Android LiveData:如何执行ArrayList< LiveData< RetrofitObject>&gt ;? [英] Android LiveData: How to do an ArrayList<LiveData<RetrofitObject>>?

问题描述

我正在创建具有MVVM架构的应用程序，但遇到了一个问题，该问题是获取要在View中显示的LiveData列表.

I am creating an app with MVVM architecture and I ran into an issue of getting a list of LiveData to show in the View.

在我的ViewModel中，我有一个getAll()函数，该函数使用Room从数据库中检索字符串列表.从那里，我得到了字符串并调用我的Retrofit函数，将每个字符串分别发送到返回对象的Web服务器.这是我的问题所在.

In my ViewModel I have a getAll() function that retrieves a list of strings from the database using Room. From there, I get the strings and call my Retrofit function to send each string individually to a web-server that returns an object. Here is where my issue occurs.

从我在网上看到的MVVM教程中，它们通常具有LiveData>样式，但是在这种情况下，因为我分别获取每个对象，所以它变成了List>，但是我认为这不是正确的做法，因为在我看来视图我需要做一个ForEach循环来观察列表中的每个LiveData对象.

From the MVVM tutorials I see online, they usually have the LiveData> style but in this since I am getting each object individually, it becomes List> but I don't think this is the correct way of doing it because in my View I would need to do a ForEach loop to observe each LiveData object in the list.

我尝试了其他解决方法，但似乎没有用.有更好的方法吗?

I have tried other work arounds but it doesn't seem to work. Is there a better way of doing this?

DAO

@Query("SELECT * FROM table")
    fun getAll(): LiveData<List<String>>

存储库

fun getAll(): LiveData<List<String>> {
        return dao.getAll()
    }

fun getRetrofitObject(s: String): LiveData<RetrofitObject> {
        api = jsonApi.getRetrofitObjectInfo(s, API_KEY)
        val retrofitObject: MutableLiveData<RetrofitObject> = MutableLiveData()
        api.enqueue(object : Callback<RetrofitObject> {
            override fun onFailure(call: Call<RetrofitObject>?, t: Throwable?) {
                Log.d("TEST", "Code: " + t.toString())
            }

            override fun onResponse(call: Call<RetrofitObject>?, response: Response<RetrofitObject>?) {
                if (response!!.isSuccessful) {
                    retrofitObject.value = response.body()
                }
            }
        })
        return retrofitObject
    }

MainActivityViewModel(ViewModel)

MainActivityViewModel (ViewModel)

var objectList ArrayList<LiveData<retrofitObject>> = ArrayList() 

// This is getting objects using Retrofit
fun getRetrofitObject(s: String): LiveData<retrofitObject> {
        return repo.getRetrofitObject(s)
    }

// This is getting all the strings from the internal database
fun getAll(): ArrayList<LiveData<retroFitObject>> {
        repo.getAll().value?.forEach {it ->
            objectList.add(getRetrofitObject(it)) //How else would I be able to do this?
        }
        return objectList
    }

MainActivity(视图)

MainActivity (View)

override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        mainActivityViewModel.getAll().forEach {
                        it.observe(this, Observer {it ->
                            mainActivityViewModel.objectList.add(it) //Here is part of the issue since I don't want to use a forloop in the View

                        })
                    }
                    adapter.objectList = mainActivityViewModel.objectList
                    recyclerView.adapter = adapter
}

谢谢，让我知道是否还有其他需要或困惑！

Thanks, let me know if there is anything else needed or confusion!

推荐答案

可能存在其他我不知道的方法.

There might be other methods exist I don't know about them.

但是您可以使用Transformations处理情况，以获取更多信息，请查看文档页面. Transformations.switchMap(LiveData触发器，功能> func)

But you can deal with situation using Transformations for more information please look at documentation page. Transformations.switchMap(LiveData trigger, Function> func)

您不必将实时数据观察器放入for循环中.

You don't have to put the live data observer inside for loop.

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