iOS generated image numeric letter verification effect

#import ""

#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]) {

     = 5.0; //Set the layer rounded corner radius     = YES; //Hide boundaries     = kRandomColor;

    //    [UIColor grayColor]

    //Show a random verification code    [self changeCaptcha];
  }

  return self;
}
#pragma mark Change verification code and get the string of the replaced verification code-(void)changeCaptcha
{
  //<1> Randomly extract the corresponding number of characters from the character array to form a verification code string  //The array stores all optional characters, either letters or Chinese   = [[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];

  //If you can determine the maximum required capacity, use initWithCapacity: to set it. The advantage is that when the number of elements does not exceed the capacity, adding elements does not require reallocating memory.  NSMutableString *getStr = [[NSMutableString alloc] initWithCapacity:kCharCount];
   = [[NSMutableString alloc] initWithCapacity:kCharCount];

  // Randomly select the characters that require a number from the array, and then splice them into a string  for(int i = 0; i &lt; kCharCount; i++)
  {
    NSInteger index = arc4random() % ([ count] - 1);
    getStr = [ objectAtIndex:index];

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

#pragma mark Called when clicking on the view, because the current class itself is a UIView. Click to change the verification code to write it directly into this method without adding additional gestures-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
  //Click on the interface to switch the verification code  [self changeCaptcha];

  //setNeedsDisplay calls the drawRect method to implement view drawing  [self setNeedsDisplay];
}

#pragma mark draw interface (automatically called after initialization; 2. It will be automatically called when calling the setNeedsDisplay method)- (void)drawRect:(CGRect)rect {
  // To override the parent class method, you must first call the parent class method  [super drawRect:rect];

  //Set random background colors   = kRandomColor;

  //Get the string to display the verification code, and calculate the approximate position of each character according to the length.  NSString *text = [NSString stringWithFormat:@"%@",];
  CGSize cSize = [@"S" sizeWithAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:20.0]}];
  int width =  /  - ;
  int height =  - ;
  CGPoint point;

  //Draw each character in sequence, and you can set the font size, color, style, etc. of each character displayed.  float pX, pY;
  for (int i = 0; i &lt; ; i++)
  {
    pX = arc4random() % width +  /  * 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}];
  }

    //Call drawRect: Before, the system will press a CGContextRef into the stack, and calling UIGraphicsGetCurrentContext() will take the CGContextRef at the top of the stack.    CGContextRef context = UIGraphicsGetCurrentContext();
    //Set the line drawing width    CGContextSetLineWidth(context, kLineWidth);

    //Draw the colored lines of interference    for(int i = 0; i &lt; kLineCount; i++)
    {
      //Set the random color of the line      UIColor *color = kRandomColor;
      CGContextSetStrokeColorWithColor(context, [color CGColor]);
      //Set the starting point of the line      pX = arc4random() % (int);
      pY = arc4random() % (int);
      CGContextMoveToPoint(context, pX, pY);
      //Set the end point of the line      pX = arc4random() % (int);
      pY = arc4random() % (int);
      CGContextAddLineToPoint(context, pX, pY);
      //Draw lines      CGContextStrokePath(context);
    }
}
@end