I'm dynamically adding Views to my items in a RecyclerView. These added Views should only be related to the item which they're added to, but I'm having a problem when I scroll. It seems the View is recycled and a new item is loaded, but those previously added views are still there, only now on the wrong item.
I'm assuming that it's just because the ViewHolder is being reused, so the added items show up again with a new item, when loaded.
How would one go about solving this?
This was an old question of mine. A bounty was placed on it, hence the surge of popularity and the multiple new and irrelevant answers.
As stated in both my comment to this answer and #CQM's comment below my original question, the answer is to override the onViewRecycled() method and perform any needed operations there. This method is called when a view is recycled, and any cleanup operations can be done here.
Documentation on this method can be found here.
In my case, it was a matter of deleting the invisible TextView's attached to the view. The text itself had been deleted, but the view remained. If many invisible TextView's accumulate on the view and aren't properly recycled when scrolling, the scroll will begin to lag.
You need to track what views have been added based on the backing data. I would probably add any necessary extra views in onBindViewHolder(), and remove any that might be present in onViewRecycled(). Then when you want to make one appear dynamically, change whatever variable you have tracking whether it should be visible, and call notifyItemChanged().
Based on this:
but those previously added Views are still there, but now on the wrong item.
Basically, as per the RecyclerView documentation, You have to reset the views everytime inside the onBindViewHolder() method,
so let say, you have a method that sets a view param if its your profile, so the code for the same goes as follows,
if (list.get(position).getId()==PreferenceManager.getUserID())
{
// do some view change here
setViewParam(true);
}else
{
// reset the view change here
setViewParam(false);
}
So what you're doing here is giving recycled ViewHolder a chance to reset.
Do comment if you need help!
You can use this! setItemViewCacheSize(int size)
Check here RecyclerViewDocumentation.
The offscreen view cache stays aware of changes in the attached adapter, allowing a LayoutManager to reuse those views unmodified without needing to return to the adapter to rebind them.
First of all, can you share some more code please?
Second, why would you want to dynamically add new views on fly? Why don't you use different VIEWTYPE or just have those view already on your layout and just make them visible/invisible or visible/gone? (I believe it will be more efficient this way).
Let me remind you something about RecyclerView, yes when user is scrolling viewHolder are being reused (few of them can be created, even more than it needs to fill the screen). So if it happened that you added some views on "item A" and user scroll to "item Z", that viewHolder can be reused for that "item Z", hence the show up of the previously added views.
How can you solve that?
Well always check on every items if you need to add new views, if yes add them if not already added, else always remove those views (if present) to return to default viewHolder state (or whatever you call it).
Hope this will help you.
Save Information by tags for items with new child each time the Add newView operation occur. (In shared preference for example)
Tag: create with item position onBindViewHolder.
...
SharedPreference sharedPref = getSharedPreference("text" + position, context);
SharedPreference.Editor editor = sharedPref.edit();
editor.putString("view", "ImageView");
...
when load Adapter get this value and put default as null.
I am not sure about its efficiency but i will work.
...
String viewType = sharedPref.getString("view", null);
//it will return ImageView
if you know some possible viewTypes for example always going to be ImageView & TextView so with some if statement it will be ok.
if(viewType.equals("ImageVIew")){
item(position).addView(new ImageVIew(context));
}
Good Luck
In your adapter class of your recyclerView,
in the onBindViewHolder method,
create another adapter and do the same methods for your new adapter.
The hierarchy will be,
mainRecyclerView -> item1(->childRecyclerView1) , item2(->childRecyclerView2), item3(->childRecyclerView3)
This way you can achieve what you want without wrong values to be viewed on wrong items.
You should take any Empty Layout like Linearlayout in your child item layout XML and then add views into that LinearLayout of your particular item in this way when you scroll List all of you child views which you have added to LinearLayout also scroll with that item .
Related
I have a dialog with RecyclerView of IDs in it. While I was choosing an id it changes its background. I did it by replacing adapter where I am putting newly selected position. And in my adapter item layout was chosen by its position where if equals to selected, it has another layout.
So after resetting a new adapter to recycler it losses current scroll position. I tried to use scrscrollToPosition, but it still not perfect, due to the situation that scrolled position is always on a beginning of RecyclerView.
So as I understand the problem I need to remember reference or some other scrolling data for setting it on the new adapter.
So If someone knew relevant RecyclerView methods or good practice for this problem, it would be nice =)
I don't think that here I need some code, cause it more practice question, but if someone need it I would add it.
Update: Meantime I found this method for getting offset of RecyclerView but still looking how to use this data in new adapter.
int offset = recyclerViewDialog.computeHorizontalScrollOffset();
I am designing an android game, and I'm trying to use ListView. The list uses a BaseAdapter, and is filled with an ArrayList. When the user pressed the ok button, I scroll to the top of the list, and then iterate through each soldier in the list. I set the background drawable of one of the child views of the soldier so that it's a short animation that displays "hit" or "miss". I used a Handler.postDelayed() so that each animation for the one before it to finish.
The problem is that I cannot modify the views that are invisible. I will have up to 13 soldiers in my list at a time, but only a maximum of 5 can be displayed. So once I hit the sixth soldier, I get a null pointer exception from using ListView.getChildAt(soldierArrayIndex). My solution was to add smoothScrollTo(soldierArrayIndex) before the getChildAt() call so that it would become visible, but the problem persisted.
So my question isn't exactly "how to fix my code?". I'm more wondering if there is a way to disable the recycling that ListView does. The reason I'm using getChildAt() is because I need to use findViewById() on the view it returns, and then modify the view that was found by ID. However, if the view was never recycled, getChildAt() wouldn't return null.
Another idea I had was to just use a scroll view, enter 13 instances of the Soldier View that I created, and then set the ones I'm not currently using to "gone". My only problem is I don't know how to iterate through those views.
TL;DR: How to update views that are not currently visible in listview (they are currently "recycled")?
I think you are confusing Model and View here.
Adapter Views take an adapter that usually has access to the whole dataset. So even though your ListView will only render as many items as are visible on the screen, you should still be able to access your off-screen items by calling getItem(position) on your adapter.
It seems like you are calling getView directly on your adapter.
I’m suggesting you shouldn’t do this since this is not how AdapterViews and Adapters are designed. Instead, you need to indicate to your ListView when something in your model is changed (via notifyDataSetChanged) and leave it up to your ListView to call your adapter’s getView method on your behalf.
I imagine the sequence of events being something like this:
Update Soldier Object
Call notifyDataSetChanged on your adapter which will tell your ListView it needs to redraw stuff
ListView iterates through the visible Soldier items calling getView(int position, View convertView, ViewGroup parent) on each.
Your getView implementation in your adapter gets the Soldier at the specified position and determines what the View should look like at that point in time.
For "offscreen" Soldiers (ones that are not visible in the scroll area of the ListView,) there is no need for the ListView to render them, so it will not call getView on those positions.
However, if a Soldier that was offscreen is now scrolled into view, the ListView will call your adapter's getView method with that Soldier's position in your array.
Finally, if you want finer-grained control over how an AdapterView should update itself, you might consider RecyclerView as it allows you to notify changes on an item by item basis.
I want to update single row of listview which contains a image after certain time of addition to listview. I am using notifyDataSetChanged for this but when other visible views contains a imageView, it gets a jerk felling on other visible imageViews due to notifyDataSetChanged.
Can someone suggest a better way to do it.
Thanks
Keep a reference to the imageview when you create/update it in the adapter. You can then change the image later on. However, since list items get recycled, you will want to set a tag on it with some id of the content so that you make sure you're still updating the right item.
Regarding the lisview recycle, I'm reusing the views with viewholder, but now I need to add a number of Views(ImageViews and textviews) not clearcut( the number of views isnt always the same).
How can I add these items, without create a new view on every getView() method and without affecting the performance of the list?
No way to create different layouts without overriding getView(). You can reuse as much view types as you want, read this answer.
If you have perfomance issue, try a new widjet RecyclerView, available at Support-V7 library.
my strategy to implement what you described without creating new view every time getView() is called, is:
let's say you have at the most 10 image views. your view xml will contain 10 ImageView items,
but when getView() been called - you'll set the visibility of the un-needed elements to View.GONE, and the only ones you needed to View.Visible.
working great for me, and that's the only why not to create new view...
My problem is similar to ListView getChildAt returning null for visible children, but despite searching I cannot find a solution.
I have a ListView with a Scroll. The ListView has 10 items, 7 of which are visible and 3 are hidden by scroll. I also have an external method (out of adapter) that must get all of the children from this ListView (e.g. using getChildAt()).
I need all 10 of the items, but the last 3 are null objects. I've tried code like the following:
getListView().smoothScrollToPosition();
But this doesn't work.
I think that I don't need to post the rest of my code, as the description says everything?
As you have already seen you can't get all the child row views from a ListView simply because a ListView holds only the views for the visible rows(plus some recycled rows but you can't reach those). The correct way to do what you want is to store whatever data in the adapter's data and retrieve it from there.
But the ListView doesn't keep the current values from RadioGroup in
running time.
I've seen that you have some problems with this so I've adapted some old code to build a basic example, code that you can find here.
I don't think so you need to add scroll view for a listView. Scroll automatically works on ListView. Try your application without adding scroll view and I'm sure it'll work as you needed.
The reason those children are null it's because they really do not exist and they will never exist, if only 7 children are on the screen at one time, the system will only create 7 and re-use by passing the convertView back to the adapter getView() method.
If you want to grab information regarding your whole dataset you should search on the dataset itself, instead of the views on the screen. E.g. if it's an ArrayAdapter, loop the array; if it's a CursorAdapter, loop the cursor; etc.
The non-visible children of a listView don't actually exist. When they become visible, one of the redundant views is recycled or a new view is generated. So you can't actually access all the views. Why do you want to? Whatever changes you want to make should be made to the data that populates the views rather than the views themselves.
There are a few point that you need to take care of:
1. List view provides inbuilt scroll functionality, So don't use Scroll view. It will only mess up things.
2. List view doesn't contain ALL the children. When you scroll it, it creates only visible items on run time.
3. If you want to get all the children altogether, Better keep an ArrayList of the child objects that your list has. You can add or remove children to this ArrayList as per requirement.