6.1.3 模型和视图 - Reference Documentation
Authors: Graeme Rocher, Peter Ledbrook, Marc Palmer, Jeff Brown, Luke Daley, Burt Beckwith
Version: null
6.1.3 模型和视图
Returning the Model
A model is a Map that the view uses when rendering. The keys within that Map correspond to variable names accessible by the view. There are a couple of ways to return a model. First, you can explicitly return a Map instance:def show() {
[book: Book.get(params.id)]
}The above does not reflect what you should use with the scaffolding views - see the scaffolding section for more details.If no explicit model is returned the controller's properties will be used as the model, thus allowing you to write code like this:
class BookController { List books
List authors def list() {
books = Book.list()
authors = Author.list()
}
}This is possible due to the fact that controllers are prototype scoped. In other words a new controller is created for each request. Otherwise code such as the above would not be thread-safe, and all users would share the same data.In the above example the
books and authors properties will be available in the view.A more advanced approach is to return an instance of the Spring ModelAndView class:import org.springframework.web.servlet.ModelAndViewdef index() { // get some books just for the index page, perhaps your favorites def favoriteBooks = ... // forward to the list view to show them return new ModelAndView("/book/list", [ bookList : favoriteBooks ]) }
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返回模型
模型是在渲染的时候给视图用的一个映射(Map)。映射的键对应于视图中的命名变量。有很多方法都可以返回一个模型。首先,你可以通过明确返回映射(Map)实例的方式:def show() {
[book: Book.get(params.id)]
}上述示例并 不会 影响到脚手架的视图-更多信息请参考脚手架章节。如果没有明确指定模型,那么控制器的属性将作为模型返回给视图,象如下代码所示那样:
class BookController { List books
List authors def list() {
books = Book.list()
authors = Author.list()
}
}这是可行的,因为控制器的缺省作用域是prototype。换句话说,每一个请求都将创建一个新的控制器。否则的话,上述的代码就不是线程安全的了,所有的用户将共享同样的数据。在上述示例中,
books和authors属性在视图中将是有效的。另外一个更高级的方式是返回一个Spring ModelAndView类的一个实例:import org.springframework.web.servlet.ModelAndViewdef index() { // get some books just for the index page, perhaps your favorites def favoriteBooks = ... // forward to the list view to show them return new ModelAndView("/book/list", [ bookList : favoriteBooks ]) }
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Selecting the View
In both of the previous two examples there was no code that specified which view to render. So how does Grails know which one to pick? The answer lies in the conventions. Grails will look for a view at the locationgrails-app/views/book/show.gsp for this list action:class BookController {
def show() {
[book: Book.get(params.id)]
}
}def show() {
def map = [book: Book.get(params.id)]
render(view: "display", model: map)
}grails-app/views/book/display.gsp. Notice that Grails automatically qualifies the view location with the book directory of the grails-app/views directory. This is convenient, but to access shared views you need instead you can use an absolute path instead of a relative one:def show() {
def map = [book: Book.get(params.id)]
render(view: "/shared/display", model: map)
}grails-app/views/shared/display.gsp.Grails also supports JSPs as views, so if a GSP isn't found in the expected location but a JSP is, it will be used instead.
选择视图
在前面的两个示例中,我们并没有指定要用那个视图来渲染。那么Grails是如何知道那个将被选择?答案是规约依赖。在下面的示例中,Grails将自动的寻找位于grails-app/views/book/show.gsp的视图:class BookController {
def show() {
[book: Book.get(params.id)]
}
}def show() {
def map = [book: Book.get(params.id)]
render(view: "display", model: map)
}grails-app/views/book/display.gsp来渲染。注意,Grails会根据grails-app/views下的book目录来自动地限定视图的位置。常规是这样的,但是要访问那些共享的视图,你还是需要使用绝对路径来替代相对路径:def show() {
def map = [book: Book.get(params.id)]
render(view: "/shared/display", model: map)
}grails-app/views/shared/display.gsp来渲染。Grails也支持JSP的视图,因此如果一个预期的GSP没有找到,但是有相应的JSP,那么它将使用此JSP。Rendering a Response
Sometimes it's easier (for example with Ajax applications) to render snippets of text or code to the response directly from the controller. For this, the highly flexiblerender method can be used:render "Hello World!"// write some markup
render {
for (b in books) {
div(id: b.id, b.title)
}
}// render a specific view render(view: 'show')
// render a template for each item in a collection
render(template: 'book_template', collection: Book.list())// render some text with encoding and content type render(text: "<xml>some xml</xml>", contentType: "text/xml", encoding: "UTF-8")
MarkupBuilder to generate HTML for use with the render method be careful of naming clashes between HTML elements and Grails tags, for example:import groovy.xml.MarkupBuilder … def login() { def writer = new StringWriter() def builder = new MarkupBuilder(writer) builder.html { head { title 'Log in' } body { h1 'Hello' form { } } } def html = writer.toString() render html }
MarkupBuilder). To correctly output a <form> element, use the following:def login() {
// …
body {
h1 'Hello'
builder.form {
}
}
// …
}渲染响应
有时候在控制器中直接渲染文本或者代码片段到响应是很容易的(比如Ajax的应用)。这时,就可以使用灵活性很高的render方法了:render "Hello World!"// write some markup
render {
for (b in books) {
div(id: b.id, b.title)
}
}// render a specific view render(view: 'show')
// render a template for each item in a collection
render(template: 'book_template', collection: Book.list())// render some text with encoding and content type render(text: "<xml>some xml</xml>", contentType: "text/xml", encoding: "UTF-8")
MarkupBuilder来生成HTML来供render方法使用,这时,你要注意HTML元素和Grails标签名字的冲突,比如:import groovy.xml.MarkupBuilder … def login() { def writer = new StringWriter() def builder = new MarkupBuilder(writer) builder.html { head { title 'Log in' } body { h1 'Hello' form { } } } def html = writer.toString() render html }
MarkupBuilder忽略)。要正确地输出<form>元素,需要使用如下的例子:def login() {
// …
body {
h1 'Hello'
builder.form {
}
}
// …
}
