二、Filter
MVC中有四种类型的Filter：IAuthorizationFilter，IActionFilter，IResultFilter，IExceptionFilter
这四个接口有点拦截器的意思，例如：当有异常出现时会被IExceptionFilter类型的Filter拦截，当Action在执行前和执行结束会被IActionFilter类型的Filter拦截。
通过实现IExceptionFilter我们可以自定义一个用来记录日志的Log4NetExceptionFilter：
public class Log4NetExceptionFilter : IExceptionFilter
{
private readonly ILog _logger;
public Log4NetExceptionFilter()
{
_logger = LogManager.GetLogger(GetType());
}
public void OnException(ExceptionContext context)
{
_logger.Error("Unhandled exception", context.Exception);
}
}
最后需要将自定义的Filter加入MVC的Filter列表中：
public class FilterConfig
{
public static void RegisterGlobalFilters(GlobalFilterCollection filters)
{
filters.Add(new Log4NetExceptionFilter());
}
}
为了记录Action的执行时间，我们可以在Action执行前计时，Action执行结束后记录log：
public class StopwatchAttribute : ActionFilterAttribute
{
private const string StopwatchKey = "StopwatchFilter.Value";
private readonly ILog _logger= LogManager.GetLogger(typeof(StopwatchAttribute));
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
filterContext.HttpContext.Items[StopwatchKey] = Stopwatch.StartNew();
}
public override void OnActionExecuted(ActionExecutedContext filterContext)
{
var stopwatch = (Stopwatch)filterContext.HttpContext.Items[StopwatchKey];
stopwatch.Stop();
var log=string.Format("controller:{0},action:{1},execution time:{2}ms",filterContext.ActionDescriptor.ControllerDescriptor.ControllerName,filterContext.ActionDescriptor.ActionName,stopwatch.ElapsedMilliseconds)
_logger.Info(log);
}
}
ActionFilterAttribute是一个抽象类，它不但继承了IActionFilter, IResultFilter等Filter，还继承了FilterAttribute类型，这意味着我们可以将这个自定义的类型当作Attribute来标记到某个Action或者Controller上,同时它还是一个Filter，仍然可以加在MVC的Filter中起到全局拦截的作用。
三、HtmlHelper
在Razor页面中，如果需要写一段公用的用来展示html元素的逻辑，你可以选择使用@helper标记，例如：
@helper ShowProduct(List products, string style)
{
@foreach (var product in products)
{
@product.Name
}
}
这一段代码有点像一个方法定义，只需要传入一个list类型和字符串就会按照定义的逻辑输出html：
Product list using helper
@ShowProduct(Model.SportProducts, "list-group-item-info")
@ShowProduct(Model.BookProducts, "list-group-item-warning")
@ShowProduct(Model.FoodProducts, "list-group-item-danger")
这样抽取的逻辑只对当前页面有效，如果我们想在不同的页面公用这一逻辑如何做呢？
在Razor中输入@Html即可得到HtmlHelper实例，例如我们可以这样用：@Html.TextBox(“name”)。由此可见我们可以将公用的逻辑扩展在HtmlHelper上：
public static class HtmlHelperExtensions { public static ListGroup ListGroup(this HtmlHelper htmlHelper) { return new ListGroup(); } } public class ListGroup { public MvcHtmlString Info(List data, Func getName) { return Show(data,getName, "list-group-item-info"); } public MvcHtmlString Warning(List data, Func getName) { return Show(data,getName, "list-group-item-warning"); } public MvcHtmlString Danger(List data, Func getName) { return Show(data,getName, "list-group-item-danger"); } public MvcHtmlString Show(List data, Func getName, string style) { var ulBuilder = new TagBuilder("ul"); ulBuilder.AddCssClass("list-group"); foreach (T item in data) { var liBuilder = new TagBuilder("li"); liBuilder.AddCssClass("list-group-item"); liBuilder.AddCssClass(style); liBuilder.SetInnerText(getName(item)); ulBuilder.InnerHtml += liBuilder.ToString(); } return new MvcHtmlString(ulBuilder.ToString()); } } |
有了上面的扩展，就可以这样使用了：
Product list using htmlHelper
@Html.ListGroup().Info(Model.SportProducts,x=>x.Name)
@Html.ListGroup().Warning(Model.BookProducts,x => x.Name)
@Html.ListGroup().Danger(Model.FoodProducts,x => x.Name)
效果：
四、RazorViewEngine
通过自定义RazorViewEngine可以实现同一份后台代码对应不同风格的View。利用这一扩展能够实现不同的Theme风格切换。再比如站点可能需要在不同的语言环境下切换到不同的风格，也可以通过自定义RazorViewEngine来实现。
下面就让我们来实现一个Theme切换的功能，首先自定义一个ViewEngine：
public class ThemeViewEngine: RazorViewEngine { public ThemeViewEngine(string theme) { ViewLocationFormats = new[] { "~/Views/Themes/" + theme + "/{1}/{0}.cshtml", "~/Views/Themes/" + theme + "/Shared/{0}.cshtml" }; PartialViewLocationFormats = new[] { "~/Views/Themes/" + theme + "/{1}/{0}.cshtml", "~/Views/Themes/" + theme + "/Shared/{0}.cshtml" }; AreaViewLocationFormats = new[] { "~Areas/{2}/Views/Themes/" + theme + "/{1}/{0}.cshtml", "~Areas/{2}/Views/Themes/" + theme + "/Shared/{0}.cshtml" }; AreaPartialViewLocationFormats = new[] { "~Areas/{2}/Views/Themes/" + theme + "/{1}/{0}.cshtml", "~Areas/{2}/Views/Themes/" + theme + "/Shared/{0}.cshtml" }; } } |
当我们启用这一ViewEngine时，Razor就会在/Views/Themes/文件夹下去找View文件。为了启用自定义的ViewEngine，需要将ThemeViewEngine加入到ViewEngines
public class MvcApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
if (!string.IsNullOrEmpty(ConfigurationManager.AppSettings["Theme"]))
{
var activeTheme = ConfigurationManager.AppSettings["Theme"];
ViewEngines.Engines.Insert(0, new ThemeViewEngine(activeTheme));
};
//...
}
}
