Develop Reference

ListView.setSelection(int) not selecting item

It's a common question, I know.
I have a ListView of 100 items having 0 to 99 positions. Only first 10 items are visible when the list is rendered for the first time, right? I can use setSelection(int) in ListView.post(Runnable) for positions 0 to 9, that's working correctly. What if I want to select an item having position 45? setSelection(int) doesn't seem to work because when the list is rendered we do not have any item having position 45 rather it will be rendered when we scroll down. So my question is:
How can I select an item (and make it visible) even the item is not rendered?

try the following code:
listview.post(new Runnable()
{
#Override
public void run()
{
listview.setSelection(45); // your position
View view = listview.getChildAt(45);
if (view != null)
{
view.requestFocus(); //request focus on row
}
}
});
}

RecyclerView keeps repeating cached (?) subview and not looking to onBindViewHolder

I have RecyclerView where every list item has an ImageButton, thee image of which I define in the adapter's onBindViewHolder():
int myVote = getMyVote();
if (myVote != 0) {
Log.d("dbg", myVote + "");
holder.ratingButton.setImageResource(R.drawable.ic_star_grey600_36dp);
}
So ratingButton is a star in the right bottom corner of the list item layout. Its shape is filled with gray color (and accordingly, a log record is pushed) if the condition (myVote != 0) is satisfied.
The problem is that when I scroll the list down I can watch other stars became filled even though I can see the only one record in the log window (for the correct list item). Moreover, this list items with incorrectly changed buttons repeat every 5 rows, and that's what's confusing me. If I changemListView.setItemViewCacheSize(0); the repeat period changes to 3, so we can assume it somehow connected with the RecyclerView's caching and recycling mechanism.
Please, help me to work the problem out. Thanks!

Don't forget to implement
public long getItemId(int position) {}
otherwise, you'll see repeated items in RecyclerView.

Try to change your code to:
if (myVote != 0) {
Log.d("dbg", myVote + "");
holder.ratingButton.setImageResource(R.drawable.ic_star_grey600_36dp);
} else {
holder.ratingButton.setImageResource(int another resource);
}
}

You may also have to write else part of main condition with some another resource like:
if (myVote != 0) {
Log.d("dbg", myVote + "");
holder.ratingButton.setImageResource(R.drawable.ic_star_grey600_36dp);
} else {
holder.ratingButton.setImageResource(int another_resource);
}
It is worked for me.

ListView with date as section headers position varies onScroll

Im trying to load custom callLogs in a listView based on date as section header.In ListAdapter i compare each date with the previous date and set SectionHeaderLayout Visible/Invisible. When the ListView has been loaded the section header are displayed correctly but when i scroll the section headers are set Visible to wrong ListItems.
Please help me to figure out a solution.
This is how im trying to set SectionHeader through the adapter.
if (position == 0) {
checkDate = mDateStr;
holder.sectionHeaderDate.setVisibility(View.VISIBLE);
holder.sectionHeaderText.setText(mDateStr);
}
} else if (checkDate == null || !checkDate.equals(mDateStr)) {
checkDate = mDateStr;
holder.sectionHeaderDate.setVisibility(View.VISIBLE);
holder.sectionHeaderText.setText(mDateStr);
} else {
holder.sectionHeaderDate.setVisibility(View.GONE);
}
Thanks in Advance

I see this is old question, you have probably solved your problem, but I'll answer for others who will have the same problem.
If you want to show header based on previous date you can't do that by remembering last item that was passed to getView function.
The reason is scrolling, i.e. different direction when going up and down.
For example, if you have items
1,
2,
3,
4,
5
when you're going down, and current item is 3, previous was 2, and all will work.
But if you are going up, your previous item for 3 was actually 4, and that's where your problem happens.
so instead of keeping item, you should use positions.
this would be the sketch of solution that you can call inside of your getView function:
private void showHeader(ViewHolder holder, Call item, int position) {
boolean shouldShowHeader = false;
if (position == 0
|| !DateHelper.isSameDay(item.getDateTime(),
items.get(position - 1).getDateTime()))
shouldShowHeader = true;
if (shouldShowHeader) {
holder.header.setVisibility(View.VISIBLE);
holder.date.setText(DateHelper.getSimpleDate(item.getDateTime()));
} else {
holder.header.setVisibility(View.GONE);
}
}

Adding items to ListView, maintaining scroll position and NOT seeing a scroll jump

I'm building an interface similar to the Google Hangouts chat interface. New messages are added to the bottom of the list. Scrolling up to the top of the list will trigger a load of previous message history. When the history comes in from the network, those messages are added to the top of the list and should not trigger any kind of scroll from the position the user had stopped when the load was triggered. In other words, a "loading indicator" is shown at the top of the list:
Which is then replaced in-situ with any loaded history.
I have all of this working... except one thing that I've had to resort to reflection to accomplish. There are plenty of questions and answers involving merely saving and restoring a scroll position when adding items to the adapter attached to a ListView. My problem is that when I do something like the following (simplified but should be self-explanatory):
public void addNewItems(List<Item> items) {
final int positionToSave = listView.getFirstVisiblePosition();
adapter.addAll(items);
listView.post(new Runnable() {
#Override
public void run() {
listView.setSelection(positionToSave);
}
});
}
Then what the user will see is a quick flash to the top of the ListView, then a quick flash back to the right location. The problem is fairly obvious and discovered by many people: setSelection() is unhappy until after notifyDataSetChanged() and a redraw of ListView. So we have to post() to the view to give it a chance to draw. But that looks terrible.
I've "fixed" it by using reflection. I hate it. At its core, what I want to accomplish is reset the first position of the ListView without going through the rigamarole of the draw cycle until after I've set the position. To do that, there's a helpful field of ListView: mFirstPosition. By gawd, that's exactly what I need to adjust! Unfortunately, it's package-private. Also unfortunately, there doesn't appear to be any way to set it programmatically or influence it in any way that doesn't involve an invalidate cycle... yielding the ugly behavior.
So, reflection with a fallback on failure:
try {
Field field = AdapterView.class.getDeclaredField("mFirstPosition");
field.setAccessible(true);
field.setInt(listView, positionToSave);
}
catch (Exception e) { // CATCH ALL THE EXCEPTIONS </meme>
e.printStackTrace();
listView.post(new Runnable() {
#Override
public void run() {
listView.setSelection(positionToSave);
}
});
}
}
Does it work? Yes. Is it hideous? Yes. Will it work in the future? Who knows? Is there a better way? That's my question.
How do I accomplish this without reflection?
An answer might be "write your own ListView that can handle this." I'll merely ask whether you've seen the code for ListView.
EDIT: Working solution with no reflection based on Luksprog's comment/answer.
Luksprog recommended an OnPreDrawListener(). Fascinating! I've messed with ViewTreeObservers before, but never one of these. After some messing around, the following type of thing appears to work quite perfectly.
public void addNewItems(List<Item> items) {
final int positionToSave = listView.getFirstVisiblePosition();
adapter.addAll(items);
listView.post(new Runnable() {
#Override
public void run() {
listView.setSelection(positionToSave);
}
});
listView.getViewTreeObserver().addOnPreDrawListener(new OnPreDrawListener() {
#Override
public boolean onPreDraw() {
if(listView.getFirstVisiblePosition() == positionToSave) {
listView.getViewTreeObserver().removeOnPreDrawListener(this);
return true;
}
else {
return false;
}
}
});
}
Very cool.

As I said in my comment, a OnPreDrawlistener could be another option to solve the problem. The idea of using the listener is to skip showing the ListView between the two states(after adding the data and after setting the selection to the right position). In the OnPreDrawListener(set with listViewReference.getViewTreeObserver().addOnPreDrawListener(listener);) you'll check the current visible position of the ListView and test it against the position which the ListView should show. If those don't match then make the listener's method return false to skip the frame and set the selection on the ListView to the right position. Setting the proper selection will trigger the draw listener again, this time the positions will match, in which case you'd unregister the OnPreDrawlistener and return true.

I was breaking up my head until I found a solution similar to this.
Before adding a set of items you have to save top distance of the firstVisible item and after adding the items do setSelectionFromTop().
Here is the code:
// save index and top position
int index = mList.getFirstVisiblePosition();
View v = mList.getChildAt(0);
int top = (v == null) ? 0 : v.getTop();
// for (Item item : items){
mListAdapter.add(item);
}
// restore index and top position
mList.setSelectionFromTop(index, top);
It works without any jump for me with a list of about 500 items :)
I took this code from this SO post: Retaining position in ListView after calling notifyDataSetChanged

The code suggested by the question author works, but it's dangerous.
For instance, this condition:
listView.getFirstVisiblePosition() == positionToSave
may always be true if no items were changed.
I had some problems with this aproach in a situation where any number of elements were added both above and below the current element. So I came up with a sligtly improved version:
/* This listener will block any listView redraws utils unlock() is called */
private class ListViewPredrawListener implements OnPreDrawListener {
private View view;
private boolean locked;
private ListViewPredrawListener(View view) {
this.view = view;
}
public void lock() {
if (!locked) {
locked = true;
view.getViewTreeObserver().addOnPreDrawListener(this);
}
}
public void unlock() {
if (locked) {
locked = false;
view.getViewTreeObserver().removeOnPreDrawListener(this);
}
}
#Override
public boolean onPreDraw() {
return false;
}
}
/* Method inside our BaseAdapter */
private updateList(List<Item> newItems) {
int pos = listView.getFirstVisiblePosition();
View cell = listView.getChildAt(pos);
String savedId = adapter.getItemId(pos); // item the user is currently looking at
savedPositionOffset = cell == null ? 0 : cell.getTop(); // current item top offset
// Now we block listView drawing until after setSelectionFromTop() is called
final ListViewPredrawListener predrawListener = new ListViewPredrawListener(listView);
predrawListener.lock();
// We have no idea what changed between items and newItems, the only assumption
// that we make is that item with savedId is still in the newItems list
items = newItems;
notifyDataSetChanged();
// or for ArrayAdapter:
//clear();
//addAll(newItems);
listView.post(new Runnable() {
#Override
public void run() {
// Now we can finally unlock listView drawing
// Note that this code will always be executed
predrawListener.unlock();
int newPosition = ...; // Calculate new position based on the savedId
listView.setSelectionFromTop(newPosition, savedPositionOffset);
}
});
}

Android: Help required in card matching game?

I have 20 cards of which there are 10 pair of images. The player is meant to find a match of each card/image.
The problem is that if a player taps or clicks each card twice then that card gets decremented from the remaining ones . I need to disable the click listener of the ImageView. How can do that?
ivOne = (ImageView)findViewById(R.id.ivOne);
ivOne.setId(a[0]);
//final ImageView ivOne = (ImageView)findViewById(R.id.ivOne);
//ivOne.setEnabled(false);
ivOne.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
ivOne.setBackgroundResource(images[a[0]]);
Log.e("r[0]:", Integer.toString(a[0]));
if (firstTap)
{
firstId = v.getId();
firstTap = false;
}
else
{
//ivOne.setEnabled(false);
int secondId = v.getId();
Log.e("secondId", Integer.toString(secondId));
if ((secondId == firstId) && (score != 0))
{
//ivOne.setEnabled(false);
if (ivOneScored == false)
{
score--;
ivOneScored = true;
}
}
firstTap = true;
}
tvScore.setText("Remaining:" + Integer.toString(score));
}
});

I have a memory matching game on the market that works very similar. What I did was make a class that represents the card (with image and id properties) and assign an id (0-9) to the cards and the image as I loaded them into a temporary arraylist of just the 10 image objects.
public class GameTile {
public int id;
public Drawable image;
}
Then I iterated over the list twice and added the cards to the main arraylist that I use for my adapter... after which I used Collections.shuffle to shuffle the cards... Now... on to the selection. AS you know, in a memory game, you only want 2 cards flipped at any time. I am using a gridview to hold my cards... so what I did was use the OnItemClickListener from the gridview and not the imageview. Secondly, when a card is clicked, I add the position to another arraylist called "selected" that never contains more than 2 items... the position of the items we are attempting to match... In the OnItemClickListener, when the event is fired, I check to see if the item already exists in "selected" and return if it does... in effect ignoring the click.
if (selected.contains(position)) {
return;
}
When "selected" contains 2 items, I ignore all clicks until the handler finishes checking for a match.
if (selected.size() > 1) {
return;
}
So when a user has selected 2 items, I set a handler to call a runnable that checks for a match. If a match is made (by comparing the id fields I set when I first loaded the images), I add the two positions to another arraylist that contains only matched items and that handler also clears "selected" and, if there were matches, I change the images to blanks. When all 20 cards have been matched I fire a win which does all of the win stuff and resets the gameboard.

You have to make sure that those cards have the same symbol, but are not the same card.
So your line
if ((secondId == firstId) && (score != 0))
must rather look like something in the lines of
if ((firstCard != secondCard) && (secondId == firstId) && (score != 0))
where firstCard and secondCard identify the card on the table (not the symbol on the card)

If I understand you right, you just need to say view.setOnClickListener(null) if those two match? If you want to disable both of them, you just store a map to link an ID to a View, and then clear the click listener for both "view" and whichever view belongs to the second ID.