如果类A扩展了类B扩展了Activity，如何正确使用findViewById

Question

In Android, I have a class A which extends class B which extends an ActionBarActivity. Class A sets the content view. For some reason, I'm unable to access the view elements from Class B. How can I access the view elements (ex: TextView)? When I attempt to use findViewById in class B, it is always null.

public class A extends B {
    @Override
    protected void onCreate(Bundle savedInstanceState)  {
        setContentView(R.layout.activity_main);
        super.onCreate(savedInstanceState);
    }
}

public class B extends ActionBarActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        TextView myTextView = (TextView) findViewById(R.id.myTextView);
        // myTextView is null
    }
}

Answer 1

you're inheriting things backwards. Class B doesn't ever setContentView.

I think this is what you want:

public class A extends ActionBarActivity {
@Override
protected void onCreate(Bundle savedInstanceState)  {
    setContentView(R.layout.activity_main);
    super.onCreate(savedInstanceState);
    }
}

public class B extends A {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        // A called setContentView(), so now we can find views by id.
        TextView myTextView = (TextView) findViewById(R.id.myTextView);
        // myTextView now is not null.