Android 在Activity中關閉Activity

情景一：在Activity A關閉指定Activity B，（不確定ActivityB是否開啓）

    1.在ActivityB中，設置靜態變量

	public static TheFirstPage_win8style instance;
	public static TheFirstPage_win8style getInstance(){
		return instance;
	}
        @Override
	protected void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		instance=this;
	}
       @Override
	protected void onDestroy() {
		super.onDestroy();
		instance=null;
	}

    2.在ActivityA中，添加

       //如果IM界面的Activity，開啓了。就關閉掉
       if(ActivityB.instance!=null){
	 ActivityB.instance.finish();
	}