Question

In my app i have a button that turns bluetooth on and off, something that i noticed is that when i move the togglebutton defintion to the top of the class and out of onResume(); the app crashes with nullpointerexception, here is the short version of the code that crashes:

    public class MainActivity extends Activity {
        static final BluetoothAdapter myBluetooth = BluetoothAdapter.getDefaultAdapter();
        final ToggleButton tglbtn = (ToggleButton)findViewById(R.id.ToggleButton01);

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
        if(myBluetooth == null){
            setContentView(R.layout.notsupported);  
        }
        else{
            setContentView(R.layout.supported);
        }
    }

        @Override
        public void onResume()
        {
            super.onResume();
            tglbtn.setChecked(myBluetooth.isEnabled());
            tglbtn.setOnClickListener(new OnClickListener(){
                 public void onClick(View v) { .......}
            }
        }
    }

When i move final ToggleButton tglbtn = (ToggleButton)findViewById(R.id.ToggleButton01);
back into onResume(), the app works fine and doesn’t crash, can someone explain why this happens?

Answer 1

You are assigning your Views in the onCreate() right? Specifically it should be happening after the setContentView(X). The reason for this is because all views will be non-null at this point.