iOS 判断当前字符串是否都为数字

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