从 activity 更新片段内的值

Question

我想将我的旧应用程序转移到 MVVM，所以你能帮我做这个测试吗：

共享视图模型：

class SharedViewModel : ViewModel() {

    private var _numberF1 = MutableLiveData<Int>().apply { postValue(0)}
    val numberF1: LiveData<Int>
        get() = _numberF1


    fun addNumberF1() {
         _numberF1.value = _numberF1.value?.plus(1)
    }
}

片段：

class Fragment1 : Fragment() {

    companion object {
        fun newInstance() = Fragment1()
    }

    private lateinit var viewModel: SharedViewModel

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {

        val view: View = inflater.inflate(R.layout.fragment_1, container, false)
        
        return view
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
        viewModel = ViewModelProvider(this).get(SharedViewModel::class.java)

        viewModel.numberF1.observe(this, {
        Log.d("DTAG","Should be updated")
        textViewNumberF1.text = it.toString()
    })

    }

}

主要活动：

    class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

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

        var fragment1 = Fragment1.newInstance()
        navigateToFragment(fragment1)

        buttonFrag1Up.setOnClickListener { viewModel.addNumberF1() }

    }

    private fun navigateToFragment(fragment: Fragment) {

        val fragmentTransaction = supportFragmentManager.beginTransaction()
        fragmentTransaction.addToBackStack(null)
        fragmentTransaction.replace(R.id.mainFrame, fragment)
        fragmentTransaction.commit()

    }
}

该值未更新正确的做法是什么？

Answer 1

如果你想分享 viewModel 你应该在你的片段中这样写 :

val viewModel = ViewModelProvider(requireActivity()).get(SharedViewModel::class.java)

而不是你所拥有的：

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

从 activity 更新片段内的值

Updating value inside fragment from activity

android

mvvm

observable

android-viewmodel