判斷是不是一個有效的郵箱地址。

-(BOOL)is_email_can_be_open:(NSString*)email
{ 
    if( (0 != [email rangeOfString:@"@"].length) &&  (0 != [email rangeOfString:@"."].length) ) 
    { 
        NSMutableCharacterSet *invalidCharSet = [[[[NSCharacterSet alphanumericCharacterSet] invertedSet]mutableCopy]autorelease]; 
        [invalidCharSet removeCharactersInString:@"_-"]; 
       
        NSRange range1 = [email rangeOfString:@"@" options:NSCaseInsensitiveSearch]; 
       
        // If username part contains any character other than "."  "_" "-" 
       
        NSString *usernamePart = [email substringToIndex:range1.location]; 
        NSArray *stringsArray1 = [usernamePart componentsSeparatedByString:@"."]; 
        for (NSString *string in stringsArray1)
        { 
            NSRange rangeOfInavlidChars=[string rangeOfCharacterFromSet: invalidCharSet]; 
            if(rangeOfInavlidChars.length !=0 || [string isEqualToString:@""]) 
            {
                return NO;
            }
        } 
       
        NSString *domainPart = [email substringFromIndex:range1.location+1]; 
        NSArray *stringsArray2 = [domainPart componentsSeparatedByString:@"."]; 
       
        for (NSString *string in stringsArray2)
        { 
            NSRange rangeOfInavlidChars=[string rangeOfCharacterFromSet:invalidCharSet]; 
            if(rangeOfInavlidChars.length !=0 || [string isEqualToString:@""]) 
            {
                return NO;
            }
        } 
       
        return YES; 
    } 
    return NO;
} 

摘自 雲懷空－abel