Sorry for asking this but I recently started develop android and new to Java.
Currently I am able to "Toast" onPostExecute results in "BackgroundWorkerLocation.java". What I need is to somehow pass these results back to "MainActivty.java" from where I execute this class.
MainActivity.java
String type = "get_location";
String tLatitude = String.valueOf(latitude);
String tLongitude = String.valueOf(longitude);
BackgroundWorkerLocation backgroundWorkerLocation = new BackgroundWorkerLocation(getApplicationContext());
backgroundWorkerLocation.execute(type, tLatitude, tLongitude);
// I need "Results" here
BackgroundWorkerLocation.java
public class BackgroundWorkerLocation extends AsyncTask<String,Void,String> {
Context context;
BackgroundWorkerLocation(Context ctx){
context = ctx;
}
#Override
protected String doInBackground(String... params) {
// Some background work
}
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
// Currently I am able to Toast "RESULT" here
}
#Override
protected void onProgressUpdate(Void... values) {
super.onProgressUpdate(values);
}
}
You'll need to create an interface that you can use as a callback:
interface MyCallback {
void onResult(String result);
}
In your activity you create an anonymous implementation of this callback.
Pass it into your ASyncTask.
String type = "get_location";
String tLatitude = String.valueOf(latitude);
String tLongitude = String.valueOf(longitude);
BackgroundWorkerLocation backgroundWorkerLocation = new BackgroundWorkerLocation(getApplicationContext(), new MyCallback() {
#Override
public void onResult(String result) {
// I need "Results" here
}
});
backgroundWorkerLocation.execute(type, tLatitude, tLongitude);
When the ASyncTask completes, you call the "onResult" method of the callback.
public class BackgroundWorkerLocation extends AsyncTask<String,Void,String> {
Context context;
private final MyCallback myCallback;
BackgroundWorkerLocation(Context ctx, MyCallback myCallback){
context = ctx;
this.myCallback = myCallback;
}
#Override
protected String doInBackground(String... params) {
// Some background work
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
// Currently I am able to Toast "RESULT" here
myCallback.onResult(result);
}
}
This is how you can share data between two classes.
Note that because the callback implementation is anonymous, it has a reference to your Activity, therefore if your task lives longer than your activity it can cause a memory leak. (your next problem :-))
i have a main activity.
from this activity i call a method from another public class.
in the main activity i call this method like this:
// Background Task
new Sync.SyncMYSQL().execute();
is there an way to start in intent (out of the main activity) if the called method is finish ?
public class Sync {
static class SyncMYSQL extends AsyncTask<String, String, String> {
#Override
protected String doInBackground(String... params) {
// DO SOMETHING
return null;
}
protected void onPostExecute(String result) {
// DO SOMETHING
}
}
}
YES ,
In your asyncTask Class you can override onPostExecute method and write your activity start code there
As it executes after doInBackground method :)
Inside your post execute pre-initialize all possible Intents and handle with a switch or if else
Sample
public class Sync {
static class SyncMYSQL extends AsyncTask<String, String, String> {
int type;
public SyncMYSQL(int intentType){
type=intentType;
}
#Override
protected String doInBackground(String... params) {
// DO SOMETHING
return null;
}
protected void onPostExecute(String result) {
switch(type){
case 0: Intent in=new Intent(context,destinationActivity1);
startActivity(in);
break;
case 1: Intent in=new Intent(context,destinationActivity2);
startActivity(in);
break;
}
}
}
}
call this async task like this
new Sync.SyncMYSQL(<integer_value>).execute();
Use interface for doing this task like.
1> Create interface
public interface AsyncTaskListener {
public void onHttpResponse(String callResponse);
public void onError(String error, int pageId);
}
2> Than on Async Activity use this
AsyncTaskListener listener;
private void sendResponse(String response) {
if (listener != null) {
listener.onResponse(response);
}
}
And use sendResponse method on AsyncTask OnPost and on response String enter "Success" and After this implement the interface to your first activity and and check if response is "Success" than pass the intent.
I have asyncTask class:
public class DownloadJar {
public DownloadJar(String serialnum)
{
if (serialnum!=null)
{
this.serialnum = serialnum;
new Download().execute();
}
}
private class Download extends AsyncTask<String, Integer, String>
{
#Override
protected String doInBackground(String... params) {
//Downloading stuff
return null;
}
#Override
protected void onProgressUpdate(Integer... values) {
//Need to notify main class
super.onProgressUpdate(values);
}
}
}
I activate it via main class:
public class FTPDownload extends Activity{
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_ftpdownload);
Bundle extras = getIntent().getExtras();
if (extras != null)
{
serialnum = extras.getString("serialnum");
}
if (serialnum!=null)
{
DownloadJar dj = new DownloadJar(serialnum);
}
}
}
How can I create callback from the DownloadJar to notify my main class about the progress?
If you need onProgressUpdate() inside your main class, override it there. like,
DownloadJar dj = new DownloadJar(serialnum){
#Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
}
};
Pass a handler created in the activity along with the serialnumString in the constructor of the DownloadJar Async and call it like this from your onProgressUpdate:
handler.sendEmptyMessage(0);
where you can pass data through messages from your AsyncTask, you can receive the events in your Activity like this
handler = new Handler() {
#Override
public void handleMessage(Message msg) {
//do something
}
};
For further info: http://www.vogella.com/articles/AndroidBackgroundProcessing/article.html
You can create interface ie:
interface UpdateProgress {
void progressUpdate(String s)
}
make your class FTPDownload (its your main class?) implement it. Then when creating DownloadJar, pass reference to your activity to it. Then you can call in onProgressUpdate from your DownloadJar.Download asynctask progressUpdate on main activity. You must remember to update this reference on configuration changes.
If on the other hand DownloadJar is your main class, then you already have access to it, your asynctask is internal to it.
you have make Interface so that you can set data in that interface method from onPostExecute method of AsyncTask. and pass interface method as Anonymous inner class as like onClickListner.
here you can find nice explanation.
I have a requirement where i need to parse the content of a URL in JSON format. I am able to do that successfully. But i need to save the contents of the URL in a array list and pass them back to the calling functions. Below is the code snippet of what i am trying to achieve.
#Override
protected ArrayList<String> onPostExecute(String result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
dialog.dismiss();
return ar; // ar is the arraylist i have created and updated it with the content of the url.
}
But running this gives an error. Can anyone please suggest how i can make this possible. However, when i make the return type of onPostExecute as void and toast the contents, its displaying properly. When i call this after the execute, its returning null even though i have updated the contents in doinbackground(). Hence i am unable to get the return values on arraylist format.
// Calling function
Myadapter.execute();
ArrayList<string> str = new ArrayList<string>();
str = print();
// Here str is getting null
// Called function
public ArrayList<String> print() {
ArrayList<String> names = new ArrayList<String>();
for(int i=0;i<al.size();i++)
{
names.add(al.get(i).getConstituencyName());
}
return names;
}
Use a handler
In your activity
mHandler = new Handler() {
#Override public void handleMessage(Message msg) {
ArrayList s=(ArrayList)msg.obj;
tv.setText("Result = "+s.get(0));
}
};
In your onPostexecute
Message msg=new Message();
msg.obj=ar;
mHandler.sendMessage(msg);
The proper way would be to let your activity implement an interface, and when you instantiate the AsyncTask pass the current activity as a parameter to the constructor. Then in onPostExecute() invoke the callback method defined in the Activity and pass the json result as an argument.
Something like this:
interface OnTaskFinished {
void onTaskFinished(String result);
}
public class MainActivity extends Activity implements OnTaskFinished {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// ....
new MyAsyncTask(this).execute();
}
#Override
public void onTaskFinished(String result) {
// Process the json result here how you need.
}
}
And this is how the scheleton of your AsyncTask should look like:
private class MyAsyncTask extends AsyncTask<Void, Void, String> {
private final OnTaskFinished listener;
public MyAsyncTask(OnTaskFinished listener) {
this.listener = listener;
}
// ...
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
listener.onTaskFinished(result);
}
}
I have this two classes. My main Activity and the one that extends the AsyncTask, Now in my main Activity I need to get the result from the OnPostExecute() in the AsyncTask. How can I pass or get the result to my main Activity?
Here is the sample codes.
My main Activity.
public class MainActivity extends Activity{
AasyncTask asyncTask = new AasyncTask();
#Override
public void onCreate(Bundle aBundle) {
super.onCreate(aBundle);
//Calling the AsyncTask class to start to execute.
asyncTask.execute(a.targetServer);
//Creating a TextView.
TextView displayUI = asyncTask.dataDisplay;
displayUI = new TextView(this);
this.setContentView(tTextView);
}
}
This is the AsyncTask class
public class AasyncTask extends AsyncTask<String, Void, String> {
TextView dataDisplay; //store the data
String soapAction = "http://sample.com"; //SOAPAction header line.
String targetServer = "https://sampletargeturl.com"; //Target Server.
//SOAP Request.
String soapRequest = "<sample XML request>";
#Override
protected String doInBackground(String... string) {
String responseStorage = null; //storage of the response
try {
//Uses URL and HttpURLConnection for server connection.
URL targetURL = new URL(targetServer);
HttpURLConnection httpCon = (HttpURLConnection) targetURL.openConnection();
httpCon.setDoOutput(true);
httpCon.setDoInput(true);
httpCon.setUseCaches(false);
httpCon.setChunkedStreamingMode(0);
//properties of SOAPAction header
httpCon.addRequestProperty("SOAPAction", soapAction);
httpCon.addRequestProperty("Content-Type", "text/xml; charset=utf-8");
httpCon.addRequestProperty("Content-Length", "" + soapRequest.length());
httpCon.setRequestMethod(HttpPost.METHOD_NAME);
//sending request to the server.
OutputStream outputStream = httpCon.getOutputStream();
Writer writer = new OutputStreamWriter(outputStream);
writer.write(soapRequest);
writer.flush();
writer.close();
//getting the response from the server
InputStream inputStream = httpCon.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
ByteArrayBuffer byteArrayBuffer = new ByteArrayBuffer(50);
int intResponse = httpCon.getResponseCode();
while ((intResponse = bufferedReader.read()) != -1) {
byteArrayBuffer.append(intResponse);
}
responseStorage = new String(byteArrayBuffer.toByteArray());
} catch (Exception aException) {
responseStorage = aException.getMessage();
}
return responseStorage;
}
protected void onPostExecute(String result) {
aTextView.setText(result);
}
}
Easy:
Create interface class, where String output is optional, or can be whatever variables you want to return.
public interface AsyncResponse {
void processFinish(String output);
}
Go to your AsyncTask class, and declare interface AsyncResponse as a field :
public class MyAsyncTask extends AsyncTask<Void, Void, String> {
public AsyncResponse delegate = null;
#Override
protected void onPostExecute(String result) {
delegate.processFinish(result);
}
}
In your main Activity you need to implements interface AsyncResponse.
public class MainActivity implements AsyncResponse{
MyAsyncTask asyncTask =new MyAsyncTask();
#Override
public void onCreate(Bundle savedInstanceState) {
//this to set delegate/listener back to this class
asyncTask.delegate = this;
//execute the async task
asyncTask.execute();
}
//this override the implemented method from asyncTask
#Override
void processFinish(String output){
//Here you will receive the result fired from async class
//of onPostExecute(result) method.
}
}
UPDATE
I didn't know this is such a favourite to many of you. So here's the simple and convenience way to use interface.
still using same interface. FYI, you may combine this into AsyncTask class.
in AsyncTask class :
public class MyAsyncTask extends AsyncTask<Void, Void, String> {
// you may separate this or combined to caller class.
public interface AsyncResponse {
void processFinish(String output);
}
public AsyncResponse delegate = null;
public MyAsyncTask(AsyncResponse delegate){
this.delegate = delegate;
}
#Override
protected void onPostExecute(String result) {
delegate.processFinish(result);
}
}
do this in your Activity class
public class MainActivity extends Activity {
MyAsyncTask asyncTask = new MyAsyncTask(new AsyncResponse(){
#Override
void processFinish(String output){
//Here you will receive the result fired from async class
//of onPostExecute(result) method.
}
}).execute();
}
Or, implementing the interface on the Activity again
public class MainActivity extends Activity
implements AsyncResponse{
#Override
public void onCreate(Bundle savedInstanceState) {
//execute the async task
new MyAsyncTask(this).execute();
}
//this override the implemented method from AsyncResponse
#Override
void processFinish(String output){
//Here you will receive the result fired from async class
//of onPostExecute(result) method.
}
}
As you can see 2 solutions above, the first and third one, it needs to create method processFinish, the other one, the method is inside the caller parameter. The third is more neat because there is no nested anonymous class.
Tip: Change String output, String response, and String result to different matching types in order to get different objects.
There are a few options:
Nest the AsyncTask class within your Activity class. Assuming you don't use the same task in multiple activities, this is the easiest way. All your code stays the same, you just move the existing task class to be a nested class inside your activity's class.
public class MyActivity extends Activity {
// existing Activity code
...
private class MyAsyncTask extends AsyncTask<String, Void, String> {
// existing AsyncTask code
...
}
}
Create a custom constructor for your AsyncTask that takes a reference to your Activity. You would instantiate the task with something like new MyAsyncTask(this).execute(param1, param2).
public class MyAsyncTask extends AsyncTask<String, Void, String> {
private Activity activity;
public MyAsyncTask(Activity activity) {
this.activity = activity;
}
// existing AsyncTask code
...
}
You can try this code in your Main class.
That worked for me, but i have implemented methods in other way
try {
String receivedData = new AsyncTask().execute("http://yourdomain.com/yourscript.php").get();
}
catch (ExecutionException | InterruptedException ei) {
ei.printStackTrace();
}
I felt the below approach is very easy.
I have declared an interface for callback
public interface AsyncResponse {
void processFinish(Object output);
}
Then created asynchronous Task for responding all type of parallel requests
public class MyAsyncTask extends AsyncTask<Object, Object, Object> {
public AsyncResponse delegate = null;//Call back interface
public MyAsyncTask(AsyncResponse asyncResponse) {
delegate = asyncResponse;//Assigning call back interfacethrough constructor
}
#Override
protected Object doInBackground(Object... params) {
//My Background tasks are written here
return {resutl Object}
}
#Override
protected void onPostExecute(Object result) {
delegate.processFinish(result);
}
}
Then Called the asynchronous task when clicking a button in activity Class.
public class MainActivity extends Activity{
#Override
public void onCreate(Bundle savedInstanceState) {
Button mbtnPress = (Button) findViewById(R.id.btnPress);
mbtnPress.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
MyAsyncTask asyncTask =new MyAsyncTask(new AsyncResponse() {
#Override
public void processFinish(Object output) {
Log.d("Response From Asynchronous task:", (String) output);
mbtnPress.setText((String) output);
}
});
asyncTask.execute(new Object[] { "Your request to aynchronous task class is giving here.." });
}
});
}
}
Thanks
This answer might be late but I would like to mention few things when your Activity dependent on AsyncTask. That would help you in prevent crashes and memory management. As already mentioned in above answers go with interface, we also say them callbacks. They will work as an informer, but never ever send strong reference of Activity or interface always use weak reference in those cases.
Please refer to below screenshot to findout how that can cause issues.
As you can see if we started AsyncTask with a strong reference then there is no guarantee that our Activity/Fragment will be alive till we get data, so it would be better to use WeakReference in those cases and that will also help in memory management as we will never hold the strong reference of our Activity then it will be eligible for garbage collection after its distortion.
Check below code snippet to find out how to use awesome WeakReference -
MyTaskInformer.java Interface which will work as an informer.
public interface MyTaskInformer {
void onTaskDone(String output);
}
MySmallAsyncTask.java AsyncTask to do long running task, which will use WeakReference.
public class MySmallAsyncTask extends AsyncTask<String, Void, String> {
// ***** Hold weak reference *****
private WeakReference<MyTaskInformer> mCallBack;
public MySmallAsyncTask(MyTaskInformer callback) {
this.mCallBack = new WeakReference<>(callback);
}
#Override
protected String doInBackground(String... params) {
// Here do whatever your task is like reading/writing file
// or read data from your server or any other heavy task
// Let us suppose here you get response, just return it
final String output = "Any out, mine is just demo output";
// Return it from here to post execute
return output;
}
#Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
// Here you can't guarantee that Activity/Fragment is alive who started this AsyncTask
// Make sure your caller is active
final MyTaskInformer callBack = mCallBack.get();
if(callBack != null) {
callBack.onTaskDone(s);
}
}
}
MainActivity.java This class is used to start my AsyncTask implement interface on this class and override this mandatory method.
public class MainActivity extends Activity implements MyTaskInformer {
private TextView mMyTextView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mMyTextView = (TextView) findViewById(R.id.tv_text_view);
// Start your AsyncTask and pass reference of MyTaskInformer in constructor
new MySmallAsyncTask(this).execute();
}
#Override
public void onTaskDone(String output) {
// Here you will receive output only if your Activity is alive.
// no need to add checks like if(!isFinishing())
mMyTextView.setText(output);
}
}
You can do it in a few lines, just override onPostExecute when you call your AsyncTask. Here is an example for you:
new AasyncTask()
{
#Override public void onPostExecute(String result)
{
// do whatever you want with result
}
}.execute(a.targetServer);
I hope it helped you, happy codding :)
in your Oncreate():
`
myTask.execute("url");
String result = "";
try {
result = myTask.get().toString();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (ExecutionException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}`
Why do people make it so hard.
This should be sufficient.
Do not implement the onPostExecute on the async task, rather implement it on the Activity:
public class MainActivity extends Activity
{
#Override
public void onCreate(Bundle savedInstanceState) {
//execute the async task
MyAsyncTask task = new MyAsyncTask(){
protected void onPostExecute(String result) {
//Do your thing
}
}
task.execute("Param");
}
}
You can call the get() method of AsyncTask (or the overloaded get(long, TimeUnit)). This method will block until the AsyncTask has completed its work, at which point it will return you the Result.
It would be wise to be doing other work between the creation/start of your async task and calling the get method, otherwise you aren't utilizing the async task very efficiently.
You can write your own listener. It's same as HelmiB's answer but looks more natural:
Create listener interface:
public interface myAsyncTaskCompletedListener {
void onMyAsynTaskCompleted(int responseCode, String result);
}
Then write your asynchronous task:
public class myAsyncTask extends AsyncTask<String, Void, String> {
private myAsyncTaskCompletedListener listener;
private int responseCode = 0;
public myAsyncTask() {
}
public myAsyncTask(myAsyncTaskCompletedListener listener, int responseCode) {
this.listener = listener;
this.responseCode = responseCode;
}
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected String doInBackground(String... params) {
String result;
String param = (params.length == 0) ? null : params[0];
if (param != null) {
// Do some background jobs, like httprequest...
return result;
}
return null;
}
#Override
protected void onPostExecute(String finalResult) {
super.onPostExecute(finalResult);
if (!isCancelled()) {
if (listener != null) {
listener.onMyAsynTaskCompleted(responseCode, finalResult);
}
}
}
}
Finally implement listener in activity:
public class MainActivity extends AppCompatActivity implements myAsyncTaskCompletedListener {
#Override
public void onMyAsynTaskCompleted(int responseCode, String result) {
switch (responseCode) {
case TASK_CODE_ONE:
// Do something for CODE_ONE
break;
case TASK_CODE_TWO:
// Do something for CODE_TWO
break;
default:
// Show some error code
}
}
And this is how you can call asyncTask:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Some other codes...
new myAsyncTask(this,TASK_CODE_ONE).execute("Data for background job");
// And some another codes...
}
Hi you can make something like this:
Create class which implements AsyncTask
// TASK
public class SomeClass extends AsyncTask<Void, Void, String>>
{
private OnTaskExecutionFinished _task_finished_event;
public interface OnTaskExecutionFinished
{
public void OnTaskFihishedEvent(String Reslut);
}
public void setOnTaskFinishedEvent(OnTaskExecutionFinished _event)
{
if(_event != null)
{
this._task_finished_event = _event;
}
}
#Override
protected void onPreExecute()
{
super.onPreExecute();
}
#Override
protected String doInBackground(Void... params)
{
// do your background task here ...
return "Done!";
}
#Override
protected void onPostExecute(String result)
{
super.onPostExecute(result);
if(this._task_finished_event != null)
{
this._task_finished_event.OnTaskFihishedEvent(result);
}
else
{
Log.d("SomeClass", "task_finished even is null");
}
}
}
Add in Main Activity
// MAIN ACTIVITY
public class MyActivity extends ListActivity
{
...
SomeClass _some_class = new SomeClass();
_someclass.setOnTaskFinishedEvent(new _some_class.OnTaskExecutionFinished()
{
#Override
public void OnTaskFihishedEvent(String result)
{
Toast.makeText(getApplicationContext(),
"Phony thread finished: " + result,
Toast.LENGTH_SHORT).show();
}
});
_some_class.execute();
...
}
Create a static member in your Activity class. Then assign the value during the onPostExecute
For example, if the result of your AsyncTask is a String, create a public static string in your Activity
public static String dataFromAsyncTask;
Then, in the onPostExecute of the AsyncTask, simply make a static call to your main class and set the value.
MainActivity.dataFromAsyncTask = "result blah";
I make it work by using threading and handler/message.
Steps as follow:
Declare a progress Dialog
ProgressDialog loadingdialog;
Create a function to close dialog when operation is finished.
private Handler handler = new Handler() {
#Override
public void handleMessage(Message msg) {
loadingdialog.dismiss();
}
};
Code your Execution details:
public void startUpload(String filepath) {
loadingdialog = ProgressDialog.show(MainActivity.this, "Uploading", "Uploading Please Wait", true);
final String _path = filepath;
new Thread() {
public void run() {
try {
UploadFile(_path, getHostName(), getPortNo());
handler.sendEmptyMessage(0);
} catch (Exception e) {
Log.e("threadmessage", e.getMessage());
}
}
}.start();
}
You need to use "protocols" to delegate or provide data to the AsynTask.
Delegates and Data Sources
A delegate is an object that acts on behalf of, or in coordination with, another object when that object encounters an event in a program. (Apple definition)
protocols are interfaces that define some methods to delegate some behaviors.
Here is a complete example!!!
try this:
public class SomAsyncTask extends AsyncTask<String, Integer, JSONObject> {
private CallBack callBack;
public interface CallBack {
void async( JSONObject jsonResult );
void sync( JSONObject jsonResult );
void progress( Integer... status );
void cancel();
}
public SomAsyncTask(CallBack callBack) {
this.callBack = callBack;
}
#Override
protected JSONObject doInBackground(String... strings) {
JSONObject dataJson = null;
//TODO query, get some dataJson
if(this.callBack != null)
this.callBack.async( dataJson );// asynchronize with MAIN LOOP THREAD
return dataJson;
}
#Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
if(this.callBack != null)
this.callBack.progress(values);// synchronize with MAIN LOOP THREAD
}
#Override
protected void onPostExecute(JSONObject jsonObject) {
super.onPostExecute(jsonObject);
if(this.callBack != null)
this.callBack.sync(jsonObject);// synchronize with MAIN LOOP THREAD
}
#Override
protected void onCancelled() {
super.onCancelled();
if(this.callBack != null)
this.callBack.cancel();
}
}
And usage example:
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final Context _localContext = getContext();
SomeAsyncTask.CallBack someCallBack = new SomeAsyncTask.CallBack() {
#Override
public void async(JSONObject jsonResult) {//async thread
//some async process, e.g. send data to server...
}
#Override
public void sync(JSONObject jsonResult) {//sync thread
//get result...
//get some resource of Activity variable...
Resources resources = _localContext.getResources();
}
#Override
public void progress(Integer... status) {//sync thread
//e.g. change status progress bar...
}
#Override
public void cancel() {
}
};
new SomeAsyncTask( someCallBack )
.execute("someParams0", "someParams1", "someParams2");
}
Probably going overboard a bit but i provided call backs for both the execution code and the results. obviously for thread safety you want to be careful what you access in your execution callback.
The AsyncTask implementation:
public class AsyncDbCall<ExecuteType,ResultType> extends AsyncTask<ExecuteType, Void,
ResultType>
{
public interface ExecuteCallback<E, R>
{
public R execute(E executeInput);
}
public interface PostExecuteCallback<R>
{
public void finish(R result);
}
private PostExecuteCallback<ResultType> _resultCallback = null;
private ExecuteCallback<ExecuteType,ResultType> _executeCallback = null;
AsyncDbCall(ExecuteCallback<ExecuteType,ResultType> executeCallback, PostExecuteCallback<ResultType> postExecuteCallback)
{
_resultCallback = postExecuteCallback;
_executeCallback = executeCallback;
}
AsyncDbCall(ExecuteCallback<ExecuteType,ResultType> executeCallback)
{
_executeCallback = executeCallback;
}
#Override
protected ResultType doInBackground(final ExecuteType... params)
{
return _executeCallback.execute(params[0]);
}
#Override
protected void onPostExecute(ResultType result)
{
if(_resultCallback != null)
_resultCallback.finish(result);
}
}
A callback:
AsyncDbCall.ExecuteCallback<Device, Device> updateDeviceCallback = new
AsyncDbCall.ExecuteCallback<Device, Device>()
{
#Override
public Device execute(Device device)
{
deviceDao.updateDevice(device);
return device;
}
};
And finally execution of the async task:
new AsyncDbCall<>(addDeviceCallback, resultCallback).execute(device);
Hope you been through this , if not please read.
https://developer.android.com/reference/android/os/AsyncTask
Depending on the nature of result data, you should choose best possible option you can think of.
It is a great choice to use an Interface
some other options would be..
If the AsyncTask class is defined inside the very class you want to
use the result in.Use a static global variable or get() , use it from
outer class (volatile variable if necessary). but should be aware of the AsyncTask progress or should at least make sure that it have finished the task and result is
available through global variable / get() method. you may use
polling, onProgressUpdate(Progress...), synchronization or interfaces (Which ever suits best for you)
If the Result is compatible to be a sharedPreference entry or it is okay to be saved as a file in the memory you could save it even from
the background task itself and could use the onPostExecute() method
to get notified when the result is available in the memory.
If the string is small enough, and is to be used with start of an
activity. it is possible to use intents (putExtra()) within
onPostExecute() , but remember that static contexts aren't that safe
to deal with.
If possible, you can call a static method from the
onPostExecute() method, with the result being your parameter