原文链接：http://www.cnblogs.com/jerehedu/p/4527707.html

效果图：

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" alt="" />

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:@"",@"",@"",@"",@"",@"",@"",@"",@"",@"",@"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 = ; i < kCharCount; i++)

    {

        NSInteger index = arc4random() % ([self.changeArray count] - );

        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:]}];

    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 = ; 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 = ; 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