How to get an Instance of ViewModel in activity in 2020?

问题

I am new to the mvvm pattern. I created a ViewModel for the main activity. Now I want to get an instance of the ViewModel in the main activity.

Most Tutorials and answers here on Stackoverflow suggest using ViewModelProviders.of(..., but this is depreceated.

So according to this question on stackoverflow: ViewModelProviders is deprecated in 1.1.0 main activity in onCreate, I do the following (and I could swear I already had it running): mainActivityViewModel = new ViewModelProvider(this).get(MainActivityViewModel.class);

However, I am getting an error telling me, that no suitable constructor has been found.

error: no suitable constructor found for ViewModelProvider(MainActivity)

Alternatively to make absolutely clear, that the MainActivity shall be the ViewModelStoreOwner, I created a variable ViewModelStoreOwner vmso = this; and put that variable into the constructor like so: mainActivityViewModel = new ViewModelProvider(vmso).get(MainActivityViewModel.class);

回答1:

You should update your gradle file to:

implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'

And due to this change you can pass Activity to the constructor you mentioned:

mainActivityViewModel = new ViewModelProvider(this).get(MainActivityViewModel.class);

回答2:

ViewModel viewModel = ViewModelProviders.of(this).get(ViewModel.class);

Android Support library version is depreciated. So you need to make sure that you import Androidx. And you need to implement androidx dependency in Gradle file.

It is not advised to create a new ViewModel object with "new" keyword.

回答3:

Duplicate question and already answered here

Simply replace:

This:

boardViewModel = ViewModelProviders.of(this).get(BoardViewModel::class.java)

With this:

boardViewModel = ViewModelProvider(this).get(BoardViewModel::class.java)

回答4:

For now, the only thing working for me was to use: MainActivityViewModel = new ViewModelProvider(this, new ViewModelProvider.NewInstanceFactory()).get(MainActivityViewModel.class);

However, I am still thankful for any advice, how this can be done different using new ViewModelProvider(this).get(MainActivityViewModel.class);

来源：https://stackoverflow.com/questions/59952673/how-to-get-an-instance-of-viewmodel-in-activity-in-2020