ViewModel使用的越來(lái)越多了涣觉，嚴(yán)格來(lái)說(shuō)官册，官方并不建議你在ViewModel中添加Context的引用难捌。同時(shí)，ViewModel的構(gòu)造方法是沒有任何參數(shù)的员淫，有的時(shí)候會(huì)很不靈活击敌。以下記錄兩種方法。

1.通過(guò)kotlin的拓展函數(shù)

fun <T : ViewModelProvider, V : ViewModel> T.get(
    key: String,
    modelClass: Class<V>,
    context: FragmentActivity
): V {
    val model = get(key, modelClass)
    if (model is TestViewModel) {
        model.addContext(context)
    }
    return model
}

fun <T : ViewModelProvider, V : ViewModel> T.get(
    key: String,
    modelClass: Class<V>,
    context: Context
): V {
    val model = get(key, modelClass)
    if (model is TestViewModel) {
        model.addContext(context)
    }
    return model
}

fun <T : ViewModelProvider, V : ViewModel> T.get(
    modelClass: Class<V>,
    context: FragmentActivity
): V {
    val model = get(modelClass)
    if (model is TestViewModel) {
        model.addContext(context)
    }
    return model
}

fun <T : ViewModelProvider, V : ViewModel> T.get(
    modelClass: Class<V>,
    context: Context
): V {
    val model = get(modelClass)
    if (model is TestViewModel) {
        model.addContext(context)
    }
    return model
}

在TestViewModel中添加如下的方法

class TestViewModel : ViewModel() {
    protected lateinit var context: Context
    open fun addContext(context: FragmentActivity) {
        this.context = context
    }

    open fun addContext(context: Context) {
        this.context = context
    }
}

使用方法

val viewModel = ViewModelProvider(this).get(TestViewModel::class.java, this)

2.通過(guò)自定義ViewModelProvider.Factory

class CoreViewModelFactory(private val context: Context) : ViewModelProvider.Factory {
    override fun <T : ViewModel?> create(modelClass: Class<T>): T {
        try {
            for (constructor in modelClass.constructors) {
                if (arrayOf(Context::class.java).contentEquals(constructor.parameterTypes)) {
                    return (constructor as Constructor<T>).newInstance(context)
                }
            }
            return modelClass.newInstance()
        } catch (e: InstantiationException) {
            throw RuntimeException("Cannot create an instance of $modelClass", e)
        } catch (e: IllegalAccessException) {
            throw RuntimeException("Cannot create an instance of $modelClass", e)
        }
    }
}

關(guān)于這一塊挤聘，仔細(xì)閱讀ViewModelProvider的代碼组去，會(huì)發(fā)現(xiàn)步淹，里面同樣提供了兩三種的Factory。針對(duì)可以直接擁有context的AndroidViewModel键闺，提供了ViewModelProvider.AndroidViewModelFactory澈驼，只是在引用的時(shí)候尔艇，不要再自己添加一遍了。

以下是你的TestViewModel

class TestViewModel(private val context: Context) : ViewModel() {
    init {
        L.i(" context $context ")
    }
}

使用方法

val viewModel = ViewModelProvider(this, CoreViewModelFactory(this)).get(TestViewModel::class.java)

以上兩種方法也可以用來(lái)幫助你自定義一些你要傳入的參數(shù)内边。