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了解 ASP.NET Eval() 和 Bind()

发布于 2024-08-12 05:50:10 字数 114 浏览 6 评论 0原文

任何人都可以向我展示一些绝对最小的 ASP.NET 代码来理解 Eval() 和 Bind() 吗？

最好为我提供两个单独的代码片段或者网络链接。

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筱武穆 2024-08-19 05:50:10

对于只读控件，它们是相同的。对于 2 路数据绑定，使用要通过声明性数据绑定进行更新、插入等操作的数据源，您需要使用 Bind。

例如，想象一下带有 ItemTemplate 和 EditItemTemplate 的 GridView。如果您在 ItemTemplate 中使用 Bind 或 Eval，则不会有任何区别。如果您在 EditItemTemplate 中使用 Eval，该值将无法传递给 DataSource 的 Update 方法code> 网格绑定到的。

更新：我想出了这个例子：

<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Data binding demo</title>
</head>
<body>
    <form id="form1" runat="server">
        <asp:GridView 
            ID="grdTest" 
            runat="server" 
            AutoGenerateEditButton="true" 
            AutoGenerateColumns="false" 
            DataSourceID="mySource">
            <Columns>
                <asp:TemplateField>
                    <ItemTemplate>
                        <%# Eval("Name") %>
                    </ItemTemplate>
                    <EditItemTemplate>
                        <asp:TextBox 
                            ID="edtName" 
                            runat="server" 
                            Text='<%# Bind("Name") %>' 
                        />
                    </EditItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>
    </form>

    <asp:ObjectDataSource 
        ID="mySource" 
        runat="server"
        SelectMethod="Select" 
        UpdateMethod="Update" 
        TypeName="MyCompany.CustomDataSource" />
</body>
</html>

这是用作对象数据源的自定义类的定义：

public class CustomDataSource
{
    public class Model
    {
        public string Name { get; set; }
    }

    public IEnumerable<Model> Select()
    {
        return new[] 
        {
            new Model { Name = "some value" }
        };
    }

    public void Update(string Name)
    {
        // This method will be called if you used Bind for the TextBox
        // and you will be able to get the new name and update the
        // data source accordingly
    }

    public void Update()
    {
        // This method will be called if you used Eval for the TextBox
        // and you will not be able to get the new name that the user
        // entered
    }
}

For read-only controls they are the same. For 2 way databinding, using a datasource in which you want to update, insert, etc with declarative databinding, you'll need to use Bind.

Imagine for example a GridView with a ItemTemplate and EditItemTemplate. If you use Bind or Eval in the ItemTemplate, there will be no difference. If you use Eval in the EditItemTemplate, the value will not be able to be passed to the Update method of the DataSource that the grid is bound to.

UPDATE: I've come up with this example:

<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Data binding demo</title>
</head>
<body>
    <form id="form1" runat="server">
        <asp:GridView 
            ID="grdTest" 
            runat="server" 
            AutoGenerateEditButton="true" 
            AutoGenerateColumns="false" 
            DataSourceID="mySource">
            <Columns>
                <asp:TemplateField>
                    <ItemTemplate>
                        <%# Eval("Name") %>
                    </ItemTemplate>
                    <EditItemTemplate>
                        <asp:TextBox 
                            ID="edtName" 
                            runat="server" 
                            Text='<%# Bind("Name") %>' 
                        />
                    </EditItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:GridView>
    </form>

    <asp:ObjectDataSource 
        ID="mySource" 
        runat="server"
        SelectMethod="Select" 
        UpdateMethod="Update" 
        TypeName="MyCompany.CustomDataSource" />
</body>
</html>

And here's the definition of a custom class that serves as object data source:

public class CustomDataSource
{
    public class Model
    {
        public string Name { get; set; }
    }

    public IEnumerable<Model> Select()
    {
        return new[] 
        {
            new Model { Name = "some value" }
        };
    }

    public void Update(string Name)
    {
        // This method will be called if you used Bind for the TextBox
        // and you will be able to get the new name and update the
        // data source accordingly
    }

    public void Update()
    {
        // This method will be called if you used Eval for the TextBox
        // and you will not be able to get the new name that the user
        // entered
    }
}

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疾风者 2024-08-19 05:50:10

Darin Dimitrov 完美地回答了这个问题，但从 ASP.NET 4.5 开始，现在有更好的方法来设置这些绑定来替换* Eval() 和 Bind()，利用强类型绑定。

*注意：仅当您不使用SqlDataSource或匿名对象时，此方法才有效。它需要一个强类型对象（来自EF模型或任何其他类）。

此代码段显示了如何将 Eval 和 Bind 用于 ListView 控件（InsertItem 需要 Bind，正如 Darin Dimitrov 上面所解释的，ItemTemplate 是只读的（因此它们是标签），所以只需要一个 Eval）：

<asp:ListView ID="ListView1" runat="server" DataKeyNames="Id" InsertItemPosition="LastItem" SelectMethod="ListView1_GetData" InsertMethod="ListView1_InsertItem" DeleteMethod="ListView1_DeleteItem">
    <InsertItemTemplate>
        <li>
            Title: <asp:TextBox ID="Title" runat="server" Text='<%# Bind("Title") %>'/><br />         
            Description: <asp:TextBox ID="Description" runat="server" TextMode="MultiLine" Text='<%# Bind("Description") %>' /><br />        
            <asp:Button ID="InsertButton" runat="server" Text="Insert" CommandName="Insert" />        
        </li>
    </InsertItemTemplate>
    <ItemTemplate>
        <li>
            Title: <asp:Label ID="Title" runat="server" Text='<%#  Eval("Title") %>' /><br />
            Description: <asp:Label ID="Description" runat="server" Text='<%# Eval("Description") %>' /><br />        
            <asp:Button ID="DeleteButton" runat="server" Text="Delete" CommandName="Delete" CausesValidation="false"/>
        </li>
      </ItemTemplate>

来自 ASP.NET 4.5+ 中，数据绑定控件已通过新属性 ItemType 进行了扩展，该属性指向您分配给其数据源的对象类型。

<asp:ListView ItemType="Picture" ID="ListView1" runat="server" ...>

Picture 是强类型对象（来自 EF 模型）。然后我们替换：

Bind(property) -> BindItem.property
Eval(property) -> Item.property

所以这个：

<%# Bind("Title") %>      
<%# Bind("Description") %>         
<%#  Eval("Title") %> 
<%# Eval("Description") %>

会变成这样：

<%# BindItem.Title %>         
<%# BindItem.Description %>
<%# Item.Title %>
<%# Item.Description %>

与 Eval 和 Eval 相比的优点绑定：

IntelliSense 可以找到您正在使用的对象的正确属性
如果属性被重命名/删除，您将在浏览器中查看页面之前收到错误
外部工具（需要完整的当您重命名对象上的属性时，VS 版本）将正确重命名标记中的项目

Source：来自这本优秀的书

The question was answered perfectly by Darin Dimitrov, but since ASP.NET 4.5, there is now a better way to set up these bindings to replace* Eval() and Bind(), taking advantage of the strongly-typed bindings.

*Note: this will only work if you're not using a SqlDataSource or an anonymous object. It requires a Strongly-typed object (from an EF model or any other class).

This code snippet shows how Eval and Bind would be used for a ListView control (InsertItem needs Bind, as explained by Darin Dimitrov above, and ItemTemplate is read-only (hence they're labels), so just needs an Eval):

<asp:ListView ID="ListView1" runat="server" DataKeyNames="Id" InsertItemPosition="LastItem" SelectMethod="ListView1_GetData" InsertMethod="ListView1_InsertItem" DeleteMethod="ListView1_DeleteItem">
    <InsertItemTemplate>
        <li>
            Title: <asp:TextBox ID="Title" runat="server" Text='<%# Bind("Title") %>'/><br />         
            Description: <asp:TextBox ID="Description" runat="server" TextMode="MultiLine" Text='<%# Bind("Description") %>' /><br />        
            <asp:Button ID="InsertButton" runat="server" Text="Insert" CommandName="Insert" />        
        </li>
    </InsertItemTemplate>
    <ItemTemplate>
        <li>
            Title: <asp:Label ID="Title" runat="server" Text='<%#  Eval("Title") %>' /><br />
            Description: <asp:Label ID="Description" runat="server" Text='<%# Eval("Description") %>' /><br />        
            <asp:Button ID="DeleteButton" runat="server" Text="Delete" CommandName="Delete" CausesValidation="false"/>
        </li>
      </ItemTemplate>

From ASP.NET 4.5+, data-bound controls have been extended with a new property ItemType, which points to the type of object you're assigning to its data source.

<asp:ListView ItemType="Picture" ID="ListView1" runat="server" ...>

Picture is the strongly type object (from EF model). We then replace:

Bind(property) -> BindItem.property
Eval(property) -> Item.property

So this:

<%# Bind("Title") %>      
<%# Bind("Description") %>         
<%#  Eval("Title") %> 
<%# Eval("Description") %>

Would become this:

<%# BindItem.Title %>         
<%# BindItem.Description %>
<%# Item.Title %>
<%# Item.Description %>

Advantages over Eval & Bind:

IntelliSense can find the correct property of the object your're working with
If property is renamed/deleted, you will get an error before page is viewed in browser
External tools (requires full versions of VS) will correctly rename item in markup when you rename a property on your object

Source: from this excellent book

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