Friday, September 12, 2014

Android Async Task With Example Use Case

Why Async Task


Androids Application UI is single threaded and executed by one Thread called UI Thread. If we want to execute slightly long running processing by UI Thread then the Application would become unresponsive and the User experience will not be great.

AsyncTask enables proper and easy use of the UI thread. This class allows to perform background operations and publish results on the UI thread.

An asynchronous task is defined by 3 generic types, called Params, Progress and Result,

AsyncTask have Four Main Method...

  1. onPreExecute() 
  2. doInBackground()
  3. onProgressUpdate()
  4. onPostExecute() 

onPreExecute()

This task is run on the main UI Thread, This method can show update the UI on the Activity hinting the start of the background process, like updating the UI with Progress Indicator.

doInBackground(Params......)

Invoked on the Background Thread.This method is executed right after onPreExecute() method is finished. Code for long running operations like updating Database, Retrieving Data from API etc should be implemented here.

onProgressUpdate(Progress......)

This method is executed on the UI Thread. This method is used to show progress made by the background process on the UI while the long running background process is still running.
This method is invoked after we make a call to  publishProgress(Progress...) mostly from doInBackground() method.

onPostExecute(Result);

Invoked on the UI Thread once the background process is complete.


Sample Use Case for Async Task

Following Example Demonstrates a Use case for User Registration.  Activity Class uses the UpdateStudentInfoTask for storing the User Registration Data like username, email etc and updates the UI. It does so by invoking UpdateStudentInfoTask.execute() method.

Activity Class Code Sample


protected void onCreate(Bundle savedInstanceState)
  {
     ## ..............Other boiler plate Codes has been removed for simplicity
     {
      @Override
      public void onClick(View v)
      {
        StudentInfo sInfo = new StudentInfo();
        EditText registerName = (EditText)rootView.findViewById(R.id.registerName);
        EditText registerEmail = (EditText)rootView.findViewById(R.id.registerEmail);
        sInfo.setName(registerName.getText().toString());
        sInfo.setEmail(registerEmail.getText().toString());
      
        UpdateStudentInfoTask asyncTask = new UpdateStudentInfoTask(getApplicationContext(),WelcomeActivity.this );
        asyncTask.execute(sInfo);
      }
    });

UpdateStudentInfoTask AsyncTask Example

This Class stores the new User Data in Database. Assuming that We need to validate the User input data(like duplicate Username, Duplicate email ids etc) all the processing is done in doInBackground() method. 
onProgressUpdate() method is used to periodically notify the UI about the Progress made.
And finally when onPostExecute() is completed the User is Navigated to the next Activity WelcomeActivity.

 private Context mContext;
 private WelcomeActivity mActivity;

  public UpdateStudentInfoTask(Context c, WelcomeActivity a)
  {
    mContext = c;
    mActivity = a;
  }

  @Override
  public Long doInBackground(StudentInfo... s)
  {
    StudentInfo currentStudent = s[0];
    
    publishProgress("Creating New User");
    
    DatabaseHelper dbHelper = DatabaseHelper.getInstance(mContext);
    long newStudentID = dbHelper.addUpdateStudentInfo(currentStudent);

    publishProgress("Saving New User in Session");

   return newStudentID;
  }

  @Override
  protected void onProgressUpdate(String... values)
  {
      Toast.makeText(mContext,  values[0], Toast.LENGTH_SHORT).show();
      super.onProgressUpdate(values);
  }
  
  @Override
  protected void onPostExecute(Long result)
  {
    super.onPostExecute(result);
    mActivity.gotoWelcomeActivity();
  }



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