无法使用数据绑定设置imageview的背景

<ImageView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:backgroundImage="@{viewModel.backgroundImage}" />

public class ViewModel {
    public ObservableField<Drawable> backgroundImage = new ObservableField<>();
}

public class CustomBindingAdapters {
    @BindingAdapter("backgroundImage")
    public static void setBackgroundImage(ImageView imageView, Drawable background) {
        imageView.setBackground(background);
    }
}

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <data>
        <variable
            name="viewModel"
            type="com.example.ViewModel" />
    </data>

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:backgroundImage="@{viewModel.backgroundImage}" />

</layout>