Can not use BindingAdapter in Kotlin

Question

I used to create DataBindingAdapter for creating custom xml attributes in data binding.

object DataBindingAdapter {
    @BindingAdapter("android:src")
    fun setImageByRes(imageView: ImageView, @DrawableRes resId: Int) {
        imageView.setImageResource(resId)
    }
}

It was working well in Java. But not working in kotlin.

As I understand object in kotlin are similer to static method of Java. But its not working in data binding.

java.lang.IllegalStateException: Required DataBindingComponent is null in class FragmentBottomBarBinding. A BindingAdapter in acr.browser.lightning.utils.DataBindingAdapter is not static and requires an object to use, retrieved from the DataBindingComponent. If you don't use an inflation method taking a DataBindingComponent, use DataBindingUtil.setDefaultComponent or make all BindingAdapter methods static.

If you're facing interop problems (Java calling Kotlin code), a good approach is to decompile the generated bytecode to Java and see how the result looks. This often makes it immediately clear where the interface mismatches. — TheOperator, Aug 16 '18 at 11:27
Because you did not answer, so I did your work. You can now answer. I will mark it right, You deserve it. — Khemraj Sharma, Aug 16 '18 at 12:09

Moinkhan · Accepted Answer · 2018-08-16T12:25:06.553

26

Just add the @Jvmstatic annotation on setImageByRes method.

object DataBindingAdapter {
    @BindingAdapter("android:src")
    @JvmStatic
    fun setImageByRes(imageView: ImageView, @DrawableRes resId: Int) {
        imageView.setImageResource(resId)
    }
}

as per the @Jvmstatic doc

Specifies that an additional static method needs to be generated from this element if it's a function. If this element is a property, additional static getter/setter methods should be generated.

In short method declared in one place and used from multiple languages of JVM. If you're calling a method from Java, then you should declare it as @JvmStatic, because adding the @JvmStatic annotation in one place will allow you to leave out multiple .Companion references in multiple places.

edited Aug 16 '18 at 12:25

answered Aug 16 '18 at 12:11

Moinkhan

12,732
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If you add a little info about JvmStatic for new comers, that will be great. – Khemraj Sharma Aug 16 '18 at 12:13
Hi @Moinkhan how to link this DataBindingAdapter with recycler view or adapter ? – Milan Sheth Sep 25 '20 at 14:25

score 7 · Answer 2 · answered Aug 16 '18 at 11:30

7

No. Object in kotlin is same like singleton. I think u dont need put it in Object. Just make new file lets say BindingAdapters.kt and u dont need write any class or object keywords.

It should look like this. Nothing else. If u need more functions just add it below this one. Again no class keyword or brackets are needed. It will be global function. Maybe u should also use ContextCompat for getting resource properly with context from imageView. And i would rather name it differently than android:src. What about imageResBinder

@BindingAdapter("imageResBinder")
fun setImageByRes(imageView: ImageView, @DrawableRes resId: Int) {
    imageView.setImageResource(resId)
}

and after that in your .xml file

<android.support.v7.widget.AppCompatImageView
    style="@style/Image.SomeImageStyle"
    app:imageResBinder="@{viewModel.getImageRes()}" />

answered Aug 16 '18 at 11:30

Kebab Krabby

1,574
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21

If I need, How can I call this function from another kotlin? – Khemraj Sharma Aug 16 '18 at 11:34
U cant. Only thing u can is to call it from different .xml file because its global method only for databinding. So u cant lets say call it in fragment onViewCreated(). Of course u can make a static class for loading resources but i think u should not if u are using databinding. U can also put this bindingAdapter only into some model class: https://stackoverflow.com/questions/40845767/where-to-place-android-bindingadapter-method – Kebab Krabby Aug 16 '18 at 11:38
Then I will prefer @JvmStatic because there can be some common function which can be useful to call from another activity also. – Khemraj Sharma Aug 16 '18 at 11:40

Can not use BindingAdapter in Kotlin

2 Answers2