How to call a returning value function in AsyncTask

问题:

I am new to andorid programming I've just stucked into a problem to call returning value function inside AsyncTask's doInBackground() Simple question is How to wait for AsyncTask to complete and then execute return statement without freezing UI, i've also studied onPostExecute() but it doesn't solve problem. following is sample code

public String hello()  {    String result = null;    //calling asynctaske execute method    retrun result; } 

回答1:

For myself i do this with a callback Function, that i invoke after onPostExecute.

public AsyncUnzip(Activity ctx, Observer callback) {     this.ctx = ctx;     this.callback = callback; } 

and

@Override protected void onPreExecute() {     super.onPreExecute();     dia = new ProgressDialog(ctx);     dia.setTitle("Bitte warten");     dia.setMessage("Geodatenpaket wird entpackt...");     dia.setCancelable(false);     dia.show(); } 

and

@Override public void onPostExecute( Boolean result ) {     super.onPostExecute(result);     dia.dismiss();     callback.update(null, returnFolder);     System.out.println("Unzipped to: " + returnFolder.getName() ); } 

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In that case your call of Async Task would look like that:

AsyncUnzip unzipThread = new AsyncUnzip(ImportActivity.this, new Observer() {     @Override     public void update( Observable observable, Object data ) {//your code invoked after Async Task } }); unzipThread.execute(selectedFile); //Start Unzip in external Thread. 

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Note: This is a quick and diry solution with a annonymous Observer implementation and without an observable.

回答2:

You can create an Interface and return value from onPostExecute() of AsyncTask or you can register a BroadcastReceiver and fire in from onPostExecute() method of AsyncTask. I had created a demo using Interface and BroadcastReceiver you can download and check it.

文章来源: How to call a returning value function in AsyncTask