c# - 在ASP.NET Core中在 Controller OnActionExecuting之前执行全局过滤器

Question

在ASP.NET Core 2.0应用程序中，我试图在执行Controller的变体之前执行全局过滤器的OnActionExecuting。预期的行为是，我可以在全局之前准备一些东西，然后将结果值传递给 Controller ​​。但是，当前的行为是执行顺序被设计颠倒了。

该文档告诉我有关default order of execution的信息:

Every controller that inherits from the Controller base class includes OnActionExecuting and OnActionExecuted methods. These methods wrap the filters that run for a given action: OnActionExecuting is called before any of the filters, and OnActionExecuted is called after all of the filters.

这使我解释说， Controller 的OnActionExecuting是在任何过滤器之前执行的。说得通。但是文档还通过实现IOrderedFilter声明了the default order can be overridden。

我在过滤器中实现此操作的尝试如下:

public class FooActionFilter : IActionFilter, IOrderedFilter
{
    // Setting the order to 0, using IOrderedFilter, to attempt executing
    // this filter *before* the BaseController's OnActionExecuting.
    public int Order => 0;

    public void OnActionExecuting(ActionExecutingContext context)
    {
        // removed logic for brevity
        var foo = "bar";

        // Pass the extracted value back to the controller
        context.RouteData.Values.Add("foo", foo);
    }
}

该过滤器在启动时注册为:

services.AddMvc(options => options.Filters.Add(new FooActionFilter()));

最后，我的BaseController看起来像下面的示例。这最好地说明了我要实现的目标:

public class BaseController : Controller
{
    public override void OnActionExecuting(ActionExecutingContext context)
    {
        // The problem: this gets executed *before* the global filter.
        // I actually want the FooActionFilter to prepare this value for me.
        var foo = context.RouteData.Values.GetValueOrDefault("foo").ToString();
    }
}

将Order设置为0，甚至是一个非零值(如-1)，似乎都不会对执行顺序产生任何影响。

我的问题:我该怎么做才能使全局过滤器在(Base)Controller的OnActionExecuting之前执行OnActionExecuting？

Answer 1

你快到了。您的小错误是 Controller 过滤器执行的默认顺序不是0。此顺序在ControllerActionFilter类中定义为int.MinValue(source code):

public class ControllerActionFilter : IAsyncActionFilter, IOrderedFilter
{
    // Controller-filter methods run farthest from the action by default.
    /// <inheritdoc />
    public int Order { get; set; } = int.MinValue;

    // ...
}

因此，您应该对当前代码进行的唯一更改是将FooActionFilter.Order设置为int.MinValue:

public class FooActionFilter : IActionFilter, IOrderedFilter
{
    public int Order => int.MinValue;

    //  ...
}

现在FooActionFilter和ControllerActionFilter具有相同的顺序。但是FooActionFilter是全局过滤器，而ControllerActionFilter是 Controller 级过滤器。这就是为什么基于this statement首先执行FooActionFilter的原因:

The Order property trumps scope when determining the order in which filters will run. Filters are sorted first by order, then scope is used to break ties.