输入的字符串格式不正确 [英] input string was not in the correct format error

问题描述

我不知道为什么会发生此错误，任何人都可以告诉我

I have no idea why this error is occurring can anyone tell me

 long? Max = row["MAX"].ToString() != null || row["MAX"].ToString() != "" ? long.Parse(row["MAX"].ToString()) : (long?)null;

推荐答案

如果您要检查 row ["MAX"] 是否为 null ，则应进行更改检查到:

If your intent is to check if row["MAX"] is null then you should change that check to:

row["MAX"] != null

这是因为 ToString()的返回值永远不会是 null ，但是如果在上调用它，则会抛出 NullReferenceException > null 对象(然后 row ["MAX"].ToString()对于 null 对象将失败).

This because return value of ToString() is never null but it'll throw a NullReferenceException if you invoke it on a null object (then row["MAX"].ToString() will fail for null objects).

在您的情况下，它不是 null ，而是空字符串，您可以更改为:

In your case it's not null but it's an empty string, you may change to this:

long? Max = (row["MAX"] != null && row["MAX"].ToString() != "") 
    ? long.Parse(row["MAX"].ToString()) : (long?)null;

但是正如您所看到的那样，它并不是很可读，我将更改(跳过任何其他验证)为:

But as you can see it's not really readable, I would change (skipping any other validation) to:

long? Max = null;
if (row["MAX"] != null && row["MAX"].ToString() != "")
    Max = Long.Parse(row["MAX"].ToString());

编辑，如 Jota WA的答案(我认为是正确的)中指出的那样，如果您的第 object 行来自数据库(实际上我们不知道其类型，因此我们只能猜测并假设它是 object 的字典)，您可能会有 DBNull.Value 而不是 null .在这种情况下， row ["MAX"]！= null 为 false ，但是第二次检查 row ["MAX"].ToString()会捕获此条件！=" .也就是说，如果这是您的情况，并且您确定自己的字典不包含任何 real null 值，则可以使其更简单:

EDIT as pointed out in Jota WA's answer (which I consider right) if your row object comes from a database (actually we don't know its type so we can just guess and assume it's kind of dictionary of object) you may have DBNull.Value instead of null. In this case row["MAX"] != null is false but this condition is catched by 2nd check row["MAX"].ToString() != "". That said if this is your case and you're sure your dictionary doesn't contain any real null value you may make it simpler:

if (row["MAX"].ToString() != "")

甚至:

if (row["MAX"] != DBValue.Null)

我想您可能需要 add 验证，然后应使用 TryParse 这样:

I suppose you may need to add validation then you should use TryParse like this:

// Here you may handle row["MAX"] == null case, if it may happen
string MaxText = row["MAX"].ToString();

long? Max = null;
if (MaxText  != "")
{
    long value;
    if (long.TryParse(MaxText, out value))
    {
        // You may add more validation here, for example
        // to check value's range
        Max = value;
    }
}

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