无法在Kotlin中创建类ViewModel的实例 [英] Cannot create an instance of class ViewModel in Kotlin

问题描述

我正在尝试在Fragment中初始化 viewmodel ，但是每次我想在viewmodel构造函数中传递接口时，都会引发错误无法创建ViewModel类的实例
另外，我在 kotlin-kapt 或任何生命周期注释

中都没有问题，在这里

是我的ViewModel类

  class SettingsViewModel（
 var settingsView：SettingsView 
）：ViewModel（）{} 
  

这是我要初始化视图模型的片段

 类SettingsFragment：Fragment（），SettingsView {
 
 var viewmodel：SettingsViewModel？ = null 
 
覆盖fun onCreate（savedInstanceState：Bundle？）{
 super.onCreate（savedInstanceState）
} 
 
覆盖fun onCreateView（
 inflater：LayoutInflater，容器：ViewGroup ?， 
 savedInstanceState：捆绑包？
）：视图？ {
 //为该片段添加布局
 
 viewmodel = ViewModelProviders.of（this）.get（SettingsViewModel（this）:: class.java）
 
 val binding = 
 DataBindingUtil.inflate< FragmentSettingsBinding>（inflater，R.layout.fragment_settings，container，false）
 .apply {} 
 
 
返回binding.root 
} 
  

解决方案

初始化ViewModel时通过没有工厂的ViewModelProviders，这意味着您只能实例化没有构造函数参数的ViewModel。像这样：

  viewmodel = ViewModelProviders.of（this）.get（SettingsViewModel :: class.java）
  

请注意，由于您没有调用构造函数，因此无法将参数传递给.class调用

由于ViewModel具有构造函数参数，因此需要实现ViewModelProvider.Factory才能使用给定的参数检索其实例。

此处是对Android开发人员的引用： https://developer.android.com/reference/ android / arch / lifecycle / ViewModelProvider

此处指的是一篇可以为您提供有关如何实现工厂的见解的文章： https://medium.com/ @ marco_cattaneo / android-viewmodel-and-factoryprov使用dagger-2-d9e20a07084c的ider-好的管理方法

I'm trying to initialize viewmodel in Fragment but each time I want to pass the interface in my viewmodel constructor it throws the error Cannot create an instance of class ViewModel Also I don't have any problem in kotlin-kapt or any lifecycle annotations

here is my ViewModel class

class SettingsViewModel (
       var settingsView: SettingsView
    ) : ViewModel(){ }

and here is my fragment where i want to initialize the viewmodel

class SettingsFragment : Fragment(), SettingsView {

     var viewmodel :SettingsViewModel? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate the layout for this fragment

         viewmodel = ViewModelProviders.of(this).get(SettingsViewModel(this)::class.java)

        val binding =
            DataBindingUtil.inflate<FragmentSettingsBinding>(inflater, R.layout.fragment_settings, container, false)
                .apply{}


        return binding.root
    }

解决方案

When you are initialising the ViewModel through ViewModelProviders without a factory, this means that you can only instantiate a ViewModel which has no constructor arguments. Like this:

viewmodel = ViewModelProviders.of(this).get(SettingsViewModel::class.java)

Notice that you cannot pass arguments to a .class call because you are not calling the constructor

Since your ViewModel has constructor arguments you need to implement a ViewModelProvider.Factory in order to be able to retrieve its instance with given parameters.

Here is a reference to android devs: https://developer.android.com/reference/android/arch/lifecycle/ViewModelProvider

Here refers to an article that can give you a insight on how to implement the factory: https://medium.com/@marco_cattaneo/android-viewmodel-and-factoryprovider-good-way-to-manage-it-with-dagger-2-d9e20a07084c

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