Android :: Android - Why UI Still Blocks When Worker Thread Used?

package com.commonsware.android.threads;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;

public class HandlerDemo extends Activity {
Thread mBackground; ProgressBar bar;
Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
bar.incrementProgressBy(5);
} }; boolean isRunning = false;
@Override
public void onCreate(Bundle icicle) { super.onCreate(icicle);
setContentView(R.layout.main); bar = (ProgressBar) findViewById(R.id.progress);
} public void onStart() { super.onStart(); bar.setProgress(0);
mBackground = new Thread(new Runnable() { public void run() { try { int a = 0;
for (int i = 0; i < 20 && isRunning; i++) { for (int j = 0; j < 2000; j++) {
for (int k = 0; k < 1000; k++) { a++;
} } handler.sendMessage(handler.obtainMessage());
} } catch (Throwable t) { // just end the background thread } } } );
findViewById(R.id.LoginButton).setOnClickListener(
new OnClickListener() { public void onClick(View v) { mBackground.run();
} } );
isRunning = true;
} public void onStop() { super.onStop();
isRunning = false;
} }