...
//... do your stuff over here...
}
}
});
}
EDIT:
sometimes when I try to fetch the data from the server I don't receive
anything
Simple! If your network request fails, try to catch an exception. If it is SocketTimeOutException, Retry doing the same request again. If there is an another exception(could be from the back-end or front-end), Get it fixed.

Check if your recycler view is nested inside NestedScrollView or something...
Remove the nested scroll view and it will work.
You can achieve any kind of feed by just using recycler view and use the VIEW_TYPE concept of recycler view

If you developing for min sdk level 23 then you can use setOnScrollChangeListener
recyclerView.setOnScrollChangeListener(new View.OnScrollChangeListener() {
#Override
public void onScrollChange(View v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {
}
});