C# CodeGeneration 变量作为类型

发布于 2024-10-22 20:18:55 字数 473 浏览 2 评论 0原文

，生成代码来执行强制转换，如下所示：（类型也是生成的类，我提供了一个仅包含 object 和 string 的示例）

object o;
string s = (string)o;

在现有应用程序中类型为 int，则抛出 InvalidCastException。因此，我想将代码更改为：

object o;
string s = o as string;

并稍后检查 string s 是否为 null。

System.CodeDom 用于执行代码生成。转换是使用 CodeCastExpression 类生成的。

我找不到生成变量作为类型的方法...有人可以帮助我吗？谢谢！

原文

In an existing application, code is generated to perform a cast, like below: (the types are also generated classes, I provide an example with just object and string)

object o;
string s = (string)o;

When o is of type int, an InvalidCastException is thrown. Therefore, I want to change the code into:

object o;
string s = o as string;

and check later on whether string s is null.

The System.CodeDom is used to perform the code generation. The cast is generated using the CodeCastExpression Class.

I cannot find a way to generate the variable as type way... Can someone help me out? Thanks!

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难忘№最初的完美 2024-10-29 20:18:55

使用 System.ComponentModel.TypeConverter 怎么样？
Type) 的方法，并具有“通用”ConvertTo 方法，该方法接受对象并返回对象：

public Object ConvertTo(
    Object value,
    Type destinationType
)

它具有检查是否 CanConvertFrom(Type) 和 CanConvertTo ( 看这里： http://msdn.microsoft.com/en -us/library/system.componentmodel.typeconverter.aspx

What about using System.ComponentModel.TypeConverter.
It has methods to check whether it CanConvertFrom(Type) and CanConvertTo(Type) and has the "universal" ConvertTo Method which accepts an Object in and gives an Object back:

public Object ConvertTo(
    Object value,
    Type destinationType
)

Have a look here: http://msdn.microsoft.com/en-us/library/system.componentmodel.typeconverter.aspx

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奢华的一滴泪 2024-10-29 20:18:55

也许你想尝试这个：

//For string...
string s = (o == null ? null : o.ToString());
//For int...
int i = (o == null ? 0 : Convert.ToInt32(o));

也许你可以在前面放一个 if 语句，这样代码就会显示：

TheType s = null;

if (o is TheType)
    s = (TheType)o

这仅适用于非值类型。有关如何实现“is”的信息，请参阅这篇文章操作员。

Maybe you want to try this instead:

//For string...
string s = (o == null ? null : o.ToString());
//For int...
int i = (o == null ? 0 : Convert.ToInt32(o));

Maybe you can just put an if statement before so the code would read:

TheType s = null;

if (o is TheType)
    s = (TheType)o

This will only work with non-value-types. See this post for information on how to accomplish the "is" operator.

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寻找我们的幸福 2024-10-29 20:18:55

问题是，“as”运算符不能与非引用类型一起使用。

例如：

public class ConverterThingy
{
    public T Convert<T>(object o)
        where T : class
    {
        return o as T;
    }

    public T Convert<T>(object o, T destinationObj)
        where T : class
    {
        return o as T;
    }
}

这应该适用于大多数情况。您可以执行从任何对象到另一种引用类型的 as 转换。

SomeClass x = new ConverterThingy().Convert<SomeClass>(new ExpandoObject());
// x is null
SomeClass x = null;
x = new ConverterThingy().Convert(new ExpandoObject(), x);
// x is null, the type of x is inferred from the parameter

The problem is, the 'as' operator cannot be used with a non reference type.

For example:

public class ConverterThingy
{
    public T Convert<T>(object o)
        where T : class
    {
        return o as T;
    }

    public T Convert<T>(object o, T destinationObj)
        where T : class
    {
        return o as T;
    }
}

This should work for most of it. You can do the as conversion from any object to another reference type.

SomeClass x = new ConverterThingy().Convert<SomeClass>(new ExpandoObject());
// x is null
SomeClass x = null;
x = new ConverterThingy().Convert(new ExpandoObject(), x);
// x is null, the type of x is inferred from the parameter

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