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