ASP.NET 4 Unleased - p 48 pdf

LISTING 10.3 ProgrammaticDataBinding.aspx /// /// Represents an item in the /// shopping cart /// public class CartItem { private int _id; public string _description; public int I

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LISTING 10.3 ProgrammaticDataBinding.aspx

<%@ Page Language=”C#” %>

<%@ Import Namespace=”System.Collections.Generic” %>

<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.1//EN”

“http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd”>

/// <summary>

/// Represents an item in the

/// shopping cart

/// </summary>

public class CartItem

{

private int _id;

public string _description;

public int Id

{

get { return _id; }

}

public string Description

FIGURE 10.3 Show list items with programmatic binding

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{

get { return _description; }

}

public CartItem(int id, string description)

{

_id = id;

_description = description;

}

void Page_Load()

{

if (!IsPostBack)

{

// Create shopping cart

List<CartItem> shoppingCart = new List<CartItem>();

shoppingCart.Add(new CartItem(1, “Notebook Computer”));

shoppingCart.Add(new CartItem(2, “HD Plasma Television”));

shoppingCart.Add(new CartItem(3, “Lava Lamp”));

// Bind ListBox to shopping cart

lstShoppingCart.DataSource = shoppingCart;

lstShoppingCart.DataBind();

}

</script>

<title>Programmatic DataBinding</title>

</head>

<body>

<div>

<asp:ListBox

id=”lstShoppingCart”

DataTextField=”Description”

DataValueField=”Id”

Runat=”server” />

</div>

</form>

</body>

</html>

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In Listing 10.3, the ListBox is bound to the collection in the Page_Load() method The

DataTextField and DataValueField properties of the ListBox control represent properties

of the CartItem class

NOTE

A List control’s DataTextField and DataValueField properties can refer to any public

property of a class, but you cannot bind a List control to a public field

Determining the Selected List Item

Displaying options with the List controls is all very nice, but at some point you need to

determine which option a user has selected The List controls support three properties that

you can use to determine the selected list item:

SelectedIndex—Gets or sets the index of the selected list item

SelectedItem—Gets the first selected list item

SelectedValue—Gets or sets the value of the first selected list item

For example, the page in Listing 10.4 enables you to select an item from the DropDownList

control and display the value of the selected item’s Text property (see Figure 10.4)

FIGURE 10.4 Selecting an item from a DropDownList control

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LISTING 10.4 SelectMovie.aspx

protected void btnSelect_Click(object sender, EventArgs e)

{

lblSelectedMovie.Text = ddlMovies.SelectedItem.Text;

}

</script>

<title>Select Movie</title>

</head>

<body>

<div>

<asp:DropDownList

id=”ddlMovies”

DataSourceID=”srcMovies”

DataTextField=”Title”

<asp:Button

id=”btnSelect”

Text=”Select”

OnClick=”btnSelect_Click”

<hr />

<asp:Label

id=”lblSelectedMovie”

<asp:SqlDataSource

id=”srcMovies”

SelectCommand=”SELECT Id, Title FROM Movies”

ConnectionString=”<%$ ConnectionStrings:Movies %>”

</div>

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</form>

</body>

</html>

The SelectedItem property retrieves the selected ListItem control from the DropDownList

control The value of the selected item’s Text property displays in the Label control

You can use these properties when you want to associate a List control with another

DataBound control For example, the page in Listing 10.5 contains a DropDownList control

that displays a list of movie categories and a GridView control that displays a list of

movies that match the selected category (see Figure 10.5)

FIGURE 10.5 Master/Details form with a list control

LISTING 10.5 ShowMoviesByCategory.aspx

.gridView

{

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margin-top:20px;

}

.gridView td, gridView th

{

padding:10px;

}

</style>

<title>Show Movies by Category</title>

</head>

<body>

<div>

<asp:DropDownList

id=”ddlMovieCategory”

DataSourceID=”srcMovieCategories”

DataTextField=”Name”

<asp:Button

id=”btnSelect”

Text=”Select”

<asp:GridView

id=”grdMovies”

CssClass=”gridView”

<asp:SqlDataSource

id=”srcMovieCategories”

SelectCommand=”SELECT Id, Name FROM MovieCategories”

<asp:SqlDataSource

id=”srcMovies”

SelectCommand=”SELECT Title,Director FROM Movies

WHERE CategoryId=@Id”

Runat=”server”>

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<asp:ControlParameter

Name=”Id”

ControlID=”ddlMovieCategory”

PropertyName=”SelectedValue” />

</SelectParameters>

</asp:SqlDataSource>

</div>

</form>

</body>

</html>

The DropDownList control is bound to the srcMovieCategories SqlDataSource control,

and the GridView control is bound to the srcMovies SqlDataSource control The

srcMovies SqlDataSource control includes a ControlParameter, which represents the

SelectedValue property of the DropDownList control When you select a movie category

from the DropDownList control, the selected value changes, and the GridView control

displays a list of matching movies

Appending Data Items

You can mix the list items that you declare in a List control and the list items that are

added to the control when it is bound to a data source This is useful when you want to

display a default selection

For example, imagine that you create a form in which you want to require a user to pick

an item from a List control In this situation, you should add a default item to the List

control so that you can detect whether a user has actually picked an item

You can mix declarative list items with databound list items by assigning the value True to

the AppendDataBoundItems property The page in Listing 10.6 illustrates how you can add

a default list item to a List control (see Figure 10.6)

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LISTING 10.6 AppendListItems.aspx

<title>Append List Items</title>

</head>

<body>

<div>

<asp:DropDownList

id=”ddlMovies”

AppendDataBoundItems=”True”

Runat=”server”>

<asp:ListItem

Text=”Select a Movie”

Value=”” />

FIGURE 10.6 Displaying a default list item

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</asp:DropDownList>

<asp:RequiredFieldValidator

id=”valMovies”

Text=”(Required)”

ControlToValidate=”ddlMovies”

<asp:Button

id=”btnSubmit”

Text=”Submit Form”

<asp:SqlDataSource

id=”srcMovies”

SelectCommand=”SELECT Id, Title FROM Movies”

</div>

</form>

</body>

</html>

The page in Listing 10.6 includes both a DropDownList control and a

RequiredFieldValidator control The DropDownList control includes a list item that

displays the text Select a Movie The Value property of this list item is set to the empty

string If you attempt to submit the form without selecting a list item other than the

default list item, the RequiredFieldValidator displays an error message

The DropDownList control includes an AppendDataBoundItems property that is set to the

value True If you neglect to set this property, the databound list items overwrite any

declarative list items

Enabling Automatic PostBacks

All the List controls, except for the BulletedList control, support a property named the

AutoPostBack property When this property is assigned the value True, the form

contain-ing the List control is automatically posted back to the server whenever a new selection is

made

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For example, the page in Listing 10.7 contains a DropDownList control that has its

AutoPostBack property enabled When you select a new item from the DropDownList

control, the page is automatically posted back to the server and the Label control displays

the selected item

LISTING 10.7 AutoPostBackListControl.aspx

protected void ddlMovies_SelectedIndexChanged(object sender, EventArgs e)

{

lblSelectedMovie.Text = ddlMovies.SelectedItem.Text;

}

</script>

<title>AutoPostBack List Control</title>

</head>

<body>

<div>

<asp:DropDownList

id=”ddlMovies”

AutoPostBack=”true”

OnSelectedIndexChanged=”ddlMovies_SelectedIndexChanged”

<asp:Label

id=”lblSelectedMovie”

<asp:SqlDataSource

id=”srcMovies”

Tiêu đề	Using List Controls
Trường học	University of Wow! eBook
Chuyên ngành	Computer Science
Thể loại	Essay
Năm xuất bản	2025
Thành phố	City Name

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