为什么没有setDisplayHomeAsUpEnabled()时出现向上按钮？

Question

根据谷歌的文档,getActionBar().setDisplayHomeAsUpEnabled(true)需要显示向上按钮.我使用Eclipse中的向导创建了一个裸骨活动,并指定了它的父活动.我getActionBar().setDisplayHomeAsUpEnabled(true)在自动生成的代码中找不到任何内容,但是当此活动启动并且按预期工作时,会出现向上按钮.谁能对此有所了解？

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

当您在中指定a parentActivityName时AndroidManifest,Acitivty 将检查该内容并自动启用"up"可用性(如果存在).