[android-developers] Re: Fragments navigation and backstack issue

Hi, thanks. This is not quite what I need, but the OnBackStackChangedListener could be useful.

I ended just enabling the default behaviour of letting the backstack increase endlessly when the user switches screens with the navigation. Somebody in StackOverflow adviced this, in order to "not confuse the users". On the other side I think it's bad if the app crashes because out of memory. But I let it like that because I hadn't more time.

Am Sonntag, 4. August 2013 18:13:56 UTC+2 schrieb Nobu Games:

Hi!

I remember the pain with fragments and the back stack while working on an app last year. My solution was the following. In the activity's onCreate method I would do the following:

FragmentManager fm = getSupportFragmentManager();
fm.addOnBackStackChangedListener(new OnBackStackChangedListener() {
    @Override
    public void onBackStackChanged() {
        FragmentManager fm = getSupportFragmentManager();

        if(fm.getBackStackEntryCount() == 0) {
            finish();
        }
    }
});

It basically listens to fragment back stack changes and forces the Activity to finish when the stack is empty

On Sunday, August 4, 2013 4:47:47 AM UTC-5, user123 wrote:

Im trying to implement a fragment based navigation pattern, which can be reduced to this:

In words: There is:

• Home fragment

• Fragment A

• Fragment B

The fragments are shown in FrameLayout "content". The navigation bar is part of the activity.

Workflow should be: Press back on home: Exit App. Press back on A or B: show Home.

Most of it works as it should, but I have the problem that with a complex workflow like this:

Start(home) - A - B - A - Back - B - Back

I expect that it will show home, but instead it shows A. I think it's because the first transaction (home - A) it's in the backstack and it shows A. But I don't understand why then it works correctly in the simple cases?

The code:

public class MainActivity extends FragmentActivity {    boolean isInHome; //a flag to control when we add fragment to the backstack or not    @Override  protected void onCreate(Bundle savedInstanceState) {      super.onCreate(savedInstanceState);      setContentView(R.layout.activity_main);        //set home fragment programmatically first time      FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();      Fragment fragmentHome = new FragmentHome();      transaction.replace(R.id.content, fragmentHome);      transaction.commit();        isInHome = true;        //initialize layout      Button home = (Button) findViewById(R.id.home);      Button a = (Button) findViewById(R.id.a);      Button b = (Button) findViewById(R.id.b);        home.setOnClickListener(new View.OnClickListener() {          @Override          public void onClick(View v) {              //clear complete backstack (in this case, just pop home transaction)              getSupportFragmentManager().popBackStackImmediate(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);                //show home fragment              FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();              Fragment fragmentHome = new FragmentHome();              transaction.replace(R.id.content, fragmentHome);              transaction.commit();                isInHome = true;          }      });        a.setOnClickListener(new View.OnClickListener() {          @Override          public void onClick(View v) {              FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();              Fragment fragmentA = new FragmentA();              transaction.replace(R.id.content, fragmentA);              if (isInHome) { //add the home transaction to the backstack, such that press back on this fragment shows home again                  transaction.addToBackStack("home");              }              transaction.commit();              isInHome = false;          }      });        b.setOnClickListener(new View.OnClickListener() {          @Override          public void onClick(View v) {              FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();              Fragment fragmentB = new FragmentB();              transaction.replace(R.id.content, fragmentB);              if (isInHome) { //add the home transaction to the backstack, such that press back on this fragment shows home again                  transaction.addToBackStack("home");              }              transaction.commit();              isInHome = false;          }      });  }    @Override  public void onBackPressed() {      super.onBackPressed();        isInHome = true; //quick solution to update status - when press back on A or B, we are in home (and press back in home exits the app, so this doesn't matter)  }

}

What's wrong here?

Thanks in advance.

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