利用iOS绘制图片生成随机验证码示例代码

@property (nonatomic, retain) NSArray *changeArray;
@property (nonatomic, retain) NSMutableString *changeString;
@property (nonatomic, retain) UILabel *codeLabel;

-(void)changeCode;
@end

@synthesize changeArray = _changeArray;
@synthesize changeString = _changeString;
@synthesize codeLabel = _codeLabel;

- (id)initWithFrame:(CGRect)frame
{
  self = [super initWithFrame:frame];
  if (self) {
    // Initialization code

    float red = arc4random() % 100 / 100.0;
    float green = arc4random() % 100 / 100.0;
    float blue = arc4random() % 100 / 100.0;
    UIColor *color = [UIColor colorWithRed:red green:green blue:blue alpha:0.2];
    self.backgroundColor = color;
    [self change];
  }
  return self;
}

-(void)changeCode
{
  [self change];
  [self setNeedsDisplay];
}

- (void)change
{
  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];

  NSMutableString *getStr = [[NSMutableString alloc] initWithCapacity:5];

  self.changeString = [[NSMutableString alloc] initWithCapacity:6];
  for(NSInteger i = 0; i < 4; i++)
  {
    NSInteger index = arc4random() % ([self.changeArray count] - 1);
    getStr = [self.changeArray objectAtIndex:index];

    self.changeString = (NSMutableString *)[self.changeString stringByAppendingString:getStr];
  }
}

- (void)drawRect:(CGRect)rect 
{
  [super drawRect:rect];

  float red = arc4random() % 100 / 100.0;
  float green = arc4random() % 100 / 100.0;
  float blue = arc4random() % 100 / 100.0;

  UIColor *color = [UIColor colorWithRed:red green:green blue:blue alpha:0.5];
  [self setBackgroundColor:color];

  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;

  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:[UIFont systemFontOfSize:20]}];
  }

  CGContextRef context = UIGraphicsGetCurrentContext();
  CGContextSetLineWidth(context, 1.0);
  for(int cout = 0; cout < 10; cout++)
  {
    red = arc4random() % 100 / 100.0;
    green = arc4random() % 100 / 100.0;
    blue = arc4random() % 100 / 100.0;
    color = [UIColor colorWithRed:red green:green blue:blue alpha:0.2];
    CGContextSetStrokeColorWithColor(context, [color CGColor]);
    pX = arc4random() % (int)rect.size.width;
    pY = arc4random() % (int)rect.size.height;
    CGContextMoveToPoint(context, pX, pY);
    pX = arc4random() % (int)rect.size.width;
    pY = arc4random() % (int)rect.size.height;
    CGContextAddLineToPoint(context, pX, pY);
    CGContextStrokePath(context);
  }
}
@end

_codeView = [[CodeView alloc] initWithFrame:CGRectMake(15+(SCREEN_WIDTH-30)/3*2, 75, (SCREEN_WIDTH-30)/3, 39)];
 //手势
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapClick:)];
[_codeView addGestureRecognizer:tap];
[self.view addSubview: _codeView];

- (void)tapClick:(UITapGestureRecognizer*)tap
{
  [_codeView changeCode];
}