java - 如何在类之间异步发送数据？

Question

我需要知道该怎么做？

我有两种观点

• ActivityMain.java
• 电影 Activity

在 MainActivity 中，我创建了一个从第二个 View 获取一些信息的 Intent :

 @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);

        CustomGridviewAdapter customGridviewAdapter = new CustomGridviewAdapter(filmList, getApplicationContext());
        simpleGrid.setAdapter(customGridviewAdapter);
        simpleGrid.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Intent intent = new Intent(getApplicationContext(), FilmActivity.class);
                intent.putExtra("FilmBoster", filmList.get(position).getBackdrop_path())
                        .putExtra("FilmImage", filmList.get(position).getPoster_path())
                        .putExtra("FilmName", filmList.get(position).getTitle())
                        .putExtra("FilmDate", filmList.get(position).getRelease_date())
                        .putExtra("FilmDisc", filmList.get(position).getOverview())
                        .putExtra("isFavFilm", filmList.get(position).getIsLiked());
                startActivityForResult(intent, 2);
            }
        });
    }

第二个 View :

 private void sendDataToMainActivity(String isPressed) {
    Intent intent = new Intent();
    intent.putExtra("isPressed" , isPressed);
    setResult(1 , intent);
    finish();
}

我在MainActivity中使用了AsyncTask。第二个 Activity 在 onActivityResult 中发送数据，但 ( onActivityResult ) 在 AsyncTask 之后执行，并且在 AsyncTask 中，我在 DB 上设置了一些数据。这样第二个Activity返回的数据就等于null。

一些有帮助的代码

 @NonNull
    private String convertToString(InputStream in) {
        String res = "";
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        StringBuilder sd = new StringBuilder();
        try {
            while ((res = reader.readLine()) != null) {
                sd.append(res).append("/n");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        parseString(sd.toString());
        db.userDao().updateFilmList(filmList);
        return sd.toString();
    }

  private void parseString(String json) {
        try {
            JSONObject jsonObject = new JSONObject(json);
            JSONArray jsonArray = jsonObject.getJSONArray("results");
            for (int i = 0; i < jsonArray.length(); i++) {
                JSONObject filmObject = jsonArray.getJSONObject(i);
                Film film = new Film(filmObject.getString("title")
                        ,filmObject.getString("overview")
                        , filmObject.getString("poster_path")
                        , filmObject.getString("release_date")
                        ,db.userDao().getIsFave());
                filmList.add(film);
            }

        } catch (JSONException e) {
            e.printStackTrace();
        }

    }

这是AsyncTask内部将数据保存到db的两个方法

如果我想将数据返回到AsyncTask并设置到DB上，该怎么办？

Answer 1

在 MainActivity 类的 onCreate 或 onResume 方法中执行以下操作:

    // filmList should be an empty array at this point
    CustomGridviewAdapter customGridviewAdapter = new CustomGridviewAdapter(filmList, getApplicationContext());
    simpleGrid.setAdapter(customGridviewAdapter);
    simpleGrid.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            Intent intent = new Intent(getApplicationContext(), FilmActivity.class);
            intent.putExtra("FilmBoster", filmList.get(position).getBackdrop_path())
                    .putExtra("FilmImage", filmList.get(position).getPoster_path())
                    .putExtra("FilmName", filmList.get(position).getTitle())
                    .putExtra("FilmDate", filmList.get(position).getRelease_date())
                    .putExtra("FilmDisc", filmList.get(position).getOverview())
                    .putExtra("isFavFilm", filmList.get(position).getIsLiked());
            startActivityForResult(intent, 2);
        }
    });

然后，在 postExecute 方法中，您只需执行以下操作(假设您已在异步任务中重新填充 filmList):

    CustomGridviewAdapter customGridviewAdapter = new CustomGridviewAdapter(filmList, getApplicationContext());
    simpleGrid.setAdapter(customGridviewAdapter);

onItemClicked 处理程序会将单击的项目发送到 FilmActivity.java 类 Activity 。在该 Activity 的 onCreate 中，您需要读取从 MainActivity 传递给它的数据:

 public void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);

 setContentView(R.layout.film_activity_layout); 

 FilmName = (String) getIntent().getExtra("FilmName");

 ...
 }

您需要显示 MainActivity 中的 onActivityResult 代码