Not clear why error happened, is due to incorrect usage of AsyncTask?
I'm now developing an android calendar app. I want to have synchronize function which allow user can synchronize their data to server or vice verse.
When user open the app, it fetch data from server and update the new data to sqlite database on android device.
And whenever user create new data, it send this data to server to update to database on server.
I implemented my ideal like this.
1. MainActivity class to do sync action
public class MainActivity extends Activity {
DataSyncTask syncTask;
public void onCreate(Bundle savedInstanceState){
Button insertBt = (Button) findViewById(R.id.bt_insert);
// get data1
Data1 data1;
syncTask = new DataSyncTask(this);
syncTask.syncOnStart(data1);
insertBt.setOnClickListener(new OnClickListener(){
public void onClick(View v){
Data2 data2;
// get data2
syncTask.syncOnInsert(data2);
}
});
}
}
2. DataSyncTask to collect asyncTask
public class DataSyncTask {
Context mContext;
public DataSyncTask(Context context){
mContext = context;
}
private class SyncWhenStartTask extends AsyncTask<Data1, Integer, String>{
protected String doInBackground(Data1... data1s){
Object obj1 = ServerUtilities.sendDataForStep1(data1s[0]);
Data2 data2;
// Process Object
Object obj2 = ServerUtilities.sendDataToInsert(data2);
return "Success";
}
}
private class SyncWhenInsertTask extends AsyncTask<Data2, Integer, String>{
protected String doInBackground(Data2... datas){
Object obj2 = ServerUtilities.sendDataToInsert(datas[0]);
return "Success";
}
}
public void syncOnStart(Data1 data1){
new SyncWhenStartTask().execute(data1);
}
public void syncOnInsert(Data2 data2){
new SyncWhenInsertTask().execute(data2);
}
}
3. ServerUtilities class
public final class ServerUtilities {
static final String SERVER_URL = "http://172.2.100.99:8080";
public static String sendDataForStep1(Data1 data1) {
String url = SERVER_URL + "/sendDataForStep1";
ServerUtil<Data1, String> server = ServerUtil<Data1, String>();
return server.post(url, data1, String.class);
}
public static String sendDataToInsert(Data2 data2) {
String url = SERVER_URL + "/sendDataToInsert";
ServerUtil<Data2, String> server = ServerUtil<Data2, String>();
return server.post(url, data2, String.class);
}
private static class ServerUtil<T1, T2> {
public T2 post(String url, T1 obj, Class<T2> returnType) {
HttpHeaders requestHeaders = new HttpHeaders();
// Sending a JSON or XML object i.e. "application/json" or
// "application/xml"
requestHeaders.setContentType(MediaType.APPLICATION_JSON);
// Populate the Message object to serialize and headers in an
// HttpEntity object to use for the request
try {
HttpEntity<T1> requestEntity = new HttpEntity<T1>(
object, requestHeaders);
// Create a new RestTemplate instance
RestTemplate restTemplate = new RestTemplate(true);
// Make the network request, posting the message, expecting
// a list of SyncData in response from the server
ResponseEntity<T2> response = restTemplate
.exchange(url, HttpMethod.POST, requestEntity, returnType);
if(response != null) {
return response.getBody();
}
} catch (Exception e) {
Log.e(TAG + "-Exception", e.getMessage()); // Line 345 in logcat
}
return null;
}
}
}
When i start MainActivity, it connect to server, fetch data, update to sqlite database and send new data from device to server to update sucess, everything is ok. But when i create a new data, when execute syncTask.syncOnInsert(), it get Exception:
11-30 14:38:25.849: W/dalvikvm(14140): threadid=12: thread exiting with uncaught exception (group=0x40a13300)
11-30 14:38:25.869: E/AndroidRuntime(14140): FATAL EXCEPTION: AsyncTask #2
11-30 14:38:25.869: E/AndroidRuntime(14140): java.lang.RuntimeException: An error occured while executing doInBackground()
11-30 14:38:25.869: E/AndroidRuntime(14140): at android.os.AsyncTask$3.done(AsyncTask.java:299)
11-30 14:38:25.869: E/AndroidRuntime(14140): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
11-30 14:38:25.869: E/AndroidRuntime(14140): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
11-30 14:38:25.869: E/AndroidRuntime(14140): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
11-30 14:38:25.869: E/AndroidRuntime(14140): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
11-30 14:38:25.869: E/AndroidRuntime(14140): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
11-30 14:38:25.869: E/AndroidRuntime(14140): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
11-30 14:38:25.869: E/AndroidRuntime(14140): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
11-30 14:38:25.869: E/AndroidRuntime(14140): at java.lang.Thread.run(Thread.java:856)
11-30 14:38:25.869: E/AndroidRuntime(14140): Caused by: java.lang.NullPointerException: println needs a message
11-30 14:38:25.869: E/AndroidRuntime(14140): at android.util.Log.println_native(Native Method)
11-30 14:38:25.869: E/AndroidRuntime(14140): at android.util.Log.e(Log.java:231)
11-30 14:38:25.869: E/AndroidRuntime(14140): at vn.com.bip.office.smart.form.ServerUtilities$ServerUtil.post(ServerUtilities.java:345)
11-30 14:38:25.869: E/AndroidRuntime(14140): at vn.com.bip.office.smart.form.ServerUtilities.sendSyncData(ServerUtilities.java:283)
11-30 14:38:25.869: E/AndroidRuntime(14140): at vn.com.bip.office.smart.util.DataSyncTask$SyncWhenChangeOnScheduleTask.doInBackground(DataSyncTask.java:158)
11-30 14:38:25.869: E/AndroidRuntime(14140): at vn.com.bip.office.smart.util.DataSyncTask$SyncWhenChangeOnScheduleTask.doInBackground(DataSyncTask.java:1)
11-30 14:38:25.869: E/AndroidRuntime(14140): at android.os.AsyncTask$2.call(AsyncTask.java:287)
11-30 14:38:25.869: E/AndroidRuntime(14140): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
11-30 14:38:25.869: E/AndroidRuntime(14140): ... 5 more
Can anyone explain me why this happen and teach me how to resolve this error.
Thanks in advance!
