我已经在另一个stackoverflow帖子上搜索了2个小时，但仍然无法解决此问题。我在copyAudioListIqro活动类中有一个名为DetailMemilihIqro的变量，其列表字符串数据类型为。当AsyncTask类中的变量audioIqros（恰好在onPostExecute方法中）时，此列表具有json中的值，我想通过updateData方法（在asynctask类外部）将audioIqros变量复制到copyAudioListIqro。当我在updateData方法上看到日志监视器时，可以看到copyAudioListIqro中的值，但是问题是，当我通过readDataAudioURL方法（在asynctask类之外）访问它时，copyAudioListIqro变量变为null。
这个问题有什么解决方案？
谢谢
这是整体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
最佳答案
应该移动readDataAudioURL()调用，即普通的Log调用。实际上，任务本质上是异步的，因此很容易在任务开始后立即初始化变量copyAudioListIqro（.execute()方法）。
无论如何，您做得对，在未将数据集更改发布到列表中……您也应该将其移动到postExecute中。
我建议将所有“网络后”代码移至该postExecute，以便仅在可用数据时且不阻塞主线程的情况下，才可以异步更新UI。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();
}
}
一个更复杂的模式将包括广播接收器和意图，但是我想这超出了这个问题的范围。
关于java - 如何获取异步方法之外的列表的值？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/47537423/