when is onAttach invoked?-CodePudding

The android documentation says that The onAttach() callback is invoked when the fragment has been added to a FragmentManager and is attached to its host activity.

A piece of my code in the activity:

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

        setContentView(R.layout.activity_main);

        FragmentManager fm = getSupportFragmentManager();
        Fragment fragment  = fm.findFragmentById(R.id.fragment_container);
        if(fragment == null){
            fragment = new CrimeFragment();
            fm.beginTransaction().add(R.id.fragment_container, fragment).commit();
        }

        Log.d(MAIN_ACTIVITY_LOG_TAG, "onCreate(Bundle)");
    }
...

A piece of my code in the fragment:

...
    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        Log.d(CRIME_FRAGMENT_LOG_TAG, "onAttach(Context)");
    }
...

The log:

...
2022-08-03 12:36:42.512 26035-26035/com.bignerdranch.android.criminalintent D/main_activity_log_tag: onCreate(Bundle)
2022-08-03 12:36:42.514 26035-26035/com.bignerdranch.android.criminalintent D/crime_fragment_log_tag: onAttach(Context)
...

As you can see onAttach() isn't invoked when the fragment is added to the FragmentManager.

So when actually is onAttach() invoked?

CodePudding user response：

Fragment transactions are asynchronous by default. They are not executed immediately but just scheduled for execution at a later point.

If you want to make your fragment transaction synchronous, change commit() to commitNow(). Most of the cases you don't really need that.