为什么我的LiveData不是 <Drawable> 被显示为背景？

Question

I want to change the background of a button dynamically via a LiveData object.

My ViewModel:

public class ViewModel {
    public ViewModel(Context context) {
    }

    public LiveData<Drawable> getBackDrawable(){
        MutableLiveData background = new MutableLiveData<>();
        background.postValue(new ColorDrawable(Color.parseColor("#FF0000")));

        return background;

    }
}

My Xml:

<layout
    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"
    tools:context=".MainActivity">

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

    <android.support.constraint.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <Button
            android:id="@+id/activation_button"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Test Button"
            android:background="@{ViewModel.getBackDrawable}" />
    </android.support.constraint.ConstraintLayout >
</layout>

Why won't the drawable that I inserted into the LiveData via .postValue() displayed as background?

Answer 1

you are assigning LiveData<Drawable> to backgorund property so you cannot achieve what you want.

Observe Livedata in your Activity and apply backgorund to your Button . and try yourBindingvar.executePendingBindings() . it may Helps You.