如何实现Kotlin通用ViewModelProvider.Factory避免重复代码？

基础无参ViewModel实现 #

如果你的ViewModel都是无参构造的，这个基础版本的通用工厂类可以帮你避免重复编写多个工厂：

import androidx.lifecycle.ViewModel
import androidx.lifecycle.ViewModelProvider

class GenericViewModelFactory(private val viewModelClass: Class<out ViewModel>) : ViewModelProvider.Factory {
    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        if (modelClass.isAssignableFrom(viewModelClass)) {
            @Suppress("UNCHECKED_CAST")
            return viewModelClass.newInstance() as T
        }
        throw IllegalArgumentException("Unknown ViewModel class: ${modelClass.name}")
    }
}

调用方式 #

在Fragment中直接传入对应ViewModel的Class对象即可：

• Fragment A：

val factory = GenericViewModelFactory(AViewModel::class.java)
val viewModel = ViewModelProvider(this, factory)[AViewModel::class.java]

• Fragment B：

val factory = GenericViewModelFactory(BViewModel::class.java)
val viewModel = ViewModelProvider(this, factory)[BViewModel::class.java]

扩展支持带参数的ViewModel #

如果你的ViewModel需要构造参数（比如依赖Repository等），可以扩展通用工厂类来支持参数传递：

import androidx.lifecycle.ViewModel
import androidx.lifecycle.ViewModelProvider

class GenericViewModelFactory<T : ViewModel>(
    private val viewModelClass: Class<T>,
    private vararg val constructorArgs: Any
) : ViewModelProvider.Factory {
    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        return try {
            // 获取匹配参数的构造函数
            val paramTypes = constructorArgs.map { it.javaClass }.toTypedArray()
            val constructor = viewModelClass.getConstructor(*paramTypes)
            constructor.newInstance(*constructorArgs) as T
        } catch (e: Exception) {
            throw RuntimeException("Failed to create ViewModel instance", e)
        }
    }
}

带参数调用示例

假设AViewModel需要传入UserRepository：

val userRepository = UserRepository()
val factory = GenericViewModelFactory(AViewModel::class.java, userRepository)
val viewModel = ViewModelProvider(this, factory)[AViewModel::class.java]

内容的提问来源于stack exchange，提问作者gee3107