Android and Custom ProgressBar

package com.myapp;

import android.os.Bundle;
import android.os.Handler;
import android.app.Activity;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;

public class MainActivity extends Activity {
	 
		Button btnDoWork;
		ProgressBar progressBar;
		private int progressBarStatus = 0;
		private Handler progressBarHandler = new Handler();
	 
 
		@Override
		public void onCreate(Bundle savedInstanceState) {
			super.onCreate(savedInstanceState);
			setContentView(R.layout.activity_main);
			
			progressBar = (ProgressBar) findViewById(R.id.progressBar1);
			
			progressBar.setVisibility(View.INVISIBLE);  // Hide ProgressBar
			
			// button1 Do Work
			btnDoWork = (Button) findViewById(R.id.button1);
			btnDoWork.setOnClickListener(new View.OnClickListener() {
		            public void onClick(View v) { // Start Event onClick
		
		            	progressBar.setVisibility(View.VISIBLE);
						progressBar.setProgress(0);
						progressBar.setMax(100);
						progressBar.setProgressDrawable(v.getResources().getDrawable(
				                R.drawable.custom_progress));
			 

						progressBarStatus = 0;
			 
								new Thread(new Runnable() {
								  public void run() {
									while (progressBarStatus < 100) {
					 
									  // process some tasks
									  progressBarStatus = DoWork();
					 
										try {
											Thread.sleep(300);
										} catch (InterruptedException e) {
											e.printStackTrace();
										}
						 
									  // Update the progress bar
									  progressBarHandler.post(new Runnable() {
										public void run() {
										  progressBar.setProgress(progressBarStatus);
										}
									  });
									}
							
						  }
					   }).start();
									
					
		            } // End Event onClick
		            
		        });
	 
		}
	 

	 
		// DoWork & Set Status Progress Bar
		public int DoWork() {
			
			// Do some work EG: Save , Download , Insert , ..
			// **** Work
			// **** Work
			// **** Work
			// **** Work
			progressBarStatus++; // Work process and return status
			
			if( progressBarStatus < 100)
			{
				return progressBarStatus;
			}
			
			// When Finish
			try {
				Thread.sleep(1000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}

			return 100;
	 
		}
	 
	}

<?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" >
 
    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical|center_horizontal|center"
        android:text="Do Work!" />

 
</LinearLayout>