- (void)drawRect:(CGRect)rect {

    [super drawRect:rect];

    //步骤一:得到当前绘制画布上下文，用于后续将内容绘制在画布上

    CGContextRef context = UIGraphicsGetCurrentContext();

    //步骤二：将坐标系上下翻转。对于底层的绘制引擎来说，屏幕左下角是（0，0）坐标。而对于上层的UIKit来说，左上角是（0，0）坐标。所以我们为了之后的坐标系描述按UIKit来显示，这里做了一个坐标系上下翻转操作。翻转之后，底层和上层的（0，0）坐标就是重合的了。

    CGContextSetTextMatrix(context, CGAffineTransformIdentity);

    CGContextTranslateCTM(context, , self.bounds.size.height);

    CGContextScaleCTM(context, 1.0, -1.0);

    //步骤三：创建绘制区域

    CGMutablePathRef path = CGPathCreateMutable();

    CGPathAddRect(path, NULL, self.bounds); 

//    CGPathAddEllipseInRect(path, NULL, self.bounds);

    //步骤四

    NSAttributedString *attString = [[NSAttributedString alloc] initWithString:@"ScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhangScottZhang"];

    CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attString);

    CTFrameRef frame = CTFramesetterCreateFrame(framesetter, CFRangeMake(, [attString length]), path, NULL);

    //步骤五

    CTFrameDraw(frame, context);

    //步骤六

    CFRelease(frame);

    CFRelease(path);

    CFRelease(framesetter);

}