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Introduction简介

Questions regarding databinding, in one form or another, are probably the most asked in the ASP.NET newsgroups. It's clear everyone loves the idea of databinding but that more advanced functionality, such as event handling, conditional formatting and fine-tuning, aren't straightforward. The goal of this tutorial is to shed light on some of the more common and frequently asked questions about the capabilities of databinding.ASP.NET里数据绑定方面的问题多。它受欢迎，但是更高级的功能，比如事件处理，条件格式化和微调并不直观。本文对常见问题进行了解释。
The Sample Program
Throughout this tutorial, we'll use two separate data sources. The first will be your every-day DataSet, the other will be a strongly-typed custom collection containing strongly-typed objects.本文里使用了2个独立的数据源。第一个是常用的DataSet，另外一个是包含有强类型对象的强类型定制集合。
Our DataSet will contain two tables, Customers and Orders:我们的DataSet会包含2个表，Customers 和Orders

Customer Structure				Order Structure
Name	Type	Description		Name	Type	Description
CustomerId1	Int32	Unique customer identifier		OrderId	Int32	Unique order identifier
Name	String	Name of the customer		CustomerId1	Int32	Identifier of the customer who placed the order
Zip	String	Customer's primary ZIP or Portal code		Ordered	DateTime	Date the order was placed on
Enabled	Boolean	Whether the customer is currently active/enabled		Amount	Decimal	Dollar value of the order

1A DataRelation exists between the Customer.CustomerId and Order.CustomerId columns. Customer.CustomerId 和 Order.CustomerId columns之间有关系。
Our business entities will consist of an Owner and a Pet class:商业实体对象由Owner 和 Pet类组成：

Owner Structure				Pets Structure
Name	Type	Description		Name	Type	Description
OwnerId	Int32	Unique owner identifier		PetId	Int32	Unique pet identifier
YearOfBirth	Int32	The year the owner was born in		Name	String	Name of the pet
FirstName	String	Owner's first name		IsNeutured	Boolean	Whether or not the pet is neutered
LastName	String	Owner's last name		Type	PetType	Indicates the type of pet (Dog, Cat, Fish, Bird, Rodent, Other)
Pets	PetCollection	Collection of pets the owner has

Understanding DataItem理解DataItem
You've undoubtedly made frequent use of the DataItem property, namely when using the DataBinding syntax, to output a value:常用DataItem属性来输出值，这是DataBinding语法的体现。
1: <%# DataBinder.Eval(Container.DataItem, "customerId") %>
It's important to understand that DataItem is actually an object, and that when you use the DataBinder.Eval function, it basically needs to figure out what type of object it is and how to get "customerId" from it. That's because your data source can be different things, such as a DataSet or DataView, an ArrayList or HashTable, a custom collection, and more. Binding happens on a row-by-row basis, and DataItem actually represents the current row being bound. For a DataSet, DataTable, or DataView, DataItem is actually an instance of DataRowView. (You might think that the DataItem for a DataSet or DataTable would be an instance of DataRow, but when you bind either of these, the DefaultView is actually used, therefore DataItem will always be a DataRowView.) When you are binding to a collection, DataItem is an instance of the item within the collection. We can observe this more clearly with the following code:要理解DataItem是个对象，基本上DataBinder.Eval函数需要估计出对象类型和怎样得到”customerId”。这也是为什么你的数据源可以变化的原因，比如可用DataSet也可用DataView，也可是ArrayList或HashTable，更可以是定制集合，也可以是其它更多情况。绑定以行行数据为基本处理形式，DataItem实际上代表了绑定上的当前行。对于DataSet、DataTable和DataView，DataItem实际上是DataRowView的实例。（你可能认为，在服务于DataSet或DataTable时，DataItem会是DataRow的实例，但是绑定上时，实际用的是DefaultView，这样DataItem会总是一个DataRowView）当你用集合时，DataItem是集合的项。如下的代码对此规则有详细的解说：
1: <%@ Import namespace="System.Data" %>

2: <%@ Import namespace="BindingSample" %>
3: <asp:Repeater id="dataSetRepeater" Runat="server">
4: <ItemTemplate>
5: <%# ((DataRowView)Container.DataItem)["customerId"] %> -
6: <%# ((DataRowView)Container.DataItem)["Name"] %> <br />

7: </ItemTemplate>
8: <AlternatingItemTemplate>
9: <%# DataBinder.Eval(Container.DataItem, "customerId") %> -
10: <%# DataBinder.Eval(Container.DataItem, "Name") %> <br />
11: </AlternatingItemTemplate>
12: </asp:Repeater>

13:
14: <br><br>
15:
16: <asp:Repeater id="collectionRepeater" Runat="server">
17: <ItemTemplate>
18: <%# ((Owner)Container.DataItem).OwnerId %> -
19: <%# ((Owner)Container.DataItem).FirstName %> <br />

20: </ItemTemplate>
21: <AlternatingItemTemplate>
22: <%# DataBinder.Eval(Container.DataItem, "OwnerId") %> -
23: <%# DataBinder.Eval(Container.DataItem, "FirstName") %> <br />
24: </AlternatingItemTemplate>
25: </asp:Repeater>

In the first Repeater, we are binding to a DataSet, the ItemTemplate shows how to access values by casting DataItem to a DataRowView [5, 6], the AlternateItemTemplate will output the same information but through DataBinder.Eval [9, 10].在第一个Repeater，我们绑定到DataSet，ItemTemplate里把DataItem转换到DataRowView [5, 6]，AlternateItemTemplate通过DataBinder.Eval [9, 10]输出同样的信息。

In the second Repeater, we bind to a custom collection. Again, the ItemTemplate shows how to cast DataItem to the right type and access the fields directly [18, 19] while the AlternateItemTemplate shows how the same is accomplished with