前面我们介绍了Filter的基本使用，但各种Filter要在合适的时机运行起来，需要预先准备好，现在看看ASP.NET MVC框架是怎么做的。
一.Filter集合
在ControlerActionInvoker的InvokeAction方法中，只有一行代码FilterInfo filterInfo = GetFilters(controllerContext, actionDescriptor), 把收集的Filter信息放到了FilterInfo中，我们来看看
访类型的定义:
public class FilterInfo
{ public FilterInfo(); public FilterInfo(IEnumerable<Filter> filters); public IList<IActionFilter> ActionFilters { get; }
public IList<System.Web.Mvc.Filters.IAuthenticationFilter> AuthenticationFilters { get; } public IList<IAuthorizationFilter> AuthorizationFilters { get; } public IList<IExceptionFilter> ExceptionFilters { get; } public IList<IResultFilter> ResultFilters { get; }
}
可以看到，这个类型定义的5种系统Filter集合信息. 来看看它带参的构造函数:
public FilterInfo(IEnumerable<Filter> filters)
{
// Determine the override scope for each filter type and cache the filters list.
OverrideFilterInfo processed = ProcessOverrideFilters(filters);
// Split the cached filters list based on filter type and override scope.
SplitFilters(processed);
}
可以看到分两步:
1 .ProcessOverrideFilters处理前面的提到IOverrideFilter接口
2. 从列表中把Filter分离到各自的Filter接口集合
ProcessOverrideFilters方法的代码如下:
private static OverrideFilterInfo ProcessOverrideFilters(IEnumerable<Filter> filters)
{
OverrideFilterInfo result = new OverrideFilterInfo
{
ActionOverrideScope = FilterScope.First,
AuthenticationOverrideScope = FilterScope.First,
AuthorizationOverrideScope = FilterScope.First,
ExceptionOverrideScope = FilterScope.First,
ResultOverrideScope = FilterScope.First,
Filters = new List<Filter>()
}; // Evaluate the 'filters' enumerable only once since the operation can be quite expensive.
foreach (Filter filter in filters)
{
if (filter == null)
{
continue;
}
IOverrideFilter overrideFilter = filter.Instance as IOverrideFilter; if (overrideFilter != null)
{
if (overrideFilter.FiltersToOverride == typeof(IActionFilter)
&& filter.Scope >= result.ActionOverrideScope)
{
result.ActionOverrideScope = filter.Scope;
}
else if (overrideFilter.FiltersToOverride == typeof(IAuthenticationFilter)
&& filter.Scope >= result.AuthenticationOverrideScope)
{
result.AuthenticationOverrideScope = filter.Scope;
}
else if (overrideFilter.FiltersToOverride == typeof(IAuthorizationFilter)
&& filter.Scope >= result.AuthorizationOverrideScope)
{
result.AuthorizationOverrideScope = filter.Scope;
}
else if (overrideFilter.FiltersToOverride == typeof(IExceptionFilter)
&& filter.Scope >= result.ExceptionOverrideScope)
{
result.ExceptionOverrideScope = filter.Scope;
}
else if (overrideFilter.FiltersToOverride == typeof(IResultFilter)
&& filter.Scope >= result.ResultOverrideScope)
{
result.ResultOverrideScope = filter.Scope;
}
} // Cache filters to avoid having to enumerate it again (expensive). Do so here to avoid an extra loop.
result.Filters.Add(filter);
} return result;
}
这段代码遍历Filter列表，记录实现了IOverrideFilter的Filter的最高OverrideScope， 在下面的SplitFilters处理中，少于OverrideScope的Filter将不会添加到最终的集合中
SplitFilters方法代码如下:
private void SplitFilters(OverrideFilterInfo info)
{
Contract.Assert(info.Filters != null); foreach (Filter filter in info.Filters)
{
Contract.Assert(filter != null); IActionFilter actionFilter = filter.Instance as IActionFilter; if (actionFilter != null && filter.Scope >= info.ActionOverrideScope)
{
_actionFilters.Add(actionFilter);
} IAuthenticationFilter authenticationFilter = filter.Instance as IAuthenticationFilter; if (authenticationFilter != null && filter.Scope >= info.AuthenticationOverrideScope)
{
_authenticationFilters.Add(authenticationFilter);
} IAuthorizationFilter authorizationFilter = filter.Instance as IAuthorizationFilter; if (authorizationFilter != null && filter.Scope >= info.AuthorizationOverrideScope)
{
_authorizationFilters.Add(authorizationFilter);
} IExceptionFilter exceptionFilter = filter.Instance as IExceptionFilter; if (exceptionFilter != null && filter.Scope >= info.ExceptionOverrideScope)
{
_exceptionFilters.Add(exceptionFilter);
} IResultFilter resultFilter = filter.Instance as IResultFilter; if (resultFilter != null && filter.Scope >= info.ResultOverrideScope)
{
_resultFilters.Add(resultFilter);
}
}
}
实现各个Filter的分离，代码很简单，不再说明。
二. Filter收集
在ASP.NET MVC5中最终通过FilterProviders.Providers.GetFilters方法得到所有的Filter列表，我们先来看看FilterProviders这个类型,定义如下：
public static class FilterProviders
{
static FilterProviders()
{
Providers = new FilterProviderCollection();
Providers.Add(GlobalFilters.Filters);
Providers.Add(new FilterAttributeFilterProvider());
Providers.Add(new ControllerInstanceFilterProvider());
} public static FilterProviderCollection Providers { get; private set; }
}
从中我们可以看到系统定义了三个FilterProvider,它们都实现了IFilterProvider接口，该接口定义如下:
public interface IFilterProvider
{
IEnumerable<Filter> GetFilters(ControllerContext controllerContext, ActionDescriptor actionDescriptor);
}
现在来看看这几个Provider:
a. GlobalFilters.Filters
这个故名思义是收集全局范围运行的Filter,代码如下:
public static class GlobalFilters
{
static GlobalFilters()
{
Filters = new GlobalFilterCollection();
} public static GlobalFilterCollection Filters { get; private set; }
}
比如通常的项目模板在App_Start的FilterConfig中有如下代码,添加全局出错处理
public static void RegisterGlobalFilters(GlobalFilterCollection filters)
{
filters.Add(new HandleErrorAttribute());
}
b. FilterAttributeFilterProvider
该类型是帮助收集应用在Controller和Action上的Filter，代码如下:
public class FilterAttributeFilterProvider : IFilterProvider
{
private readonly bool _cacheAttributeInstances; public FilterAttributeFilterProvider()
: this(true)
{
} public FilterAttributeFilterProvider(bool cacheAttributeInstances)
{
_cacheAttributeInstances = cacheAttributeInstances;
} protected virtual IEnumerable<FilterAttribute> GetActionAttributes(ControllerContext controllerContext, ActionDescriptor actionDescriptor)
{
return actionDescriptor.GetFilterAttributes(_cacheAttributeInstances);
} protected virtual IEnumerable<FilterAttribute> GetControllerAttributes(ControllerContext controllerContext, ActionDescriptor actionDescriptor)
{
return actionDescriptor.ControllerDescriptor.GetFilterAttributes(_cacheAttributeInstances);
} public virtual IEnumerable<Filter> GetFilters(ControllerContext controllerContext, ActionDescriptor actionDescriptor)
{
// Results are low in number in the common case so use yield return to avoid creating intermediate collections or nested enumerables
if (controllerContext.Controller != null)
{
foreach (FilterAttribute attr in GetControllerAttributes(controllerContext, actionDescriptor))
{
yield return new Filter(attr, FilterScope.Controller, order: null);
}
foreach (FilterAttribute attr in GetActionAttributes(controllerContext, actionDescriptor))
{
yield return new Filter(attr, FilterScope.Action, order: null);
}
}
}
}
c. ControllerInstanceFilterProvider
controller本身也实现了一些Filter接口，通过该Provider加入,代码如下:
public class ControllerInstanceFilterProvider : IFilterProvider
{
public IEnumerable<Filter> GetFilters(ControllerContext controllerContext, ActionDescriptor actionDescriptor)
{
if (controllerContext.Controller != null)
{
// Use FilterScope.First and Order of Int32.MinValue to ensure controller instance methods always run first
yield return new Filter(controllerContext.Controller, FilterScope.First, Int32.MinValue);
}
}
}
接下来看一看FilterProviderCollection的GetFilters实现:
public IEnumerable<Filter> GetFilters(ControllerContext controllerContext, ActionDescriptor actionDescriptor)
{
//省略检查代码
IFilterProvider[] providers = CombinedItems;
List<Filter> filters = new List<Filter>();
for (int i = ; i < providers.Length; i++)
{
IFilterProvider provider = providers[i];
foreach (Filter filter in provider.GetFilters(controllerContext, actionDescriptor))
{
filters.Add(filter);
}
} filters.Sort(_filterComparer); if (filters.Count > )
{
RemoveDuplicates(filters);
}
return filters;
}
从中我们可以看到，主要分为三步:
1. 通过FilterProviders 把Filter收集到一个Filter列表
2. 对列表进行排序，排序规则是根据Order和Scope
3. 列表去重
FilterComparer是Filter排序比较器，代码如下, 从中我们可以看到Order 和 Scope是怎么影响排序顺序
private class FilterComparer : IComparer<Filter>
{
public int Compare(Filter x, Filter y)
{
// Nulls always have to be less than non-nulls
if (x == null && y == null)
{
return ;
}
if (x == null)
{
return -;
}
if (y == null)
{
return ;
} // Sort first by order... if (x.Order < y.Order)
{
return -;
}
if (x.Order > y.Order)
{
return ;
} // ...then by scope if (x.Scope < y.Scope)
{
return -;
}
if (x.Scope > y.Scope)
{
return ;
} return ;
}
}
最后返回列表传递给FilterInfo类型，FilterInfo内部处理见上面.