添加视图 Adding a View

在本小节你将修改HelloWorldController类，使用视图模板文件来整洁的封装生成HTML应答给客户端的处理。（这句翻译得不好，希望高手给点帮助，谢谢）

In this section you're going to modify the HelloWorldController class to use view template files to cleanly encapsulate the process of generating HTML responses to a client.

你将使用ASP.NET MVC 3介绍过的Razor视图引擎创建一个模板文件。基于Razor有视图模板有一个 .cshtml的文件扩展名，使用C#提供一种简洁的方法创建HTML输出。Razor只需要很少的键入字符就能够快速的、流畅的流程编写一个视图模板。

You'll create a view template file using the Razor view engine introduced with ASP.NET MVC 3. Razor-based view templates have a .cshtml file extension, and provide an elegant way to create HTML output using C#. Razor minimizes the number of characters and keystrokes required when writing a view template, and enables a fast, fluid coding workflow.

 目前在控制器类的 Index方法是使用硬编码的方式返回一个字符串消息。改变这个方法返回一个视图对象，就像下面看到的代码那样：

Currently the Index method returns a string with a message that is hard-coded in the controller class. Change theIndex method to return a View object, as shown in the following code:

public ActionResult Index() 
{ 
    return View(); 
}

 Index方法使用一个视图模板生成HTML响应给浏览器。

The Index method above uses a view template to generate an HTML response to the browser. Controller methods (also known as action methods), such as the Index method above, generally return an ActionResult (or a class derrived from ActionResult), not primitive types like string.

In the project, add a view template that you can use with the Index method. To do this, right-click inside the Indexmethod and click Add View.

The Add View dialog box appears. Leave the defaults the way they are and click the Add button:

The MvcMovie\Views\HelloWorld folder and the MvcMovie\Views\HelloWorld\Index.cshtml file are created. You can see them in Solution Explorer:

The following shows the Index.cshtml file that was created:

Add the following HTML under the <h2> tag.

<p>Hello from our View Template!</p>

　　

 The complete MvcMovie\Views\HelloWorld\Index.cshtml file is shown below.

@{
    ViewBag.Title = "Index";
}

<h2>Index</h2>

<p>Hello from our View Template!</p>

　　

If you are using Visual Studio 2012, in solution explorer, right click the Index.cshtml file and select View in Page Inspector.

The Page Inspector tutorial has more information about this new tool.

Alternatively, run the application and browse to the HelloWorld controller (http://localhost:xxxx/HelloWorld). TheIndex method in your controller didn't do much work; it simply ran the statement return View(), which specified that the method should use a view template file to render a response to the browser. Because you didn't explicitly specify the name of the view template file to use, ASP.NET MVC defaulted to using the Index.cshtml view file in the\Views\HelloWorld folder. The image below shows the string "Hello from our View Template!" hard-coded in the view.

Looks pretty good. However, notice that the browser's title bar shows  "Index My ASP.NET A" and the big link on the top of the page says "your logo here." Below the "your logo here." link are registration and log in links, and below that links to Home, About and Contact pages. Let's change some of these.

Changing Views and Layout Pages

First, you want to change the "your logo here." title at the top of the page. That text is common to every page. It's actually implemented in only one place in the project, even though it appears on every page in the application. Go to the /Views/Shared folder in Solution Explorer and open the _Layout.cshtml file. This file is called a layout pageand it's the shared "shell" that all other pages use.

Layout templates allow you to specify the HTML container layout of your site in one place and then apply it across multiple pages in your site. Find the @RenderBody() line. RenderBody is a placeholder where all the view-specific pages you create show up, "wrapped" in the layout page. For example, if you select the About link, theViews\Home\About.cshtml view is rendered inside the RenderBody  method.

Change the site-title heading in the layout template from "your logo here" to "MVC Movie".

<div class="float-left">
    <p class="site-title">@Html.ActionLink("MVC Movie", "Index", "Home")</p>
</div>

　　

Replace the contents of the title element with the following markup:

<title>@ViewBag.Title - Movie App</title>

　　

Run the application and notice that it now says "MVC Movie ". Click the About link, and you see how that page shows "MVC Movie", too. We were able to make the change once in the layout template and have all pages on the site reflect the new title.

Now, let's change the title of the Index view.

Open MvcMovie\Views\HelloWorld\Index.cshtml. There are two places to make a change: first, the text that appears in the title of the browser, and then in the secondary header (the <h2> element). You'll make them slightly different so you can see which bit of code changes which part of the app.

@{
    ViewBag.Title = "Movie List";
}

<h2>My Movie List</h2>

<p>Hello from our View Template!</p>

　　

To indicate the HTML title to display, the code above sets a Title property of the ViewBag object (which is in theIndex.cshtml view template). If you look back at the source code of the layout template, you’ll notice that the template uses this value in the <title> element as part of the <head> section of the HTML that we modified previously. Using this ViewBag approach, you can easily pass other parameters between your view template and your layout file.

Run the application and browse to http://localhost:xx/HelloWorld. Notice that the browser title, the primary heading, and the secondary headings have changed. (If you don't see changes in the browser, you might be viewing cached content. Press Ctrl+F5 in your browser to force the response from the server to be loaded.) The browser title is created with the  ViewBag.Title we set in the Index.cshtml view template  and the additional  "- Movie App" added in the layout file.

Also notice how the content in the Index.cshtml view template was merged with the _Layout.cshtml view template and a single HTML response was sent to the browser. Layout templates make it really easy to make changes that apply across all of the pages in your application.

Our little bit of "data" (in this case the "Hello from our View Template!" message) is hard-coded, though. The MVC application has a "V" (view) and you've got a "C" (controller), but no "M" (model) yet. Shortly, we'll walk through how create a database and retrieve model data from it.

Passing Data from the Controller to the View

Before we go to a database and talk about models, though, let's first talk about passing information from the controller to a view. Controller classes are invoked in response to an incoming URL request. A controller class is where you write the code that handles the incoming browser requests, retrieves data from a database, and ultimately decides what type of response to send back to the browser. View templates can then be used from a controller to generate and format an HTML response to the browser.

Controllers are responsible for providing whatever data or objects are required in order for a view template to render a response to the browser. A best practice: A view template should never perform business logic or interact with a database directly. Instead, a view template should work only with the data that's provided to it by the controller. Maintaining this "separation of concerns" helps keep your code clean, testable and more maintainable.

Currently, the Welcome action method in the HelloWorldController class takes a name and a numTimes parameter and then outputs the values directly to the browser. Rather than have the controller render this response as a string, let’s change the controller to use a view template instead. The view template will generate a dynamic response, which means that you need to pass appropriate bits of data from the controller to the view in order to generate the response. You can do this by having the controller put the dynamic data (parameters) that the view template needs in a ViewBag object that the view template can then access.

Return to the HelloWorldController.cs file and change the Welcome method to add a Message and NumTimes value to the ViewBag object. ViewBag is a dynamic object, which means you can put whatever you want in to it; the ViewBagobject has no defined properties until you put something inside it. The ASP.NET MVC model binding systemautomatically maps the named parameters (name and numTimes) from the query string in the address bar to parameters in your method. The complete HelloWorldController.cs file looks like this:

usingSystem.Web;
usingSystem.Web.Mvc;

namespaceMvcMovie.Controllers
{
    publicclassHelloWorldController:Controller
    {
        publicActionResultIndex()
        {
            returnView();
        }

        publicActionResultWelcome(string name,int numTimes =1)
        {
            ViewBag.Message="Hello "+ name;
            ViewBag.NumTimes= numTimes;

            returnView();
        }
    }
}

　　

Now the ViewBag object contains data that will be passed to the view automatically.

Next, you need a Welcome view template! In the Build menu, select Build MvcMovie to make sure the project is compiled.

Then right-click inside the Welcome method and click Add View.

Here's what the Add View dialog box looks like:

Click Add, and then add the following code under the <h2> element in the new Welcome.cshtml file. You'll create a loop that says "Hello" as many times as the user says it should. The complete Welcome.cshtml file is shown below.

@{
    ViewBag.Title="Welcome";
}

<h2>Welcome</h2>

<ul> 
   @for (int i=0; i < ViewBag.NumTimes; i++) { 
      <li>@ViewBag.Message</li> 
   } 
</ul>

　　

Run the application and browse to the following URL:

http://localhost:xx/HelloWorld/Welcome?name=Scott&numtimes=4

Now data is taken from the URL and passed to the controller using the model binder. The controller packages the data into a ViewBag object and passes that object to the view. The view then displays the data as HTML to the user.

 In the sample above, we used a ViewBag object to pass data from the controller to a view. Latter in the tutorial, we will use a view model to pass data from a controller to a view. The view model approach to passing data is generally much preferred over the view bag approach. See the blog entry Dynamic V Strongly Typed Views for more information.

Well, that was a kind of an "M" for model, but not the database kind. Let's take what we've learned and create a database of movies.