英文:
Converting Java To Kotlin: Type mismatch. Required: MenuSlidingTabStrip.OnTabSelectedListener? Found: (Nothing, Nothing) → Boolean
问题
我正在将一款最初用Java编写的Android应用转换为Kotlin。
我正在努力理解以下错误消息：
类型不匹配。
所需：
MenuSlidingTabStrip.OnTabSelectedListener?
找到：
(Nothing，Nothing) → Boolean
以下是发出错误信号的代码片段（在转换之前，它完全正常运行）：
private var tabs: MenuSlidingTabStrip? = null //Kotlin化后的类
tabs!!.setOnTabSelectedListner{ tab, category -> /*类型不匹配...*/
listView!!.post {
...
}
}
在将此Java代码（位于MenuSlidingTabStrip中）转换为Kotlin后出现了问题：
public void setOnTabSelectedListner(OnTabSelectedListener listener) {
this.listener = listener;
}
public interface OnTabSelectedListener {
public void OnTabSelected(View tab, MenuCategory category);
}
转换为Kotlin：
fun setOnTabSelectedListner(listener: OnTabSelectedListener?) {
this.listener = listener
}
interface OnTabSelectedListener {
fun onTabSelected(tab: View?, category: MenuCategory?)
}
你能看出问题吗？需要更多的代码吗？
英文:
I am converting an Android app that was originally written in Java to Kotlin.
I am struggling to understand the following error message:
> Type mismatch.
Required:
MenuSlidingTabStrip.OnTabSelectedListener?
Found:
(Nothing, Nothing) → Boolean
Here is the fragment of code where the error is being signalled (and it was working perfectly fine before the conversion):
private var tabs: MenuSlidingTabStrip? = null //The Kotlinized class
tabs!!.setOnTabSelectedListner{ tab, category -> /*Type mismatch...*/
listView!!.post {
...
}
}
The issue arose after converting this Java code (found in MenuSlidingTabStrip) :
public void setOnTabSelectedListner(OnTabSelectedListener listener) {
this.listener = listener;
}
public interface OnTabSelectedListener {
public void OnTabSelected(View tab, MenuCategory category);
}
To Kotlin
fun setOnTabSelectedListner(listener: OnTabSelectedListener?) {
this.listener = listener
}
interface OnTabSelectedListener {
fun onTabSelected(tab: View?, category: MenuCategory?)
}
Can you see the issue? Do you need more code?
答案1
得分: 2
我建议您使用本地支持的 lambda 表达式，如下所示：
// 使 `this.listener` 的外观也像 lambda 签名一样
fun setOnTabSelectedListner(listener: (tab: View?, category: MenuCategory?) -> Unit) {
this.listener = listener
}
tabs!!.setOnTabSelectedListner { tab, category ->
// ...
}
如果您仍然希望使用手动定义的接口进行 SAM 转换，那么可以根据 Kotlin 1.4-M1 发布说明 中的描述，使用 fun 关键字标记该接口（仅适用于 Kotlin 1.4）：
fun interface OnTabSelectedListener {
fun onTabSelected(tab: View?, category: MenuCategory?)
}
// 使用以下方式调用该方法：
tabs!!.setOnTabSelectedListner(OnTabSelectedListener { tab, category ->
// ...
})
如果您尚未切换到 Kotlin 1.4（仍处于 beta 阶段），并且不愿意使用本地提供的 lambda 语法，则必须手动实例化匿名对象：
tabs!!.setOnTabSelectedListner(object : OnTabSelectedListener {
override fun onTabSelected(tab: View?, category: MenuCategory?) {
// ...
}
})
英文:
I'd suggest you to use the natively supported lambdas as:
// make `this.listener` look like lambda signature as well
fun setOnTabSelectedListner(listener: (tab: View?, category: MenuCategory?) -> Unit) {
this.listener = listener
}
tabs!!.setOnTabSelectedListner { tab, category ->
// ...
}
If you still wanna use the SAM conversion with the manually defined interface, then mark the interface with the fun keyword as described in Kotlin 1.4-M1 Release changelog (will only work with Kotlin 1.4):
fun interface OnTabSelectedListener {
fun onTabSelected(tab: View?, category: MenuCategory?)
}
// call that method like this:
tabs!!.setOnTabSelectedListner(OnTabSelectedListener { tab, category ->
// ...
})
If you've not switched to Kotlin-1.4 (which is still in beta state), you have to manually instantiate the anonymous object if you are not willing to use the natively provided lambda syntax:
tabs!!.setOnTabSelectedListner(object : OnTabSelectedListener {
override fun onTabSelected(tab: View?, category: MenuCategory?) {
// ...
}
})
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