android-databinding-binding-adapter-pass-object-to-customview.md

title: Android: Passing objects to custom views with databinding tags: android,android-databinding,android-custom-views

Update: There's now a much, much simplier version of this.

This is a bit voodoo, but that said... Let's say you include something like this as a static method anywhere in your codebase.

@BindingAdapter("app:thing")
public static void setThing(View v, Object s) {
  Log.d("A log, innit", "Called setThing");
}

Note that the method name setThing is derived from app:thing. And the first parameter is a View and the second is an Object.

And then, in a databinding layout file, have something like

<layout xmlns:android="http://schemas.android.com/apk/res/android"
       xmlns:app="http://schemas.android.com/apk/res-auto">
  <data>
    <variable
        name="thing"
        type="String"/>
  </data>
  <com.example.blar.myapplication.CustomView
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      app:thing="@{thing}"
      />
  ...

Then the above static method will be called when we try to set the app:thing attribute.

If in your static method you have something like this:

CustomViewDatabindingSettable st = (CustomViewDatabindingSettable) v;
st.passedDataBindingObject(s);

Then, providing your custom view implements CustomViewDatabindingSettable, you can call passedDataBindingObject passing through the databound variable.

For example, your custom view could be:

public class ListView extends FrameLayout implements CustomViewDatabindingSettable {
  ...
  @Override
  public void passedDataBindingObject(Object o) {
    Log.d("HIYA", "We're in passedDataBindingObject: " + o);
    // Now do something with the data bound object.
  }
  ...
}

Databinding and 'instant run' seems to mess up the autogeneration sometimes, in Android Studio 2.0 beta anyhow.

I had to uninstall the project from the device occassionally to remove dead code.