Android menu为什么打不开

 注意按手机菜单键需要 继而 v7包下的AppCompatActivity

@Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_setting_app, menu);
        menu.add(0, 1, 0, "1");
        menu.add(0, 3, 1,"2");
        menu.add(0, 4, 2,"3");
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        return super.onOptionsItemSelected(item);
    }

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto">

    <item
        android:id="@+id/item_setting"
        android:title=""
        android:orderInCategory="100"
        app:showAsAction="ifRoom"/>
    <item
        android:id="@+id/item_message"
        android:title=""
        android:orderInCategory="100"
        app:showAsAction="ifRoom"/>
</menu>

不是V7包的用此方法

@Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        switch (keyCode) {
            case KeyEvent.KEYCODE_MENU:
               .......
                return false;
        }
        return super.onKeyDown(keyCode, event);
    }