Where to place android BindingAdapter method?

Question

This has to be the most basic of question but after a full day of reading tutorials and the documentation here I can't seem to understand where to put these methods. None of the guides mention where this thing is placed it just mentions to use the annotation on a static method. What static method? Any static method at all regardless of class? What is a good practice? do I create a CustomBinding class to host all these static methods?

So long as I have the method has a BindingAdapter annotation and the first parameter is a View, it will work?

I assume if the first parameter is of type View I can place the binding attribute on any type of views and it will trigger the method? So if I have specific view say EditText, does this mean the method is only called when the attribute is found in an EditText view in the layout file?

Ellis

see how it is done with already existing adapters, like TextViewBindingAdapter and parent folder – Heaviness

Answer 1

After navigating through the internet I've finally found some info from one of the developers themselves. I wish they would have been more clear on the basics in the documentation.

Quote:

Binding adapters are annotated methods in any class that are used to do just this. Typically, you’d organize your adapters into [-a] classes based on the target View type.

This obviously means that at compile time all methods in any class with the annotation BindingAdapter will generate the BindingAdapter.

Ellis

Thanks a lot! You saved hours of my time – Orthoepy

or you can go right here about defining the recommended ways (if you using kotlin) to optimize @BindingAdapter method – Morass

Answer 2

You place it in your model class.

Example:

XML:

 <data>

    <variable
        name="item"
        type="com.yourpackage.Model"/>
      </data>
         ......

           <ImageView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:src="@{item.resId}"/>

Model:

public class Model {

    @DrawableRes
    private final int resId;

    public Model(int resId) {
        this.resId = resId;
    }

    public int getResId() {
        return resId;
    }

    @BindingAdapter ("android:src")
    public static void setImageResource(ImageView imageView, int resource){
        imageView.setImageResource(resource);
    }
}

Stairs

Please explain whether this is the only way to do it or is this your way? There are some BindingAdapters that are grouped in a class, eg android.googlesource.com/platform/frameworks/data-binding/+/… – Ellis

I don't think model class is not a good place to put this BindingAdapter because it is not meant to couple with the model. For example, I can't do two @BindingAdapter ("android:src") - one to scale the image to 200x200 and another to scale image to 400x400. I think it might be better to put them in a class specifically for binding (eg. BindingAdapterUtils). – Failing

@Failing do you have any idea while using Binding Adapter without custom views? I tried to bring to other file but don't know how to put it in tag – Defence

@TruongHieu, you do not need a custom view. You can use it for anything. Just create a new file (eg. BindingUtils) and place a static method there. Remember to declare @BindingAdapter (eg. @BindingAdapter ("android:src")). – Failing

Sure I tried it with custom attribute successfully. But why I didnt see inspection of that custom attribute? @Failing – Defence

Hi Truong, I don't quite understand your question. Perhaps open a new question thread with more detail explanation :) – Failing

another example: github.com/google/iosched/blob/… – Phase