Changes

As described in “An Overview of Android Jetpack Data Binding”, in order to be able to use data binding, the layout hierarchy must have a layout component as the root view. This requires that the following changes be made to the main_fragment.xml layout file (app -> res -> layout -> main_fragment.xml). Open this file in the layout editor tool, switch to Text mode and make these changes:

 

        <android.support.constraint.ConstraintLayout

            android:id="@+id/main"

            android:layout_width="match_parent"

Build and run the app once again to make sure that these changes take effect.

The next step is to modify the code within the MainFragment.java file to obtain a reference to the binding class instance. This is best achieved by rewriting the onCreateView() method:

 

        return binding.getRoot();

    }

.

With these changes made, the next step is to begin inserting some binding expressions into the view elements of the data binding layout file.

The first binding expression will bind the resultText TextView to the result value within the model view. Edit the main_fragment.xml file, locate the resultText element and modify the text property so that the element reads as follows:

    android:layout_width="wrap_content"

    android:layout_height="wrap_content"

    android:text='@{safeUnbox(myViewModel.result) == 0.0 ? "Enter value" : String.valueOf(safeUnbox(myViewModel.result)) + " euros"}'

    app:layout_constraintBottom_toBottomOf="parent"