CODEWITHSUNDEEP
javaandroidandroid-studio
Selin Aksu
Selin Aksu

Reputation: 17

My Android app crashes when I use method from MainActivity in an other Activity

I have two activities MainActivity and Additem

in MainActivity I have this method:

public void updateUI() {
    helper = new TaskDBHelper(MainActivity.this);
    SQLiteDatabase sqlDB = helper.getReadableDatabase();
    Cursor cursor = sqlDB.query(TaskContract.TABLE,
            new String[]{TaskContract.Columns._ID, TaskContract.Columns.TASK},
            null,null,null,null,null);

    listAdapter = new SimpleCursorAdapter(
            this,
            R.layout.task_view,
            cursor,
            new String[] { TaskContract.Columns.TASK},
            new int[] { R.id.taskTextView},
            0
    );

    ListView listView = (ListView)findViewById(R.id.list);
    listView.setAdapter(listAdapter);

}

It updates the tasklist on the Mainscreen.

But when I use updateUI(); in Additem, on saving the task it returns back but the app crashes en restarts itself.

As error I got this:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference

This is my code where I use updateUI() in Additem:

public void saveItem(View view){
    EditText editText = (EditText)findViewById(R.id.editText);
    String task = editText.getText().toString();
    Log.d("Additem", task);

    helper = new TaskDBHelper(Additem.this);
    SQLiteDatabase db = helper.getWritableDatabase();
    ContentValues values = new ContentValues();

    values.clear();
    values.put(TaskContract.Columns.TASK, task);

    db.insertWithOnConflict(TaskContract.TABLE, null, values,
            SQLiteDatabase.CONFLICT_IGNORE);



    updateUI();


    finish();
}

Could someone help me with this problem?

Thanks in advance,

Kind regards, Selin

Upvotes: 1

Views: 237

Answers (2)

SohailAziz
SohailAziz

Reputation: 8034

Your listview is null and when you call it from other activity [when the MainActivity is paused/stopped] you are actually doing null.setAdapter which is causing crash.

You should post some sort of event to MainActivity and update the list/adapter when MainActivity resumes. OR you can always refresh/update the adapter in onCreate/onResume of MainActivity.

Upvotes: 2

sam100rav
sam100rav

Reputation: 3783

I would suggest you to initialize the listView and listAdapter in your MainActivity and in update UI just refresh your view by using 

listAdapter.notifyDataSetChanged()

Upvotes: 0

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