在 C # 中运行时加载 DLL

我想知道你怎样才能进口和使用一个。在 C # 应用程序中运行 dll。使用汇编。LoadFile ()我已经设法让我的程序加载 dll (这一部分肯定是工作的，因为我可以用 ToString ()得到类的名称) ，但是我不能在我的控制台应用中使用“ Output”方法。我正在编译。然后将其移动到我的控制台项目中。在 CreateInstance 和能够使用这些方法之间是否有一个额外的步骤？

这是我 DLL 中的类:

namespace DLL
{
using System;


public class Class1
{
public void Output(string s)
{
Console.WriteLine(s);
}
}
}

这是我想加载 DLL 的应用程序

namespace ConsoleApplication1
{
using System;
using System.Reflection;


class Program
{
static void Main(string[] args)
{
var DLL = Assembly.LoadFile(@"C:\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\DLL.dll");


foreach(Type type in DLL.GetExportedTypes())
{
var c = Activator.CreateInstance(type);
c.Output(@"Hello");
}


Console.ReadLine();
}
}
}
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小开
最佳答案

Members must be resolvable at compile time to be called directly from C#. Otherwise you must use reflection or dynamic objects.

Reflection

namespace ConsoleApplication1
{
using System;
using System.Reflection;


class Program
{
static void Main(string[] args)
{
var DLL = Assembly.LoadFile(@"C:\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\DLL.dll");


foreach(Type type in DLL.GetExportedTypes())
{
var c = Activator.CreateInstance(type);
type.InvokeMember("Output", BindingFlags.InvokeMethod, null, c, new object[] {@"Hello"});
}


Console.ReadLine();
}
}
}

Dynamic (.NET 4.0)

namespace ConsoleApplication1
{
using System;
using System.Reflection;


class Program
{
static void Main(string[] args)
{
var DLL = Assembly.LoadFile(@"C:\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\DLL.dll");


foreach(Type type in DLL.GetExportedTypes())
{
dynamic c = Activator.CreateInstance(type);
c.Output(@"Hello");
}


Console.ReadLine();
}
}
}
小开

Right now, you're creating an instance of every type defined in the assembly. You only need to create a single instance of Class1 in order to call the method:

class Program
{
static void Main(string[] args)
{
var DLL = Assembly.LoadFile(@"C:\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\DLL.dll");


var theType = DLL.GetType("DLL.Class1");
var c = Activator.CreateInstance(theType);
var method = theType.GetMethod("Output");
method.Invoke(c, new object[]{@"Hello"});


Console.ReadLine();
}
}
小开

You need to create an instance of the type that expose the Output method:

static void Main(string[] args)
{
var DLL = Assembly.LoadFile(@"C:\visual studio 2012\Projects\ConsoleApplication1\ConsoleApplication1\DLL.dll");


var class1Type = DLL.GetType("DLL.Class1");


//Now you can use reflection or dynamic to call the method. I will show you the dynamic way


dynamic c = Activator.CreateInstance(class1Type);
c.Output(@"Hello");


Console.ReadLine();
}
小开

Activator.CreateInstance() returns an object, which doesn't have an Output method.

It looks like you come from dynamic programming languages? C# is definetly not that, and what you are trying to do will be difficult.

Since you are loading a specific dll from a specific location, maybe you just want to add it as a reference to your console application?

If you absolutely want to load the assembly via Assembly.Load, you will have to go via reflection to call any members on c

Something like type.GetMethod("Output").Invoke(c, null); should do it.

小开

It's not so difficult.

You can inspect the available functions of the loaded object, and if you find the one you're looking for by name, then snoop its expected parms, if any. If it's the call you're trying to find, then call it using the MethodInfo object's Invoke method.

Another option is to simply build your external objects to an interface, and cast the loaded object to that interface. If successful, call the function natively.

This is pretty simple stuff.

小开 
foreach (var f in Directory.GetFiles(".", "*.dll"))
Assembly.LoadFrom(f);

That loads all the DLLs present in your executable's folder.

In my case I was trying to use Reflection to find all subclasses of a class, even in other DLLs. This worked, but I'm not sure if it's the best way to do it.

EDIT: I timed it, and it only seems to load them the first time.

Stopwatch stopwatch = new Stopwatch();
for (int i = 0; i < 4; i++)
{
stopwatch.Restart();
foreach (var f in Directory.GetFiles(".", "*.dll"))
Assembly.LoadFrom(f);
stopwatch.Stop();
Console.WriteLine(stopwatch.ElapsedMilliseconds);
}

Output: 34 0 0 0

So one could potentially run that code before any Reflection searches just in case.


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