iOS 限制UITextField只可以输入数字，限制文字长度

1：设置文本输入框的代理UITextFieldDelegate

self.pwdTextField.delegate = self;

2：在代理方法中加入限制

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    return [self validateNumber:string];
}

- (BOOL)validateNumber:(NSString*)number {
    BOOL res = YES;
    NSCharacterSet* tmpSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789"];
    int i = 0;
    while (i < number.length) {
        NSString * string = [number substringWithRange:NSMakeRange(i, 1)];
        NSRange range = [string rangeOfCharacterFromSet:tmpSet];
        if (range.length == 0) {
            res = NO;
            break;
        }
        i++;
    }
    return res;
} 

3:如果有字数要求，也在该代理方法中实现。

//交易密码长度
#define kTradePWD_LENGTH_LIMIT 6

#pragma mark - 限定文本框输入的文字个数
-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    NSString * aString = [textField.text stringByReplacingCharactersInRange:range withString:string];
    if ([self validateNumber:string]) {
        //文字长度限制
        if ([aString length] > kTradePWD_LENGTH_LIMIT) {
            textField.text = [aString substringToIndex:kTradePWD_LENGTH_LIMIT];
            
            return NO;
        }
    }else
    {
        [MBProgressHUD showError:@"输入六位数字组合的密码"];
        return NO;
    }
    return YES;
}
- (BOOL)validateNumber:(NSString*)number {
    BOOL res = YES;
    NSCharacterSet* tmpSet = [NSCharacterSet characterSetWithCharactersInString:@"0123456789"];
    int i = 0;
    while (i < number.length) {
        NSString * string = [number substringWithRange:NSMakeRange(i, 1)];
        NSRange range = [string rangeOfCharacterFromSet:tmpSet];
        if (range.length == 0) {
            res = NO;
            break;
        }
        i++;
    }
    return res;
}