Fragments Behave Weirdly When Using addToBackStack()

问题

An SSCCE for this issue is available on GitHub.

For future readers, the original example is on a branch of the same project, and the fix is available in this diff.

This SSCCE has a ListView and a row of buttons. The buttons are supposed to change the data in the ListView, and the listView rows (when clicked) are supposed to open a new fragment and advance the backstack while staying in the same activity.

If do the following things, it produces the following result:

1. Open the app.
2. Tap the ListView. - FragmentTransaction.replace(...) with addToBackStack(true)
3. Tap any of the buttons. - FragmentTransaction.replace(...) with addToBackStack(false)
4. Tap the back button.

Result:

Both fragments become visible, but I only want the first loaded fragment (ListTwoFragment in code) to display. Is this how fragments are supposed to work? If so, how can I get the desired effect?

MainActivity.java:

public class MainActivity extends FragmentActivity implements ListTwoFragment.Callbacks,
    ListThreeFragment.Callbacks {
    public static final String KEY_ARGS = "args";

    private String curUri = "";
    private String curArgs = "";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        selectContent(false);
    }

    private void selectContent(boolean addToBackStack) {
        Fragment fragment;

        if (curUri.isEmpty()) {
            // Use default fragment
            fragment = new ListTwoFragment();
            curUri = ListTwoFragment.class.getName();
        }
        else {
            try {
                Class<Fragment> fragmentClass = (Class<Fragment>) Class.forName(curUri);
                fragment = fragmentClass.newInstance();
            }
            catch (Exception e) { // ClassNotFound, IllegalAccess, etc.
                return;
            }
        }

        // Configure fragment
        Bundle args = new Bundle();
        args.putString(KEY_ARGS, curArgs);
        fragment.setArguments(args);

        attachFragment(fragment, addToBackStack, curUri + ";" + curArgs, R.id.fragment_container);
    }

    protected void attachFragment(Fragment fragment, boolean addToBackStack, String tag, int replaceId) {
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.replace(replaceId, fragment, tag);
        if (addToBackStack) transaction.addToBackStack(tag);
        transaction.commit();
    }

    @Override
    public void onTwoButtonClick(String title) {
        curUri = ListTwoFragment.class.getName();
        curArgs = title;
        selectContent(false);
    }

    @Override
    public void onTwoListClick() {
        curUri = ListThreeFragment.class.getName();
        curArgs = "";
        selectContent(true);
    }

    @Override
    public void onThreeButtonClick(String title) {
        curUri = ListThreeFragment.class.getName();
        curArgs = title;
        selectContent(false);
    }
}

回答1:

I'm working with Fragments to, and the way I'm doing it: to go forward (add to stack), and backwords (remove from stack) are two different functions

to Add to Stack and change Fragment:

public void changeFragmentAddToStack(Fragment myNewFragment) {
        FragmentTransaction t = getSupportFragmentManager().beginTransaction();
        t.add(R.id.main_fragment, myNewFragment);
        t.addToBackStack(null);
        t.commit();
    }

To go back Stack:

        public void goBackStackMain() {
    FragmentManager man = getSupportFragmentManager();

                if(man.getBackStackEntryCount()>0){ 
                    man.popBackStack(man.getBackStackEntryAt(0).getName(), FragmentManager.POP_BACK_STACK_INCLUSIVE);
            }
}

And if you want to do both: To go back stack and change fragment:

    public void goBackStackAndReplaceFragment(Fragment myNewFragment) {
FragmentManager man = getSupportFragmentManager();
            if(man.getBackStackEntryCount()>0){ 
                int n = man.getBackStackEntryCount();
                man.popBackStack(man.getBackStackEntryAt(n-1).getName(), FragmentManager.POP_BACK_STACK_INCLUSIVE);
            }

        FragmentTransaction t = getSupportFragmentManager().beginTransaction();
        t.replace(R.id.main_fragment, myNewFragment);
        t.commit();
    }

I hope to help you !

来源：https://stackoverflow.com/questions/17978374/fragments-behave-weirdly-when-using-addtobackstack