android：观察2个变量

Question

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

// ViewModelFolder.selectFolder is MutableLiveData<String>
ViewModelFolder.selectFolder.observe(viewLifecycleOwner, Observer { name ->
  name?.let {
    taskViewModel.getTasksByFolder(it, false)
      .observe(viewLifecycleOwner, Observer { tasks ->
        tasks?.let { taskAdapter.setTasks(it) }
      })
    }
  })
}

当ViewModelFolder.selectFolder 或任务发生变化时，我想致电taskViewModel.getTasksByFolder。但是，内部观察者被多次调用。 我该如何解决？

Answer 1

我认为 MediatorLiveData 可能有助于解决这个问题。

在你的视图模型中写一个这样的函数。

fun mergeResult(): MediatorLiveData<String> {
        val mediatorLiveData = MediatorLiveData<String>()
        var result = ""

        mediatorLiveData.addSource(selectFolder) {
            // your logic goes here.
            result = ...
        }

        mediatorLiveData.addSource(getTasksByFolder) {
            // your logic goes here.
            result = ...
        }

        mediatorLiveData.value = result

        return mediatorLiveData
    }

并在你的片段中观察它。

viewmodel.mergeResult().observe(viewLifecycleOwner, Observer {
 . . .
}