在 Android 的 onClickListener 中多次观察到 LiveData

Question

我有这样的存储库设置

class ServerTimeRepo @Inject constructor(private val retrofit: Retrofit){
    var liveDataTime = MutableLiveData<TimeResponse>()
    fun getServerTime(): LiveData<TimeResponse> {
        val serverTimeService:ServerTimeService = retrofit.create(ServerTimeService::class.java)
        val obs = serverTimeService.getServerTime()
        obs.subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread()).unsubscribeOn(Schedulers.io())
                .subscribe(object : Observer<Response<TimeResponse>> {
                    override fun onComplete() {

                    }

                    override fun onSubscribe(d: Disposable) {

                    }

                    override fun onNext(t: Response<TimeResponse>) {
                        val gson = Gson()
                        val json: String?
                        val code = t.code()
                        val cs = code.toString()
                        if (!cs.equals("200")) {
                            json = t.errorBody()!!.string()
                            val userError = gson.fromJson(json, Error::class.java)
                        } else {

                            liveDataTime.value = t.body()
                        }

                    }

                    override fun onError(e: Throwable) {

                    }

                })
        return liveDataTime
    }
}

然后我有一个像这样调用这个 repo 的视图模型

class ServerTimeViewModel @Inject constructor(private val serverTimeRepo: ServerTimeRepo):ViewModel() {

    fun getServerTime(): LiveData<TimeResponse> {
        return serverTimeRepo.getServerTime()
    }
}

然后我有一个 activity，我有一个 onClickListener，我在其中观察实时数据，就像这样

tvPWStart.setOnClickListener {
         val stlv=  serverTimeViewModel.getServerTime()

            stlv.observe(this@HomeScreenActivity, Observer {
                //this is getting called multiple times??

            })
        }

我不知道这是怎么回事。谁能指出我正确的方向？谢谢

Answer 1

问题是每次触发 ClickListener 时，您都会一次又一次地观察到 LiveData。因此，您可以通过以下解决方案解决该问题：

在你的 ViewModel 中私下拿一个 MutableLiveData 对象并观察它 LiveData.

class ServerTimeViewModel @Inject constructor(private val serverTimeRepo: ServerTimeRepo):ViewModel() {

    private val serverTimeData = MutableLiveData<TimeResponse>() // We make private variable so that UI/View can't modify directly

    fun getServerTime() {
        serverTimeData.value = serverTimeRepo.getServerTime().value // Rather than returning LiveData, we set value to our local MutableLiveData
    }

    fun observeServerTime(): LiveData<TimeResponse> {
        return serverTimeData //Here we expose our MutableLiveData as LiveData to avoid modification from UI/View
    }
}

现在，我们直接在 ClickListener 之外观察这个 LiveData 并且我们只是从按钮点击调用 API 方法，如下所示：

//Assuming that this code is inside onCreate() of your Activity/Fragment
//first we observe our LiveData
serverTimeViewModel.observeServerTime().observe(this@HomeScreenActivity, Observer {
        //In such case, we won't observe multiple LiveData but one
})
//Then during our ClickListener, we just do API method call without any callback.
tvPWStart.setOnClickListener {
    serverTimeViewModel.getServerTime()
}

在 Android 的 onClickListener 中多次观察到 LiveData

LiveData is observed multiple times inside onClickListener in Android

android

kotlin

android-livedata

android-viewmodel

android-architecture-components