Android databinding and animation

Question

Can someone point me in the direction of how to trigger an animation when using databinding?

I've got an icon which changes according to data in my viewmodel. How do I animate icon change when the viewmodel changes (that is, when a property changes in the viewmodel)?

Answer 1

One possible solution is to use a binding adapter. Here's a quick sample to show you the way to go:

First we define a custom binding adapter:

import android.databinding.BindingAdapter;
import android.support.v4.view.animation.FastOutSlowInInterpolator;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.Interpolator;
import android.view.animation.RotateAnimation;
import android.view.animation.TranslateAnimation;

public class ViewBusyBindings {
    private static final Interpolator INTERPOLATOR = new FastOutSlowInInterpolator();

    @BindingAdapter("isBusy")
    public static void setIsBusy(View view, boolean isBusy) {
        Animation animation = view.getAnimation();
        if (isBusy && animation == null) {
            view.startAnimation(createAnimation());
        } else if (animation != null) {
            animation.cancel();
            view.setAnimation(null);
        }
    }

    private static Animation createAnimation() {
        RotateAnimation anim = new RotateAnimation(0, 360, Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
        anim.setInterpolator(INTERPOLATOR);
        anim.setDuration(1400);
        anim.setRepeatCount(TranslateAnimation.INFINITE);
        anim.setRepeatMode(TranslateAnimation.RESTART);
        return anim;

    }
}

The example layout will look like this:

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto">
    <data>
        <variable
            name="vm"
            type="de.example.exampleviewmodel"/>
    </data>

    <FrameLayout 
                 android:layout_width="match_parent"
                 android:layout_height="wrap_content"
                 >
        <ImageButton
            android:id="@+id/btnPlay"
            style="?attr/borderlessButtonStyle"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="right|bottom"
            android:src="@drawable/ic_play_circle_filled_white_36dp"
            app:isBusy="@{vm.isBusy}"/>

    </FrameLayout>
</layout>

As you can see, the 'isBusy' property of your viemodel is bound to the view (imagebutton). You can use this adapter at any view not only at a imagebutton.

Of course, the 'isBusy' property must be bindable (e.g. your viewmodel extends BaseObservable or as a minimum it's a ObservableBoolean).

So whenever you change the 'isBusy' property to true it will trigger the animation to start. Set it to false, it stops.

Hope this helps ?