Like I need to check whether a username already existed in database, and the program won't continue until response arrives.
it seems you need asynctask, this is an example how to use it..
public class YourFragment extends Fragment implements YourAsyncTask.YourInterface {
public YourFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_your, container, false);
//do your initial things
.
.
.
YourAsyncTask yourAsyncTask = new YourAsyncTask(this);
yourAsyncTask.execute();
return view;
}
#Override
public void onJobFinishListener(YourDataType yourData) {
//when this method is trigered by your asynctask
//it means that you are in ui thread and update your ui component
//TODO: update ui component with your data
}
}
and this is the asynctask;
public class YourAsyncTask extends AsyncTask {
private YourInterface yourInterfaceListener;
private YourDataType yourData; //this data should be calculated in doInBackground method and send via interface
public YourAsyncTask(YourInterface yourInterfaceListener) {
this.yourInterfaceListener = yourInterfaceListener;
}
#Override
protected Object doInBackground(Object[] objects) {
//do your all background tasks here
.
.
.
yourData = do something here to fill your data..
return null;
}
#Override
protected void onPostExecute(Object o) {
super.onPostExecute(o);
yourInterfaceListener.onJobFinishListener(yourData);
}
public interface YourInterface{
void onJobFinishListener(YourDataType yourData);
}
}
Use AsyncTask to perform network operations
public class TalkToServer extends AsyncTask<Void, Void, Void> {
#Override
protected void onPreExecute() {
/*
* do things before doInBackground() code runs
* such as preparing and showing a Dialog or ProgressBar
*/
}
#Override
protected void onProgressUpdate(Void... values) {
/*
* updating data
* such a Dialog or ProgressBar
*/
}
#Override
protected Void doInBackground(Void... params) {
//do your work here
return null;
}
#Override
protected void onPostExecute(Void result) {
/*
* do something with data here
* display it or send to mainactivity
* close any dialogs/ProgressBars/etc...
*/
}
}
And you can execute it using
TalkToServer myTask = new MyTask(); // can add params for a constructor if needed
myTask.execute(); // here is where you would pass data to doInBackground()
After the network call is done and response obtained onPostExecute() is called. If the AsyncTask is in inner class of your activity you can update UI inside onPostExecute(). Otherwise you can use an Interface to create a callback to activity.
You can find AsyncTask Docs here
You have to use async task. Then you can uae it your_async_class.execute().get() in your activiry this ..get method you want to it. Main thread will wait your async task. You have to change your_async_class extends AsyncTask
I have a top-level Fetch class that extends AsyncTask and I have a MainActivity. I can't get the Fetch class to make a toast due to not having an instance of the MainActivity or its context. I have tried to pass the MainActivity to the Fetch class but it potentially leaks memory. I have tried setting a WeakReference instance of the context, but I can't make a toast from that.
I have read many other posts about this and most seem to have a static inner-class but mine is top-level and I would prefer to keep it that way.
The MainActivity creates an instance of Fetch and then executes it.
public class Fetch extends AsyncTask<Void, Integer, List<List<String>>>
{
#Override
protected void onPreExecute()
{
super.onPreExecute();
}
#Override
protected List<List<String>> doInBackground(Context... params)
{
// run tasks
}
#Override
protected void onProgressUpdate(Integer... progress)
{
}
#Override
protected void onPostExecute(List<List<String>> result)
{
super.onPostExecute(result);
}
}
One way, in doInBackground:
runOnUiThread(new Runnable() {
public void run() {
Toast.makeText(<your class name>.this, "hello", Toast.LENGTH_SHORT).show();
}
});
Or in onPostExecute(which invoked on the UI thread after the background computation finishes)
Toast.makeText(<your class name>.this, "hello", Toast.LENGTH_SHORT).show();
Edited: if you want to pass context to AsyncTask，you could do like:
public class MyAsyncTask extends AsyncTask<Void, Integer, List<List<String>>>
private final Context mContext;
public MyAsyncTask(final Context context) {
mContext = context;
}
}
And in MainActivity ：
final MyAsyncTask task = new MyAsyncTask(getApplicationContext());
task.execute();
Edited again:
I tested WeakReference successfully.
public class ExampleAsyncTask extends AsyncTask {
private WeakReference<Context> contextRef;
public ExampleAsyncTask(Context context) {
contextRef = new WeakReference<>(context);
}
#Override
protected void onPostExecute(Object result) {
Context context = contextRef.get();
if (context != null) {
Toast.makeText(context, "hello", Toast.LENGTH_SHORT).show();
}
}
}
In MainActivity:
new ExampleAsyncTask(MainActivity.this).execute();
yeah,Don't be worry ，you can use the application context.may be as follow:
implement your App.getContext() in your Application.
and use it in your "Fetch" class and execute it in MainThread.
Hi I'm making Login page that access MySQL database. But my Activity always runs the code that check fail/success before it finishes the AsyncTask.
I tried using asynctask.get() method, but it just freeze my UI and doesn't work.
I tried this answer that said I should call the result-checker method inside onPostExecute().
But since I need to change the TextView to show success/failed, it results in NullPointerException because I instantiate the TextView inside onCreate().
I can't move the TextView instantiation into constructor because it will return NullPointerException unable to instantiate activity ComponentInfo.
Login.java
public class Login extends Activity{
//declare global Views here
protected void onCreate(Bundle bundle){
//Setup views
}
protected void onClick(View v){
//Setup necessary variables
AsyncClass async = new AsyncClass(this);
async.execute(username, password);
}
public void checkSuccess(boolean success){
if(success)
textView1.setText("Success");
else
textView1.setText("Failed");
}
}
AsyncClass.java
public class AsyncClass extends AsyncTask<String, String, JSONObject>{
protected JSONObject doInBackground(String... params){
//access database
}
protected void onPostExecute(JSONObject json){
//read the json result
Login login = new Login();
login.checkSuccess(true);
}
}
Any solution? Thanks
How about making AsyncTask as your inner class?
So your code should look something like below.
public class Login extends Activity {
//declare global Views here
protected void onCreate(Bundle bundle) {
//Setup views
}
protected void onClick(View v) {
new AsyncClass().execute(username, password);
}
public void checkSuccess(boolean success) {
if (success) textView1.setText("Success");
else textView1.setText("Failed");
}
class AsyncClass extends AsyncTask < String, String, JSONObject > {
protected JSONObject doInBackground(String...params) {
//access database
}
protected void onPostExecute(JSONObject json) {
checkSuccess(true / false);
}
}
}
try this
protected void onPostExecute(JSONObject json){
//read the json result
Login login = (Login)context; // object that you pass to task constructor
login.checkSuccess(true);
}
Also you can add progress dialog to your task to indicate some job execution
public class BaseTask<T> extends AsyncTask<Object, Void, T> {
public Context context;
public ProgressDialog dialog;
public BaseTask(Context context) {
this.context = context;
this.dialog = new ProgressDialog(context);
}
#Override
protected void onPreExecute() {
this.dialog.setMessage(context.getResources().getString(R.string.loading));
this.dialog.show();
}
#Override
protected T doInBackground(Object... objects) {
//....
return something;
}
#Override
protected void onPostExecute(T result) {
if (dialog != null && dialog.isShowing())
dialog.dismiss();
// do something
}
}
You cannot edit the UI from the async task thread. In order to make updates to the UI thread, use the onProgressUpdate() method. This method is part of your AsyncTask class, is actually executed in the main UI Thread (I hope you use the async task as a nested class btw, since it is declared public I guess your not. You should change that). The onProgressUpdate() Method is called by the OS itself if you call publishProgress(...) inside your Async task.
A small sample:
protected JSONObject doInBackground(String... params){
publishProgress("test");
}
/**
* This method is part of the Async Task
*/
protected void onProgressUpdate(String... progress) {
login.checkSuccess(true);
}
I would use it this way, just override your onPostExecute where you need it or create a own interface
//create a object f your asyncclass and
//override the onPostExecute where you need it
mInfo = new ASYNCCLASS({
#Override
public void onPostExecute(Object result){
//doSomething something with your views!
}
}).execute();
Waiting is not the answer, because you do not know how long your Asynctask will take to end.
Code above is not tested, just pseudoce, but it should show what i mean.
Do not have my IDE round here, so if anybody would correct the brackets if neccessary would be great!
Greetz
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
I hate inner class.
I've a main activity who launches a 'short-life' AsyncTask.
AsyncTask is in a separate file, is not an inner class of main activity
I need async task updates a textView from main Activity.
I know i can update a TextView from onProgressUpdate, if AsyncTask is a inner class
But how from an external, indipendent, async task ?
UPDATE: This looks like working :
In acitivty i call the task
backgroundTask = new BackgroundTask(this);
backgroundTask.execute();
In the constructor i've
public BackgroundTask(Activity myContext)
{
debug = (TextView) myContext.findViewById(R.id.debugText);
}
where debug was a private field of AsyncTask.
So onProgressUpdate I can
debug.append(text);
Thanks for all of you suggestions
AsyncTask is always separate class from Activity, but I suspect you mean it is in different file than your activity class file, so you cannot benefit from being activity's inner class. Simply pass Activity context as argument to your Async Task (i.e. to its constructor)
class MyAsyncTask extends AsyncTask<URL, Integer, Long> {
WeakReference<Activity> mWeakActivity;
public MyAsyncTask(Activity activity) {
mWeakActivity = new WeakReference<Activity>(activity);
}
...
and use when you need it (remember to NOT use in during doInBackground()) i.e. so when you would normally call
int id = findViewById(...)
in AsyncTask you call i.e.
Activity activity = mWeakActivity.get();
if (activity != null) {
int id = activity.findViewById(...);
}
Note that our Activity can be gone while doInBackground() is in progress (so the reference returned can become null), but by using WeakReference we do not prevent GC from collecting it (and leaking memory) and as Activity is gone, it's usually pointless to even try to update it state (still, depending on your logic you may want to do something like changing internal state or update DB, but touching UI must be skipped).
Using Interface
1) Create one Interface
public interface OnDataSendToActivity {
public void sendData(String str);
}
2) Implements it in your Activity
public class MainActivity extends Activity implements OnDataSendToActivity{
#Override
protected void onCreate(Bundle savedInstanceState) {
new AsyncTest(this).execute(new String[]{"AnyData"}); // start your task
}
#Override
public void sendData(String str) {
// TODO Auto-generated method stub
}
}
3) Create constructor in AsyncTask(Activity activity){}
Register your Interface in AsyncTask file
and call interface method as below.
public class AsyncTest extends AsyncTask<String, Integer, String> {
OnDataSendToActivity dataSendToActivity;
public AsyncTest(Activity activity){
dataSendToActivity = (OnDataSendToActivity)activity;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
dataSendToActivity.sendData(result);
}
}
Here, your OnPostExecute will call after all task done by AsyncTask and will get "result"
as a parameter, returned by doInBackground(){ return "";}.
While "dataSendToActivity.sendData(result);" it will call activity's overrided method "public void sendData(String str) {}".
An edge case to remember: Be sure to pass this, i.e. you current activity's context to AsyncTask and not create another instance of your activity, otherwise your Activity will be destroyed and new one is created.
Make an static function in your activity class passing context in it to update your text view and then call this function in your AsynkTask class to update.
In Activity class:
public static void updateTextView(){
//your code here
}
In AynckTask class call this function.
Just pass the context (activity or whatever) to your AsyncTask in a constructor and then in onSuccess or onProgressUpdate call whatever you need on the context.
I wrote a small extension to AsyncTask for this kind of scenario. It allows you to keep your AsyncTask in a separate class, but also gives you convenient access to the Tasks's completion:
public abstract class ListenableAsyncTask<Params, Progress, Result> extends AsyncTask<Params, Progress, Result>{
#Override
protected final void onPostExecute(Result result) {
notifyListenerOnPostExecute(result);
}
private AsyncTaskListener<Result> mListener;
public interface AsyncTaskListener<Result>{
public void onPostExecute(Result result);
}
public void listenWith(AsyncTaskListener<Result> l){
mListener = l;
}
private void notifyListenerOnPostExecute(Result result){
if(mListener != null)
mListener.onPostExecute(result);
}
}
So first you extend ListenableAsyncTask instead of AsyncTask. Then in your UI code, make a concrete instance and set listenWith(...).
The Question has already been answered, still im posting how it should be done i guess..
Mainactivity class
public class MainActivity extends Activity implements OnClickListener
{
TextView Ctemp;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Ctemp = (TextView) findViewById(R.id.Ctemp);
doConv = (Button) findViewById(R.id.doConv);
doConv.setOnClickListener(this);
}
#Override
public void onClick(View arg0) // The conversion to do
{
new asyncConvert(this).execute();
}
}
now in the async class
public class asyncConvert extends AsyncTask<Void, Void, String>
{
SoapPrimitive response = null;
Context context;
public asyncConvert(Context callerclass)
{
contextGUI = callerclass;
}
.
.
.
.
protected void onPostExecute(String result)
{
((MainActivity) contextGUI).Ctemp.setText(result); // changing TextView
}
}
/**
* Background Async Task to Load all product by making HTTP Request
* */
public static class updateTExtviewAsyncTask extends AsyncTask<String, String, String> {
Context context;
ProgressDialog pDialog;
String id, name;
String state_id;
//--- Constructor for getting network id from asking method
public updateTExtviewAsyncTask(Context context,String id,String city)
{
context = context;
state_id = id;
city_name = city;
}
/* *
* Before starting background thread Show Progress Dialog
* */
#Override
protected void onPreExecute()
{
super.onPreExecute();
pDialog = ProgressDialog.show(context, "","Please wait...", true, true);
pDialog.show();
}
/**
* getting All products from url
* */
protected String doInBackground(String... args)
{
return null;
}
/**
* After completing background task Dismiss the progress dialog
* **/
protected void onPostExecute(String file_url) {
YourClass.UpdateTextViewData("Textview data");
}
}
// place this code inside your activity class and also declare updating textview static
public static void UpdateTextViewData(String tvData)
{
tv.setText(tvData);
}