在ASP.net MVC的一个开源项目MvcContrib中,为我们提供了几个视图引擎,例如NVelocity, Brail, NHaml, XSLT.那么如果我们想在ASP.NET MVC中实现我们自己的一个视图引擎,我们应该要怎么做呢?
我们知道呈现视图是在Controller中通过传递视图名和数据到RenderView()方法来实现的。好,我们就从这里下手。我们查看一下ASP.NET MVC的源代码,看看RenderView()这个方法是如何实现的:
protected virtual void RenderView(string viewName, string
masterName, object viewData) {
ViewContext viewContext = new ViewContext(
ControllerContext, viewName, masterName, viewData, TempData);
ViewEngine.RenderView(viewContext);
}//
这是P2的源码,P3略有不同,原理差不多,从上面的代码我们可以看到,Controller中的RenderView()方法主要是将ControllerContext, viewName, masterName, viewData, TempData这一堆东西封装成ViewContext,然后把ViewContext传递给ViewEngine.RenderView(viewContext)。嗯,没错,我们这里要实现的就是ViewEngine的RenderView()方法。
ASP.NET MVC为我们提供了一个默认的视图引擎,这个视图引擎叫做:WebFormsViewEngine. 从名字就可以看出,这个视图引擎是使用ASP.NET web forms来呈现的。在这里,我们要实现的视图引擎所使用的模板用HTML文件吧,简单的模板示例代码如下:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html XMLns=""http://www.w3.org/1999/xhtml"">
http://www.w3.org/1999/xhtml" >
<head>
<title>自定义视图引擎示例</title>
</head>
<body>
<h1>{$ViewData.Title}</h1>
<p>{$ViewData.Message}</p>
<p>The following fruit is part of a string array: {$ViewData.FruitStrings[1]}</p>
<p>The following fruit is part of an object array: {$ViewData.FruitObjects[1].Name}</p>
<p>Here's an undefined variable: {$UNDEFINED}</p>
</body>
< ml>
下面马上开始我们的实现。首先,毫无疑问的,我们要创建一个ViewEngine,就命名为 SimpleViewEngine 吧,注意哦,ViewEngine要实现IViewEngine接口:
public class SimpleViewEngine : IViewEngine
{
#region Private members
IViewLocator _viewLocator = null;
#endregion
#region IViewEngine Members : RenderView()
public void RenderView(ViewContext viewContext)
{
string viewLocation = ViewLocator.GetViewLocation
(viewContext, viewContext.ViewName);
if (string.IsNullOrEmpty(viewLocation))
{
throw new InvalidOperationException(string.Format
("View {0} could not be found.", viewContext.ViewName));
}
string viewPath = viewContext.HttpContext.Request.MapPath(viewLocation);
string viewTemplate = File.ReadAllText(viewPath);
//以下为模板解析
IRenderer renderer = new PrintRenderer();
viewTemplate = renderer.Render(viewTemplate, viewContext);
viewContext.HttpContext.Response.Write(viewTemplate);
}
#endregion
#region Public properties : ViewLocator
public IViewLocator ViewLocator
{
get
{
if (this._viewLocator == null)
{
this._viewLocator = new SimpleViewLocator();
}
return this._viewLocator;
}
set
{
this._viewLocator = value;
}
}
#endregion
}