如何从外部活动膨胀SupportActionBar菜单

// 导入必要的类
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

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

    // 加载菜单资源文件
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu_main, menu);
        return true;
    }

    // 处理菜单项点击事件
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.menu_item1:
                // 执行菜单项1的操作
                Toast.makeText(this, "点击了菜单项1", Toast.LENGTH_SHORT).show();
                return true;
            case R.id.menu_item2:
                // 执行菜单项2的操作
                Toast.makeText(this, "点击了菜单项2", Toast.LENGTH_SHORT).show();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }
}