Android Fragment onAttach() deprecated

Question

I have updated my app to use the latest support library (version 23.0.0), I've found out that they deprecated the onAttach() function of the Fragment class.

Instead of:

onAttach (Activity activity)

It's now:

onAttach (Context context)

As my app uses the activity passed before deprecation, a possible solution i think is:

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    activity = getActivity();
}

Would that be the correct way to do it?

UPDATE:

If i run a device with API lower than 23, the new onAttach() is not even being called. I hope that this is not what they intended to do!

UPDATE 2:

Issue has been resolved with the latest updates to the SDK.

I have tested on my API 22 device and onAttach(Context) is being called.

Click here to follow the bug report I've opened a couple of weeks ago and the answers from the guys at Google.

Answer 1

Activity is a context so if you can simply check the context is an Activity and cast it if necessary.

@Override
public void onAttach(Context context) {
    super.onAttach(context);

    Activity a;

    if (context instanceof Activity){
        a=(Activity) context;
    }

}

Update: Some are claiming that the new Context override is never called. I have done some tests and cannot find a scenario where this is true and according to the source code, it should never be true. In all cases I tested, both pre and post SDK23, both the Activity and the Context versions of onAttach were called. If you can find a scenario where this is not the case, I would suggest you create a sample project illustrating the issue and report it to the Android team.

Update 2: I only ever use the Android Support Library fragments as bugs get fixed faster there. It seems the above issue where the overrides do not get called correctly only comes to light if you use the framework fragments.

Answer 2

This is another great change from Google ... The suggested modification: replace onAttach(Activity activity) with onAttach(Context context) crashed my apps on older APIs since onAttach(Context context) will not be called on native fragments.

I am using the native fragments (android.app.Fragment) so I had to do the following to make it work again on older APIs (< 23).

Here is what I did:

@Override
public void onAttach(Context context) {
    super.onAttach(context);

    // Code here
}

@SuppressWarnings("deprecation")
@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);

    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
        // Code here
    }
}

Answer 3

If you use the the framework fragments and the SDK version of the device is lower than 23, OnAttach(Context context) wouldn't be called.

I use support fragments instead, so deprecation is fixed and onAttach(Context context) always gets called.

Answer 4

Currently from the onAttach Fragment code, it is not clear if the Context is the current activity: Source Code

public void onAttach(Context context) {
    mCalled = true;
    final Activity hostActivity = mHost == null ? null : mHost.getActivity();
    if (hostActivity != null) {
        mCalled = false;
        onAttach(hostActivity);
    }
}

If you will take a look at getActivity you will see the same call

/**
 * Return the Activity this fragment is currently associated with.
 */
final public Activity getActivity() {
    return mHost == null ? null : mHost.getActivity();
}

So If you want to be sure that you are getting the Activity then use getActivity() (in onAttach in your Fragment) but don't forget to check for null because if mHost is null your activity will be null

Answer 5

@Override
public void onAttach(Context context) {
    super.onAttach(context);

    Activity activity = context instanceof Activity ? (Activity) context : null;
}

Answer 6

Although it seems that in most cases it's enough to have onAttach(Context), there are some phones (i.e: Xiaomi Redme Note 2) where it's not being called, thus it causes NullPointerExceptions. So to be on the safe side I suggest to leave the deprecated method as well:

// onAttach(Activity) is necessary in some Xiaomi phones
@SuppressWarnings("deprecation")
@Override
public void onAttach(Activity activity) {
    super.onAttach(activity);
    _onAttach(activity);
}

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    _onAttach(context);
}

private void _onAttach(Context context) {
    // do your real stuff here
}

Answer 7

Download newest Support library with the sdk manager and include

compile 'com.android.support:appcompat-v7:23.1.1'

in gradle.app and set compile version to api 23

Answer 8

The answer below is related to this deprecation warning occurring in the Fragments tutorial on the Android developer website and may not be related to the posts above.

I used this code on the tutorial lesson and it did worked.

public void onAttach(Context context){
    super.onAttach(context);

    Activity activity = getActivity();

I was worried that activity maybe null as what the documentation states.

getActivity

FragmentActivity getActivity () Return the FragmentActivity this fragment is currently associated with. May return null if the fragment is associated with a Context instead.

But the onCreate on the main_activity clearly shows that the fragment was loaded and so after this method, calling get activity from the fragment will return the main_activity class.

getSupportFragmentManager().beginTransaction() .add(R.id.fragment_container, firstFragment).commit();

I hope I am correct with this. I am an absolute newbie.

Answer 9

you are probably using android.support.v4.app.Fragment. For this instead of onAttach method, just use getActivity() to get the FragmentActivity with which the fragment is associated with. Else you could use onAttach(Context context) method.

Answer 10

This worked for me when i have userdefined Interface 'TopSectionListener', its object activitycommander:

  //This method gets called whenever we attach fragment to the activity
@Override
public void onAttach(Context context) {
    super.onAttach(context);
    Activity a=getActivity();
    try {
        if(context instanceof Activity)
           this.activitycommander=(TopSectionListener)a;
    }catch (ClassCastException e){
        throw new ClassCastException(a.toString());}

}