原文链接：http://www.cnblogs.com/jerehedu/p/4527707.html
效果图：
CaptchaView.h
@interface CaptchaView : UIView @property (nonatomic, retain) NSArray *changeArray; //字符素材数组 @property (nonatomic, retain) NSMutableString *changeString; //验证码的字符串
CaptchaView.m
#import "CaptchaView.h" #define kRandomColor [UIColor colorWithRed:arc4random() % 256 / 256.0 green:arc4random() % 256 / 256.0 blue:arc4random() % 256 / 256.0 alpha:1.0]; #define kLineCount 6 #define kLineWidth 1.0 #define kCharCount 4 #define kFontSize [UIFont systemFontOfSize:arc4random() % 5 + 15] @implementation CaptchaView @synthesize changeString,changeArray; - (instancetype)initWithFrame:(CGRect)frame { if (self = [super initWithFrame:frame]) { self.layer.cornerRadius = 5.0; //设置layer圆角半径 self.layer.masksToBounds = YES; //隐藏边界 self.backgroundColor = kRandomColor; //显示一个随机验证码 [self changeCaptcha]; } return self; } #pragma mark 更换验证码,得到更换的验证码的字符串 -(void)changeCaptcha { //<一>从字符数组中随机抽取相应数量的字符，组成验证码字符串 //数组中存放的是全部可选的字符，可以是字母，也可以是中文 self.changeArray = [[NSArray alloc] initWithObjects:@"0",@"1",@"2",@"3",@"4",@"5",@"6",@"7",@"8",@"9",@"A",@"B",@"C",@"D",@"E",@"F",@"G",@"H",@"I",@"J",@"K",@"L",@"M",@"N",@"O",@"P",@"Q",@"R",@"S",@"T",@"U",@"V",@"W",@"X",@"Y",@"Z",@"a",@"b",@"c",@"d",@"e",@"f",@"g",@"h",@"i",@"j",@"k",@"l",@"m",@"n",@"o",@"p",@"q",@"r",@"s",@"t",@"u",@"v",@"w",@"x",@"y",@"z",nil]; //如果能确定最大需要的容量，使用initWithCapacity:来设置，好处是当元素个数不超过容量时，添加元素不需要重新分配内存 NSMutableString *getStr = [[NSMutableString alloc] initWithCapacity:kCharCount]; self.changeString = [[NSMutableString alloc] initWithCapacity:kCharCount]; //随机从数组中选取需要个数的字符，然后拼接为一个字符串 for(int i = 0; i < kCharCount; i++) { NSInteger index = arc4random() % ([self.changeArray count] - 1); getStr = [self.changeArray objectAtIndex:index]; self.changeString = (NSMutableString *)[self.changeString stringByAppendingString:getStr]; } //<2>从网络获取字符串，然后把得到的字符串在本地绘制出来（网络获取步骤在这省略） } #pragma mark 点击view时调用，因为当前类自身就是UIView，点击更换验证码可以直接写到这个方法中，不用再额外添加手势 -(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { //点击界面，切换验证码 [self changeCaptcha]; //setNeedsDisplay调用drawRect方法来实现view的绘制 [self setNeedsDisplay]; } #pragma mark 绘制界面（1.UIView初始化后自动调用； 2.调用setNeedsDisplay方法时会自动调用） - (void)drawRect:(CGRect)rect { // 重写父类方法，首先要调用父类的方法 [super drawRect:rect]; //设置随机背景颜色 self.backgroundColor = kRandomColor; //获得要显示验证码字符串，根据长度，计算每个字符显示的大概位置 NSString *text = [NSString stringWithFormat:@"%@",self.changeString]; CGSize cSize = [@"S" sizeWithAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:20]}]; int width = rect.size.width / text.length - cSize.width; int height = rect.size.height - cSize.height; CGPoint point; //依次绘制每一个字符,可以设置显示的每个字符的字体大小、颜色、样式等 float pX, pY; for (int i = 0; i < text.length; i++) { pX = arc4random() % width + rect.size.width / text.length * i; pY = arc4random() % height; point = CGPointMake(pX, pY); unichar c = [text characterAtIndex:i]; NSString *textC = [NSString stringWithFormat:@"%C", c]; [textC drawAtPoint:point withAttributes:@{NSFontAttributeName:kFontSize}]; } //调用drawRect：之前，系统会向栈中压入一个CGContextRef，调用UIGraphicsGetCurrentContext()会取栈顶的CGContextRef CGContextRef context = UIGraphicsGetCurrentContext(); //设置画线宽度 CGContextSetLineWidth(context, kLineWidth); //绘制干扰的彩色直线 for(int i = 0; i < kLineCount; i++) { //设置线的随机颜色 UIColor *color = kRandomColor; CGContextSetStrokeColorWithColor(context, [color CGColor]); //设置线的起点 pX = arc4random() % (int)rect.size.width; pY = arc4random() % (int)rect.size.height; CGContextMoveToPoint(context, pX, pY); //设置线终点 pX = arc4random() % (int)rect.size.width; pY = arc4random() % (int)rect.size.height; CGContextAddLineToPoint(context, pX, pY); //画线 CGContextStrokePath(context); } } @end