[源码学习]RazorTemplateEngine.GenerateCodeCore之CreateParser()方法

接上篇的GenerateCodeCore方法中

            // Run the parser
            RazorParser parser = CreateParser();
            Debug.Assert(parser != null);
            parser.Parse(input, consumer);

RazorParser parser = CreateParser();中的CreateParser代码如下：

        protected internal virtual RazorParser CreateParser() {
            return new RazorParser(Host.DecorateCodeParser(Host.CodeLanguage.CreateCodeParser()),
                                                          Host.DecorateMarkupParser(Host.CreateMarkupParser())) {
                                                              DesignTimeMode = Host.DesignTimeMode
                                                          };
        }

Host是RazorTemplateEngine的属性，类型是RazorEngineHost

        /// <summary>
        /// The RazorEngineHost which defines the environment in which the generated template code will live
        /// </summary>
        public RazorEngineHost Host { get; private set; }

在构造函数中传入并赋值，传入的是RazorEngineHost的派生类WebPageRazorHost

        /// <summary>
        /// Constructs a new RazorTemplateEngine with the specified host
        /// </summary>
        /// <param name="host">The host which defines the environment in which the generated template code will live</param>
        public RazorTemplateEngine(RazorEngineHost host) {
            if (host == null) { throw new ArgumentNullException("host"); }

            Host = host;
        }

传入的是RazorEngineHost的派生类WebPageRazorHost，在System.Web.WebPages.Razor命名空间中，这个类的GetCodeLanguage
调用了RazorCodeLanguage.GetLanguageByExtension确定了CodeLanguage的实际类型，override MarkupParser CreateMarkupParser()确定了MarkupParser的实际类型。

以下只研究一下CodeLanguage是CSharpRazorCodeLanguage的情况。

传入参数时调用Host的两个方法Host.DecorateCodeParser和Host.DecorateMarkupParser，只是看起来两个判断是否为null用的方法

        /// <summary>
        /// Gets an instance of the code parser and is provided an opportunity to decorate or replace it
        /// </summary>
        /// <param name="incomingCodeParser">The code parser</param>
        /// <returns>Either the same code parser, after modifications, or a different code parser</returns>
        public virtual ParserBase DecorateCodeParser(ParserBase incomingCodeParser) {
            if (incomingCodeParser == null) { throw new ArgumentNullException("incomingCodeParser"); }
            return incomingCodeParser;
        }

        /// <summary>
        /// Gets an instance of the markup parser and is provided an opportunity to decorate or replace it
        /// </summary>
        /// <param name="incomingMarkupParser">The markup parser</param>
        /// <returns>Either the same markup parser, after modifications, or a different markup parser</returns>
        public virtual MarkupParser DecorateMarkupParser(MarkupParser incomingMarkupParser) {
            if (incomingMarkupParser == null) { throw new ArgumentNullException("incomingMarkupParser"); }
            return incomingMarkupParser;
        }

第一个方法的参数Host.CodeLanguage.CreateCodeParser()即CSharpRazorCodeLanguage.CreateCodeParser()

        /// <summary>
        /// Constructs a new instance of the code parser for this language
        /// </summary>
        public override ParserBase CreateCodeParser() {
            return new CSharpCodeParser();
        }

第二个方法的参数Host.CreateMarkupParser()即WebPageRazorHost.CreateMarkupParser()

        public override MarkupParser CreateMarkupParser() {
            return new HtmlMarkupParser();
        }

RazorParser的构造函数直接就是两行赋值语句，下篇分析parser.Parse(input, consumer);吧