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android – Navigation drawer, handling the back button to go to previous fragments?

Posted by: admin April 23, 2020 Leave a comment

Questions:

I’m using the built in navigation drawer to run my app. I can’t quite figure out how to handle the back button. When it’s pressed I want it to load the very first fragment again. Fragment1.

So when the app launches you see Fragment1 launched. They can then click on Fragment 2-5 to go to other pages. Within all of these pages I want the back button to take the user back to Fragment1. The only place the user should be able to exit the app via the back button is Fragment1.

SInce it’s all handled by a FragmentActivity I tried messing with the backbutton there. I keep getting a force close error however:

(01-11 14:09:33.114: E/AndroidRuntime(8292): android.view.InflateException: Binary XML file line #7: Error inflating class fragment)

This is what I have so far:

I’ve made sure to add the fragments to the back stack like this:

fm.beginTransaction().replace(R.id.main, newFragment).addToBackStack("fragBack").commit();

Back button:

@Override
public void onBackPressed() {
    if (getSupportFragmentManager().findFragmentByTag("fragBack") != null) {

    }
    else {
        super.onBackPressed();
        return;
    }
    if (getSupportFragmentManager().getBackStackEntryCount() != 0) {
        Toast.makeText(getApplicationContext(), "Test", Toast.LENGTH_LONG).show();
        Fragment frag = getSupportFragmentManager().findFragmentByTag("fragBack");
        FragmentTransaction transac = getSupportFragmentManager().beginTransaction().remove(frag);
                transac.commit();
    }

}

Does anyone know what I need to do? Do I need to call onBackPressed in every fragment (if that’s even possible) rather than the FragmentActivity that controls the drawer? In my past apps I’ve been OK with the back button closing the app regardless of which Fragment the user is on but the one I’m making now I want the back button to go back to Fragment1.

Would really appreciate some help, thank you.

onItemClick

@Override
        public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {

            Fragment newFragment = new MapsPage();
            FragmentManager fm = getSupportFragmentManager();
            switch(i) {
            case 0:
                newFragment = new Fragment2();
                break;
            case 1:
                newFragment = new Fragment3();
                break;
            case 2:
                newFragment = new Fragment4();
                break;
            case 3:
                newFragment = new Fragment5();
                break;
            }
            fm.beginTransaction().add(R.id.main, newFragment).addToBackStack("fragback").commit();
            drawerLayout.closeDrawer(rl);
        }
How to&Answers:

Instead of:

fm.beginTransaction().replace(R.id.main, newFragment).addToBackStack("fragBack").commit();

Call:

fm.beginTransaction().add(R.id.main, newFragment).addToBackStack("fragBack").commit();

addToBackStack works with add.

replace function removes previous fragment and places new fragment so on your back-stack there is only one fragment all the time. So use add function to keep previous fragments on stack.

To always goto fragemnt1 from any fragment onBackPress try to do following:

getFragmentManager().popBackStack();
fm.beginTransaction().add(R.id.main, newFragment).addToBackStack("fragBack").commit();

this will remove last transaction from backstack and add new one.
Try this.

Answer:

Just wanted to report my findings even though this question is a little old for anyone else who may have had the same problem with the accepted answer. For me, doing the method suggested in the accepted answer, made the layers overlap, quickly making them unreadable. The code below (adapted from the accepted answer) avoids the overlaying but still adds the screen to the back stack.

fragmentManager.beginTransaction().replace(R.id.container, fragment).addToBackStack("fragBack").commit();

Hope this helps someone!

Answer:

in some cases you have to use replace then you cant work with addtobackstack() so you can use this code in mainActivity. in this code when you press back key you always go to first Fragment( i call it HomeFragment ) and when you are in Home Fragment it ask twice time to go out from application (sorry for my poor English)

 private Boolean exit = false;
@Override
    public void onBackPressed() {
        if (exit) {
            super.onBackPressed();
            return;
        }

    try {
        FragmentManager fragmentManager = getSupportFragmentManager();
        Fragment fragment = fragmentManager.findFragmentByTag("HOME");
        if (fragment != null) {
            if (fragment.isVisible()) {
                this.exit = true;
                Toast.makeText(this, "Press Back again to Exit", Toast.LENGTH_SHORT).show();
            }
        }
        else {
            fragment = HomeFragment.class.newInstance();
            getFragmentManager().popBackStack();
            fragmentManager.beginTransaction().replace(R.id.flContent, fragment, "HOME").commit();
        }
    } catch (Exception e) {

    }
    new Handler().postDelayed(new Runnable() {
        @Override
        public void run() {
            exit = false;
        }
    }, 2000);
}

Answer:

 - @Override
       public void onBackPressed() {
           DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
           int backstack = getSupportFragmentManager().getBackStackEntryCount();
           if (drawer.isDrawerOpen(GravityCompat.START)) {
               drawer.closeDrawer(GravityCompat.START);
           } else if (backstack > 0) {
              for (int i = 0; i < backstack; i++) {
                   getSupportFragmentManager().popBackStackImmediate();
            }
       } else {
           this.finish();
        }
    }

Answer:

I would suggest avoiding an override of onBackPressed() altogether by managing your transactions properly in the first place. This will help to avoid having to implement crazy logic down the road.

To do this first we need to set a private class variable in that will enable initialization:

private boolean popNext = false;

The following code allows us to setup the initial back function by placing it on the stack. Every time thereafter, when popNext is set to true, we pop the initial transaction and push the new one. So we are replacing the 1>X transaction with the 1>Y transaction.

The extra embedded if statements deal with selecting the initial item, since we don’t want to go from 1>1. If it’s our initial case we just close the drawer. The other case needs to act like the back button, but we need to remember to set it as if it is returning to the initial state!

if(popNext){
    if(i == INITIAL_POSITION){
        onBackPressed();
        mDrawerLayout.closeDrawer(mDrawerList);
        popNext = false;
        return;
    }
    getFragmentManager().popBackStackImmediate();
}
else{
    if(i == INITIAL_POSITION){
        mDrawerLayout.closeDrawer(mDrawerList);
        return;
    }
    popNext=true;
}
getFragmentManager()
.beginTransaction()
.replace(R.id.fragment_container, fragment)
.addToBackStack(null)
.commit();

Note: My code uses getFragmentManager() instead of getSupportFragmentManager() which is a native function, I believe as of Honeycomb.