In my main activity I got an arraylist called data. I call an asynctask and do some stuff that gives me a different arraylist called values.
In the post execute of the asynctask I want to use items in 'values' to add some objects to 'data'. However, when debugging I noticed that the objects dont get added.
public class MainActivity extends Activity
{
ArrayList<DataItem> data;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
data = new ArrayList<DataItem>();
update();
}
public void update()
{
AsyncCallAWS thisTask = new AsyncCallAWS();
thisTask.execute();
}
private class AsyncCallAWS extends AsyncTask<String, Void, Void>
{
ArrayList<String> values = new ArrayList<String>();
protected void onPostExecute(Void result)
{
Log.i(TAG, "onPostExecute");
DataItem d;
for(String s : values)
{
d = new DataItem();
d.setValue(s);
d.setDataStreamName("test");
data.add(d);
}
}
//code to fill array
I'm guessing it's because I try to add items from the asynctask? Idk how to solve this, I need the data arraylist for a listview.
In AsyncTask class override method onProgressUpdate(), where you will add elements to array. Then in doInBackground() call publishProgress() for sending elements to onProgressUpdate(). Here http://developer.android.com/reference/android/os/AsyncTask.html -is great example.
private class TestAsyncTask extends AsyncTask<Object, String, Object> {
#Override
protected Object doInBackground(Object... params) {
String item = "";
//Do some stuff
publishProgress(item);
return null;
}
#Override
public void onProgressUpdate(String... value) {
data.add(value[0]);
}
#Override
protected void onPostExecute(Object result) {
}
}
I dont think you should create objects in the onPostExecute-method. Instead create it in the doInBackground-method of the class that extends AsyncTask, and then use set-methods in the onPostExecute-metod.
how do I return a List generated in an AsyncTask back to the Activity?
My LoadStringsAsync class:
public class LoadStringsAsync extends AsyncTask<Void, Void, List<String> > {
List<String> str;
#Override
protected void onPreExecute() {
super.onPreExecute();
...
}
#Override
protected List<String> doInBackground(Void... arg0) {
...
get content from the internet
and
fill the list
...
}
#Override
protected void onPostExecute(List<String> str) {
super.onPostExecute(events);
...
}
}
and I need the List back in my Activity to work with it. (No not only to show it in ListView :P)
Any suggestions how to do this? :-)
Thanks so far!
your Activity:
public class YourActivity extends Activity {
private List<String> list = new ArrayList<String>();
public void onCreate(Bundle state) {
//...
}
public void setList(List<String> list) {
this.list = list;
}
private void fireYourAsyncTask() {
new LoadStringsAsync(this).execute();
}
}
AsyncTask:
public class LoadStringsAsync extends AsyncTask<Void, Void, List<String>> {
List<String> str;
private YourAcitivity activity;
public LoadStringsAsync(YourAcitivity activity) {
this.activity = activity;
}
#Override
protected List<String> doInBackground(Void... arg0) {
}
#Override
protected void onPostExecute(List<String> str) {
super.onPostExecute(events);
activity.setList(str);
}
}
If you make your AsyncTask an inner class in your Activity, then onPostExecute will be in the same context as the Activity, and you can use the List as you would anywhere in the Activity.
If you don't make your AsyncTask an inner class in your Activity, then you need to set up a listener to call back to your Activity when the AsyncTask finishes. If you prefer to go that route look at this post.
There is also this post that is similar to your question.
According to the documentation from android link you can use the get method to return computational result. Since your AsyncTask shows that you are returning a List, then you can try the following code in the class you are calling the asynchronous class
List<String> returnedlist=new LoadStringAsync().execute().get();
Hoping this option helps.
Place code that uses the list, or sets it to a variable, inside onPostExecute().
Better run your task from parent Activity like:
public class MyActivity extends Activity{
private List<String> mData = new ArrayList<String>();
private void runTask(){
new LoadStringsAsync(){
#Override
protected void onPostExecute(List<String> str) {
super.onPostExecute(events);
mData.clear();
mData.addAll(str);
}
}.execute();
}
}
You can send your list to a handler inside a Message :
Message msg = Message.obtain();
msg.obj = myList;
handler.sendMessage(msg);
More infos : http://developer.android.com/reference/android/os/Message.html
In an existing app I have an activity with an inner class which extends AsyncTask, this looks like the following:
public class Activity_1 extends BaseActivity {
....
new async().execute();
...
public class asyncextends AsyncTask<Void, Void, String> {
protected String doInBackground(Void... progress) { ... }
protected void onPreExecute() { ... }
protected void onPostExecute(String result) { ... }
}
}
Now, I need to call the same doInBackground-method from another activity, but the onPostExecute() of the this inner class operates on some local UI variables and hence it's not possible to use it from outside the clas.
Is there any way I can call this AsyncTask, and just override the onPostExecute andonPreExecute-method, or shall I create yet another inner-class in the other activity, do the same background thing (of course move it to common utility-class or something), etc...?
You can make a separate abstract package private class, extending AsyncTask and implementing doInBackground() method:
abstract class MyAsyncTask extends AsyncTask<Void, Void, String> {
#Override
final protected String doInBackground(Void... progress) {
// do stuff, common to both activities in here
}
}
And in your activities just inherit from MyAsyncTask (new class probably should be private, by the way), implementing onPostExecute() and onPreExecute() methods:
public class Activity_1 extends BaseActivity {
...
new Async1().execute();
...
private class Async1 extends MyAsyncTask {
#Override
protected void onPreExecute(){
// Activity 1 GUI stuff
}
#Override
protected void onPostExecute(String result) {
// Activity 1 GUI stuff
}
}
}
If onPreExecute and onPostExecute contain some common actions as well, you can apply the following pattern:
abstract class MyAsyncTask extends AsyncTask<Void, Void, String> {
public interface MyAsyncTaskListener {
void onPreExecuteConcluded();
void onPostExecuteConcluded(String result);
}
private MyAsyncTaskListener mListener;
final public void setListener(MyAsyncTaskListener listener) {
mListener = listener;
}
#Override
final protected String doInBackground(Void... progress) {
// do stuff, common to both activities in here
}
#Override
final protected void onPreExecute() {
// common stuff
...
if (mListener != null)
mListener.onPreExecuteConcluded();
}
#Override
final protected void onPostExecute(String result) {
// common stuff
...
if (mListener != null)
mListener.onPostExecuteConcluded(result);
}
}
and use it in your activity as following:
public class Activity_1 extends BaseActivity {
...
MyAsyncTask aTask = new MyAsyncTask();
aTask.setListener(new MyAsyncTask.MyAsyncTaskListener() {
#Override
void onPreExecuteConcluded() {
// gui stuff
}
#Override
void onPostExecuteConcluded(String result) {
// gui stuff
}
});
aTask.execute();
...
}
You can also have your Activity implement MyAsyncTaskListener as well:
public class Activity_1 extends BaseActivity implements MyAsyncTask.MyAsyncTaskListener {
#Override
void onPreExecuteConcluded() {
// gui stuff
}
#Override
void onPostExecuteConcluded(String result) {
// gui stuff
}
...
MyAsyncTask aTask = new MyAsyncTask();
aTask.setListener(this);
aTask.execute();
...
}
I wrote the code from the head, so it might contain errors, but it should illustrate the idea.
Its so simple just Simply build an object of main class and than call the inner class like this
OuterMainClass outer = new OuterMainClass();
outer.new InnerAsyncClass(param)
.execute();
this answer is too late to help you but hope it help others.
Thanks
1.Create a constructor of AsynckTask in ClassOne.
2.Crate object or ClassOne by new keyword.
3.Call Async Task by object
ClassOne{
class AsyncParmas extends AsyncTask {
public ADDloadGeofenceDetails() {
}
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected Object doInBackground(Object... params) {
}
}
Class ClassTwo{
ClassOne obj= new ClassOne ();
obj.new AsyncParmas ().execute();
}
}
GoodLuck Who were facing problem.
If we create one static method which is in one class and and will be execute in any class in doInBackground of AsyncTask we can easily update UI through same class and even in different class .
Hey i don't know if that's the right way to do it but if it is how can i do it...
I have one abstact class with AsyncTask
public abstract class A{
A(){
new Task().execute();
}
public abstract void postAction();
private class Task extends AsyncTask<String, String, String>{
protected String doInBackground(String... args)
{
//smth
}
protected void onPostExecute(String file_url){
postAction();
}
}
}
After that i have class that extends A class and overrides it's postAction() method:
public class B extends A{
B(){
//smth
}
postAction(){
//some action
}
}
In my activity i have instance of B and i want to perform action when postAction is called... so i want function listener if possible and how can i do it
class C extends Activity{
public void onCreate(Bundle savedInstance) {
super.onCreate(savedInstance);
//somethingggg happeiningggg
}
MyListener listener = new MyListener(){
onPostActionCalled()
{
//start another activity or smt :D
}
};
}
So i have class for json response(class A) and class B that extends it and overrides it's post method so i can do what i want for specific situation(expect different data or smth else nvm)
In my activity i want to perform action when class B's post method is called
I don't know if i need to do listener or handler idk at all....
Stefan is right, why complicate things?
See this real simple example of threading:
public class MyActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
new MyTask(new TaskListener() {
#Override
public void finished(boolean result) {
// back on main thread after task finishes
}
}).execute();
}
private interface TaskListener{
void finished(boolean result);
}
private class MyTask extends AsyncTask<Object, Integer, Boolean>{
private TaskListener mListener;
public MyTask(TaskListener mListener) {
super();
this.mListener = mListener;
}
#Override
protected Boolean doInBackground(Object... params) {
// long running background operation
return true;
}
#Override
protected void onPostExecute(Boolean result) {
mListener.finished(result);
super.onPostExecute(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