AsyncTask Return Value to Caller

http://instinctcoder.com/android-studio-asynctask-return-value-to-caller/

Objectives

In order to demonstrate this, We’ll create a Calculator + application that helping us to add up a list of numbers. The app is a simple app which allows user to key in a list of numbers and hit the button and return a result. Assuming this is a very complex math  which will take a long time to process so we decided to put that complex math into a separate thread and will extend AsyncTask to accomplish this.

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Android Studio AsyncTask Return Value to Caller

1. Let’s start to create a project and name it AsyncTaskCallback, and the rest of step should be as standard, if you need guide on this step , please refer this link. These are the basic setting i’ve set.
   
2. In src > main > res > layout > activity_main.xml. Add Button, EditText and TextView into activity_main.xml and it will look like this.

activity_main.xml

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<pre class="lang:default decode:true">&lt;FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:id="@+id/container"     android:layout_width="match_parent"     android:layout_height="match_parent"     tools:context="com.instinctcoder.asynctaskcallback.MainActivity"     tools:ignore="MergeRootFrame"     android:longClickable="false"&gt;       &lt;Button         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="Calculate"         android:id="@+id/btnCount"         android:singleLine="true"         android:layout_span="@integer/abc_max_action_buttons"         android:layout_gravity="right|top"         android:layout_marginTop="150dp" /&gt;       &lt;EditText         android:layout_width="fill_parent"         android:layout_height="wrap_content"         android:id="@+id/editText"         android:layout_marginTop="110dp" /&gt;       &lt;TextView         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:textAppearance="?android:attr/textAppearanceLarge"         android:text='Key in numbers separate with ,'         android:id="@+id/textView2"         android:layout_gravity="left|top"         android:singleLine="true"         android:layout_marginTop="80dp" /&gt;   &lt;/FrameLayout&gt;</pre>

1. We need to create an interface this interface is our main objective of this tutorial So whenever you need to call to another thread and expecting some result return you need to implement this interface so let’s see the code. In src > main > java > com.instinctcoder.asynctaskcallback, add a class and named it TaskCompleted.java. Paste below code into TaskCompleted.java

TaskCompleted.java

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package com.instinctcoder.asynctaskcallback;   public interface TaskCompleted {         // Define data you like to return from AysncTask         public void onTaskComplete(Integer result); }

1. In src > main > java > com.instinctcoder.asynctaskcallback, add a class and named it AsyncComplex.java. Paste below code into AsyncComplex.java

AsyncComplex.java

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package com.instinctcoder.asynctaskcallback;   import android.app.ProgressDialog; import android.content.Context; import android.os.AsyncTask;   public class AsyncComplex extends AsyncTask <String, String, Integer> {     private Context mContext;       ProgressDialog mProgress;     private TaskCompleted mCallback;       public AsyncComplex(Context context){         this.mContext = context;         this.mCallback = (TaskCompleted) context;       }       @Override     public void onPreExecute() {         mProgress = new ProgressDialog(mContext);         mProgress.setMessage("Downloading nPlease wait...");         mProgress.show();     }       @Override     protected void onProgressUpdate(String... values) {         mProgress.setMessage(values[0]);     }       @Override     protected Integer doInBackground(String... values) {         Integer iResult=0;         try {             //This is to simulate the calculation is super hard to calculate             //and we make it slow down by 500 ms for each number             String[] numbers = values[0].split(",");             Integer iLength = numbers.length;             for (int i =0; i<=iLength;i++){                 publishProgress("Task Completed :" + Integer.toString(i) + " of " + Integer.toString(iLength));                 Thread.sleep(500);                 iResult +=Integer.parseInt(numbers[i]);             }           } catch (Exception e) {             e.printStackTrace();         }         return iResult;       }       @Override     protected void onPostExecute(Integer results) {         mProgress.dismiss();         //This is where you return data back to caller         mCallback.onTaskComplete(results);     } }

1. In src > main > java > com.instinctcoder.asynctaskcallback, update MainActivity.java to look like below.
   The code is quite self-explanatory it’s basically call AsyncComplex class when button is click and then calculated result will display via onTaskComplete.

Main_Activity.java

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package com.instinctcoder.asynctaskcallback;   import android.support.v7.app.ActionBarActivity; import android.support.v4.app.Fragment; import android.os.Bundle; import android.view.LayoutInflater; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.view.ViewGroup; import android.widget.Button; import android.widget.EditText; import android.widget.Toast;   public class MainActivity extends ActionBarActivity implements TaskCompleted {       @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);           if (savedInstanceState == null) {             getSupportFragmentManager().beginTransaction()                     .add(R.id.container, new PlaceholderFragment())                     .commit();         }         Button btnCount = (Button) findViewById(R.id.btnCount);           btnCount.setOnClickListener(new View.OnClickListener() {               @Override             public void onClick(View v) {                 EditText editText = (EditText) findViewById(R.id.editText);                 new AsyncComplex(MainActivity.this).execute(editText.getText().toString());               }         });     }       @Override     public boolean onCreateOptionsMenu(Menu menu) {           // Inflate the menu; this adds items to the action bar if it is present.         getMenuInflater().inflate(R.menu.main, menu);         return true;     }       @Override     public boolean onOptionsItemSelected(MenuItem item) {         // Handle action bar item clicks here. The action bar will         // automatically handle clicks on the Home/Up button, so long         // as you specify a parent activity in AndroidManifest.xml.         int id = item.getItemId();         if (id == R.id.action_settings) {             return true;         }         return super.onOptionsItemSelected(item);     }       @Override     public void onTaskComplete(Integer result) {           Toast.makeText(this,"The result is " + Integer.toString(result),Toast.LENGTH_LONG).show();     }       /**      * A placeholder fragment containing a simple view.      */     public static class PlaceholderFragment extends Fragment {           public PlaceholderFragment() {         }           @Override         public View onCreateView(LayoutInflater inflater, ViewGroup container,                 Bundle savedInstanceState) {             View rootView = inflater.inflate(R.layout.fragment_main, container, false);             return rootView;         }     }   }

1. That’s all! Click Run (Shift +F10). and should see a screen like below. Input few numbers separate with comma after that click Calculate button and the result will display.
   
   Hope you enjoy the post.