FireAndIce FireAndIce - 5 months ago 12
Android Question

How to replace fragment C with fragment A when back button is pressed?

My scenario : Activity 1 consists of Fragments A-> B-> C. All the fragments are added using this code :

FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.content, fragment, TAG);
ft.addToBackStack(TAG);
ft.commit();


Now, from fragment C, I want to directly return to Fragment A. Therefore, I've commented
ft.addToBackStack(TAG)
while adding Fragment C. So when I press back button from C I directly get Fragment A on the screen.

However, Fragment C is not replaced by A. In fact, both the fragments are visible. How do I solve this issue?

Answer

Theory

Use the addToBackStack(tag:String):FragmentTransaction method from within the FragmentTransaction in order to mark a point where you want to return to. This method returns the FragmentTransaction instance for chain-ability only.

Then Return with the popBackStackImmediate(tag:String,flag:int):void method from the FragmentManager. The tag is what you specified before. The flag is either the constant POP_BACK_STACK_INCLUSIVE to include the transaction marked or 0.

Example

What follows is an example with the following layout having a FrameLayout with id content_frame where the fragments are loaded into.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

<TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/hello_world" />

<FrameLayout
    android:id="@+id/content_frame"
    android:layout_below="@id/textView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

</RelativeLayout>

The code below marks a fragment by it's fragment class name when replacing the content of the layout element with id content_frame.

public void loadFragment(final Fragment fragment) {

    // create a transaction for transition here
    final FragmentTransaction transaction = getSupportFragmentManager()
            .beginTransaction();

    // put the fragment in place
    transaction.replace(R.id.content_frame, fragment);

    // this is the part that will cause a fragment to be added to backstack,
    // this way we can return to it at any time using this tag
    transaction.addToBackStack(fragment.getClass().getName());

    transaction.commit();
}

And to complete this example a method that allows you to get back to that exact same fragment using the tag when you loaded it.

public void backToFragment(final Fragment fragment) {

    // go back to something that was added to the backstack
    getSupportFragmentManager().popBackStackImmediate(
            fragment.getClass().getName(), 0);
    // use 0 or the below constant as flag parameter
    // FragmentManager.POP_BACK_STACK_INCLUSIVE);

}

When implementing this for real you might want to add a null check on the fragment parameter ;-).