初学Android,图形图像之游戏画面中飞行的飞机(三十)

上面的飞机移动背景是用定时器不断挖取源位图的块，从而形成背景移动的假象

控制图片背景不断下移，就会感觉飞机在不断的飞行

本程序有两个位图，一个背景图，高度远超过屏幕的高度，然后是一张飞机的位图

package WangLi.Graphics.MoveBack;

import java.util.Timer;
import java.util.TimerTask;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;

public class MoveBack extends Activity
{
	@Override
	public void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		setContentView(new MyView(this));
	}
	class MyView extends View
	{
		//记录背景位图的实际高度
		final int BACK_HEIGHT = 1700;
		//背景图片
		private Bitmap back;
		private Bitmap plane;
		//背景图片的开始位置
		final int WIDTH = 371;
		final int HEIGHT = 440;
		private int startY = BACK_HEIGHT - HEIGHT;		
		public MyView(Context context)
		{
			super(context);
			// TODO Auto-generated constructor stub
			back = BitmapFactory.decodeResource(context.getResources()
				, R.drawable.back_img);
			plane = BitmapFactory.decodeResource(context.getResources()
				, R.drawable.plane);			
			final Handler handler = new Handler()
			{
				public void handleMessage(Message msg)
				{
					if (msg.what == 0x123)
					{
						//重新开始移动
						if (startY <= 0)
						{
							startY = BACK_HEIGHT - HEIGHT;
						}
						else
						{
							startY -= 3;
						}
					}
					invalidate();
				}
			};
			new Timer().schedule(new TimerTask()
			{
				@Override
				public void run()
				{
					handler.sendEmptyMessage(0x123);					
				}
				
			}, 0 , 10);
		}
		@Override
		public void onDraw(Canvas canvas)
		{
			// 根据原始位图和Matrix创建新图片
			Bitmap bitmap2 = Bitmap.createBitmap(back, 0, startY
				, WIDTH , HEIGHT);
			// 绘制新位图
			canvas.drawBitmap(bitmap2, 0 , 0  , null);
			// 绘制飞机
			canvas.drawBitmap(plane, 160 , 380  , null);				
		}		
	}
}