Android:Handler

Different Ways to update UI in a none-ui thread:

The following is a little demo showing three different ways to update ui in a none-ui thread and the best way i will commend is by a Handler.

package com.slowalker.handlerdemo;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.Window;

public class MainActivity extends Activity {
	
	private static final String TAG = MainActivity.class.getSimpleName();
	private static final boolean DEBUG = true;
	
	private static final int FLAG_INVALIDATE = 0x100;
	
	private Ball mBall;
	
	/*create a handler.*/
	private Handler mHandler = new Handler() {

		@Override
		public void handleMessage(Message msg) {
			if (msg == null) {
				return;
			}
			switch (msg.what) {
			case FLAG_INVALIDATE:
				mBall.invalidate();
				break;
			default:
				break;
			}
		}
	};
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		requestWindowFeature(Window.FEATURE_NO_TITLE);
		setContentView(mBall = new Ball(this));
		//testWay1();
		//testWay2();
		testWay3();
	}
	
	/*The first way to update UI in a none-ui thread --- by Handler*/
	private void testWay1() {
		new Thread(new Runnable() {

			@Override
			public void run() {
				while (!Thread.currentThread().isInterrupted()) {
					Message msg = Message.obtain();
					msg.what = FLAG_INVALIDATE;
					mHandler.sendMessage(msg);
					try {
						Thread.sleep(100);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
			
		}).start();
	}
	
	/*The second way to update UI in a none-ui thread by View.postInvalidate()*/
	
	private void testWay2() {

		new Thread(new Runnable() {

			@Override
			public void run() {
				while (!Thread.currentThread().isInterrupted()) {
					/*If you use invalidate(), app will crash.*/
					mBall.postInvalidate();
					try {
						Thread.sleep(100);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}).start();
	}
	/*The third way to update UI in a none-ui thread by Handler.post().*/
	private void testWay3() {
		
		mHandler.post(new Runnable() {

			@Override
			public void run() {
				Message msg = Message.obtain();
				msg.what = FLAG_INVALIDATE;
				mHandler.sendMessageDelayed(msg, 1000);
			}
		});
	}
	
	/*Draw a ball on mobile screen.*/
	private class Ball extends View {

		private final String TAG = Ball.class.getSimpleName();
		
		private float posX = 10;
		
		public Ball(Context context) {
			super(context);
		}

		@Override
		protected void onDraw(Canvas canvas) {
			if (DEBUG) {
				Log.d(TAG, "onDraw");
			}
			super.onDraw(canvas);
			posX += 10;
			if (DEBUG) {
				Log.d(TAG, "posX = " + posX);
			}
			Paint mPaint = new Paint();
			mPaint.setAntiAlias(true);
			mPaint.setColor(Color.GREEN);
			canvas.drawCircle(posX, 50, 50, mPaint);
		}
	}

}