利用UIBezierPath這個類繪制圓形圖片，如下：

- (UIImage*)drawImageWithSize:(CGSize)size imageName:(NSString *)imageName

{

    // 申請一塊特定大小的畫布

    UIGraphicsBeginImageContext(size);

    // 畫出一個與畫布等大的圓

    UIBezierPath *path = [UIBezierPathbezierPathWithOvalInRect:CGRectMake(0,0, size.width, size.height)];

    // 將這個圓以外的部分設置為無效區

    [path addClip];

    UIImage *oldImage = [UIImageimageNamed:imageName];

    [oldImage drawInRect:CGRectMake(0,0, size.width, size.height)];

    UIImage *newImage =UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return newImage;

}

imageView.image =newImage;