CODEWITHSUNDEEP
androidandroid-mvvm
Sam
Sam

Reputation: 621

How to use mvvm pattern using databinding

I am working on an application where there is a log in form.I am bit confused with the pattern as I don't understand as how I will open the new activity as my login is successful.As per my understanding when I click on submit button a method in viewmodel which authenticates will get call and after my successful login I do not know how to navigate it to activity file so that I can call new activity.

Upvotes: 1

Views: 259

Answers (3)

Chintan Soni
Chintan Soni

Reputation: 25267

Thumb Rule:

No package from android.* should lie in ViewModel. You can ignore package import for ViewModel

Also, you can do it with normal ViewModel as well.

How to proceed?

Lets make it simple. Suppose, you are making Login page.

Lets have below things in ViewModel itself:

  • Fields of email & password with two-way binding
  • Form Validation logic
  • Button Click Event
  • Api Call

All these things lie in your ViewModel.

Now, your Activity needs to react to the result of your Api Call. So, let your ViewModel have a separate LiveData where T is the type of Response from your Api Call.

For example: 

val loginApiStatus = MutableLiveData<LoginResponse>()

And then, let your Activity observe this LiveData. It should be observed in onStart() method of Activity. I will tell you the reason why to observe in onStart(). 

viewModel.loginApiStatus.observe(this, Observer{ loginResponse->
    // respond accordingly
})

Now, once you receive response from Api, simply update the LiveData in your ViewModel as:

loginApiStatus.value = loginResponse // Login Api Response

With this structure, you have total control over handling the Api Response. Even if, your activity goes into background, after launching Api Call, you will still have the state of what happened to that Api call. Now, when you return to Login screen again from background, you start observing the LiveData again (because we are observing the state LiveData in onStart() as I said earlier), and you will get the state to react upon.

Life becomes a lot easier when you start storing states of your View / Fragment / Activity, in your ViewModel itself.

Upvotes: 5

Birju Vachhani
Birju Vachhani

Reputation: 6353

You can simply implement a click listener in activity and handle opening new activity from there. As far as I know, ViewModel should only be used to persist data or do other communication with Repository/model. It should not be used for navigation.

Although if you want to use then you can use AndroidViewModel class which provides a context object that can be used for navigating to another activity/fragment.

Upvotes: 0

PJain
PJain

Reputation: 566

for that, you can use AndroidViewModel which gives Application Context and then using intent you can navigate to the new activity.

Upvotes: 0

Related Questions