Develop Reference

How to get a reference of next RecyclerView item

I have created a RecyclerView with alternating row color like this:
Whenever I delete an row from the list say for example I delete row whose product name is cookies my list gets updated like this:
as you can see the updated list no longer supports alternating row color. The simple solution would be to change the background color of next View (row) after deleting the current View. For that I first need a reference of next View but as a beginner in android I don't know how to get it.
Adapter:
public class Adapter extends RecyclerView.Adapter<Adapter.ViewHolder>{
private List<Model> originalList;
Adapter(List<Model> list){ originalList = list; }
#Override
public void onBindViewHolder(final Adapter.ViewHolder holder, final int position) {
Model list = originalList.get(position);
if (position % 2 == 1)
holder.itemView.setBackgroundColor(Color.parseColor("#e9e9e9"));
final View holder.nextItemView = ? // how to get reference to next View here
holder.product.setText(list.getName());
holder.price.setText(String.valueOf(list.getPrice()));
holder.quantity.setText(String.valueOf(list.getQuantity()));
holder.options.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
showPopupMenu(holder.options, nextItemView, position);
}
});
}
private void showPopupMenu(View options, final View view, final int position){
final PopupMenu popup = new PopupMenu(options.getContext(), options);
MenuInflater inflater = popup.getMenuInflater();
inflater.inflate(R.menu.options_menu, popup.getMenu());
popup.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
#Override
public boolean onMenuItemClick(MenuItem item) {
String menuItem = item.toString();
if (menuItem.equals("Delete")){
originalList.remove(position);
notifyItemRemoved(position);
int count = originalList.size();
if (count != 0){
int color = Color.TRANSPARENT;
Drawable background = view.getBackground();
if (background instanceof ColorDrawable)
color = ((ColorDrawable) background).getColor();
if (color == Color.parseColor(#e9e9e9))
color = Color.TRANSPARENT;
view.setBackground(color);
}
}
return true;
}
});
popup.show();
}
}
options is a ImageButton on the click of which I show a popup menu with item labelled as Delete on click of which the row gets deleted from the list.

Quick fix you can call notifyDataSetChanged() instead of notifyItemRemoved(position)
and add an else part
if (position % 2 == 1)
holder.itemView.setBackgroundColor(Color.parseColor("#e9e9e9")); // gray
else
holder.itemView.setBackgroundColor(Color.parseColor("#ffffff")); // white
but this solution will do heavy operations if your list contains a lot of items
the solution which I recommend is using ListAdapter with DiffUtil which will trigger the operation for the only modified items , you can find a sample for it here link1 ,link2, link3

when an item removed. background of all items after that need to be updated.
Method 1
so after you remove item with position of p from list of itemList and notify it you have to do this.
if (itemList.size - p > 0)
notifyItemRangeChanged(p, itemList.size - p)
Method 2
at this point it should work but it can be more optimized. you need just change background but now it will call onBindViewHolder for each items after p.
you can use payload to just change background and do nothing more.
add a const value:
const val PAYLOAD_BACKGROUND = 10
change first method code into this. it says that only update background.
if (itemList.size - p > 0)
notifyItemRangeChanged(p, itemList.size - p, PAYLOAD_BACKGROUND)
override this method
onBindViewHolder(holder, position, payloads)
after you implemented this method the previous onBindViewHolder method will not call anymore. and you have to do all of that inside this method.
onBindViewHolder(holder, position, payloads) {
if (payloads.contains(PAYLOAD_BACKGROUND) || payloads.isEmpty()) {
// set background color
}
if (payloads.isEmpty()) {
// do anything else that you were doing inside onBindViewHolder
}
}
if payloads is not empty it means this is a partial update. but if payloads is empty means this is a complete update like the old onBindViewHolder

RecyclerView scroll makes findViewHolderForAdapterPosition return null

I have a RecyclerView with a Horizontal LinerLayout. It displays numbers from 10 to 1, that is used to rate something.
When I select 10 and scroll back to 1 and select 1. I have to update the UI to remove selection on 10 and update selection on 1. But, when I use findViewHolderForAdapterPosition() to remove the selection on 10 it gives me a NullPointerException
I am getting the position in the ViewHolder with getAdapterPosition().
Then, I use that position to get the ViewHolder by calling findViewHolderForAdapterPosition() on my recycler view object and update the UI to remove the selection from 10.
vh = (RatingRecyclerAdapter.ViewHolder)
mRecycler.findViewHolderForAdapterPosition(previousPosition);
vh.textRating.setBackgroundResource(R.drawable.rating_background_selected_orange);;
With some tests, I found out when I try to do the same thing without scrolling it works fine. However, only when I am scrolling it gives me a NullPointerException
How do I fix this?
As requested here is some important code from Adapter class.
#Override
public void onBindViewHolder(RatingRecyclerAdapter.ViewHolder holder, int position) {
String itemText = itemList.get(position);
holder.textRating.setText(itemText);
}
public class ViewHolder extends RecyclerView.ViewHolder {
TextView textRating;
public ViewHolder(View itemView) {
super(itemView);
textRating = (TextView) itemView.findViewById(R.id.text_rating);
textRating.setOnClickListener(ratingClickListener);
}
private final View.OnClickListener ratingClickListener = new View.OnClickListener() {
#Override
public void onClick(View v) {
int position = getAdapterPosition();
if (callback != null) {
callback.onClickRating(v, position);
}
}
};
}
Activity Class
#Override
public void onClickRating(View view, int position) {
RatingRecyclerAdapter.ViewHolder vh;
int color;
int previousPosition = mAdapter.getSelectedPosition(); //Get previously clicked postion if any.
if (previousPosition == Constants.NO_ITEM_SELECTED) {
// An item was selected first time
vh = (RatingRecyclerAdapter.ViewHolder)
mRecycler.findViewHolderForAdapterPosition(position);
mAdapter.setSelectedPosition(position); // Save new item selected position.
color = Utility.getItemColor(mAdapter.getSelectedRating());
mAdapter.setSelectedRatingResource(vh, color);
return;
}
if (position == previousPosition) // Same item was selected
return;
vh = (RatingRecyclerAdapter.ViewHolder)
mRecycler.findViewHolderForAdapterPosition(previousPosition);
color = Utility.getItemColor(mAdapter.getSelectedRating());
mAdapter.setUnselectedRatingResource(vh, color); // Remove the previous selected item drawables.
vh = (RatingRecyclerAdapter.ViewHolder)
mRecycler.findViewHolderForAdapterPosition(position);
mAdapter.setSelectedPosition(position); // Save new item selected position.
color = Utility.getItemColor(mAdapter.getSelectedRating());
mAdapter.setSelectedRatingResource(vh, color); // Set the new selected item drawables. Setting some background to indicate selection.
}

As Sevastyan has written in the comment, the RecyclerView immediately recycles the view as soon as the item is out of the screen. So if we call findViewHolderForAdapterPosition() for a view which is outside the screen we get a null value. (I am not confirming this is the actual case. But, this is what it seems to me.)
So I created a class that stores all the data about an item in the RecyclerView and stored all the colours and value of that item in the class. And when we are populating the view, set the all the colours based on data stored in that class.
PS: I THANK Sevastyan for not giving me the answer directly. But, only giving me the reason for getting that Exception.

If your view is out of the screen, it can be recycled OR cached.
In case it's recycled, you can handle in onViewRecycled() method or setup the view again inside onBind() when the view becomes visible (you can save the state on the object of your list if needed).
In case it's not recycled (onViewRecycled method not called for that position), it's probably cached. You can set the cache size to zero to prevent this state from happening.
recycler.setItemViewCacheSize(0)

Android RecyclerView: why is first item in list already selected?

I have a RecyclerView list of CardViews with a defaultbackground of white. I set up a OnLongClickListener to select the CardView and load a DialogFragment to confirm deletion for the item (CardView) and change the background color to red.
Everything is working correctly except the first CardView created in the list is already showing a red background even though the user has not OnLongClicked the CardView. Thereafter, the newest CardView added always shows the red background even when the user has not yet OnLongClicked the CardView. What am I missing here?
background_selector.xml:
...
<!-- Normal state. -->
<item android:drawable="#color/list_contact_item_default"
android:state_pressed="false"
android:state_selected="false" />
<!-- Selected state. -->
<item android:drawable="#color/item_selected"
android:state_pressed="false"
android:state_selected="true" />
</selector>
list_contact_tem.xml:
<android.support.v7.widget.CardView
xmlns:card_view="http://schemas.android.com/apk/res-auto"
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/singlecard_view1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"
card_view:cardCornerRadius="6dp"
card_view:cardElevation="4dp" >
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="#drawable/background_selector">
...
Adapter file:
public class ContactListAdapter extends RecyclerView.Adapter<ContactListAdapter.ContactHolder>{
...
private int selectedPos;
#Override
public ContactHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_contact_item, parent, false);
final ContactHolder contactHolder = new ContactHolder(view);
// Attach a LongClick listener to the items's (row) view.
contactHolder.itemView.setOnLongClickListener(new View.OnLongClickListener() {
#Override
public boolean onLongClick(View view) {
// Save the new selected position.
selectedPos = contactHolder.getAdapterPosition(); // get the item position.
if (selectedPos != RecyclerView.NO_POSITION) {
if (recyclerItemClickListener != null) {
recyclerItemClickListener.onItemLongClick(selectedPos, contactHolder.itemView);
// Temporarily save the last selected position
int lastSelectedPosition = selectedPos;
// Update the previous selected row
notifyItemChanged(lastSelectedPosition);
notifyItemChanged(selectedPos);
}
}
return true;
}
});
return contactHolder;
}
#Override
public void onBindViewHolder(ContactHolder holder, int position) {
final Contact contact = contactList.get(position);
if(position == selectedPos) {
holder.itemView.setSelected(true);
} else {
holder.itemView.setSelected(false);
}
holder.thumb.setImageBitmap(letterBitmap);
holder.name.setText(contact.getName());
holder.phone.setText(contact.getPhone());
}

You need to declare an external array to keep track of the items selected. Let us have an array which have the same size as the list.
private int[] selectedArray = new int[yourList.size()];
// Now initialize the Array with all zeros
for(int i=0; i<selectedArray.length; i++)
selectedArray[i] = 0;
Now inside your adapter, when an item is clicked, set 1 in the proper position in the selectedArray. So that, we can keep track which item is selected now.
Now modify your adapter code as follows
// Attach a LongClick listener to the items's (row) view.
contactHolder.itemView.setOnLongClickListener(new View.OnLongClickListener() {
#Override
public boolean onLongClick(View view) {
// Update the selectedArray. Set 1 for the selected item
// and 0 for the others.
updateSelectedArray(contactHolder.getAdapterPosition());
if (selectedPos != RecyclerView.NO_POSITION) {
if (recyclerItemClickListener != null) {
recyclerItemClickListener.onItemLongClick(selectedPos, contactHolder.itemView);
// Repopulate the list here
notifyDatasetChanged();
}
}
return true;
}
});
And in your onBindViewHolder
final int SELECTED = 1;
if(selectedArray[position] == SELECTED) {
holder.itemView.setSelected(true);
} else {
holder.itemView.setSelected(false);
}
Your updateSelectedArray() may look like this
private void updateSelectedArray(int position) {
for(int i=0; i<selectedArray.length; i++){
if(i == position) selectedArray[i] = 1;
else selectedArray[i] = 0;
}
}
And after you delete an item from the list, you need to reset the selectedArray` as the item is no longer available in your list.
So your deleteFromList function may look like:
private void deleteFromList(int position)
{
yourList.remove(position);
selectedArray = new int[yourList.size()];
// Now re-initialize the Array with all zeros
for(int i=0; i<selectedArray.length; i++)
selectedArray[i] = 0;
}
I've taken an array to keep track of the selected item. But you can take an ArrayList or any data structure you like to keep track of it. The idea is to keep track of the selected item properly.
Update
The problem of having randomly selected items in your list is caused by not binding your views properly. So when you delete an item, you need to do the following things.
Reset your selected position in the selectedArray. i.e. selectedPos = -1
Remove the item from the list.
Call notifyDatasetChanged to take the effect of your changes in the
list.
And most importantly don't forget to set the else part. What I meant is
// Pseudo code
if(position == selected) itemView.setSelected(true);
else itemView.setSelected(true); // Don't forget this else

Click all the list view elements while scrolling using robotium

I have a listView that contains lots of elements i.e. we have to scroll down to see all the elements. Now what i want to do is, click all the listView elements. How can I do that. Right now,I am using the following code but it doesn't scroll automatically. Please help.
ListView l = solo.getCurrentListViews().get(0);
assertNotNull("No list views!", l);
assertTrue("No items in list view!", l.getChildCount() > 0);
// Get the last list item
View v = l.getChildAt(l.getChildCount());
System.out.println("getChildCount: " + l.getChildCount());
int i = 1;
while (i <= l.getChildCount()) {
solo.clickInList(i);
solo.goBack();
i++;
}

I have previously used these helper functions in a slightly different state to handle most of what we need with listviews:
public View getViewAtIndex(final ListView listElement, final int indexInList, Instrumentation instrumentation) {
ListView parent = listElement;
if (parent != null) {
if (indexInList <= parent.getAdapter().getCount()) {
scrollListTo(parent, indexInList, instrumentation);
int indexToUse = indexInList - parent.getFirstVisiblePosition();
return parent.getChildAt(indexToUse);
}
}
return null;
}
public <T extends AbsListView> void scrollListTo(final T listView,
final int index, Instrumentation instrumentation) {
instrumentation.runOnMainSync(new Runnable() {
#Override
public void run() {
listView.setSelection(index);
}
});
instrumentation.waitForIdleSync();
}
With these your method would be:
ListView list = solo.getCurrentListViews().get(0);
for(int i=0; i < list.getAdapter().getCount(); i++){
solo.clickOnView(getViewAtIndex(list, i, getInstrumentation()))
}

It looks like your code, as currently implemented, is only considering the visibile list items when controlling the loop and handling the clicking. It's important to note the behavior of two things:
First, there's a concept called view recycling in Android that helps conserve memory when dealing with ListViews. Only the views that are currently on screen are created, and once they scroll off the screen they'll be repopulated with new data. Therefore, calling methods like getChildCount and getChildAt on a ListView will only perform these operations on the visible items. To find information about the data that populates the list, you can call methods such as getCount() or getItem() on the ListView's adapter.
Second, the clickInList() method is 1-indexed, relative to the current position of the list, and can only be used for visible items. As far as I know, it will never scroll your list automatically. This means that calling clickInList(2) when at the top of the list will click the second item, but then calling clickInList(2) again when the 30th item is at the top of the list will click the 32nd.
Knowing these two things, your solution will need to consider all of the list data and perhaps have a bit more precision when making clicks. Here's how I'd rewrite your while loop to ensure you'll be able to handle every item on the list, hope this helps:
ListAdapter adapter = l.getAdapter();
for(int i=0; i < adapter.getCount(); i++)
{
//Scroll down the list to make sure the current item is visible
solo.scrollListToLine(l, i);
//Here you need to figure out which view to click on.
//Perhaps using adapter.getItem() to get the data for the current list item, so you know the text it is displaying.
//Here you need to click the item!
//Even though you're in a list view, you can use methods such as clickOnText(), which might be easier based on how your adapter is set up
solo.goBack();
}

It should help you(not tested):
public void clickAllElementsOnListView(int index) {
ListView listView = solo.getCurrentListViews().get(index);
count = listView.getAdapter() != null ? listView.getAdapter().getCount() : 0;
for (int i = 0; i < count; i++) {
scrollListToLine(listView, i);
solo.clickInList(1, index);
solo.goBack();
}
}
protected void scrollListToLine(final ListView listView, final int line) {
getInstrumentation().runOnMainSync(new Runnable() {
public void run() {
listView.setSelection(line);
}
});
}

android ListView mListView.getChildAt(i) is null, how to solve it?

I create the below code:
mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View v, int position,
long id) {
for (int i = 0; i < mListView.getCount(); i++) {
View callLogView = mListView.getChildAt(i);
mRelativeLayout = (LinearLayout)callLogView.findViewById(R.id.myShow);
if(i == position){
if(mRelativeLayout.getVisibility() == View.GONE){
mRelativeLayout.setVisibility(View.VISIBLE);
}
else{
mRelativeLayout.setVisibility(View.GONE);
}
}else{
mRelativeLayout.setVisibility(View.GONE);
}
}
}
});
I want to realize a function like when i click one item of Listview, it will show a view, and the other items of Listview will be hidden. But mListView.getChildAt(i) will have the null pointer after exceed mListView.getChildCount().
How to solve this? Thanks in advance!

AdapterView.getCount() returns the number of data items, which may be larger than the number of visible views, that's why you are getting null pointer exception, because you are trying to find views which do not exist in the current visible ListView items.
To solve this issue you will first need to find the first visible item in the ListView using getFirstVisiblePosition() and the last visible item using getLastVisiblePosition(). Change the for loop condition as:
int num_of_visible_view=mListView.getLastVisiblePosition() -
mListView.getFirstVisiblePosition();
for (int i = 0; i < num_of_visible_view; i++) {
// do your code here
}

you can not implement this in onItemClick.
As you can access only visible child not all child.
What you can do is on onItemClick
you can send the position in adapter
and then set the logic there in getView too change view
and update the adapter in listview, or notify for changes.