我似乎无法解决我遇到的这个问题。在我的MainActivity中，我正在将我的设备的应用程序数据库与我的后端数据库同步到几个Asynctasks中，每个表一个。由于我有很多不同的表，我在AsyncTask上有一个常规设置，并传入一个参数来确定要同步的表：
protected void onResume() {
if(isOnline()){
new loadFromBackendAndPlaceInDB().execute(new Integer[]{ FORENINGAR });
new loadFromBackendAndPlaceInDB().execute(new Integer[]{ INFO });
new loadFromBackendAndPlaceInDB().execute(new Integer[]{ KALENDER });
new loadFromBackendAndPlaceInDB().execute(new Integer[]{ KAMPEN });
new loadFromBackendAndPlaceInDB().execute(new Integer[]{ KARTA });
new loadFromBackendAndPlaceInDB().execute(new Integer[]{ KONTAKT });
new loadFromBackendAndPlaceInDB().execute(new Integer[]{ MEDDELANDEN });
new loadFromBackendAndPlaceInDB().execute(new Integer[]{ OVRIGINFO });
new loadFromBackendAndPlaceInDB().execute(new Integer[]{ SANGBOK });
}
}
实际的AsyncTask看起来像这样：
class loadFromBackendAndPlaceInDB extends AsyncTask<Integer, String, String> {
protected String doInBackground(Integer... params) {
int activity = params[0];
String url = urlList.get(activity);
String json = null;
try {
URL urlObject = new URL(url);
HttpURLConnection con = (HttpURLConnection) urlObject.openConnection();
con.setConnectTimeout(15000);
con.setReadTimeout(15000);
json = readStream(con.getInputStream());
} catch (Exception e) {
e.printStackTrace();
}
if(json != null){
JSONObject jObj = null;
try {
// THIS IS WHERE I'M STARTING GETTING A PROBLEM
// LINE 536
jObj = new JSONObject(json);
} catch (JSONException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
try {
// THIS IS WHERE THE RUNTIME ERROR OCCURS BECAUSE OF THE PROBLEM AT ROW 536
// LINE 546
int success = jObj.getInt(TAG_SUCCESS);
if (success == 1) {
JSONArray jsonArray = null;
jsonArray = jObj.getJSONArray(getActivityTag(activity));
getContentResolver().delete(getContentUri(activity), null, null);
for (int i = 0; i < jsonArray.length(); i++) {
JSONObject c = jsonArray.getJSONObject(i);
ContentValues values = new ContentValues();
for(int k = 0; k < getColumns(activity).size(); k++){
String TAG = getTags(activity).get(k);
String VALUE = c.getString(TAG);
String COLUMN = getColumns(activity).get(k);
values.put(COLUMN, VALUE);
}
getContentResolver().insert(getContentUri(activity), values);
}
} else {
Log.d("No Success", getActivityTag(activity));
}
} catch (JSONException e) {
e.printStackTrace();
}
}else{
}
return null;
}
protected void onPostExecute(String result) {
super.onPostExecute(result);
}
}
AsyncTask中使用的方法readStream：
private String readStream(InputStream in) {
BufferedReader reader = null;
StringBuilder sb = null;
String json = "";
try {
reader = new BufferedReader(new InputStreamReader(in));
sb = new StringBuilder();
String line = "";
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
in.close();
json = sb.toString();
} catch (IOException e) {
e.printStackTrace();
}
}
}
return json;
}
这是我的LogCat：
06-25 18:43:18.089: W/System.err(3942): org.json.JSONException: End of input at character 0 of
06-25 18:43:18.113: W/System.err(3942): at org.json.JSONTokener.syntaxError(JSONTokener.java:446)
06-25 18:43:18.113: W/System.err(3942): at org.json.JSONTokener.nextValue(JSONTokener.java:93)
06-25 18:43:18.113: W/System.err(3942): at org.json.JSONObject.<init>(JSONObject.java:154)
06-25 18:43:18.113: W/System.err(3942): at org.json.JSONObject.<init>(JSONObject.java:171)
06-25 18:43:18.113: W/System.err(3942): at se.nollekollen.main.MainActivity$loadFromBackendAndPlaceInDB.doInBackground(MainActivity.java:536)
06-25 18:43:18.113: W/System.err(3942): at se.nollekollen.main.MainActivity$loadFromBackendAndPlaceInDB.doInBackground(MainActivity.java:1)
06-25 18:43:18.113: W/System.err(3942): at android.os.AsyncTask$2.call(AsyncTask.java:185)
06-25 18:43:18.113: W/System.err(3942): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
06-25 18:43:18.117: W/System.err(3942): at java.util.concurrent.FutureTask.run(FutureTask.java:138)
06-25 18:43:18.117: W/System.err(3942): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
06-25 18:43:18.117: W/System.err(3942): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
06-25 18:43:18.117: W/System.err(3942): at java.lang.Thread.run(Thread.java:1019)
06-25 18:43:18.121: W/dalvikvm(3942): threadid=13: thread exiting with uncaught exception (group=0x40015578)
06-25 18:43:18.125: E/AndroidRuntime(3942): FATAL EXCEPTION: AsyncTask #5
06-25 18:43:18.125: E/AndroidRuntime(3942): java.lang.RuntimeException: An error occured while executing doInBackground()
06-25 18:43:18.125: E/AndroidRuntime(3942): at android.os.AsyncTask$3.done(AsyncTask.java:200)
06-25 18:43:18.125: E/AndroidRuntime(3942): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
06-25 18:43:18.125: E/AndroidRuntime(3942): at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
06-25 18:43:18.125: E/AndroidRuntime(3942): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
06-25 18:43:18.125: E/AndroidRuntime(3942): at java.util.concurrent.FutureTask.run(FutureTask.java:138)
06-25 18:43:18.125: E/AndroidRuntime(3942): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
06-25 18:43:18.125: E/AndroidRuntime(3942): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
06-25 18:43:18.125: E/AndroidRuntime(3942): at java.lang.Thread.run(Thread.java:1019)
06-25 18:43:18.125: E/AndroidRuntime(3942): Caused by: java.lang.NullPointerException
06-25 18:43:18.125: E/AndroidRuntime(3942): at se.nollekollen.main.MainActivity$loadFromBackendAndPlaceInDB.doInBackground(MainActivity.java:546)
06-25 18:43:18.125: E/AndroidRuntime(3942): at se.nollekollen.main.MainActivity$loadFromBackendAndPlaceInDB.doInBackground(MainActivity.java:1)
06-25 18:43:18.125: E/AndroidRuntime(3942): at android.os.AsyncTask$2.call(AsyncTask.java:185)
06-25 18:43:18.125: E/AndroidRuntime(3942): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
06-25 18:43:18.125: E/AndroidRuntime(3942): ... 4 more
似乎问题从第536行开始，然后在第546行导致最终的运行时错误。
错误有时只会发生，有时候很好。当我快速进入MainActivity并进入MainActivity时，它似乎就会出现 - 当我在整个应用程序中导航更慢时，它通常很好。
发生了什么，为什么会出现这种错误，解决方案是什么？感谢所有答案！
答案 0 :(得分：0)
我遇到了多个AsyncTask互相破坏的问题（虽然我的代码中没有看到任何明显的错误）。
我通常的解决方案是在IntentService中进行这样的操作，并通过广播意图将更新传达给Activity。
这意味着我在Activity中保留一个BroadcastReceiver来捕获意图并更新UI。
祝你好运。答案 1 :(得分：0)
而不是触发多个AsyncTask，为什么不只是将所有值作为参数发送到单个interger数组，并且在AsyncTask内部实现for循环以逐个循环遍历整数数组条目。