淺談ASP.NET MVC中的FluentHtml與連續(xù)接口
我們力求頁面層代碼簡潔并具有較好的可讀性,在ASP.NET MVC的平臺上,我們以新的起點來實現(xiàn)這一目標(biāo).MvcContrib.FluentHtml和Spark ViewEngine給我們做出了榜樣.本文將以MvcContrib.FluentHtml為例探究它的實現(xiàn)機(jī)制:Fluent Interface.
在MvcContrib.FluentHtml的應(yīng)用中,我們隨處可以見到下面的代碼:
- < %= this.TextBox(x => x.Person.Name).Title("Enter the person's name").Label("Name:") %>
- ……
- < %= this.Select(x => x.Person.Gender).Options(Model.Genders).Size(5).Label("Gender:")
- .Title("Select the person's gender") %>
瀏覽器中生成的代碼為:
- < LABEL id=Person_Name_Label for=Person_Name>Name:< /LABEL>
- < INPUT id=Person_Name title="Enter the person's name" value=Jeremy maxLength=50 name=Person.Name>
- .
- < SELECT id=Person_Gender title="Select the person's gender" size=5 name=Person.Gender>< OPTION selected value=M>Male< /OPTION>< OPTION value=F>Female< /OPTION>< /SELECT>
上面對動態(tài)生成TextBox和Select的代碼很有意思,我們使用普通的方式在頁面上生成同樣的客戶端代碼,CS代碼大致是這樣的:
- Label label = new Label();
- label.Text = "Name";
- TextBox textbox= new TextBox();
- textbox.ToolTip ="Enter the person's name";
- textbox.ID = "No.10001";
- textbox.ID = "Person.Name";
而FluentHtml創(chuàng)建頁面元素的方式讓我們很容易聯(lián)想到StringBuilder的使用:
- StringBuilder stringbuilder = new StringBuilder();
- stringbuilder.Append("Hello").Append(" ").Append("World!");
Fulent Interface 這種實現(xiàn)編程方式就是"Fluent Interface",這并不是什么新概念,2005年Eric Evans 和Martin Fowler就為這種實現(xiàn)方式命名.源文檔 <http://www.martinfowler.com/bliki/FluentInterface.html> 可以通過維基百科中對Fluent Interface的描述獲得一個基本的了解:In software engineering, a fluent interface (as first coined by Eric Evans and Martin Fowler) is a way of implementing an object oriented API in a way that aims to provide for more readable code.
我們分解上面的話:
它是面向?qū)ο驛PI的一種實現(xiàn)方式,目的是增加代碼的可讀性.。既然我們最熟悉的是StringBuilder,我們就從這個線索追下去:打開Reflector,很容易找到StringBuilder的Append方法:
- public StringBuilder Append(string value)
- {
- if (value != null)
- {
- string stringValue = this.m_StringValue;
- IntPtr currentThread = Thread.InternalGetCurrentThread();
- if (this.m_currentThread != currentThread)
- {
- stringstringValue = string.GetStringForStringBuilder(stringValue, stringValue.Capacity);
- }
- int length = stringValue.Length;
- int requiredLength = length + value.Length;
- if (this.NeedsAllocation(stringValue, requiredLength))
- {
- string newString = this.GetNewString(stringValue, requiredLength);
- newString.AppendInPlace(value, length);
- this.ReplaceString(currentThread, newString);
- }
- else
- {
- stringValue.AppendInPlace(value, length);
- this.ReplaceString(currentThread, stringValue);
- }
- }
- return this;
- }
閱讀這段有兩個特別要注意的點:1.方法的返回值是StringBuilder類型 2.***一句:return this;為了深刻理解,我們寫一個簡單的StringBuilder:
- public interface IContentBuilder
- {
- void WriteContent();
- IContentBuilder Append(string partialContent);
- }
- public class TestContentBuilder : IContentBuilder
- {
- string temp;
- #region IContentBuilder Members
- void IContentBuilder.WriteContent()
- {
- Console.Write(temp);
- }
- IContentBuilder IContentBuilder.Append(string partialContent)
- {
- temp += partialContent;
- return this;
- }
- #endregion
- }
- … …
- //調(diào)用代碼
- IContentBuilder t = new TestContentBuilder();
- t.Append("test").Append("Hello").WriteContent();
跑一下代碼,和StringBuilder效果是一樣的.從上面的應(yīng)用也可以看出:Fluent Interface經(jīng)常用來完成對象的構(gòu)造和屬性賦值.
言歸正傳:FluentHTML了解了Fluent Interface,我們來看一下MVCContrib.FluentHTML的實現(xiàn),這里以TextBox為例進(jìn)行考察,首先看一下它的繼承關(guān)系:
- public class TextBox : TextInput
- public abstract class TextInput : Input, ISupportsMaxLength where T : TextInput
- public abstract class Input : FormElement where T : Input, Ielement
泛型是一種高層次的算法抽象,我們就通過Input
- public abstract class Input : FormElement where T : Input, IElement
- {
- protected object elementValue;
- protected Input(string type, string name) : base(HtmlTag.Input, name)
- {
- builder.MergeAttribute(HtmlAttribute.Type, type, true);
- }
- protected Input(string type, string name, MemberExpression forMember, IEnumerable behaviors)
- : base(HtmlTag.Input, name, forMember, behaviors)
- {
- builder.MergeAttribute(HtmlAttribute.Type, type, true);
- }
- ///
- /// Set the 'value' attribute.
- ///
- /// The value for the attribute.
- public virtual T Value(object value)
- {
- elementValue = value;
- return (T)this;
- }
- ///
- /// Set the 'size' attribute.
- ///
- /// The value for the attribute.
- public virtual T Size(int value)
- {
- Attr(HtmlAttribute.Size, value);
- return (T)this;
- }
- protected override void PreRender()
- {
- Attr(HtmlAttribute.Value, elementValue);
- base.PreRender();
- }
- }
- 以Size方法為例,可以看出這是一種典型的Fluent Interface實現(xiàn):
- public virtual T Size(int value)
- {
- Attr(HtmlAttribute.Size, value);
- return (T)this;
- }
分析到這里,上面的語句中還有一點比較奇怪,就是Lambda表達(dá)式的部分:
- this.TextBox(x => x.Person.Name).Title("Enter the person's name").Label("Name:")
TextBox的實現(xiàn)代碼里面我們沒有看到對Lambda表達(dá)式的支持.那是在什么地方完成的呢?通過跟進(jìn),我們來到了ViewDataContainerExtensions,它是IViewDataCon
- namespace MvcContrib.FluentHtml
- {
- ///
- /// Extensions to IViewDataContainer
- ///
- public static class ViewDataContainerExtensions
- {
- ///
- /// Generate an HTML input element of type 'text' and set its value from ViewData based on the name provided.
- ///
- /// The view.
- /// Value of the 'name' attribute of the element.Also used to derive the 'id' attribute.
- public static TextBox TextBox(this IViewDataContainer view, string name)
- {
- return new TextBox(name).Value(view.ViewData.Eval(name));
- }
- … …
tainer 的Extension Method:
看一下return new TextBox(name).Value(view.ViewData.Eval(name));所以這里就成了TextBox定義方法鏈的***步.
FluentHtml與連續(xù)接口總結(jié)
為了能夠在View中能夠簡潔清晰的構(gòu)造HTML元素,Asp.net MVC中通過htmlHelper.InputHelper來實現(xiàn)頁面元素的構(gòu)造. 頁面層所使用的<%= Html.TextBox("username") %>,HTML也是htmlHelper的Extension Method.相比較起來,htmlHelper提供了基礎(chǔ)的頁面控件定義和構(gòu)造,而FluentHTML表現(xiàn)的更為靈活.除了FluentHTML,著名的Spark View Engine也有類似的實現(xiàn),大家可以關(guān)注一下.
【編輯推薦】
