恢复活动后Android应用程序无法正常工作

Question

I have an application where whenever I exit the application via the home hardware button, it should return to the last state the application is in. However, when I launch the application again, the application shows a white screen with only my header bar. And when I click on the header bar's button, the application crashes with the IllegalStateException where the application cannot find the method for the button clicked.

I am currently implementing with Sherlocks Fragment, where the header bar is an action bar. I'm also using HTC Rhyme, Version 2.3 (Gingerbread). The following is the codes for the addition of fragments into my main app.

Codes to add the fragments within the onCreate method in the activity:

FragmentTransaction trans = getSupportFragmentManager().beginTransaction();
Bundle bMain = getIntent().getExtras();
String statusCheck = "";
if (bMain != null) {
    statusCheck = bMain.getString("statusCheck");
}
if (statusCheck.equals("web")) {
    MyWebViewFragment webfrag = new MyWebViewFragment();
    trans.add(R.id.container,webfrag, "WebViewFragment");
} else if(statusCheck.equals("traveloguelist")) {
    MyTravelogueListFragment travelfrag = new MyTravelogueListFragment();
    trans.add(R.id.container,travelfrag, "TravelogueListFragment");
}
trans.commit();

This is the codes when I change a fragment:

MyTravelogueListFragment travelfrag = new MyTravelogueListFragment();
getSupportFragmentManager().beginTransaction().replace(R.id.container, travelfrag).addToBackStack(null).commit();

[Edit]

I realized after much reading and running that the main issuei have is that upon resuming the application, the activity is actually created again. Thus, some of the parameters i passed in does not get registered, resulting in the wrong display. I THINK this is the error that is causing that to happen:

Previously focused view reported id "myresID" during save, but can't be found during restore.

However, I don't know how you force the application to remember the previous state of the fragment? Or is there any other way around this problem?

I'm still very stuck with this problem. Will really appreciate it if someone can help me!

Answer 1

After much trial and error and many readings, I finally found a way to sort of solve my problem.

From what I understand, this problem will occur due to the Activity's life cycle. The comment by Tseng in this forum was quite comprehensive: http://forum.unity3d.com/threads/127794-Android-Apps-crashing-on-resume

It seems that during the time when other applications are invoked when a certain activity is onPause/onStop , Android might free up some of its memory the activity is currently holding on to if there is insufficient memory required. In this case, all the current objects or variable the paused activity is having will be destroyed. Thus, when the activity is back on focus, the onCreate is actually invoked again. Thus, the activity will have no idea which fragment I am currently require.

However, I realized that it will always call the saveInstanceState which is essentially a bundle object. So I did the following:

onSaveInstanceState method

  @Override
  public void onSaveInstanceState(Bundle bundle) {
      //activityFrag is a string object that tells me which fragment i am in currently
      bundle.putString("statusCheck", activityFrag);
  }

onCreate method

if (savedInstanceState != null) {
    getSupportFragmentManager().popBackStack(null, getSupportFragmentManager().POP_BACK_STACK_INCLUSIVE);
    //return;
    statusCheck = savedInstanceState.getString("statusCheck");
} else {
    statusCheck = b.getString("statusCheck");
}

What I have done is to remove all the fragments I have stacked thus far to remove any issues where there is missing information needed. So this is like starting anew again. The status check just determine which fragment the user has last visited.

After much testing, it seems like it does solve my problem. though I wouldn't say it is perfect. One of the main downfall I have is that whenever I change my fragment, I have to update and change my statusCheck to make sure the correct fragment will be called. However, I have to admit this way is a little unorthodox and might not be very correct.

If any of you have any better ideas, please feel free to share!

Answer 2

You can try to implement following:

1. Use putFragment to save all fragments, currently located in FragmentManager, into bundle in onSaveInstanceState ;
2. And then you can use getFragment to get all previously stored fragments back from bundle in onRestoreInstanceState .

Also... you'll probably need some HashMap that will help to determine the hierarchy of the fragments (in case you have containers and contained fragments) to be saved into bundle as well.

Also... when restoring from bundle you'll need to know keys for all fragment you've put there earlier. Probably, the easiest way is simply to organize an array of keys and put them into bundle when saving the fragment into instance.

This way your saving and restoring will be complete and centralized.