android - 改造 - 如何在异步请求中发出同步请求

Question

我正在实现一个两级嵌套的 recyclerView 并且两个回收器 View 都使用 retrofit 进行 API 调用。这是发出同步请求的方法:

public void loadSectionStories(String sessionKey, CuratedSection section) {
    Call<JsonArray> subCall;
    subCall = TravelersApi.endpoint().getCuratedSectionTopics(sessionKey, section.id);

    try {
        Response<JsonArray> response = subCall.execute();
        if(response.code() != 200) {
            Toast.makeText(getApplicationContext(), "Cannot load page as of the moment.", Toast.LENGTH_SHORT).show();
            return;
        }
        JsonArray rawStories = response.body();
        if(rawStories.size() == 0) {
            //TODO: show placeholder
            return;
        }
        ArrayList<CuratedSectionItem> stories = new ArrayList<>();
        for(int i = 0; i < rawStories.size(); i++) {
            JsonObject jStories = rawStories.get(i).getAsJsonObject();
            JSONObject temp = new JSONObject(jStories.toString());
            JsonObject author = jStories.get("author").getAsJsonObject();
            CuratedSectionItem story = new CuratedSectionItem();
            story.title = jStories.get("title").getAsString();
            story.avatar = author.get("profile_photo").getAsString();
            story.displayPhoto = temp.getString("primary_photo");
            story.username = author.get("username").getAsString();
            story.description = jStories.get("content").getAsString();
            story.topicId = jStories.get("id").getAsString();
            story.postId = jStories.get("first_post_id").getAsString();
            story.hasReacted = false;
            story.upvotes = jStories.get("stats").getAsJsonObject().get("upvotes").getAsInt();
            stories.add(story);
        }
        section.stories = stories;
    } catch (IOException e) {
        Log.d("ERROR!", e.toString());
        e.printStackTrace();
    } catch (JSONException e) {
        e.printStackTrace();
    }
}

这是发出异步请求并在线程中调用 loadSectionStories 的方法:

public void loadCuratedSections(final int start, final int limit) {
    SharedPreferences prefs = getSharedPreferences("user_session", MODE_PRIVATE);
    final String sessionKey = prefs.getString("session_key", null);

    Call<JsonArray> call;
    call = TravelersApi.endpoint().getCuratedSections(sessionKey);

    call.enqueue(new Callback<JsonArray>() {
        @Override
        public void onResponse(Call<JsonArray> call, Response<JsonArray> response) {
            if(response.code() != 200) {
                Toast.makeText(getApplicationContext(), "Cannot load page as of the moment.", Toast.LENGTH_SHORT).show();
                return;
            }
            JsonArray rawSections = response.body();
            if(rawSections.size() == 0) {
                return;
            }
            for (int i = start; i < limit; i++) {
                JsonObject jSection = rawSections.get(i).getAsJsonObject();
                final CuratedSection section = new CuratedSection();
                section.id = jSection.get("id").getAsString();
                section.header = jSection.get("section_header").getAsString();
                section.isShown = jSection.get("is_shown").getAsBoolean();

                Thread thread = new Thread(new Runnable() {
                    @Override
                    public void run() {
                        loadSectionStories(sessionKey, section);
                    }
                });
                thread.start();
                curatedSections.add(section);
            }

        }

        @Override
        public void onFailure(Call<JsonArray> call, Throwable t) {
            Log.d("ERROR!", t.toString());
            t.printStackTrace();
        }
    });
}

除 section.stories 返回 null 外，一切正常。这对我来说没有意义，因为 loadSectionStories 中的这条语句 section.stories = stories。

Answer 1

如果您在同步请求完成(在新线程中运行)之前使用 section.stories，那么它将返回当前正在发生的 null。

所以如果你想在你的第一个异步请求完成后使用它，你必须删除新的线程流，

或者您必须在故事更新时重新加载回收站 View 。

还有你为什么在新线程中执行你的同步请求(loadSectionStories)，这不是类似于异步请求吗？