android – 如何在一个Activity上叠加一个视图？

例如：

public class ActivityClass extends Activity
{
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        …       

        PopupClass popup = new PopupClass(this);
        popup.showPopup();
    }

}


public class PopupClass
{
    Context context;

    void Popup(Context ctx)
    {
        context = ctx;
    }

    void showPopup()
    {
        // Add a view on top of the current Activity.
    }
}

有没有办法让PopupClass能够在知道上下文的情况下将视图添加到当前Activity？

PopupClass不知道关于Activity的任何其他内容,也不能将View传递给ActivityClass以供ActivityClass添加.

http://www.androidpeople.com/android-custom-dialog-example

http://www.helloandroid.com/tutorials/how-display-custom-dialog-your-android-application