Android databinding: Layout to the view

Question

I am programming an android-App and I am using the MVVM-Pattern. I have problems seeing the data in the layout in my view. I am new to android programming, so maybe i am thinking the wrong way. In C# i had no problems creating an MVVMC-App. To be honest, i do not understand how to show the contents in the layouts in the activity :-( This is my code in the view:

@Override
protected void onCreate(Bundle savedInstanceState) {
    //This is the code which shows the white window with my data
    super.onCreate(savedInstanceState);
    ContentSelectItemBinding binding = DataBindingUtil.setContentView(this, R.layout.content_select_item);
    this.aSelectItemViewModel = new SelectItemViewModel();
    binding.setItem(this.aSelectItemViewModel.item);

    //when i add this, it will just show the empty view
    setContentView(R.layout.activity_select_item);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show();
        }
    });
}

And thats how my easy SelectItemViewModel looks like

public TestItem item;

public SelectItemViewModel() {
    item = new TestItem("Test", "User");
}

public List<TestItem> getItemList() {
    return this.aTestItemList;
}

And here are my XML-Files:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="private.testapp.view.SelectItemActivity">

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:theme="@style/AppTheme.AppBarOverlay">

    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="?attr/actionBarSize"
        android:background="?attr/colorPrimary"
        app:popupTheme="@style/AppTheme.PopupOverlay" />

</android.support.design.widget.AppBarLayout>

<include layout="@layout/content_select_item" />

<android.support.design.widget.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:layout_margin="@dimen/fab_margin"
    app:srcCompat="@android:drawable/ic_dialog_email" />

</android.support.design.widget.CoordinatorLayout>

This is my layout file

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">
<data>
    <variable name="item" type="private.testapp.model.TestItem"/>
</data>
<LinearLayout
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView android:layout_width="wrap_content"
        android:textSize="128sp"
        android:layout_height="wrap_content"
        android:text="@{item.name}"/>
    <TextView android:layout_width="wrap_content"
        android:textSize="128sp"
        android:layout_height="wrap_content"
        android:text="@{item.description}"/>
</LinearLayout>
</layout>

All i want to do first is just display the testitem... Since it displays it when i just show the layout, i am sure that the binding and my viewmodel works. I don`t understand how the data in the layout will be shown in my view.

Answer 1

Option 1- forward variable from activity xml to included xml:

First,

ContentSelectItemBinding binding = DataBindingUtil.setContentView(this,R.layout.content_select_item);
this.aSelectItemViewModel = new SelectItemViewModel();
binding.setItem(this.aSelectItemViewModel.item);

//when i add this, it will just show the empty view
setContentView(R.layout.activity_select_item);

You're setting your activity content twice which is wrong, replace it with just:

DataBindingUtil.setContentView(this,R.layout.activity_select_item);
this.aSelectItemViewModel = new SelectItemViewModel();
binding.setItem(this.aSelectItemViewModel.item);

To set your activity xml as your layout.

Next, your activity_select_item xml should also be wrapped with a <layout> tag and a <data> tag inside to denote this is a data binding layout:

   <?xml version="1.0" encoding="utf-8"?>
   <layout xmlns:android="http://schemas.android.com/apk/res/android">
   <data>
       <variable name="item" type="private.testapp.model.TestItem"/>
   </data>
   <android.support.design.widget.CoordinatorLayout        
       xmlns:android="http://schemas.android.com/apk/res/android"
       xmlns:app="http://schemas.android.com/apk/res-auto"
       xmlns:tools="http://schemas.android.com/tools"
       android:layout_width="match_parent"
       android:layout_height="match_parent"
       android:fitsSystemWindows="true"
       tools:context="private.testapp.view.SelectItemActivity">
       .
       .
       .
   </layout>

Finally, forward the variable to your included layout inside the <include> tag:

   .
   .
   .
<include 
    layout="@layout/content_select_item" 
    app:item="@{item}"/>
   .
   .
   .
</android.support.design.widget.CoordinatorLayout>

Option 2- find included view and bind it

First, mark included view with id:

<include 
    id="@+id/content"
    layout="@layout/content_select_item" />

Next, find it in code and bind it:

 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_select_item);
 View content= findViewById(R.id.content);
 ViewDataBinding binding = DataBindingUtil.bind(content);

Finally, set the variable on the generic binding using generated id inside BR class (like R class but for data binding variables):

this.aSelectItemViewModel = new SelectItemViewModel();
binding.setVariable(BR.item, aSelectItemViewModel.item);