如何使用TextView显示从列表视图中选择的项目的值

Question

Using simplesursoradapter I have raised a listview. I select an item from listview and keep it in a variable 'titlename' and able to show in Toast. Now, I want this value in 'titlename' to be passed to a text view id 'textView3' so that it could be displayed on top of the screen in the same activity. When I tried with the following code I get a NULL pointer exception at line textView.setText(v_titlename);.

a)TextView ID 'textView' and 'textView2' are in custom_row.xml

b)TextView ID 'textView3' is in Activity_Out.xml

public void onItemClick(AdapterView<?> parent, View view, int position, long thislist) {
    TextView selectedTitle = (TextView)view.findViewById(R.id.textView);
    TextView titlename= (TextView)view.findViewById(R.id.textView2);
    TextView textView = (TextView) findViewById(R.id.textView3);
    v_titlename=titlename.getText().toString();
    textView.setText(v_titlename);
    Toast.makeText(this, titlename.getText() , Toast.LENGTH_LONG).show();
    inputID=selectedTitle.getText().toString(); // the _id of this title is stored in inputID
}

Answer 1

You need to make "textView" a field on your class and call findViewById() in your activity's onCreate(). The way you have it setup now the only way for textView to not be null would be for it to be a part of your adapter view and you'd have to call it with view.findViewById(). Given that you said you wanted this to be at the top of your activity you just have it in the wrong place. textView is part of the activity, not the list.

R.id.textView3 is a unique integer in a generated Class. So, it is "valid" even though it is not part of that View. Trips lots of people up.

    public class SomeActivity extends Activity {

        private TextView textView;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.Activity_Out);
            textView = (TextView) findViewById(R.id.textView3);
            // ...
        }
    // ...
    }