activity 和 fragment 之间无法共享数据，无法通信

Question

无法在activity和片段之间共享数据，无法通信 Activity无法观察片段数据 Communicating with fragments

视图模型

  class BlankViewModel : ViewModel() {
    private val mutableSelectedItem = MutableLiveData<String?>()
    val onCallbackToDestroyFragment: LiveData<String?> = mutableSelectedItem
    fun selectItem(tag: String?) {
        mutableSelectedItem.value = tag
    }
    }

2 个片段

class BlankFragment : Fragment() {

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

private lateinit var viewModel: BlankViewModel

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    viewModel = ViewModelProvider(this).get(BlankViewModel::class.java)
    viewModel.selectItem("data")
    return inflater.inflate(R.layout.blank_fragment, container, false)
}
}

3 Activity

    class MainActivity : AppCompatActivity() {
    private lateinit var binding:ActivityMainBinding
    private val viewModel by lazy {
        ViewModelProvider(this).get(BlankViewModel::class.java)
    }
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding= ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        supportFragmentManager.beginTransaction()
            .add(binding.fl.id, BlankFragment()).commit()

        viewModel.onCallbackToDestroyFragment.observe(this , Observer {
            Log.e("观察到了吗","Did you observe the data?")
        })
    }


}

控制台没有数据

Answer 1

这是因为您正在片段中创建 ViewModel 的新实例。

如果您希望 activity 和片段共享您必须使用的同一 ViewModel 实例。

private lateinit var viewModel: BlankViewModel by activityViewModels()

并删除片段中的提供者声明 .. 或者您可以创建一个 customViewModel 工厂并共享它。

activity 和 fragment 之间无法共享数据，无法通信

Data cannot be shared between activity and fragment and cannot communicate

android

fragment

viewmodel