iOS生成图片数字字母验证效果

#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 kRandomColor [UIColor grayColor];
#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;

    //    [UIColor grayColor]

    //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];
  }
}

#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:20.0]}];
  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