- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string

{

    if (textField == _workIdTxt) {

        NSUInteger lengthOfString = string.length;

        for (NSInteger loopIndex = 0; loopIndex < lengthOfString; loopIndex++) {//只允许数字输入

            unichar character = [string characterAtIndex:loopIndex];

            if (character < 48) return NO; // 48 unichar for 0

            if (character > 57) return NO; // 57 unichar for 9

        }

        // Check for total length

        NSUInteger proposedNewLength = textField.text.length - range.length + string.length;

        if (proposedNewLength > 10 || proposedNewLength<2) return NO;//限制长度

        return YES;

    }

    return YES;

}