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

问题描述

我在尝试做一些数据转换。不幸的是，许多数据是字符串，它应该是i​​nt的或双，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，我所得到的是这样的：

So what I've got is something like:

double? amount = Convert.ToDouble(strAmount);

使用这种方法的问题是，如果strAmount是空的，如果它是空的我希望它相当于为null，所以当我将其添加到数据库中的列将为空。所以，我最后写的：

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);
}

现在这工作得很好，但我现在有五行code而不是一个。这使事情变得更难看了，尤其是当我有大量的列进行转换。

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.

我想我会用一个扩展字符串类和通用的传入的类型，这是因为它可能是一个双，或int或长。所以，我想这样的：

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;
        }
    }

但我得到的错误：'T'无法将类型字符串来

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

有没有解决的办法吗？我不是很熟悉创建使用泛型方法。

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

推荐答案

另一件事要记住的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;
}

这篇关于将字符串转换为可空类型（INT，双，等...）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！