android - 为什么在没有 setDisplayHomeAsUpEnabled() 的情况下出现向上按钮？

Question

根据 Google's document , getActionBar().setDisplayHomeAsUpEnabled(true) 需要显示向上按钮。我使用 Eclipse 中的向导创建了一个简单的 Activity 并指定了它的父 Activity 。我在自动生成的代码中找不到任何 getActionBar().setDisplayHomeAsUpEnabled(true)，但是当此 Activity 启动时向上按钮存在并且按预期工作。任何人都可以阐明这一点吗？

public class FooActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_foo);

            //more code...    
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
            //more code...  
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    /**
     * A placeholder fragment containing a simple view.
     */
    public static class PlaceholderFragment extends Fragment {

        public PlaceholderFragment() {
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            //more code...  
            return rootView;
        }
    }

}

Answer 1

当您在 AndroidManifest 中指定 parentActivityName 时，Activity will check for that and automatically enable the "up" affordance if it's present.