[英]kotlin abstract static fun in companion objects
I learn the use of ViewHolder from an offical sample named UserViewHolder. 我从一个名为UserViewHolder的官方样本中学习了ViewHolder的使用。
public class UserViewHolder extends RecyclerView.ViewHolder {
static UserViewHolder create(LayoutInflater inflater, ViewGroup parent) {
UserItemBinding binding = UserItemBinding
.inflate(inflater, parent, false);
return new UserViewHolder(binding);
}
private UserItemBinding mBinding;
private UserViewHolder(UserItemBinding binding) {
super(binding.getRoot());
mBinding = binding;
}
public void bindTo(User user) {
mBinding.setUser(user);
mBinding.executePendingBindings();
}
}
I'm going to write many ViewHolder
classes, so I hope I can write an abstract class. 我打算写很多ViewHolder
类,所以我希望我能写一个抽象类。 In Java, it looks like: 在Java中,它看起来像:
public abstract static class BaseViewHolder {
abstract static BaseViewHolder create()
abstract void bindTo()
}
I try to write it using Kotlin , but finally I find that it's not as simple as it in Java. 我尝试使用Kotlin编写它,但最后我发现它并不像Java中那么简单。
abstract class BaseViewHolder(itemView: View):RecyclerView.ViewHolder(itemView) {
abstract fun bindTo(viewModel: BaseViewModel)
}
In Kotlin, if I want a static function, I need to write the function in "companion objects". 在Kotlin中,如果我想要一个静态函数,我需要在“伴随对象”中编写该函数。 But it can't be a "abstract". 但它不可能是“抽象的”。
In Java, a abstract class with abstract classes is common. 在Java中,具有抽象类的抽象类很常见。
But how can I write it in Kotlin? 但我怎么能在Kotlin写呢?
update: 更新:
I have wrote my own SleepViewHolder . 我写了自己的SleepViewHolder 。 I'm going to write lots of ViewHolder, such as AppleViewHolder, BananaViewHolder and so on. 我要写很多ViewHolder,比如AppleViewHolder,BananaViewHolder等等。 So I want to build a BaseViewHolder as a pattern. 所以我想构建一个BaseViewHolder作为模式。 My question is that, in that case, what's the best way to write the pattern BaseViewHolder ? 我的问题是,在这种情况下,编写BaseViewHolder模式的最佳方法是什么? Should I change the constrcuter of it, or make the create function public? 我应该更改它的构造,还是将create函数公开?
open class SleepViewHolder private constructor(private val binding: ItemSleepBinding)
: RecyclerView.ViewHolder(binding.root) {
companion object {
@JvmStatic
fun create(inflater: LayoutInflater, parent: ViewGroup): SleepViewHolder {
val binding: ItemSleepBinding
= DataBindingUtil.inflate(inflater, R.layout.fragment_base, parent, false)
return SleepViewHolder(binding)
}
}
open fun bindTo(viewmodel: SleepViewModel) {
binding.vm = viewmodel
binding.executePendingBindings()
}
} }
In Kotlin
, unlike Java or C#,
classes do not have static methods. 在Kotlin
,与Java or C#,
类没有静态方法。 In most cases, it's recommended to simply use package-level functions instead. 在大多数情况下,建议只使用包级功能。
If you need to write a function that can be called without having a class instance but needs access to the internals of a class (for example, a factory method), you can write it as a member of an object declaration inside that class. 如果您需要编写一个可以在没有类实例但需要访问类的内部(例如,工厂方法)的情况下调用的函数,则可以将其写为该类中对象声明的成员。
Even more specifically, if you declare a companion object inside your class, you'll be able to call its members with the same syntax as calling static methods in Java/C#
, using only the class name as a qualifier. 更具体地说,如果在类中声明一个伴随对象,您将能够使用与在Java/C#
调用静态方法相同的语法来调用其成员,只使用类名作为限定符。
This is how you can write a companion class 这是你编写伴侣类的方法
class MyClass {
companion object { } // will be called "Companion"
}
fun MyClass.Companion.foo() { // ...
}
this is how you call foo() function... 这就是你如何调用foo()函数...
MyClass.foo()
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