android - 低估android studio中执行流程的问题

Question

以下代码使用改造和 youtubedata api 来获取两个 youtube channel 的订阅者数量。

public class NavigationActivity extends AppCompatActivity {


private static String GOOGLE_YOUTUBE_API_KEY = "AIzaSyBV4XQEZ9l1HZeBQFL6ZZvHYfMhtnqUkmw";
private static String CHANNEL_ID_TS = "UCq-Fj5jknLsUf-MWSy4_brA";
private static String CHANNEL_ID_PDP = "UC-lHJZR3Gqxm24_Vd_AJ5Yw";
public static int SUBS_TS = 0;
public static int SUBS_PDP = 0;

//?part=snippet%2CcontentDetails%2Cstatistics&id=UC_x5XG1OV2P6uZZ5FSM9Ttw&key=AIzaSyBV4XQEZ9l1HZeBQFL6ZZvHYfMhtnqUkmw

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_navigation);

    Map<String, String> qMap = new HashMap<>();
    qMap.put("part", "snippet,contentDetails,statistics");
    qMap.put("id", CHANNEL_ID_TS);
    qMap.put("key", GOOGLE_YOUTUBE_API_KEY);


    Map<String, String> qMap2 = new HashMap<>();
    qMap2.put("part", "snippet,contentDetails,statistics");
    qMap2.put("id", CHANNEL_ID_PDP);
    qMap2.put("key", GOOGLE_YOUTUBE_API_KEY);

    ApiInterface apiService = ApiClient.getClient().create(ApiInterface.class);

    Call<ChannelResponse> call = apiService.getSubs(qMap);

        call.enqueue(new Callback<ChannelResponse>() {
            @Override
            public void onResponse(Call<ChannelResponse> call, Response<ChannelResponse> response) {

                List<Channel> channels = response.body().getChannels();
                SUBS_TS = channels.get(0).getStatistics().getSubscriberCount();
                Log.d("GEEK", SUBS_TS + "");

            }

            @Override
            public void onFailure(Call<ChannelResponse> call, Throwable t) {
                Log.d("GEEK", t.toString());
            }
        });


        Call<ChannelResponse> call2 = apiService.getSubs(qMap2);
        call2.enqueue(new Callback<ChannelResponse>() {
            @Override
            public void onResponse(Call<ChannelResponse> call, Response<ChannelResponse> response) {

                List<Channel> channels = response.body().getChannels();
                SUBS_PDP = channels.get(0).getStatistics().getSubscriberCount();
                Log.d("GEEK", SUBS_PDP + "");

            }

            @Override
            public void onFailure(Call<ChannelResponse> call, Throwable t) {
                Log.d("GEEK", t.toString());
            }
        });

        //This statement seems to be executed before the SUSB_TS and SUSB_PDP variables are updated using the response. 
        Log.d("GEEK", SUBS_PDP + "AFTER");

}

为什么是

Log.d("GEEK", SUBS_PDP + "AFTER");

在 onResponse 方法之前执行的语句？

日志

2018-12-12 14:30:26.993 17518-17518/com.geek.wartube D/GEEK: 0AFTER
2018-12-12 14:30:27.863 17518-17518/com.geek.wartube D/GEEK: 76222082
2018-12-12 14:30:27.885 17518-17518/com.geek.wartube D/GEEK: 75161493

我还使用调试器检查过 onResponse 中的语句没有在最后一行的日志语句之前执行。

---

我应该怎么做才能达到预期的结果？

Answer 1

对 apiService.getSubs(qMap) 和 apiService.getSubs(qMap2) 方法的调用在后台线程中完成。这就是为什么在响应完成之前执行下一条语句的原因。因此声明 Log.d("GEEK", SUBS_PDP + "AFTER");在 onResponse() 方法之前执行

您可以在第一次调用的 onResponse() 中执行第二次调用，在第二次调用的 onResponse() 中执行您接下来想做的任何事情，或者如果可能的话使用 Rxjava。但是第一种方式很容易理解