为什么我的绑定数据不会出现在Android XML中？

Question

I have a custom layout that I want to reuse in several places, so I want to be able to pass a title to it, since that's the only value that will actually change. I know I can do that by binding data, but I can't get the data to render.

In my activity.main I have:

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
                xmlns:tools="http://schemas.android.com/tools"
                xmlns:app="http://schemas.android.com/apk/res-auto" >

    <RelativeLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                tools:context="com.r.e.MainActivity">

        <include
            layout="@layout/switch_preference_custom_title"
            app:passedTitle="@{@string/hello_world}" />

    </RelativeLayout>

</layout>

I have defined my custom layout as follows:

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools" >

    <data>
      <variable
        name="passedTitle"
        type="String"/>
    </data>

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

         <TextView
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:text="@{passedTitle}" />

    </RelativeLayout>

 </layout>

I also added

dataBinding {
    enabled = true
}

in my build.gradle. My project compiles and runs fine, and the layout does render (I can tell by giving it a background), but the text is an empty string.

Answer 1

It looks like one final linking piece was missing. Instead of having

setContentView(R.layout.activity_main);

in MainActivity, one needs to declare

DataBindingUtil.setContentView(this, R.layout.activity_main);

This connects the Data Binding library with the root layout, without which none of your data bindings will actually render.