Android用Canvas画一个真正能跑的跑马灯

以前自学，都是用帧动画来实现跑马灯，这几天常失眠，晚上学东西也学不进，所以用Canvas写个小Demo，这么无聊的应该只有我一个了吧，废话不多说，下面上内容。

老规矩，最后有源码
效果图如下：

上代码前先介绍下手机坐标系，如下图

然后是绘制草图，如下：

大概思路为，开一个耗时线程使彩色背景旋转，来达到跑马灯的效果。

核心：
1.计算出View宽高，矩形宽高，从而算出矩形的坐标点。

 int canvasWidth = canvas.getWidth();       //画布宽度
        int canvasHeight = canvas.getHeight();     //画布高度
        int canvansMax= (int) Math.sqrt(Math.pow(canvasWidth/2,2)+Math.pow(canvasHeight/2,2))+1; //正方形宽高的一半

2.绘制背景，跑马灯，幕布

  //开始绘制底层背景
        p.setColor(Color.WHITE);
        RectF oval2 = new RectF(0, 0, canvasWidth, canvasHeight);// 设置个新的长方形，扫描测量
        canvas.drawRect(oval2,p);
        //开始绘制跑马灯
        Paint p1=new Paint(p);
        Shader mShader = new LinearGradient(canvasWidth/2-canvansMax,canvasHeight/2-canvansMax , 2*canvansMax, 2*canvansMax,
                new int[] { Color.RED, Color.GREEN,Color.CYAN,Color.MAGENTA,Color.GRAY,Color.BLUE,Color.YELLOW,Color.RED, Color.GREEN,Color.CYAN,Color.MAGENTA,Color.GRAY,Color.BLUE,Color.YELLOW}, null, Shader.TileMode.REPEAT); 
        p1.setShader(mShader);
        RectF oval = new RectF(canvasWidth/2-canvansMax,canvasHeight/2-canvansMax , 2*canvansMax, 2*canvansMax);// 设置个新的长方形
        canvas.drawRect(oval,p1);
        //绘制幕布
        Paint p2=new Paint();
        p2.setColor(Color.BLACK);
        RectF oval3 = new RectF(30, 30, canvasWidth-30, canvasHeight-30);// 设置个新的长方形，扫描测量
        canvas.drawRect(oval3,p2);

3.找到旋转的依靠，并开启一个耗时任务。

   private Calendar mCalendar; // 时间对象
    public static final int START_CLOCK = 1000;// 开启时钟的标识
    Handler mHandler = new Handler() {
        public void handleMessage(android.os.Message msg) {
            switch (msg.what) {
                case DrawView.START_CLOCK:
                    mCalendar = mCalendar.getInstance();
                    invalidate();
                    sendEmptyMessageDelayed(DrawView.START_CLOCK, 10);
                    break;
                case DrawView.STOP_CLOCK:
                    break;
                default:
                    break;
            }
        }
    };

4.设置彩色正方形旋转

 canvas.rotate(sec*100,canvasWidth/2,canvasHeight/2);

5.将幕布按照彩色正方形反向旋转（不设置则跟着正方形一起旋转）；

  canvas.rotate(-sec*100,canvasWidth/2,canvasHeight/2);

源码如下：
1.完整java文件

public class MarqueeView extends View {
    private Calendar mCalendar; // 时间对象
    public static final int START_CLOCK = 1000;// 开启时钟的标识
    Handler mHandler = new Handler() {
        public void handleMessage(android.os.Message msg) {
            switch (msg.what) {
                case DrawView.START_CLOCK:
                    mCalendar = mCalendar.getInstance();
                    invalidate();
                    sendEmptyMessageDelayed(DrawView.START_CLOCK, 10);
                    break;
                case DrawView.STOP_CLOCK:
                    break;
                default:
                    break;
            }
        }
    };

    public MarqueeView(Context context) {
        super(context);
    }

    public MarqueeView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        mCalendar = mCalendar.getInstance();
        if (mCalendar == null) {
            mCalendar = mCalendar.getInstance();
        }
        mHandler.sendEmptyMessage(START_CLOCK);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        drawAxis(canvas);
    }

    //绘制
    private void drawAxis(Canvas canvas){
        Paint p=new Paint();
        int canvasWidth = canvas.getWidth();       //画布宽度
        int canvasHeight = canvas.getHeight();     //画布高度
        int canvansMax= (int) Math.sqrt(Math.pow(canvasWidth/2,2)+Math.pow(canvasHeight/2,2))+1; //正方形宽高的一半
        int sec = mCalendar.get(Calendar.SECOND);//得到当前秒数
        //开始绘制底层背景
        p.setColor(Color.WHITE);
        RectF oval2 = new RectF(0, 0, canvasWidth, canvasHeight);// 设置个新的长方形，扫描测量
        canvas.drawRect(oval2,p);
        canvas.rotate(sec*100,canvasWidth/2,canvasHeight/2);
        //开始绘制跑马灯
        Paint p1=new Paint(p);
        Shader mShader = new LinearGradient(canvasWidth/2-canvansMax,canvasHeight/2-canvansMax , 2*canvansMax, 2*canvansMax,
                new int[] { Color.RED, Color.GREEN,Color.CYAN,Color.MAGENTA,Color.GRAY,Color.BLUE,Color.YELLOW,Color.RED, Color.GREEN,Color.CYAN,Color.MAGENTA,Color.GRAY,Color.BLUE,Color.YELLOW}, null, Shader.TileMode.REPEAT);
        p1.setShader(mShader);
        RectF oval = new RectF(canvasWidth/2-canvansMax,canvasHeight/2-canvansMax , 2*canvansMax, 2*canvansMax);// 设置个新的长方形，扫描测量
        canvas.drawRect(oval,p1);
        //绘制幕布
        Paint p2=new Paint();
        canvas.rotate(-sec*100,canvasWidth/2,canvasHeight/2);
        p2.setColor(Color.BLACK);
        RectF oval3 = new RectF(30, 30, canvasWidth-30, canvasHeight-30);// 设置个新的长方形，扫描测量
        canvas.drawRect(oval3,p2);


    }
}

2.xml中调用

<com................MarqueeView
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>