java - 如何在异步方法之外获取列表的值？

Question

我已经在另一个stackoverflow帖子上搜索了2个小时，但仍然无法解决这个问题。我在 DetailMemilihIqro Activity 类中有一个名为 copyAudioListIqro 的变量，其数据类型为 List String。当 AsyncTask 类中名为 audioIqros 的变量(恰好在 onPostExecute 方法中)此列表具有来 self 的 json 的值 并且我想复制 audioIqros 变量到 copyAudioListIqro 通过 updateData 方法(在 asynctask 类之外)。当我在 updateData 方法上看到日志监视器时，我可以看到来自 copyAudioListIqro 的值，但问题是，当我通过 readDataAudioURL 方法(在 asynctask 之外)访问它时class) copyAudioListIqro 变量变为空。

这个问题的解决方案是什么？谢谢

这是整体的 DetailMemilihIqro 类

public class DetailMemilhIqro extends AppCompatActivity {

    private ProgressDialog pDialog;
    private List<ModelAudioIqro> audioIqros;
    private List<String> copyAudioListIqro;
    private AudioAdapter mAdapter;
    private RecyclerView recyclerView;
    private String TAG = DetailMemilihIqro.class.getSimpleName();
    Context context;


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

        recyclerView = (RecyclerView) findViewById(R.id.rvCVAudioIqro);
        pDialog = new ProgressDialog(this);
        audioIqros = new ArrayList<>();
        mAdapter = new AudioAdapter(getApplicationContext(), audioIqros);
        context = getApplicationContext();
        copyAudioListIqro = new ArrayList<>();


        recyclerView.setLayoutManager(new LinearLayoutManager(context));
        recyclerView.setItemAnimator(new DefaultItemAnimator());
        recyclerView.setAdapter(mAdapter);

        Bundle getPosition = getIntent().getExtras();
        int position = getPosition.getInt("positionUserClicked");
        Log.d(TAG, "Position User clicked " + position);

        if (position == 0) {
            String endpoint = "http://latihcoding.com/jsonfile/audioiqro1.json";

            new DownloadTask().execute(endpoint);


        } else if (position == 1) {
            String endpoint = "http://latihcoding.com/jsonfile/audioiqro2.json";
            new DownloadTask().execute(endpoint);


        } else if (position == 2) {
            String endpoint = "http://latihcoding.com/jsonfile/audioiqro3.json";
            new DownloadTask().execute(endpoint);

        }

        readDataAudioURL();

    }

    public void updateData(List<String> pathUrl) {

        for (int i = 0; i < pathUrl.size(); i++) copyAudioListIqro.add(pathUrl.get(i));
        Log.d(TAG, "updateData Method " + copyAudioListIqro.toString());

    }

    public void readDataAudioURL() {
        Log.d(TAG, "readDataAudioURL Method " + copyAudioListIqro.toString());
    }

    public class DownloadTask extends AsyncTask<String, Void, List<String>> {

        List<String> modelAudioIqroList;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog.setMessage("Downloading json...");
            pDialog.show();
        }

        @Override
        protected List<String> doInBackground(String... strings) {
            modelAudioIqroList = new ArrayList<>();
            int result;
            HttpURLConnection urlConnection;
            try {
                URL url = new URL(strings[0]);
                urlConnection = (HttpURLConnection) url.openConnection();
                int statusCode = urlConnection.getResponseCode();

                // 200 represents HTTP OK
                if (statusCode == 200) {
                    BufferedReader r = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
                    StringBuilder response = new StringBuilder();
                    String line;
                    while ((line = r.readLine()) != null) {
                        response.append(line);
                    }
                    parseResult(response.toString());
                    result = 1; // Successful
                    Log.d(TAG, "Result " + result);

                } else {
                    //"Failed to fetch data!";
                    result = 0;
                    Log.d(TAG, "Result " + result);
                }
            } catch (Exception e) {
                Log.d(TAG, e.getLocalizedMessage());
            }
            return modelAudioIqroList; //"Failed to fetch data!";

        }

        @Override
        protected void onPostExecute(List<String> audioIqros) {
            super.onPostExecute(audioIqros);
            pDialog.hide();
            if (!audioIqros.isEmpty()) {
                updateData(modelAudioIqroList);
            } else {
                Toast.makeText(context, "Empty", Toast.LENGTH_SHORT).show();
            }
        }

        private void parseResult(String result) {
            try {
                JSONArray response = new JSONArray(result);

                for (int i = 0; i < response.length(); i++) {
                    JSONObject object = response.getJSONObject(i);
                    ModelAudioIqro modelAudioIqro = new ModelAudioIqro();
                    modelAudioIqro.setName(object.getString("name"));
                    modelAudioIqro.setUrl(object.getString("url"));
                    String path = modelAudioIqro.getUrl();
                    Log.d(TAG, "String path " + path);

                    modelAudioIqroList.add(path);
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

            mAdapter.notifyDataSetChanged();
        }

    }

}

Log for the copyAudioListIqro in the updateDataMethod

Log for the copyAudioListIqro in the readDataAudioURL

Answer 1

readDataAudioURL() 调用，这是一个普通的 Log 调用，应该被移动。事实上，任务本质上是异步的，所以变量copyAudioListIqro不会在任务开始后立即初始化(.execute()方法)。

无论如何，您做对了，在 notyfiying 数据集更改为列表中...您也应该将其移动到 postExecute...

我建议将所有“after network”代码移动到 postExecute，这样 UI 就可以仅在数据可用时异步更新，而不会阻塞主线程。您可以在内部类中“读取”变量，因此只需将它们声明为 final:

@Override
    protected void onPostExecute(List<String> audioIqros) {
        super.onPostExecute(audioIqros);
        pDialog.hide();
        if (!audioIqros.isEmpty()) {
            updateData(modelAudioIqroList);
            //data is now updated, notify datasets and/or send broadcast
            mAdapter.notifyDataSetChanged();
            readDataAudioURL();
        } else {
            Toast.makeText(context, "Empty", Toast.LENGTH_SHORT).show();
        }

    }

更详细的模式将包括广播接收器和 Intent ，但我想这超出了这个问题的范围。