Android DataBinding Custom Binding Adapter Warning

Question

I followed the data binding documentation for Custom Binding Adapter for image loading from official Android Developers site: http://developer.android.com/tools/data-binding/guide.html

After successfully compiling the code I get a warning which is:

Warning:Application namespace for attribute bind:imageUrl will be ignored.

My Code is as follow:

@BindingAdapter({"bind:imageUrl"})
    public static void loadImage(final ImageView imageView, String url) {
        imageView.setImageResource(R.drawable.ic_launcher);
        AppController.getUniversalImageLoaderInstance().displayImage(url, imageView);
    }

Why this warning is generated?

A screenshot is also attached...

Solution 1

I believe the namespace is truly ignored in the BindingAdapter annotation. The warning occurs if you use any namespace prefix, regardless of whether it matches the one used in your layout or not. If you omit the namespace, like so:

@BindingAdapter({"imageUrl"})

...the warning doesn't occur.

I suspect the warning exists to alert us the namespace is stripped off before the string is used as a key in the annotation's implementation. Which makes sense when you consider layouts are free to declare whatever namespaces they want, e.g. app: or bind: or foo:, and the annotation needs to work across all those cases.

Solution 2

Actually there are still some tutorials which add prefix to the BindingAdapter annotation.

Use @BindingAdapter({"imageUrl"}) without any prefix.

<ImageView
    imageUrl="@{url}"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content" />

Pro Tip

You will not get warning when using android: prefix in BindingAdapter. Because that is encouraged. I will suggest to use @BindingAdapter("android:src") instead of creating a new attribute.

@BindingAdapter("android:src")
public static void setImageDrawable(ImageView view, Drawable drawable) {
    view.setImageDrawable(drawable);
}

and

@BindingAdapter("android:src")
public static void setImageFromUrl(ImageView view, String url) {
   // load image by glide, piccaso, that you use.
}

Create a new attribute only when you need it.

Solution 3

Try this, work for me!. I hope this can help you. Simple way to change image resource without binding adapter.

<ImageButton
        ...
        android:id="@+id/btnClick"
        android:onClick="@{viewModel::onClickImageButton}"
        android:src="@{viewModel.imageButton}" />

and View Model Class :

public ObservableField<Drawable> imageButton;
private Context context;

//Constructor
public MainVM(Context context) {
    this.context = context;
    imageButton = new ObservableField<>();
    setImageButton(R.mipmap.image_default); //set image default
}

public void onClickImageButton(View view) {
    setImageButton(R.mipmap.image_change); //change image
}

private void setImageButton(@DrawableRes int resId){
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        imageButton.set(context.getDrawable(resId));
    }else{
        imageButton.set(context.getResources().getDrawable(resId));
    }
}

Comments

[Lorne Laliberte]

Note that the android: namespace is the only exception: if you're setting a BindingAdapter for a built-in attribute such as android:onClick, you can include the prefix and you will not get any warning.

[ruX]

ViewModel should not use any Android-specific classes(especially views) nor have access to context as that defeats the purpose of having it at the first place