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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?

fefero
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    Hint: What happens when the framework needs to recreate your fragment? – laalto Jun 11 '16 at 16:08
  • I believe that, minding android lifecycle and with use of e.g. reactiveX, @fefero 's suggestion is perfectly valid now. See also https://stackoverflow.com/a/9610048/1870447 – Antek Feb 07 '19 at 12:03

3 Answers3

9

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.

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.

Evin1_
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There's nothing wrong with this approach for setting one off data values, you just need to be careful to make sure that the view that you want to set your name on actually exists at the point that the showName method is called.

Part of the reason that using Bundles to pass information is popular is that they can hold all types of data using keys and also they can easily be used to pass view states around during device rotation. Ultimately it's a matter of preference and exactly what your use case is.

Patrick Cavanagh
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When app is in background, the Fragment can recreated (eg: by change the theme (light/dark), language, ...).
So if you dont pass data use Bundle to Fragment, your Fragment will not have this data when it recreated

Linh
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