ViewModelProviders 和 ViewModelProvider 类有什么区别？

Question

I saw two classes with a similar name, ViewModelProviders, and ViewModelProvider. Can anyone explain what are the difference between these classes? which class actually provide the ViewModel?

Answer 1

ViewModelProviders (belongs to Maven artifact android.arch.lifecycle:extensions) is a class from android.arch.lifecycle package which contains utilities methods for ViewModelStore class & returns you object of ViewModelProvider class when you use of() method from it.

So, you can think of as wrapper around library class for ViewModelProvider .

On the other hand, ViewModelProvider (belongs to Maven artifact android.arch.lifecycle:viewmodel) is class that provides ViewModels for a scope. So it's default ViewModelProvider for an Activity or a Fragment can be obtained from ViewModelProviders class.

So, yes ! this is the main class that provides core logic for your ViewModel , but you'll need to obtain it from ViewModelProviders which returns you this class to obtain ViewModel from.

Edit:

After ViewModel version 2.2.0 :

Class ViewModelProviders has been deprecated and we can now use ViewModelProvider directly by creating it's new instance for getting ViewModel .

Something like this: ViewModelProvider(this).get(SomeViewModel::class.java)

Answer 2

The ViewModelProviderS class provides instances of ViewModelProvider class.Your call to ViewModelProviders.of("this") creates and returns a ViewModelProvider associated with the activity.

ViewModelProvider on the other hand provides instances of ViewModel of the Activity. Calling the ViewModelProviders.get(ExampleViewModel::class.java) returns an instance of ExampleViewModel class

These functions usually go together like:

ViewModelProviders.of("this").get(ExampleViewModel::class.java)

Answer 3

@andritK, it seems ViewModelProviders is deprecated now. The docs says we can straight away use ViewModelProviders in this case now. then how about changing below codes to the following: FROM

inline fun <reified T : ViewModel> Fragment.viewModel(factory: ViewModelProvider.Factory, body: T.() -> Unit): T {
    val vm = ViewModelProviders.of(this, factory)[T::class.java]
    vm.body()
    return vm
}

TO

inline fun <reified T : ViewModel> Fragment.viewModel(factory: ViewModelProvider.Factory, body: T.() -> Unit): T {
    val vm = ViewModelProvider(this, factory).get(T::class.java)
    vm.body()
    return vm
}

Does this work?