iOS实现类似微信和支付宝的密码输入框（UIKeyInput协议）

#pragma mark - UIKeyInput
/**
 * 用于显示的文本对象是否有任何文本
 */
- (BOOL)hasText {
  return self.textStore.length > 0;
}

/**
 * 插入文本
 */
- (void)insertText:(NSString *)text {
  if (self.textStore.length  0) {
    [self.textStore deleteCharactersInRange:NSMakeRange(self.textStore.length - 1, 1)];
   if ([self.delegate respondsToSelector:@selector(passWordDidChange:)]) {
      [self.delegate passWordDidChange:self];
    }
  }
  [self setNeedsDisplay];
}

/**
 * 是否能成为第一响应者
 */
- (BOOL)canBecomeFirstResponder {
  return YES;
}

/**
 * 点击成为第一相应者
 */
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
  if (![self isFirstResponder]) {
    [self becomeFirstResponder];
  }
}

/**
 * 设置正方形的边长
 */
- (void)setSquareWidth:(CGFloat)squareWidth {
  _squareWidth = squareWidth;
  [self setNeedsDisplay];
}

/**
 * 设置键盘的类型
 */
- (UIKeyboardType)keyboardType {
  return UIKeyboardTypeNumberPad;
}

/**
 * 设置密码的位数
 */
- (void)setPassWordNum:(NSUInteger)passWordNum {
  _passWordNum = passWordNum;
  [self setNeedsDisplay];
}

/**
 * 绘制
 */
- (void)drawRect:(CGRect)rect {
  CGFloat height = rect.size.height;
  CGFloat width = rect.size.width;
  CGFloat x = (width - self.squareWidth*self.passWordNum)/2.0;
  CGFloat y = (height - self.squareWidth)/2.0;
  CGContextRef cOntext= UIGraphicsGetCurrentContext();
  //画外框
  CGContextAddRect(context, CGRectMake( x, y, self.squareWidth*self.passWordNum, self.squareWidth));
  CGContextSetLineWidth(context, 1);
  CGContextSetStrokeColorWithColor(context, self.rectColor.CGColor);
  CGContextSetFillColorWithColor(context, [UIColor whiteColor].CGColor);
  //画竖条
  for (int i = 1; i <= self.passWordNum; i++) {
    CGContextMoveToPoint(context, x+i*self.squareWidth, y);
    CGContextAddLineToPoint(context, x+i*self.squareWidth, y+self.squareWidth);
     CGContextClosePath(context);
  }
  CGContextDrawPath(context, kCGPathFillStroke);
  CGContextSetFillColorWithColor(context, self.pointColor.CGColor);
  //画黑点
  for (int i = 1; i <= self.textStore.length; i++) {
    CGContextAddArc(context, x+i*self.squareWidth - self.squareWidth/2.0, y+self.squareWidth/2, self.pointRadius, 0, M_PI*2, YES);
    CGContextDrawPath(context, kCGPathFill);
  }
}