Why inflate a Layout in Fragments instead of setting one already ready? Ex: setContentView(R.layout.activity_example)

Question

I’m learning about Android and would like to better understand how this part of the system works.

Instead of inflating a layout, it would not be simpler to do as when creating an Activity, for example, overwrite the onCreate method and configure an XML layout?

Example:

public class SampleActivity extends AppCompatActivity {

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

        setContentView(R.layout.activity_sample);
    }
}

Here’s a piece of code from an example application that can be cloned from github: https://github.com/udacity/ud839_ViewPager_Example/tree/quiz

public class FridayFragment extends Fragment {

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_friday, container, false);
    }
}

Why inflate is necessary? What is his advantage? Thanks for any clarifications.

Answer 1

The LayoutInflater is the class responsible for creating a View from an XML file, therefore, you need it to instantiate and access a View.

In Fragments, like the onCreateView() requires a View return, you have to use the LayoutInflater to create and return such View.

In Activity, you don’t need to create the View using a LayoutInflater for the method setContentView() already does so internally, so it is only a practical means of creating and assigning a View to an Activity. If you look at the implementation of the method setContentView() from Activity, you will see that he also uses a LayoutInflater.

@Override
    public void setContentView(int resId) {
        ensureSubDecor();
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();

        // Cria a View baseada no id do layout passado e atribui a Activity
        LayoutInflater.from(mContext).inflate(resId, contentParent);
        mOriginalWindowCallback.onContentChanged();
    }