限制文字輸入

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




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

if ([textField.placeholder isEqualToString:@"請輸入銀行卡號"]) {
    //
    NSString *text = [textField text];
    NSCharacterSet *characterSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789\b"];
    string = [string stringByReplacingOccurrencesOfString:@" " withString:@""];
    if ([string rangeOfCharacterFromSet:[characterSet invertedSet]].location != NSNotFound) {
        return NO;
    }
    
    text = [text stringByReplacingCharactersInRange:range withString:string];
    text = [text stringByReplacingOccurrencesOfString:@" " withString:@""];
    
    NSString *newString = @"";
    while (text.length > 0) {
        NSString *subString = [text substringToIndex:MIN(text.length, 4)];
        newString = [newString stringByAppendingString:subString];
        if (subString.length == 4) {
            newString = [newString stringByAppendingString:@" "];
        }
        text = [text substringFromIndex:MIN(text.length, 4)];
    }
    newString = [newString stringByTrimmingCharactersInSet:[characterSet invertedSet]];
    if (newString.length > 24) {
        return NO;
    }
    [textField setText:newString];
    return NO;
    
}else if ([textField.placeholder isEqualToString:@"請設置6位提現密碼"]){
    //
    NSCharacterSet *cs = [[NSCharacterSet characterSetWithCharactersInString:ALPHANUM] invertedSet];
    NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];
    if (range.location >= 6) { //
        return NO;
    }
    return [string isEqualToString:filtered];
    
}else if ([textField.placeholder isEqualToString:@"請輸入提現密碼"]){
    //
    NSCharacterSet *cs = [[NSCharacterSet characterSetWithCharactersInString:ALPHANUM] invertedSet];
    NSString *filtered = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];
    if (range.location >= 6) { //
        return NO;
    }
    return [string isEqualToString:filtered];
    
}else{
    
    return YES;
}
}