MVC中IActionFilter过滤器俄罗斯套娃的实现方式
2024-08-30 17:59:26
看mvc的源码我们知道,它是在 ControllerActionInvoker 类中执行 InvokeAction 方法来实现过滤器和action方法执行的。
通过查看源码我们知道,他是通过调用 InvokeActionMethodWithFilters 方法来实现IActionFilter过滤器和action方法执行的,如图
点进去这个方法我们可以看到
protected virtual ActionExecutedContext InvokeActionMethodWithFilters(ControllerContext controllerContext, IList<IActionFilter> filters, ActionDescriptor actionDescriptor, IDictionary<string, object> parameters)
{
ActionExecutingContext preContext = new ActionExecutingContext(controllerContext, actionDescriptor, parameters);
Func<ActionExecutedContext> seed = () => new ActionExecutedContext(controllerContext, actionDescriptor, false, null)
{
Result = this.InvokeActionMethod(controllerContext, actionDescriptor, parameters)
};
return filters.Reverse<IActionFilter>().Aggregate(seed, (Func<ActionExecutedContext> next, IActionFilter filter) => () => ControllerActionInvoker.InvokeActionMethodFilter(filter, preContext, next))();
}
看到这里我直接懵逼了,由于它委托中嵌套了委托而且还简写,还调用了扩展方法Aggregate累加器,所以很难直接看懂,这到底是怎么执行代码的呐?我来把代码整理如下
public class Class1
{ protected virtual ActionExecutedContext InvokeActionMethodWithFilters(ControllerContext controllerContext, IList<IActionFilter> filters, ActionDescriptor actionDescriptor, IDictionary<string, object> parameters)
{
ActionExecutingContext preContext = new ActionExecutingContext(controllerContext, actionDescriptor, parameters); Func<ActionExecutedContext> seed = () => new ActionExecutedContext(controllerContext, actionDescriptor, false, null)
{
Result = this.InvokeActionMethod(controllerContext, actionDescriptor, parameters)
}; Func<Func<ActionExecutedContext>, IActionFilter, Func<ActionExecutedContext>> secondParam =
(Func<ActionExecutedContext> next, IActionFilter filter) =>
{
Func<ActionExecutedContext> returnFunc = () =>
{
return Class1.InvokeActionMethodFilter(filter, preContext, next);
}; return returnFunc; //这个是简写
//return () => Class1.InvokeActionMethodFilter(filter, preContext, next);
}; return filters.Reverse<IActionFilter>().Aggregate(seed,
//(Func<ActionExecutedContext> next, IActionFilter filter) => () => Class1.InvokeActionMethodFilter(filter, preContext, next)
secondParam
)
.Invoke();
} internal static ActionExecutedContext InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func<ActionExecutedContext> continuation)
{
filter.OnActionExecuting(preContext);
if (preContext.Result != null)
{
return new ActionExecutedContext(preContext, preContext.ActionDescriptor, true, null)
{
Result = preContext.Result
};
}
bool flag = false;
ActionExecutedContext actionExecutedContext = null;
try
{
actionExecutedContext = continuation();
}
catch (ThreadAbortException)
{
actionExecutedContext = new ActionExecutedContext(preContext, preContext.ActionDescriptor, false, null);
filter.OnActionExecuted(actionExecutedContext);
throw;
}
catch (Exception exception)
{
flag = true;
actionExecutedContext = new ActionExecutedContext(preContext, preContext.ActionDescriptor, false, exception);
filter.OnActionExecuted(actionExecutedContext);
if (!actionExecutedContext.ExceptionHandled)
{
throw;
}
}
if (!flag)
{
filter.OnActionExecuted(actionExecutedContext);
}
return actionExecutedContext;
} protected virtual ActionResult InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary<string, object> parameters)
{
object actionReturnValue = actionDescriptor.Execute(controllerContext, parameters);
return this.CreateActionResult(controllerContext, actionDescriptor, actionReturnValue);
} protected virtual ActionResult CreateActionResult(ControllerContext controllerContext, ActionDescriptor actionDescriptor, object actionReturnValue)
{
if (actionReturnValue == null)
{
return new EmptyResult();
}
ActionResult arg_29_0;
if ((arg_29_0 = (actionReturnValue as ActionResult)) == null)
{
arg_29_0 = new ContentResult();
//(arg_29_0 = new ContentResult()).Content = Convert.ToString(actionReturnValue, CultureInfo.InvariantCulture);
(arg_29_0 as ContentResult).Content = Convert.ToString(actionReturnValue, CultureInfo.InvariantCulture);
}
return arg_29_0;
} }
咋一看,还是不知所云,一步一步来,
首先,我们先要知道 Aggregate 这个扩展方法是怎么执行的,直接看源码如下
看了源码就很容易理解了,它就是遍历数据源来循环执行传递过来的委托,并把结果当成参数,执行下一次循环的委托。
所有我整理了一个容易理解的一串代码
public class Class2
{ public void Test()
{
var preContext = new ActionExecutingContext(); Func<ActionExecutedContext> seed = () =>
{
Console.WriteLine("执行action");
return new ActionExecutedContext();
}; int[] arr = { , , , , , , , , }; Func<Func<ActionExecutedContext>, int, Func<ActionExecutedContext>> secondParam =
(Func<ActionExecutedContext> next, int filter) =>
{
return () => this.getStr(next, filter, preContext);
}; var reFunc2 = arr.Reverse().Aggregate<int, Func<ActionExecutedContext>>(seed, secondParam);
reFunc2.Invoke(); } public ActionExecutedContext getStr(Func<ActionExecutedContext> func, int filter, ActionExecutingContext preContext)
{ Console.WriteLine("before action----" + filter + "----" + preContext.ToString()); var res = func.Invoke(); Console.WriteLine("before action----" + filter + "----" + res.ToString()); return res;
} }
我是用一个int数组来模拟IActionFilter集合,其它的写法都和mvc框架的写法一样。
运行结果为 如图
看到这里,你是否明白了,它就是通过 委托里嵌套委托 来巧妙的实现了俄罗斯套娃的形式来实现IActionFilter过滤器和Action方法的执行。
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