Kotin fragment the correct way to get ViewModel instances

1. The first way to get it ：

Usually get ViewModel Method ：

 val model : BlankViewModel by lazy{
    
        ViewModelProvider(this,BlankViewModel.BlankViewModelFactory()).get(BlankViewModel::class.java)
 }
 // This method has been abandoned ：viewModel = ViewModelProvider(this).get(MainViewModel::class.java)

Corresponding BlankViewModelFactory Method

class BlankViewModel : ViewModel() {
    
    // TODO: Implement the ViewModel

    private val number = MutableLiveData<Int>();
    private var i=0

    fun getNumber() : LiveData<Int>{
    
        return number
    }

    fun addNumber(){
    
        i++
        number.value = i
    }

    class BlankViewModelFactory(): ViewModelProvider.Factory{
    
        override fun <T : ViewModel?> create(modelClass: Class<T>): T {
    
            return BlankViewModel() as T
        }
    }
}

When we create Fragment page , And add the page to a Activity When in the page , Want to achieve in Activity Call in ViewModel The method in makes livedata Data changes , And hope Fragment The page can also listen for changes , At this point, you need to get the same ViewModel example , To ensure that the data of two pages changes at the same time .

First , stay Activity In order to get BlankViewModel , And call one of them by clicking the button addNumber Method , Let variables +1

class FragmentActivity : AppCompatActivity() {
    

    val model : BlankViewModel by lazy{
    
        ViewModelProvider(this,BlankViewModel.BlankViewModelFactory()).get(BlankViewModel::class.java)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
    
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_fragment)

        val button = findViewById<Button>(R.id.add).setOnClickListener {
    
              model.addNumber()
        }
    }
}

first Fragment page ：

class LeftFragment : Fragment() {
    

    val model : BlankViewModel by lazy{
    
        ViewModelProvider(requireActivity(),BlankViewModel.BlankViewModelFactory()).get(BlankViewModel::class.java)
    }


    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
    
        return inflater.inflate(R.layout.blank_fragment, container, false)
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    
        super.onViewCreated(view, savedInstanceState)

        val left = view.findViewById<TextView>(R.id.left_tv)

        model.getNumber().observe(requireActivity(), Observer {
    
            Log.d("IT",""+it)
            left.text = it.toString()
        })
    }
}

In obtaining ViewModel When an instance ,ViewModelProvider First parameter in ViewModelStoreOwner The object passes requireActivity Method , This method is to get the current Activity example ; If the position is still transmitted this , What we get is and Activity Different ViewModel example , such Activity When you click the button Fragment The value of the page does not change .

val model : BlankViewModel by lazy{
         
  ViewModelProvider(requireActivity(),BlankViewModel.BlankViewModelFactory()).get(BlankViewModel::class.java)
}

In the way of observing change , The same is true ：

  model.getNumber().observe(requireActivity(), Observer {
    
            left.text = it.toString()
 })

the other one Fragment The page is the same as it , I don 't want to add .

2. The second way to get it

adopt ktx simplify ：
add to ktx rely on , Note the version here , my kotlin Version is too low , Downloading a higher version will be red ：

implementation "androidx.fragment:fragment-ktx:1.2.5"
implementation "androidx.activity:activity-ktx:1.0.0-alpha03"

stay Activity On the page ：

// Other parts are omitted here 
val model by viewModels<BlankViewModel>()

stay Fragment On the page

// Other parts are omitted here 
val model by activityViewModels<BlankViewModel>()

// It can pass normally here this
model.getNumber().observe(this, Observer {
    
            Log.d("IT",""+it)
            left.text = it.toString()
})

The above is to get the same ViewModel Example method . If there is any wrong , Please correct me. .