引用庫：

    //Retrofit
    implementation "com.squareup.retrofit2:retrofit:2.4.0"
    //Gson converter
    implementation "com.squareup.retrofit2:converter-gson:2.3.0"
    //String
    implementation "com.squareup.retrofit2:converter-scalars:2.3.0"
    //okhttp
    implementation "com.squareup.okhttp3:okhttp:3.10.0"
    implementation "com.squareup.okhttp3:logging-interceptor:3.8.0"
    //Rxjava
    implementation "com.squareup.retrofit2:adapter-rxjava2:2.4.0"
    //Rxjava2
    implementation "io.reactivex.rxjava2:rxandroid:2.0.2"
    implementation "io.reactivex.rxjava2:rxjava:2.1.9"

創(chuàng)建服務(wù)接口

interface WikiApiService{
    @GET("api.php")
    fun hitCountCheck(@QueryMap options:Map<String,String>):Observable
    //an Observable, which is a Rxjava object that could analog as the endpoint fetcher result generator.
    companion object{
        fun create() :WikiApiService{
            val retrofit = Retrofit.Builder()
                .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                .addConverterFactory(GsonConverterFactory.create())
                .baseUrl("https://en.wikipedia.org/w/")
                .build()
            return retrofit.create(WikiApiService::class.java)
        }
    }
}

由于需要query的變量有些多，所以使用QueryMap來統(tǒng)一管理變量，在activity中定義HashMap。其中Observable返回的是一個object,是我們自己定義的獲取數(shù)據(jù)類，因為我們想獲取類似這種數(shù)據(jù)：

{
 batchcomplete: "",
 continue: {
  sroffset: 10,
  continue: "-||"
 },
 query: {
  searchinfo: {
   totalhits: 16776   //target data
 },
 search: [...

創(chuàng)建數(shù)據(jù)索引對象

其中totalhits是我們想獲取的數(shù)據(jù)，我們需要results -> query -> searchinfo -> totalhits ，所以我們需要創(chuàng)建一個新的object來存放數(shù)據(jù)索引：

object Model {
    data class Result(val query: Query)
    data class Query(val searchinfo: SearchInfo)
    data class SearchInfo(val totalhits: Int)
}

在Activity中使用懶加載來創(chuàng)建observable實例并創(chuàng)建可取消的disposable:

private var disposable: Disposable);null   // disposable is a cancelable object
private val wikiApiServe by lazy {
    WikiApiService.create()
}

然后創(chuàng)建功能函數(shù)：

@SuppressLint("SetTextI18n")
private fun beginSearch(srsearch : String){
    val options = HashMap()
    options["action"] = "query"
    options["format"] = "json"
    options["list"] = "search"
    options["srsearch"] = srsearch
    //Scheduler: Thread control
    disposable = wikiApiServe.hitCountCheck(options)
        .subscribeOn(Schedulers.io())  //subscribeOn(): choose a Thread to produce  I/O scheduler:（read&write data、read&write db、change info on the Internet）
        .observeOn(AndroidSchedulers.mainThread())  //observeOn(): choose a Thread to spend  AndroidSchedulers.mainThread()，on Android UI(main Thread)
        .subscribe(
            { result -> show_result.text = "${result.query.searchinfo.totalhits} results found"},
            { error -> Toast.makeText(this, error.message, Toast.LENGTH_LONG).show()}
        )
}

在需要獲取的edit text中使用這個功能函數(shù)就可以獲得該搜索詞條在wiki百科中的數(shù)目。

get_result.setOnClickListener {
    val text = edit_text.text.toString()
    if (edit_text.text.toString().isNotEmpty()){
        Toast.makeText(this, edit_text.text.toString(), Toast.LENGTH_LONG).show()
        beginSearch(text)
    }
}

在分線程中無法改變UI，也就是說必須在UI線程（AndroidSchedulers.MainThrea()）中才能改變UI布局。

創(chuàng)建接口服務(wù)的方法可以在interface中創(chuàng)建，也可以在Activity中創(chuàng)建，在interface中需要使用companion object，然后在Activity中實例化。