UITextField只要求输入数字和字母，并限制长度

只需实现UITextField的代理方法即可:

首先对字母和数字宏定义：

#define kAlphaNum @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"

#pragma mark UITextField Delegate
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange :( NSRange)range replacementString :( NSString *)string
{
//判断是否超过,注意要判断当string.leng>0
//的情况才行，如果是删除的时候，string.length==0
NSInteger length = _apartmentCell.inputTextField.text.length;
if (length > 15 && string.length >0)
{
return NO;
}

NSCharacterSet *cs;
cs = [[NSCharacterSet characterSetWithCharactersInString:kAlphaNum] invertedSet];
NSString *filtered =
[[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@"" ];
BOOL basic = [string isEqualToString:filtered];
return basic;
}