Android: ViewModel＞ has no zero argument constructor

        viewModel = ViewModelProvider(
                this,
                ViewModelProvider.AndroidViewModelFactory.getInstance(application)
        ).get(PDFBookDocumentViewModel::class.java)

使用上述方法加载viewModel报上述错误。如果您想为ViewModel类提供一个非零参数的构造函数，则可能必须创建一个自定义ViewModelFactory类来初始化ViewModel实例，该实例将实现ViewModelProvider.Factory接口

解决方案：https://*.com/questions/44194579/android-viewmodel-has-no-zero-argument-constructor

 

1. 创建一个自定义ViewModelFactory类：

class ViewModelFactory constructor(
        private val sharePref: SharedPreferences,
        private val topRepository: ITopRepository,
) : ViewModelProvider.NewInstanceFactory() {

    override fun <T : ViewModel> create(modelClass: Class<T>) =
            with(modelClass) {
                when {
                    isAssignableFrom(PDFBookDocumentViewModel::class.java) ->
                        PDFBookDocumentViewModel(PDFBookDocumentUseCase(topRepository))
                    else ->
                        throw IllegalArgumentException("Unknown ViewModel class: ${modelClass.name}")
                }
            } as T
    
    companion object {
        @Volatile
        var INSTANCE: ViewModelFactory? = null

        fun getInstance(
                sharePref: SharedPreferences,
                iTopRepository: ITopRepository,
        ): ViewModelFactory {
            if (INSTANCE == null) {
                synchronized(ViewModelFactory::class) {
                    if (INSTANCE == null) {
                        INSTANCE =
                                ViewModelFactory(
                                        sharePref,
                                        iTopRepository
                                )
                        RetrofitManager.sharedPreferences = sharePref
                    }
                }
            }
            return INSTANCE!!
        }
    }
}

 

2： 获取用于在Activity中创建ViewMode的Factory：

/**
 *
 * 获取用于在Activity中创建ViewMode的Factory
 *
 * @return ViewModelFactory
 */
fun Activity.getViewModelFactory(): ViewModelFactory {
    val sharePref = SharedPreferences(applicationContext)
    val topRepository = (applicationContext as MyApplication).topRepository
    return ViewModelFactory.getInstance(
        sharePref,
        topRepository,
    )
}

 

3： Activity中绑定viewModel的代码用如下替换：

 viewModel = viewModels<PDFBookDocumentViewModel> { getViewModelFactory() }.value

 

 

 

本文地址：https://blog.csdn.net/Crystal_xing/article/details/108868026