RecyclerView IndexOutOfBoundsException

Why exception execute when I removed some items in RecyclerView by using loop ? I used Collentions.synchronizedMap in adapter and ‘deleteItem method’ use synchronized too (the method in fragment).

public void elementController(JsonObject jsonObject , String type)   {
    if ( jsonObject == null || type == null )    {
        return;
    }

    int position =0 , resultPosition =0;
    if ( type.equals("update") || type.equals("delete"))    {

        String id = jsonObject.get(ELEMENT_ID).getAsString();
        Map<String , Element> map = gridFragment.getMap();

        synchronized (map) {  
            for (String s : map.keySet()) {
                if (s.equals(id)) {
                    resultPosition = position;
                } else {
                    position++;
                }
            }
        }
    }

    if(position-1 > gridFragment.getmAdapter().getData().size() || position <0)   {
        return;
    }
    switch (type)   {
        case "add":
            if (gridFragment.addElement(MyJsonParser.ElementParse(jsonObject),0)){
                LogUtils.logDebug(TAG,"add end");
            }
            break;
        case "update":
            if(gridFragment.updateElement( updateParser(jsonObject),resultPosition)){
                LogUtils.logDebug(TAG,"update end");
            }
            break;
        case "delete":
            if(gridFragment.deleteElement(jsonObject.get(ELEMENT_ID).getAsString(),resultPosition)){
                LogUtils.logDebug(TAG,"delete end");
            }
            break;
    }
}

public boolean deleteElement(final String id , final int position){
    new Thread(new Runnable() {
        @Override
        public void run() {
            getActivity().runOnUiThread(new Runnable(){
                @Override
                public void run() {
                    synchronized (map) {
                        map.remove(id);
                        mAdapter.setData(map);
                        mAdapter.notifyItemRemoved(position);
                    }
                }
            });
        }
    }).start();

    return true;
} 

My error Log:

java.lang.IndexOutOfBoundsException: Inconsistency detected. Invalid item position 0(offset:0).state:4
        at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:3382)
        at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:3340)
        at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:1810)
        at android.support.v7.widget.GridLayoutManager.layoutChunk(GridLayoutManager.java:356)
        at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1269)
        at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:523)
        at android.support.v7.widget.GridLayoutManager.onLayoutChildren(GridLayoutManager.java:151)
        at android.support.v7.widget.RecyclerView.dispatchLayout(RecyclerView.java:1942)
        at android.support.v7.widget.RecyclerView.resumeRequestLayout(RecyclerView.java:1171)
        at android.support.v7.widget.RecyclerView$1.run(RecyclerView.java:167)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
        at android.view.Choreographer.doCallbacks(Choreographer.java:574)
        at android.view.Choreographer.doFrame(Choreographer.java:543)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:212)
        at android.app.ActivityThread.main(ActivityThread.java:5137)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:902)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:718)
        at dalvik.system.NativeStart.main(Native Method)

device not found

Answer

Haven’t read your code because I’m not familiar with the classes that you use but I know a fix to this problem. The problem occurs when the row element deleted is not the last one because of the index discrepancy between dataList index (your ArrayList to store data) and the parameter final int position in the method onBindViewHolder. Let me explain the issue in a graphical manner:

enter image description here

suppose we have a RecyclerView with three rows and we delete the 3rd row, at dataList index 2, (note that the deleted one is not the last element) after the removal, dataList index for the last element reduces 3 from 2 however, final int position still retrieves its position as 3 and that causes the problem. So, after removal, you can’t use final int position as an index of element to be removed from dataList.

To fix this, introduce int shift=0 and in a while loop, try removing the third item at (position-shift) and if it fails (in my case, it will) increment the shift and try removing it again until no exception occurs.

 public void onBindViewHolder(RecyclerView.ViewHolder holder, final int position) {
    
    ...
    
        holder.removeButton.setOnClickListener(new View.OnClickListener(){ //button used to remove rows
                    @Override
                    public void onClick(View view) {
                        if (position == dataList.size() - 1) { // if last element is deleted, no need to shift
                            dataList.remove(position);
                            notifyItemRemoved(position);
                        } else { // if the element deleted is not the last one
                            int shift=1; // not zero, shift=0 is the case where position == dataList.size() - 1, which is already checked above
                            while (true) {
                                try {
                                    dataList.remove(position-shift);
                                    notifyItemRemoved(position);
                                    break;
                                } catch (IndexOutOfBoundsException e) { // if fails, increment the shift and try again
                                    shift++;
                                }
                            }
                        }
                    }
                });
   ...
    }

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