Detailed explanation of dynamic loading and unloading code of AppDomain and Assembly

In order to describe the problem clearly, let's first look at an example. In this example, there is a button on WinForm. When the user clicks this button, an existing Assembly will be loaded, and the Label control on the interface will be loaded. The FullName of this Assembly is displayed on . Friends who are a little familiar with Reflection know that this is a very simple thing. You only need to use the Assembly.LoadFile method to get the Assembly, and then use the FullName attribute to display it, such as The code below:

private void button1_Click(object sender, EventArgs e)  
{  
    Assembly assembly = Assembly.LoadFile(@"C:\testlib.dll");  
    label1.Text = assembly.FullName;  
}

• 
  

#Of course, the program executes normally, you won’t Any compile-time or run-time errors are found. However, when you compile the called testlib.dll without

exiting this program, you will find that Visual Studio cannot complete the compilation and prompts that the file is being other used by the process.

In fact, our program is not closely related to this testlib.dll. Our program just displays the basic information of testlib.dll. If testlib.dll is a shared library, resource exclusive issues will affect the normal work of other programs.

Assembly does not have the Unload function, but you can use Ap

pDomain to solve this problem. The basic idea is to create a new AppDomain, load the assembly in this new AppDomain, call the methods in it, and then return the results obtained. After completing all operations, call the AppDomain.Unload method to uninstall the newly created AppDomain, which also uninstalls the assembly. Note: You cannot return a loaded assembly directly to the current application domain (AppDomain).

First, create a RemoteLoader. This RemoteLoader is used to load the assembly in the newly created AppDomain and publish an attribute to the outside world so that the outside world can obtain the FullName of the assembly. RemoteLoader needs to

inherit from MarshalByRefObject. The code is as follows:

public class RemoteLoader : MarshalByRefObject  
{  
    private Assembly assembly;  
    public void LoadAssembly(string fullName)  
    {  
        assembly = Assembly.LoadFrom(fullName);  
    }  
    public string FullName  
    {  
        get { return assembly.FullName; }  
    }  
}

• 
  

#Secondly, create a Loc

alL

oader. The function of LocalLoader is to create a new AppDomain, and then call RemoteLoader in this new AppDomain to create an assembly and obtain assembly-related information through RemoteLoader. The assembly called at this time is naturally loaded in the new AppDomain. Finally, LocalLoader also needs to provide a new method, which is AppDomain uninstallation. The code is as follows:

public class LocalLoader  
{  
    private AppDomain appDomain;  
    private RemoteLoader remoteLoader;  
    public LocalLoader()  
    {  
        AppDomainSetup setup = new AppDomainSetup();  
        setup.ApplicationName = "Test";  
        setup.ApplicationBase = AppDomain.CurrentDomain.BaseDirectory;  
        setup.PrivateBinPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "private");  
        setup.CachePath = setup.ApplicationBase;  
        setup.ShadowCopyFiles = "true";  
        setup.ShadowCopyDirectories = setup.ApplicationBase;  
        appDomain = AppDomain.CreateDomain("TestDomain", null, setup);  
        string name = Assembly.GetExecutingAssembly().GetName().FullName;  
        remoteLoader = (RemoteLoader)appDomain.CreateInstanceAndUnwrap(  
            name,  
            typeof(RemoteLoader).FullName);  
    }  
    public void LoadAssembly(string fullName)  
    {  
        remoteLoader.LoadAssembly(fullName);  
    }  
    public void Unload()  
    {  
        AppDomain.Unload(appDomain);  
        appDomain = null;  
    }  
    public string FullName  
    {  
        get  
        {  
            return remoteLoader.FullName;  
        }  
    }  
}

Finally, modify the Button Click
• event processing

  process on our WinForm to the following form:

  private void button1_Click(object sender, EventArgs e)  
  {  
      LocalLoader ll = new LocalLoader();  
      ll.LoadAssembly(@"C:\testlib.dll");  
      label1.Text = ll.FullName;  
      ll.Unload();  
  }

• 
  

##at After completing the above modifications, our program can also correctly display the FullName of the assembly. Moreover, after displaying the assembly information, the program will actively uninstall the newly created AppDomain to prevent testlib.dll from being exclusive of resources and affecting the operation of other programs. .

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