Android Development: Having an AsyncTask in a separate class file
android, android-asynctask, java
Solution
How can I have the file seperate but still update the UI thread.
Okey. So at first you know that main advantage of `AsyncTask` added in Activity as inner class is that you have direct access to all UI elements and it makes possible pretty "lightweight" UI updates.
But if you decided to make AsyncTask separated from Activity(which also have some benefits e.q. code is more clean and app logic is separated from appearance) class you can:
- You can pass UI elements via constructor of class
- You can create various setters
- You can create some interface that will hold callbacks. Look at `Android AsyncTask sending Callbacks to UI`
This is all what you need i guess.
Problem
I have been playing around with various examples trying to familiarize myself with AsyncTask. So far all the examples I have seen have had the AsyncTask included into the onCreate method of the main activity. Which I don't like very much, so I was wanting to see how hard it would be to separate it into its own class. So far I have this: the main activity ``` package com.example.asynctaskactivity; import android.os.AsyncTask; import android.os.Bundle; import android.os.SystemClock; import android.app.Activity; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.ProgressBar; import android.widget.TextView; import android.widget.Toast; import com.example.asynctaskactivity.ShowDialogAsyncTask; public class AsyncTaskActivity extends Activity { Button btn_start; ProgressBar progressBar; TextView txt_percentage; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); btn_start = (Button) findViewById(R.id.btn_start); progressBar = (ProgressBar) findViewById(R.id.progress); txt_percentage= (TextView) findViewById(R.id.txt_percentage); Log.v("onCreate","Attempt set up button OnClickListener"); btn_start.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { btn_start.setEnabled(false); new ShowDialogAsyncTask().execute(); } }); Log.v("onCreate","Success!"); } } ``` the new seperate AsyncTask class ``` package com.example.asynctaskactivity; import android.os.AsyncTask; import android.os.SystemClock; import android.util.Log; import android.widget.Button; import android.widget.ProgressBar; import android.widget.TextView; import android.widget.Toast; public class ShowDialogAsyncTask extends AsyncTask<Void, Integer, Void>{ int progress_status; @Override protected void onPreExecute() { // update the UI immediately after the task is executed Log.v("onPreExecute","1"); super.onPreExecute(); Log.v("onPreExecute","2"); //Toast.makeText(AsyncTaskActivity.this,"Invoke onPreExecute()", Toast.LENGTH_SHORT).show(); progress_status = 0; Log.v("onPreExecute","3"); txt_percentage.setText("downloading 0%"); Log.v("onPreExecute","4"); } @Override protected Void doInBackground(Void... params) { Log.v("doInBackground","1"); while(progress_status<100){ progress_status += 2; publishProgress(progress_status); SystemClock.sleep(300); } return null; } @Override protected void onProgressUpdate(Integer... values) { super.onProgressUpdate(values); progressBar.setProgress(values[0]); txt_percentage.setText("downloading " +values[0]+"%"); } @Override protected void onPostExecute(Void result) { super.onPostExecute(result); //Toast.makeText(AsyncTaskActivity.this,"Invoke onPostExecute()", Toast.LENGTH_SHORT).show(); txt_percentage.setText("download complete"); btn_start.setEnabled(true); } } ``` Originally this was all in the main activity, hence the mentions to the elements that the asynctask should in theory update. Obviously at present this is causing runtime errors, which then got me thinking. How can I have the file seperate but still update the UI thread. Sorry if this is a stupid question, quite new to android development and background threads in particular.