Kotlin custom attribute databinding

问题:

I am trying to set custom attribute using the Android DataBinding Library in my Kotlin project like this:

Layout

<ImageView
    android:id="@+id/imgView”
    android:layout_width="40dp"
    android:layout_height="40dp"
    android:layout_gravity="center"
    android:adjustViewBounds="true"
    app:imageUrl="@{segment.url}"/>

Code

  class Utils {
        companion object {
            @BindingAdapter("bind:imageUrl")
            @JvmStatic
            fun loadImage(view: ImageView, url:String) 
            {Picasso.with(view.context).load(url).error(R.drawable.error).into(view)}
    }       

The runtime error I get is:

A BindingAdapter in in 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.

Any pointers to solve it?

This happens only for custom attributes. The rest of the databindings work fine

回答1:

Just keep function on the top level, no class or companion object needed, it will work since top-level functions in Kotlin translated to static member functions of Class named as FileNameKt unless overridden by @file:JvmName annotation

@BindingAdapter("imageUrl")
fun loadImage(view: ImageView, url:String) { ... }

One more option is to annotate Extension Function as @BindingAdapter, it will work since in bytecode signature will exactly match signature expected by DataBindings(generated method will still accept an object of the extended class as the first argument), the function should remain top level as well

@BindingAdapter("imageUrl")
fun ImageView.loadImage(url:String) { ... }

回答2:

Try switching the order of the annotations. It seems to fix the issue:

class Utils {
    companion object {
        @JvmStatic @BindingAdapter("imageUrl")
        fun loadImage(view: ImageView, url:String) { ... } 
    }
} 

The problem is that the databindng compiler uses getCompanion().loadImage otherwise^*.
You can verify this in the generated com.your.package.databinding.*Binding class

^* After playing around a bit I noticed that this has nothing to do with the order of the annotations, but seems to be random. It seems to change whenever I hit "rebuild". It might be a bug in kapt or in the kotlin compiler

回答3:

Adding @JvmStatic after @BindingAdapter("imageUrl") fixed my problem.

For ex:

    @BindingAdapter("android:visibility")
    @JvmStatic
    fun setVisibility(view: View, visible: Boolean) {
        view.visibility = if (visible) View.VISIBLE else View.GONE
    }
}

回答4:

Or using extension:

@BindingAdapter("imageUrl")
fun ImageView.setImageUrl(url: String?) {
    Picasso.with(context).load(url).into(this)
}

Now you can use this function anywhere else

回答5:

The function(loadImage) need to put in object(Singleton in java) not in class and set @JvmStatic before @BindingAdapter("imageUrl") like this :

<ImageView
android:id="@+id/imgView”
android:layout_width="40dp"
android:layout_height="40dp"
android:layout_gravity="center"
android:adjustViewBounds="true"
imageUrl="@{segment.url}"/>

   @JvmStatic
   @BindingAdapter("bind:imageUrl")
   fun ImageView.loadImage( url:String) {
Picasso.with(this.context).load(url).error(R.drawable.error).into(this)
}

回答6:

This is working for me. Please find it below..

Add in gradle:

apply plugin: 'kotlin-kapt'

dependencies {
 kapt "com.android.databinding:compiler:3.1.4"
}

Add in POJO:

companion object {
  @BindingAdapter("image")
    @JvmStatic
         fun loadImage(view: ImageView, imageUrl: String) {

             //am Using Glide
Glide.with(view.context).setDefaultRequestOptions(RequestOptions().circleCrop())
                 .load(imageUrl).into(view)
         }
     }

In Layout:

Add bind:image="@{movies.imageUrl}

<ImageView 
  android:id="@+id/imageView"
  android:layout_width="100dp"
  android:layout_height="100dp"
  bind:image="@{movies.imageUrl}/>

回答7:

This worked for me

object ImageUtils {

        @JvmStatic @BindingAdapter("imageUrl")
        fun ImageView.loadImage(url: String?){
                GlideHelper.loadImage(url,this)
        }
}

in xml like this:

imageUrl="@{file.thumbnailLink}"