Most of the VB Snippets Web pages display hierarchical breadcrumb links. When it comes to the display of code examples, though, the breadcrumb links make it easy for the visitor to return to the previous search page, browse page, or homepage.

Listing 15-7 contains the code for the breadcrumbs custom control. Like the navigation custom control, the breadcrumbs custom control exposes a ResourceManager property that’s used for localization purposes. The CurrentPage property identifies the last breadcrumb in the chain—the breadcrumb that is not a link. The BrowseItem property identifies the specific keyword to display in a browse breadcrumb link. (Figure 15-12 illustrates how the BrowseItem property is used.) The From property identifies the route the visitor took to arrive at the current page. VB Snippets uses session-state variables to store this information. The read-only CodePath property returns the index used by the code_example page to control the navigation menu display. If the visitor arrived via a search page, for example, the CodePath property returns the value 1.

Listing 15-7. The BreadCrumbs.vb Custom Control

Option Strict On
Imports System.Resources
Imports System.ComponentModel
Imports System.Web.UI
Imports System.Web

<DefaultProperty("CurrentPage"), _
ToolboxData("<{0}:BreadCrumbs runat=server></{0}:BreadCrumbs>")> _
Public Class BreadCrumbs
    Inherits System.Web.UI.WebControls.WebControl

    Private _rm As ResourceManager
    Private _sCrumbList As String = "Home,"
    Private _sLinkList As String = "index.aspx"
    Private _sCurrentPage As String
    Private _sFrom As String
    Private _iCodePath As Integer = 0
    Private _sBrowseItem As String = String.Empty

    <Bindable(True), Category("Behavior"), DefaultValue("")> _
    Property CurrentPage() As String
    Get
        Return _sCurrentPage
    End Get
    Set(ByVal Value As String)
        'Values: Browse, Search, Code, Terms, Privacy
        _sCurrentPage = Value
        Select Case Value
        Case "Browse"
            'Browse all unless BrowseItem set
            If _sBrowseItem = String.Empty Then
                _sCrumbList &= "BrowseAll"
            End If
        Case "Search"
            'General search unless SearchQuery set
            _sCrumbList &= "SearchFor"
        Case "Results"
            _sCrumbList = "Home,SearchFor,Results"
            _sLinkList = "index.aspx,code_search.aspx"
        Case "Code"
            'Set default
            _sCrumbList &= "Code"
            'Code breadcrumbs depend upon visitor's navigation
            If Not _sFrom = String.Empty Then
                If _sFrom = "B" Then
                    'Got here from Browse All
                    _sCrumbList = "Home,BrowseAll,Code"
                    _sLinkList = "index.aspx,code_browse_all.aspx"
                    _iCodePath = 2
                ElseIf _sFrom.StartsWith("B:") Then
                    'Got here from Browse Item
                    _sCrumbList = "Home,BrowseAll,Browse,Code"
                    _sBrowseItem = _sFrom.Substring(2)
                    _sLinkList = "index.aspx,code_browse_all.aspx,code_browse_" _
                        & _sBrowseItem & ".aspx"
                    _iCodePath = 2
               ElseIf _sFrom.StartsWith("S:") Then
                    'Got here from Search Results
                    _sCrumbList = "Home,SearchFor,Results,Code"
                    _sLinkList _
                        = "index.aspx,code_search.aspx,code_search_results.aspx"
                    _iCodePath = 1
                Else
                    'Retain defaults
                End If
            End If
        Case Else

            'Homepage only link
            _sCrumbList &= Value
        End Select
    End Set
    End Property

    <Bindable(True), Category("Behavior"), DefaultValue("")> _
    Property BrowseItem() As String
    Get
        Return _sBrowseItem
    End Get
    Set(ByVal Value As String)
        'Specific browse
        _sBrowseItem = Value
        _sCrumbList = "Home,BrowseAll,Browse"
        _sLinkList = "index.aspx,code_browse_all.aspx"
    End Set
    End Property

    <Bindable(False)> _
    Property From() As String
    Get
        Return _sFrom
    End Get
    Set(ByVal Value As String)
        _sFrom = Value
    End Set
    End Property

    <Bindable(False)> _
    ReadOnly Property CodePath() As Integer
    Get
        Return _iCodePath
    End Get
    End Property

    <Bindable(False)> _
    Property ResourceManager() As ResourceManager
    Get
        Return _rm
    End Get
    Set(ByVal Value As ResourceManager)
        _rm = Value
    End Set
    End Property

    Protected Overrides Sub Render(ByVal output As System.Web.UI.HtmlTextWriter)
        If _rm Is Nothing Then
            Throw New Exception("C15_Ctl_Lib-BreadCrumbs: " _
                & "No resource manager provided.")
        End If

        Try
            Dim asCrumb() As String = Split(_sCrumbList, ",")
            Dim asLink() As String = Split(_sLinkList, ",")

            Dim i As Integer, iMax As Integer = UBound(asCrumb)

            'All except last crumb are links
            Debug.Assert(iMax = UBound(asLink) + 1, "C15_Ctl_Lib-BreadCrumbs: " _
                & "Mismatch in list counts.")

            'Crumbs: Home, BrowseAll, Browse, SearchFor, Results, 
            '        Code, Terms, Privacy
            For i = 0 To iMax
                If asCrumb(i) = "Browse" Then
                    asCrumb(i) = _rm.GetString("Browse") _
                        & " (" & _sBrowseItem & ")"
                Else
                    asCrumb(i) = _rm.GetString(asCrumb(i))
                End If
            Next

            'Move to left margin
            output.WriteLine()

            'Render breadcrumbs paragraph
            output.AddAttribute(HtmlTextWriterAttribute.Class, "lfloatpad")
            output.RenderBeginTag(HtmlTextWriterTag.P)

            For i = 0 To iMax
                'Render arrow image
                output.AddAttribute(HtmlTextWriterAttribute.Border, "0")
                output.AddAttribute(HtmlTextWriterAttribute.Width, "6")
                output.AddAttribute(HtmlTextWriterAttribute.Height, "10")
                output.AddAttribute(HtmlTextWriterAttribute.Alt, "")
                output.AddAttribute(HtmlTextWriterAttribute.Src, _
                    "images/arrow.gif")
                output.RenderBeginTag(HtmlTextWriterTag.Img)

                If i < iMax Then
                    'Create a link
                    output.AddAttribute(HtmlTextWriterAttribute.Class, "crumb")
                    output.AddAttribute(HtmlTextWriterAttribute.Href, asLink(i))
                    output.RenderBeginTag(HtmlTextWriterTag.A)
                    output.Write(asCrumb(i))
                    output.RenderEndTag()
                Else
                    'Display current page info
                    output.AddAttribute(HtmlTextWriterAttribute.Class, "crumb")
                    output.RenderBeginTag(HtmlTextWriterTag.Span)
                    'If Not _sBrowseItem = String.Empty Then
                    '    asCrumb(i) &= " (" & _sBrowseItem & ")"
                    'End If
                    output.Write(asCrumb(i))
                    output.RenderEndTag()
                End If
            Next

            output.RenderEndTag()

            'Render log in/out link
            output.AddAttribute(HtmlTextWriterAttribute.Class, "rfloatpad")
            output.RenderBeginTag(HtmlTextWriterTag.P)
            output.AddAttribute(HtmlTextWriterAttribute.Class, "logout")

            If Page.User.Identity.IsAuthenticated Then
                'Already logged in
                output.AddAttribute(HtmlTextWriterAttribute.Href, _
                    "index.aspx?action=logout")
                output.RenderBeginTag(HtmlTextWriterTag.A)
                output.Write(_rm.GetString("LogOut"))
                output.RenderEndTag()
            ElseIf _sCurrentPage <> "LogIn" Then
                'Link to log in page
                output.AddAttribute(HtmlTextWriterAttribute.Href, "log_in.aspx")
                output.RenderBeginTag(HtmlTextWriterTag.A)
                output.Write(_rm.GetString("LogIn"))
                output.RenderEndTag()
           End If

            output.RenderEndTag()
            output.RenderEndTag()

        Catch ex As Exception
            Throw New Exception("C15_Ctl_Lib-BreadCrumbs: " & ex.Message)
        End Try
    End Sub
End Class

The breadcrumbs custom control works by building two lists: one for the text to display for each breadcrumb and another list for the link associated with each breadcrumb except the last, which represents the current page. The control stores the lists in the string variables _sCrumbList and _sLinkList until the Render method needs them. The Render method splits the strings into string arrays named asCrumb() and asLink() for processing.

The values in asCrumb() serve as keys to resource files to obtain localized strings. The Render method creates the appropriate link for each breadcrumb except for the last one in the asCrumb() array.

Previous: Deciding What Breadcrumb Links to Display
Next: Using Session State to Remember Previous Links

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