UITextField只要求輸入數字和字母，並限制長度

只需實現UITextField的代理方法便可:

首先對字母和數字宏定義：

#define kAlphaNum   @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"

#pragma mark UITextField Delegate

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

{

    //判斷是否超過,注意要判斷當string.leng>0

    //的狀況才行，若是是刪除的時候，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;

}