Use Handler.post() to update ListView

Question

I have a listView and i use ArrayAdapter.addAll to load the data.I want to use ListView.getChild(0) after use ArrayAdapter.addAll at once.But NullPointerException was thrown.

I try to add the ListView.getChild(0) to the MessageQueue by using Handler.post.The app works sometimes since as I do this, but sometimes the NullPointerException also was thrown.

My Code:

mRightAdapter.addAll(mRightDisplayDatas); 
mHandler.post(new Runnable() {
    @Override public void run() { 
    ((TextView) mLeftListView.getChildAt(0)).setCompoundDrawablesWithIntrinsicBounds(null, null, getResources().getDrawable(R.mipmap.ic_right, mContext.getTheme()), null);
   }
});

log:

FATAL EXCEPTION: main
                                                                    Process: com.buledon.volunteerapp, PID: 4787
                                                                    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setCompoundDrawablesWithIntrinsicBounds(android.graphics.drawable.Drawable, android.graphics.drawable.Drawable, android.graphics.drawable.Drawable, android.graphics.drawable.Drawable)' on a null object reference
                                                                        at com.buledon.volunteerapp.widget.CitySelectView$3.run(CitySelectView.java:130)
                                                                        at android.os.Handler.handleCallback(Handler.java:739)
                                                                        at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                        at android.os.Looper.loop(Looper.java:135)
                                                                        at android.app.ActivityThread.main(ActivityThread.java:5669)
                                                                        at java.lang.reflect.Method.invoke(Native Method)
                                                                        at java.lang.reflect.Method.invoke(Method.java:372)
                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:960)
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)

please show related code along with query will give better understading — Sohail Zahid, Jul 20 '16 at 06:28
Can we see your xml layout code that you inflating in your adapter getView() method? I think you shouldn't cast your view into TextView — Hilal, Jul 20 '16 at 06:47
I didn't use getView(), I just use the original ArrayAdapter — Paul Yang, Jul 20 '16 at 06:57
Check if getChildAt() returns null before trying to manipulate it. — greenapps, Jul 20 '16 at 07:09
Do you have scrollview, because as I understand getChildAt returns the child from the visible elements in listview. [Check this](http://stackoverflow.com/questions/10318862/sometimes-listview-getchildatint-index-returns-null-android) , [Also this](http://stackoverflow.com/questions/6766625/listview-getchildat-returning-null-for-visible-children) — Hilal, Jul 20 '16 at 07:09
So maybe you can try to use `mRightAdapter.getItem(0)` instead of `mLeftListView.getChildAt(0)` — Hilal, Jul 20 '16 at 07:20
mRightAdapter.getItem(0) can not return the view, it return the genericity Object — Paul Yang, Jul 20 '16 at 07:28
Yes you are right, so it seems the safe way is implementing `getView()` method as @chejaras said. — Hilal, Jul 20 '16 at 07:53

score 2 · Accepted Answer · answered Jul 20 '16 at 07:30

Also use mRightAdapter.notifyDataSetChanged. Also added values don't get reflected in listview immediately. Use mHandler.postDelayed and add a delay of few millisecond. You can check if getChild(0) is not null. If its null post the handler again.

A cleaner way would be to add this code in getView() method of Adapter class and check for index of the view being requested. If its 0 then execute your code. This way you will be doing your stuff at right place and right time.

Use Handler.post() to update ListView

1 Answers1