Android: Playing with a Singleton

A few weeks ago, I have shown you the steps of creating a Singleton object for Flex applications. As for this week, I am going to show you how to create a Singleton for a Android Application.

Image of Demo Android App.
The App that I am showing in this post will be using the Singleton
object to store the number of clicks.

Main application file - zcs/simpleSingleton/SimpleSingletonActivity.java

package zcs.simpleSingleton;

import android.app.Activity;
import android.os.Bundle;

public class SimpleSingletonActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
}

A reusable Custom Component File - zcs/simpleSingleton/CustomComponent.java

package zcs.simpleSingleton;

import zcs.singleton.MainSingleton;
import android.content.Context;
import android.util.AttributeSet;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.TextView;

public class CustomComponent extends LinearLayout 
{
 private TextView txt = null;
 
 public CustomComponent(Context context, AttributeSet attrs) {
  super(context, attrs);
  // TODO Auto-generated constructor stub      
  LayoutInflater.from(context).
   inflate(R.layout.layout_custom_component, this, true);
  
  Button btn = (Button) this.findViewById(R.id.btn);
  btn.setOnClickListener(clickListener);
  
  txt = (TextView) this.findViewById(R.id.txt);
 }
 
 // Create a clickListener of type OnClickListener
 // Which will be added to the Button
 private OnClickListener clickListener = new OnClickListener() 
 {
  @Override
  public void onClick(View arg0) {
   //Create an instance of MainSingleton
   MainSingleton tempObj;
   tempObj = MainSingleton.getInstance();
   //Get the current value for Counter and
   //increase it by 1
   int tempCount = tempObj.getCounter() + 1;
   //Set it back to the MainSingleton
   tempObj.setCounter(tempCount);
   
   //Update the text of the label
   txt.setText("Number of Counts:" + tempCount);
  }
 };

}

Main Singleton File - zcs/singleton/MainSingleton.java

package zcs.singleton;

public class MainSingleton 
{
 private static MainSingleton instance;
 
 public static MainSingleton getInstance()
 {
  //If the Singleton is not found, create
  //an instance of it and init / reset the
  //values.
  if(instance == null)
  {
   instance = new MainSingleton();
   instance.reset();
  }
  return instance;
 }
 
 //function to reset data
 public void reset()
 {
  _counter = 0;
 }
 
 //Variable storing the number of counter
 private int _counter = 0;

 public int getCounter() {
  return _counter;
 }

 public void setCounter(int _counter) {
  this._counter = _counter;
 }
 
}

Main Application XML Layout file - layout.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
    <zcs.simpleSingleton.CustomComponent
        android:layout_width="wrap_content"
     android:layout_height="wrap_content"/>
    <TableLayout 
        android:layout_width="fill_parent"
     android:layout_height="fill_parent">
        <LinearLayout 
            android:layout_width="fill_parent"
      android:layout_height="wrap_content">
         <zcs.simpleSingleton.CustomComponent
          android:layout_width="wrap_content"
       android:layout_height="wrap_content"/>
     </LinearLayout>
        <LinearLayout 
            android:layout_width="fill_parent"
      android:layout_height="wrap_content">
         <zcs.simpleSingleton.CustomComponent
          android:layout_width="wrap_content"
       android:layout_height="wrap_content"/>
     </LinearLayout>
     <TableLayout 
         android:layout_width="fill_parent"
      android:layout_height="fill_parent">
         <LinearLayout 
             android:layout_width="fill_parent"
       android:layout_height="wrap_content">
          <zcs.simpleSingleton.CustomComponent
           android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
      </LinearLayout>
         <LinearLayout 
             android:layout_width="fill_parent"
       android:layout_height="wrap_content">
          <zcs.simpleSingleton.CustomComponent
           android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
      </LinearLayout>
     </TableLayout>
    </TableLayout>
</LinearLayout>

Custom Component Layout File

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >
    <Button android:id="@+id/btn"         
         android:text="@string/btn_name"
         android:layout_width="wrap_content"
          android:layout_height="wrap_content"/>
    <TextView android:id="@+id/txt"    
         android:text="@string/txt_name"     
         android:layout_width="wrap_content"
          android:layout_height="wrap_content"/>
</LinearLayout>

* Click here to download the source files of this Android Demo.