继承surfaceview，用path.lineto为什么画不出线来？

我写的那个类想画由5个点链接起来的线，节点用小圆表示画出来了，可是线却画不出来。这是怎么回事，主要代码如下

public void draw() {
Canvas canvas = getHolder().lockCanvas();
canvas.drawColor(Color.WHITE);
int x=width/2,y=height/6,radius=10;
railPath.moveTo(x,y);
canvas.drawCircle(x, y, radius, circlePaint);
railPath.lineTo(x, y*2);
canvas.drawCircle(x, y*2, radius, circlePaint);
railPath.lineTo(x, y*3);
canvas.drawCircle(x, y*3, radius, circlePaint);
railPath.lineTo(x, y*4);
canvas.drawCircle(x, y*4, radius, circlePaint);
railPath.lineTo(x, y*5);
canvas.drawCircle(x, y*5, radius, circlePaint);
railPath.close();
canvas.drawPath(railPath, railPaint);
getHolder().unlockCanvasAndPost(canvas);
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
draw();

你这个railPath初始化时在哪里？

railPath初始化设置颜色了没。。。