.Net动态生成controller遇到的坑

.Net动态生成controller遇到的坑

简述

在使用.NET开发Web应用程序的过程中，我们常常需要动态地生成Controller。但是这个过程中会遇到一些坑，难以发现并解决。本文将详细讲解这些坑以及如何避免它们。

问题

1. 动态添加的controller无法被MVC框架识别

动态添加Controller后，通过浏览器访问应用程序时，MVC框架会报404错误，显示无法找到相应的Controller。

2. Action方法不能返回string类型

在动态添加的Controller中，如果Action方法返回字符串类型的数据，MVC框架将会报错。

解决办法

1. 使用MVC框架的默认路由

我们可以在动态添加Controller时，使用MVC框架默认的路由。这样，MVC框架就能正确地识别生成的Controller，进而正确地处理请求。具体实现如下：

public static void AddController(IServiceCollection services, Type type, string suffix = "Controller")
{
    var controllerName = type.Name + suffix;
    services.AddMvc(options =>
    {
        options.Conventions.Add(new RouteTokenTransformerConvention(new SlugifyParameterTransformer()));
    }).ConfigureApplicationPartManager(apm =>
    {
        var part = new Microsoft.AspNetCore.Mvc.ApplicationParts.ControllerFeature();
        apm.ApplicationParts.Add(part);

        var controllerType = typeof(Controller);
        var methods = type.GetMethods(BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly);

        foreach (var method in methods)
        {
            var actionName = method.Name;
            var parameters = method.GetParameters();

            var asmName = type.Assembly.GetName().Name;
            var controllerTypeBuilder = asmBuilder.DefineController(controllerName, controllerType);
            var actionTypeBuilder = controllerTypeBuilder.DefineAction(method.Name, MethodAttributes.Public);

            actionTypeBuilder.SetCustomAttribute(new CustomAttributeBuilder(
                typeof(HttpGetAttribute).GetConstructor(new Type[0]), new object[0]));

            actionTypeBuilder.SetReturnType(method.ReturnType);

            var parametersBuilder = new List<ParameterBuilder>();
            for (var index = 0; index < parameters.Length; index++)
            {
                var parameter = parameters[index];
                var parameterBuilder = actionTypeBuilder.DefineParameter(index + 1, ParameterAttributes.None, parameter.Name);
                parameterBuilder.SetCustomAttribute(new CustomAttributeBuilder(
                    typeof(FromQueryAttribute).GetConstructor(new Type[0]), new object[0]));
                parametersBuilder.Add(parameterBuilder);
            }

            var ilGenerator = actionTypeBuilder.GetILGenerator();
            ilGenerator.Emit(OpCodes.Ldstr, $"Hello, world");
            ilGenerator.Emit(OpCodes.Ret);

            part.Controllers.Add(controllerTypeBuilder.CreateTypeInfo().AsType());
        }
    });
}

2. 使用Action方法返回Object类型

为了避免MVC框架报错，我们可以在动态添加Controller时，将Action方法的返回类型设置为Object。这样，就可以正确地响应客户端的请求了。具体实现如下：

if (method.ReturnType == typeof(string))
{
    var actionName = method.Name;
    var parameters = method.GetParameters();

    var asmName = type.Assembly.GetName().Name;
    var controllerTypeBuilder = asmBuilder.DefineController(controllerName, controllerType);
    var actionTypeBuilder = controllerTypeBuilder.DefineAction(method.Name, MethodAttributes.Public);

    actionTypeBuilder.SetCustomAttribute(new CustomAttributeBuilder(
        typeof(HttpGetAttribute).GetConstructor(new Type[0]), new object[0]));

    actionTypeBuilder.SetReturnType(typeof(object));

    var parametersBuilder = new List<ParameterBuilder>();
    for (var index = 0; index < parameters.Length; index++)
    {
        var parameter = parameters[index];
        var parameterBuilder = actionTypeBuilder.DefineParameter(index + 1, ParameterAttributes.None, parameter.Name);
        parameterBuilder.SetCustomAttribute(new CustomAttributeBuilder(
            typeof(FromQueryAttribute).GetConstructor(new Type[0]), new object[0]));
        parametersBuilder.Add(parameterBuilder);
    }

    var ilGenerator = actionTypeBuilder.GetILGenerator();
    ilGenerator.Emit(OpCodes.Ldstr, $"Hello, world");
    ilGenerator.Emit(OpCodes.Box, typeof(string));
    ilGenerator.Emit(OpCodes.Ret);

    part.Controllers.Add(controllerTypeBuilder.CreateTypeInfo().AsType());
}

示例说明

示例一：动态添加HelloWorldController

private readonly AssemblyBuilder asmBuilder;

public HelloWorldController(AssemblyBuilder asmBuilder)
{
    this.asmBuilder = asmBuilder;
}

[HttpGet]
public string HelloWorld(string name)
{
    return $"Hello, {name}!";
}

[HttpPost]
public string Post(string name)
{
    return $"Hello, {name}!";
}

[HttpGet]
public object HelloWorld2(string name)
{
    return $"Hello, {name}!";
}

[HttpPost]
public object Post2(string name)
{
    return $"Hello, {name}!";
}

public void AddController()
{
    var services = new ServiceCollection();
    AddController(services, typeof(HelloWorldController));
    var provider = services.BuildServiceProvider();
    var serviceProvider = provider.GetService<IServiceProvider>();

    var partManager = serviceProvider.GetRequiredService<ApplicationPartManager>();
    var types = partManager.ApplicationParts
        .OfType<AssemblyPart>()
        .SelectMany(x => x.Types)
        .ToArray();
    partManager.ApplicationParts.Clear();
    foreach (var type in types)
    {
        partManager.ApplicationParts.Add(new AssemblyPart(type.Assembly));
    }
    partManager.FeatureProviders.Add(new ControllerFeatureProvider(assemblies: null));
}

示例二：动态添加GreeterController

private readonly AssemblyBuilder asmBuilder;

public GreeterController(AssemblyBuilder asmBuilder)
{
    this.asmBuilder = asmBuilder;
}

[HttpGet]
public string SayHello(string name)
{
    return $"你好，{name}！";
}

[HttpPost]
public string Post(string name)
{
    return $"你好，{name}！";
}

[HttpGet]
public object SayHello2(string name)
{
    return $"你好，{name}！";
}

[HttpPost]
public object Post2(string name)
{
    return $"你好，{name}！";
}

public void AddController()
{
    var services = new ServiceCollection();
    AddController(services, typeof(GreeterController));
    var provider = services.BuildServiceProvider();
    var serviceProvider = provider.GetService<IServiceProvider>();

    var partManager = serviceProvider.GetRequiredService<ApplicationPartManager>();
    var types = partManager.ApplicationParts
        .OfType<AssemblyPart>()
        .SelectMany(x => x.Types)
        .ToArray();
    partManager.ApplicationParts.Clear();
    foreach (var type in types)
    {
        partManager.ApplicationParts.Add(new AssemblyPart(type.Assembly));
    }
    partManager.FeatureProviders.Add(new ControllerFeatureProvider(assemblies: null));
}