Kotlin 自定义属性数据绑定 [英] Kotlin custom attribute databinding

问题描述

我正在尝试使用 Android 数据绑定库在我的 Kotlin 项目中是这样的:

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

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

代码

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)}
    }
}

    

    

我得到的运行时错误是:

The runtime error I get is:

中的 BindingAdapter不是静态的，需要使用从 DataBindingComponent 检索的对象.如果您不使用采用 DataBindingComponent 的膨胀方法，请使用 DataBindingUtil.setDefaultComponent 或将所有 BindingAdapter 方法设为静态.

A BindingAdapter in in <package.Utils.Companion> 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.

有什么解决办法吗?

这只发生在自定义属性上.其余的数据绑定工作正常

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

推荐答案

只需将函数保持在顶层，不需要类或伴生对象，它会起作用，因为 Kotlin 中的顶层函数转换为名为 Class 的静态成员函数作为 FileNameKt 除非被 @file:JvmName 注释覆盖

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) { ... }

另一种选择是将扩展函数注释为 @BindingAdapter，它会起作用，因为字节码签名将与 DataBindings 预期的签名完全匹配(生成的方法仍将接受扩展类的对象作为第一个参数)，函数也应该保持顶级

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) { ... }

另一种选择是将 BindingAdapter 与扩展属性结合起来，如下所示:

One more option is to combine BindingAdapter with the extension property like following:

@set:BindingAdapter("visible")
var View.visible
    get() = visibility == VISIBLE
    set(value) {
        visibility = if (value) VISIBLE else GONE
    }

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