详解iOS 验证码输入的实现思路

- (instancetype)initWithCount:(NSInteger)count margin:(CGFloat)margin
{
  if (self = [super init]) {
    self.itemCount = count; // itemCount是验证码的个数，比如6个
    self.itemMargin = margin; // itemMargin是每个Label之间的间距
    [self configTextField];
  }
  return self;
}

- (void)configTextField
{
  UITextField *textField = [[UITextField alloc] init];
  textField.autocapitalizationType = UITextAutocapitalizationTypeNone;
  textField.keyboardType = UIKeyboardTypeNumberPad;
  [textField addTarget:self action:@selector(tfEditingChanged:) forControlEvents:(UIControlEventEditingChanged)];
  // 小技巧：这个属性为YES，可以强制使用系统的数字键盘，缺点是重新输入时，会清空之前的内容
  // clearsOnBeginEditing 属性并不适用于 secureTextEntry = YES 时
  // textField.secureTextEntry = YES;
  [self addSubview:textField];
  self.textField = textField;
  // 小技巧：通过textField上层覆盖一个maskView，可以去掉textField的长按事件
  UIButton *maskView = [UIButton new];
  maskView.backgroundColor = [UIColor whiteColor];
  [maskView addTarget:self action:@selector(clickMaskView) forControlEvents:(UIControlEventTouchUpInside)];
  [self addSubview:maskView];
  self.maskView = maskView;
  for (NSInteger i = 0; i < self.itemCount; i++)
  {
    UILabel *label = [UILabel new];
    [self addSubview:label];
    [self.labels addObject:label];
  }
  for (NSInteger i = 0; i < self.itemCount; i++)
  {
    UIView *line = [UIView new];
    [self.lines addObject:line];
  }
}

#pragma mark - 编辑改变
- (void)tfEditingChanged:(UITextField *)textField
{
  if (textField.text.length > self.itemCount) {
    textField.text = [textField.text substringWithRange:NSMakeRange(0, self.itemCount)];
  }
  for (int i = 0; i < self.itemCount; i++)
  {
    UILabel *label = [self.labels objectAtIndex:i];
    if (i < textField.text.length) {
      label.text = [textField.text substringWithRange:NSMakeRange(i, 1)];
    } else {
      label.text = nil;
    }
  }
  // 输入完毕后，自动隐藏键盘
  if (textField.text.length >= self.itemCount) {
    [textField resignFirstResponder];
  }
}

- (instancetype)init UNAVAILABLE_ATTRIBUTE;
+ (instancetype)new UNAVAILABLE_ATTRIBUTE;