自己写了一个简易的android transformation.map

写一个单例

object SingleTon {

    val SingleTonLiveData = MutableLiveData<Int>()
}
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写一个viewModel

这里viewModel对单例的数据进行了监听，并且转发

class MainViewModel :ViewModel(){

    val viewModelLiveData = MediatorLiveData<Int>()
    init {
        viewModelLiveData.addSource(SingleTon.SingleTonLiveData){
            Log.d("leinuo", "MediatorLiveData listed")
            viewModelLiveData.postValue(it)
        }
    }
}
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mainActivity

class MainActivity : AppCompatActivity() {

    private lateinit var binding: ActivityMainBinding
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        val liveData = ViewModelProvider(this).get(MainViewModel::class.java)
        liveData.viewModelLiveData.observe(this){
            Log.d("leinuo", "what's the number $it")
        }

        var id = 0
        binding.text.setOnClickListener{
            SingleTon.SingleTonLiveData.postValue(id)
            id+=1
        }
    }
}
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实现了点击自动加一的效果