在ASP.NET Core MVC中子类Controller拦截器要先于父类Controller拦截器执行

我们知道在ASP.NET Core MVC中Controller上的Filter拦截器是有执行顺序的，那么如果我们在有继承关系的两个Controller类上，声明同一种类型的Filter拦截器，那么是父Controller类的Filter拦截器先执行呢，还是子Controller类的Filter拦截器先执行呢？

首先我们新建一个ASP.NET Core MVC项目。

然后我们新建四个IActionFilter拦截器：MyActionOneAttribute、MyActionTwoAttribute、MyActionThreeAttribute和MyActionFourAttribute

MyActionOneAttribute拦截器将会全局声明在ASP.NET Core MVC项目的所有Controller上：

/// <summary>
/// MyActionOneAttribute拦截器将会全局声明在ASP.NET Core MVC项目的所有Controller上
/// </summary>
public class MyActionOneAttribute : Attribute, IActionFilter
{
    public void OnActionExecuted(ActionExecutedContext context)
    {
        using (var writer = new StreamWriter(context.HttpContext.Response.Body))
        {
            writer.Write("<div>MyAction 1 OnActionExecuted</div></body></html>");
        }
    }

    public void OnActionExecuting(ActionExecutingContext context)
    {
        using (var writer = new StreamWriter(context.HttpContext.Response.Body))
        {
            context.HttpContext.Response.ContentType = "text/html";
            context.HttpContext.Response.StatusCode = 200;
            writer.Write("<html><head></head><body><div>MyAction 1 OnActionExecuting</div>");
        }
    }
}

MyActionTwoAttribute拦截器将会声明在父Controller类BaseController上：

/// <summary>
/// MyActionTwoAttribute拦截器将会声明在父Controller类BaseController上
/// </summary>
public class MyActionTwoAttribute : Attribute, IActionFilter
{
    public void OnActionExecuted(ActionExecutedContext context)
    {
        using (var writer = new StreamWriter(context.HttpContext.Response.Body))
        {
            writer.Write("<div>MyAction 2 OnActionExecuted</div>");
        }
    }

    public void OnActionExecuting(ActionExecutingContext context)
    {
        using (var writer = new StreamWriter(context.HttpContext.Response.Body))
        {
            writer.Write("<div>MyAction 2 OnActionExecuting</div>");
        }
    }
}

MyActionThreeAttribute拦截器将会声明在子Controller类HomeController上：

/// <summary>
/// MyActionThreeAttribute拦截器将会声明在子Controller类HomeController上
/// </summary>
public class MyActionThreeAttribute : Attribute, IActionFilter
{
    public void OnActionExecuted(ActionExecutedContext context)
    {
        using (var writer = new StreamWriter(context.HttpContext.Response.Body))
        {
            writer.Write("<div>MyAction 3 OnActionExecuted</div>");
        }
    }

    public void OnActionExecuting(ActionExecutingContext context)
    {
        using (var writer = new StreamWriter(context.HttpContext.Response.Body))
        {
            writer.Write("<div>MyAction 3 OnActionExecuting</div>");
        }
    }
}

MyActionFourAttribute拦截器将会声明在子Controller类HomeController的Index方法上：

/// <summary>
/// MyActionFourAttribute拦截器将会声明在子Controller类HomeController的Index方法上
/// </summary>
public class MyActionFourAttribute : Attribute, IActionFilter
{
    public void OnActionExecuted(ActionExecutedContext context)
    {
        using (var writer = new StreamWriter(context.HttpContext.Response.Body))
        {
            writer.Write("<div>MyAction 4 OnActionExecuted</div>");
        }
    }

    public void OnActionExecuting(ActionExecutingContext context)
    {
        using (var writer = new StreamWriter(context.HttpContext.Response.Body))
        {
            writer.Write("<div>MyAction 4 OnActionExecuting</div>");
        }
    }
}

然后我们在ASP.NET Core MVC项目中Startup类的ConfigureServices方法中，全局声明MyActionOneAttribute拦截器到项目的所有Controller上：

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc(options =>
    {
        options.Filters.Add(typeof(MyActionOneAttribute));
    });
}

然后我们定义父Controller类BaseController，它继承于Microsoft.AspNetCore.Mvc.Controller，并声明了MyActionTwoAttribute拦截器：

[MyActionTwo]
public class BaseController : Controller
{

}

然后我们定义子Controller类HomeController，它继承于BaseController，并在类上声明了MyActionThreeAttribute拦截器，Action方法Index上声明了MyActionFourAttribute拦截器：

[MyActionThree]
public class HomeController : BaseController
{
    [MyActionFour]
    public IActionResult Index()
    {
        using (var writer = new StreamWriter(HttpContext.Response.Body))
        {
            writer.Write("<div>Index</div>");
        }

        return new EmptyResult();
    }
}

并且我们在HomeController的Action方法Index中，输出了一个字符串"<div>Index</div>"。

所以现在我们相当于是在子Controller类HomeController的Index方法上，同时声明了MyActionOneAttribute、MyActionTwoAttribute、MyActionThreeAttribute和MyActionFourAttribute四个拦截器，那么这四个拦截器的执行顺序是什么样的呢？

现在我们运行ASP.NET Core MVC项目，在Web浏览器中输出结果如下：

从上图结果中，我们可以看出：

最先执行的是全局声明的MyActionOneAttribute拦截器
然后执行的是声明在子Controller类HomeController上的MyActionThreeAttribute拦截器
接着执行的是声明在父Controller类BaseController上的MyActionTwoAttribute拦截器
最后执行的是声明在子Controller类HomeController的Index方法上的MyActionFourAttribute拦截器

所以这个结果证明了声明在子Controller类上的Filter拦截器，要先于声明在父Controller类上的Filter拦截器执行！

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原文地址：https://www.cnblogs.com/OpenCoder/p/10656560.html