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Differences Between the SelectionList and List Classes

Although the SelectionList and List controls are similar, there are fundamental difference in functionality at design time and run time. Both classes maintain a collection of list items. However, whereas the List control is derived from the PagedControl and ultimately the MobileControl class, the SelectionList control is derived directly from the MobileControl class and does not have pagination handling properties, such as the ItemWeight property.

The major difference between the classes is that the SelectionList class supports single or multiple selected items. The SelectType property contains the ListSelectType enumerated value, which determines whether the SelectionList is in single or multiple selection mode.

With the List class, you can choose only single items in a list. In contrast, the SelectionList class enables you to specify a variety of list types, including CheckBox, DropDown, ListBox, MultiSelectListBox, and Radio.

SelectionList Functionality

A SelectionList control is in single selection mode when you set the SelectType property to any of the following:

Handling the Selection

To retrieve the current selected item in a SelectionList control while in single selection mode, use the SelectedIndex and Selection properties.

The CheckBox and MultiSelectListBox enumerated values indicate multiselect mode. To retrieve the selection, query each item's Selected property.

The following example shows how to retrieve the selected values from a multiselect list.

<%@ Page Language="VB"  
    Inherits="System.Web.UI.MobileControls.MobilePage" %>
<%@ Register TagPrefix="mobile"  
    Namespace="System.Web.UI.MobileControls" 
    Assembly="System.Web.Mobile" %>

<script runat="server">
    private class Person
        ' Private Fields 
        Private _Name, _Nickname As String 

        ' Constructor 
        Public Sub New(ByVal name As String, _
            ByVal nickname As String)
            Me._Name = name
            Me._Nickname = nickname
        End Sub 
        ' Public Properties 
        Public ReadOnly Property Name()
            Get 
                Return _Name
            End Get 
        End Property 
        Public ReadOnly Property Nickname()
            Get 
                Return _Nickname
            End Get 
        End Property 
    End Class 

    ' An ArrayList for the Person objects 
    Dim presidents = New ArrayList()

    Private Sub Page_Load(ByVal sender As Object, _
        ByVal e As EventArgs)

        ' Fill the presidents ArrayList
        presidents.Add( _
            New Person("George Washington", "George"))
        presidents.Add( _
            New Person("Abraham Lincoln", "Abe"))
        presidents.Add( _
            New Person("Theodore Roosevelt", "Teddy"))

        If Not IsPostBack Then 
            ' Bind the array to the list.
            SelectionList1.DataSource = presidents
            ' Specify the field to display
            SelectionList1.DataValueField = "Name"
            SelectionList1.DataBind()
        End If 
    End Sub 

    Protected Sub Command1_Click( _
        ByVal sender As Object, ByVal e As EventArgs)

        Dim retval As String = String.Empty
        Dim per As Person

        If Not SelectionList1.IsMultiSelect Then
            retval = "Value: " 

            ' Get the selected item
            per = CType(presidents(SelectionList1.SelectedIndex), Person)

            ' Get the text of the item 
            If Not IsNothing(per) Then
                retval &= per.Name & "(" & per.Nickname & ")" 
            End If 
        ElseIf SelectionList1.IsMultiSelect Then
            retval = "Values: " 
            ' Gather the text from list items 
            Dim li As MobileListItem
            Dim i As Integer = 0
            For i = 0 To SelectionList1.Items.Count - 1
                li = SelectionList1.Items(i)

                ' Gather text only from selected items 
                If li.Selected Then
                    per = CType(presidents(li.Index), Person)
                    retval &= per.Name & "(" & per.Nickname & "), " 
                End If 
            Next 
        End If 

        ' Clean ending comma, if any 
        If retval.IndexOf(", ") > -1 Then
            retval = retval.Substring(0, retval.Length - 2)
        End If 

        ' Put return value into the Label
        Label1.Text = retval

        ' Activate Form2 
        Me.ActiveForm = Form2
    End Sub 

    Protected Sub Command2_Click( _
        ByVal sender As Object, ByVal e As EventArgs)
        ' Activate Form1 
        Me.ActiveForm = Form1
    End Sub
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<body>
    <mobile:form id="Form1" runat="server">
        Select several items in the list:<br />
        <mobile:SelectionList ID="SelectionList1" 
            Runat="server" SelectType="Checkbox">
        </mobile:SelectionList>
        <mobile:Command ID="Command1" Runat="server" 
            OnClick="Command1_Click">
            Record Choices
        </mobile:Command>
    </mobile:form>
    <mobile:Form ID="Form2" Runat="server">
        <mobile:Label ID="Label1" runat="server" />
        <mobile:Command ID="Command2" Runat="server" 
            OnClick="Command2_Click">Return
        </mobile:Command>
    </mobile:Form>
</body>
</html>
<%@ Page Language="C#" 
    Inherits="System.Web.UI.MobileControls.MobilePage" %>
<%@ Register TagPrefix="mobile" 
    Namespace="System.Web.UI.MobileControls" 
    Assembly="System.Web.Mobile" %>

<script runat="server">
    private class Person
    {
        // Private Fields 
        private String _Name, _Nickname;

        // Constructor 
        public Person(string name, string nickname)
        {
            this._Name = name;
            this._Nickname = nickname;
        }
        // Public Properties 
        public String Name { get { return _Name; } }
        public String Nickname { get { return _Nickname; } }
    }

    // An ArrayList for the Person objects
    ArrayList presidents = new ArrayList();

    private void Page_Load(object sender, System.EventArgs e)
    {
        // Fill the Person object
        presidents.Add(
            new Person("George Washington", "George"));
        presidents.Add(
            new Person("Abraham Lincoln", "Abe"));
        presidents.Add(
            new Person("Theodore Roosevelt", "Teddy"));

        if (!IsPostBack)
        {
            // Bind the array to the list.
            SelectionList1.DataSource = presidents;
            // Specify the field to display
            SelectionList1.DataValueField = "Nickname";
            SelectionList1.DataBind();
        }
    }

    protected void Command1_Click(object sender, EventArgs e)
    {
        string retval = String.Empty;
        Person per;

        if (!SelectionList1.IsMultiSelect)
        {
            retval = "Value: ";
            // Get the selected item
            per = (Person)presidents[SelectionList1.SelectedIndex];

            // Get the name and nickname of the person 
            if (per != null)
                retval += per.Name + " (" + per.Nickname + ")";
        }
        else if (SelectionList1.IsMultiSelect)
        {
            retval = "Values: ";
            // Gather the text from list items 
            foreach (MobileListItem li in SelectionList1.Items)
            {
                // Gather text only from selected items 
                if (li.Selected)
                {
                    per = (Person)presidents[li.Index];
                    retval += per.Name + " (" + per.Nickname + "), ";
                }
            }
        }

        // Clean ending comma, if any 
        if (retval.IndexOf(", ") > -1)
            retval = retval.Substring(0, retval.Length - 2);

        // Put return value into the Label
        Label1.Text = retval;

        // Activate Form2 
        this.ActiveForm = Form2;
    }

    protected void Command2_Click(object sender, EventArgs e)
    {
        // Activate Form1 
        this.ActiveForm = Form1;
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<body>
    <mobile:form id="Form1" runat="server">
        Select several items in the list:<br />
        <mobile:SelectionList ID="SelectionList1" 
            Runat="server" SelectType="Checkbox">
        </mobile:SelectionList>
        <mobile:Command ID="Command1" Runat="server" 
            OnClick="Command1_Click">
            Record Choices
        </mobile:Command>
    </mobile:form>
    <mobile:Form ID="Form2" Runat="server">
        <mobile:Label ID="Label1" runat="server" />
        <mobile:Command ID="Command2" Runat="server" 
            OnClick="Command2_Click">Return
        </mobile:Command>
    </mobile:Form>
</body>
</html>

Adding Items to a List Control

A List control contains a collection of items in the MobileListItem class. There are a number of ways that you can add items to a List control:

  • Create <Item> elements inside a list. Each <Item> element becomes a MobileListItem in the list, and its properties are set from attributes of the <Item> element.

  • Programmatically add items to the list using the List control's Items collection. You can construct a MobileListItem object and add it to the collection before rendering.

  • Bind the List control to data, specifically to any object that implements the IEnumerable interface or the IListSource interface, such as ArrayList or DataSet objects.

See Also

Concepts

Accessing Data Using Listing Controls

Reference

List

ObjectList

Other Resources

Accessing Data with ASP.NET

Developing ASP.NET Mobile Web Pages

Application Developer's Guide