合成Android片段backstack

Question

I have an activity that uses fragments to change views instead of launching new activities. Lets say I have 3 fragments A, B and C. When the application launches the default fragment is set to A. The user can click a button on A to transition to B -- same with B to C.

Therefore the backstack looks like: [A] -> [B] -> [C]

What I need to do is deep link directly to fragment C from a notification while still building out the backstack so that when the activity is launched. Fragment C should be displayed while allowing the user to click the back button to get back to views B and A respectively.

Answer 1

You can make 3 separate transactions. This is a lot more natural than manually checking the state of the backstack.

@Override 
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    showFragmentA();

    if (getIntent().hasExtra("some_deep_link_flag")) {
        showFragmentB();
        showFragmentC();
    }
}

private void showFragmentA() {
    Fragment a = new Fragment();

    getSupportFragmentManager().beginTransaction()
            .replace(R.id.container, a)
            .addToBackStack(null)
            .commit();
}

private void showFragmentB() {
    Fragment b = new Fragment();

    getSupportFragmentManager().beginTransaction()
            .replace(R.id.container, b)
            .addToBackStack(null)
            .commit();
}

private void showFragmentC() {
    Fragment c = new Fragment();

    getSupportFragmentManager().beginTransaction()
            .replace(R.id.container, c)
            .addToBackStack(null)
            .commit();
}

Answer 2

If the stack is always going to A -> B -> C then you could override onBackPressed() in the activity and pop the back stack and check to see what the situation in the fragment stack is.

@Override
public void onBackPressed() {
    if (getSupportFragmentManager().getFragmentByTag("C") != null) {
        if (getSupportFragmentManager().getBackStackEntryCount() == 2) {
            getSupportFragmentManager().beginTransaction.replace(...).commit();
        } else {
            getSupportFragmentManager().popBackStack();
        }
    } else if (getSupportFragmentManager().getFragmentByTag("B") != null) {
        if (getSupportFragmentManager().getBackStackEntryCount() == 1) {
            getSupportFragmentManager().beginTransaction.replace(...).commit();
        } else {
            getSupportFragmentManager().popBackStack();
        }
    } else {
        //You are already on Fragment A
        super.onBackPressed();
    }
}

Answer 3

Like jmcdonnell40 suggests:

My guess is you should put an extra on the notification intent which makes clear that you are entering your Activity from the notification.

Then, in the activity's oncreate, check for that extra, and if it is present, just do the 2 necessary fragment transactions (fragment A -> B -> C) and add them to the backstack.

you're going to have to open your last fragment manually anyway.