Andorid学习之游戏背景移动

借助Bitmap和createBitmap方法可以挖取源位图的一块，这样可以在程序中通过定时器不断的挖取源位图中的不同块，给游戏者一种背景在移动，即对象在向前移动的假象。

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 = 480;
		final int HEIGHT = 800;
		private int startY = BACK_HEIGHT - HEIGHT;

		public MyView(Context context)
		{
			super(context);
			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()
			{
				public void run()
				{
					handler.sendEmptyMessage(0x123);
				}

			}, 0, 100);
		}
		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, 360, null);
		}
	}
}