限制键盘只能输入数字

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{
    
    return  [self validNum:string];
}
//限制只能输入数字
- (BOOL)validNum:(NSString*)number{
    BOOL res = YES;
    NSCharacterSet *set = [NSCharacterSet characterSetWithCharactersInString:@"0123456789"];
    for (int i = 0; i < number.length; i ++) {
        NSRange subRanger = NSMakeRange(i , 1);
        NSString *subStr = [number substringWithRange:subRanger];
        NSRange setRange = [subStr  rangeOfCharacterFromSet:set];
        if (setRange.length == 0) {
            res = NO;
            break;
        }
    }

    return res;
}