限制只能输入数字字母

//数字
#define NUM @"0123456789"
//字母
#define ALPHA @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
//数字和字母
#define ALPHANUM @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
NSCharacterSet *cs = [[NSCharacterSet characterSetWithCharactersInString:ALPHANUM] invertedSet];
NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];
return [string isEqualToString:filtered];
}