将字符串转换为可为空类型(int、double 等...) [英] Convert string to nullable type (int, double, etc...)

问题描述

我正在尝试进行一些数据转换.不幸的是，大部分数据都在字符串中，它应该是 int 或 double 等......

I am attempting to do some data conversion. Unfortunately, much of the data is in strings, where it should be int's or double, etc...

所以我得到的是这样的:

So what I've got is something like:

double? amount = Convert.ToDouble(strAmount);

这种方法的问题是如果 strAmount 为空，如果它为空，我希望它为空，所以当我将它添加到数据库中时，该列将为空.所以我最终写了这个:

The problem with this approach is if strAmount is empty, if it's empty I want it to amount to be null, so when I add it into the database the column will be null. So I ended up writing this:

double? amount = null;
if(strAmount.Trim().Length>0)
{
    amount = Convert.ToDouble(strAmount);
}

现在这工作正常，但我现在有五行代码而不是一行.这让阅读变得有点困难，尤其是当我有大量的列要转换时.

Now this works fine, but I now have five lines of code instead of one. This makes things a little more difficult to read, especially when I have a large amount of columns to convert.

我想我会使用字符串类和泛型的扩展来传递类型，这是因为它可以是双精度型、整数型或长型.所以我尝试了这个:

I thought I'd use an extension to the string class and generic's to pass in the type, this is because it could be a double, or an int, or a long. So I tried this:

public static class GenericExtension
{
    public static Nullable<T> ConvertToNullable<T>(this string s, T type) where T: struct
    {
        if (s.Trim().Length > 0)
        {
            return (Nullable<T>)s;
        }
        return null;
    }
}

但我收到错误:无法将类型字符串"转换为T?"

But I get the error: Cannot convert type 'string' to 'T?'

有没有办法解决这个问题?我对使用泛型创建方法不是很熟悉.

Is there a way around this? I am not very familiar with creating methods using generics.

推荐答案

要记住的另一件事是字符串本身可能为空.

Another thing to keep in mind is that the string itself might be null.

public static Nullable<T> ToNullable<T>(this string s) where T: struct
{
    Nullable<T> result = new Nullable<T>();
    try
    {
        if (!string.IsNullOrEmpty(s) && s.Trim().Length > 0)
        {
            TypeConverter conv = TypeDescriptor.GetConverter(typeof(T));
            result = (T)conv.ConvertFrom(s);
        }
    }
    catch { } 
    return result;
}

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