java - 如何防止在 Activity 关闭时添加 Fragment

Question

我正在创建一个Activity与Service通信通过 POST 从互联网下载一些数据方法。为此，我使用 Messenger 。这是我的代码，让您更清楚:

我的onCreated()方法:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_comments);

    CommentsHandler commentsHandler = new CommentsHandler(this, savedInstanceState);
    Messenger messenger = new Messenger(commentsHandler);

    Intent serviceIntent = new Intent(this, WindowService.class);
    serviceIntent.putExtra("messenger", messenger);
    serviceIntent.putExtra("state", 888);
    serviceIntent.putExtra("number", getIntent().getStringExtra("number"));
    startService(serviceIntent);
}

我的Service中的代码的线程将结果数据发布到 Activity通过Messenger对象:

    /** ... **/
    Messenger messenger = intent.getParcelableExtra("messenger");
    /** ... **/
    Message resultMsg = this.obtainMessage();
    resultMsg.obj = jParser.getArrayList(); //This is an ArrayList of my downloaded data.
    messenger.send(resultMsg);

Activity中的代码处理 Message来自Service :

public static class CommentsHandler extends Handler {
    Bundle mSavedInstanceState;
    ActionBarActivity activity;

    public CommentsHandler(Activity a, Bundle savedInstanceState) {
        activity = (ActionBarActivity) a;
        mSavedInstanceState = savedInstanceState;
    }

    @Override
    public void handleMessage(Message msg) {
        comments = (ArrayList<HashMap<String, String>>) msg.obj;
        if (mSavedInstanceState == null && msg.arg1 != 793) {
            activity.getSupportFragmentManager().beginTransaction()
                .add(R.id.container, new CommentsFragment()).commit();
        } else if (msg.arg1 == 793) { //793 is my preferred code to determine
                                      //if the internet connection could not be
                                      //established when the Service was trying
                                      //to download the data.
            activity.finish();
        }
    }
}

问题是:如果我打开Activity并在下载数据之前将其关闭，此代码.add(R.id.container, new CommentsFragment()).commit();给我错误 Can not perform this action after onSaveInstanceState ，因为此代码仅在我的 Service 中的数据之后执行通过 Messenger 处理并发送对象，但当时Activity已被用户关闭，因此 Fragment无法添加。如何解决这个问题？如何检查 Activity 是否在添加 Fragment 之前未关闭/正在关闭？或者，更好的是，如何停止在 Activity 上运行该代码的线程的onDestroy()方法，因此如果 Activity 则不会执行它关闭了？提前致谢!

Answer 1

在您的 Activity 中，您应该创建一个 boolean 值来检查 Activity 是否可见:

public ActionBarActivity extends Activity {
  private boolean isActivityVisible = false;

  @Override
  protected void onResume(){
     isActivityVisible = true;
  }

  @Override
  protected void onPause(){
     isActivityVisible = false;
  }

  public boolean isVisible(){
     return this.isActivityVisible;
  }
}

然后修改 Handler 类定义:

public static class CommentsHandler extends Handler {
Bundle mSavedInstanceState;
ActionBarActivity activity;

public CommentsHandler(Activity a, Bundle savedInstanceState) {
    activity = (ActionBarActivity) a;
    mSavedInstanceState = savedInstanceState;
}

@Override
public void handleMessage(Message msg) {
    // here you check if your activity is no longer visible and then break up
    if(activity == null || !activity.isVisible())
        return;

    comments = (ArrayList<HashMap<String, String>>) msg.obj;
    if (mSavedInstanceState == null && msg.arg1 != 793) {
        activity.getSupportFragmentManager().beginTransaction()
            .add(R.id.container, new CommentsFragment()).commit();
    } else if (msg.arg1 == 793) { //793 is my preferred code to determine
                                  //if the internet connection could not be
                                  //established when the Service was trying
                                  //to download the data.
        activity.finish();
    }
}
}