android - Why use bundle to pass data to fragment?

Question

I have a fragment that is always visible. I don't understand why I should use bundles to pass data to it from activity.

Most of the questions here recommend this method of passing data:

Bundle bundle=new Bundle();
bundle.putString("name", "From Activity");
Fragmentclass fragobj=new Fragmentclass();
fragobj.setArguments(bundle);

I prefer creating Fragment object in OnCreate function of activity and then use this object to display fragment(FragmentTransaction.add). As I have refence to this fragment I can create create function showName() in it and call it from activity like that:

myFragment.showName("name");

Is there anything wrong with this approach?

Answer 1

The Android documentation states:

Every fragment must have an empty constructor, so it can be instantiated when restoring its activity's state. It is strongly recommended that subclasses do not have other constructors with parameters, since these constructors will not be called when the fragment is re-instantiated; instead, arguments can be supplied by the caller with setArguments(Bundle) and later retrieved by the Fragment with getArguments().

That's why it's better to use a bundle and set the parameters of the Fragment this way, it's easier for the system to restore its values when the fragment is re-instantiated.

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Now, I wouldn't use myFragment.showName("name"); because you don't know if the lifecycle of the fragment has already finished (attached to the activity and inflated the views), so instead, I would call the showName("name") in the onActivityCreated or onViewCreated callbacks.

Applications should generally not implement a constructor. The first place application code can run where the fragment is ready to be used is in onAttach(Activity), the point where the fragment is actually associated with its activity. Some applications may also want to implement onInflate(Activity, AttributeSet, Bundle) to retrieve attributes from a layout resource, though should take care here because this happens for the fragment is attached to its activity.