TreeNode.Value Właściwość

  • Odwołanie

Definicja

Przestrzeń nazw:
System.Web.UI.WebControls
Zestaw:
System.Web.dll

Pobiera lub ustawia nie wyświetlaną wartość używaną do przechowywania wszelkich dodatkowych danych dotyczących węzła, takich jak dane używane do obsługi zdarzeń zwrotnych.

public:
 property System::String ^ Value { System::String ^ get(); void set(System::String ^ value); };
public string Value { get; set; }
member this.Value : string with get, set
Public Property Value As String

Wartość właściwości

String

Dodatkowe dane dotyczące węzła, który nie jest wyświetlany. Wartością domyślną jest ciąg pusty ("").

Przykłady

W poniższym przykładzie kodu pokazano, jak używać Value właściwości do przechowywania pola klucza.


<%@ Page Language="C#" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.SqlClient" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">

  void PopulateNode(Object sender, TreeNodeEventArgs e)
  {

    // Call the appropriate method to populate a node at a particular level.
    switch(e.Node.Depth)
    {
      case 0:
        // Populate the first-level nodes.
        PopulateCategories(e.Node);
        break;
      case 1:
        // Populate the second-level nodes.
        PopulateProducts(e.Node);
        break;
      default:
        // Do nothing.
        break;
    }
    
  }

  void PopulateCategories(TreeNode node)
  {
    
    // Query for the product categories. These are the values
    // for the second-level nodes.
    DataSet ResultSet = RunQuery("Select CategoryID, CategoryName From Categories");

    // Create the second-level nodes.
    if(ResultSet.Tables.Count > 0)
    {
    
      // Iterate through and create a new node for each row in the query results.
      // Notice that the query results are stored in the table of the DataSet.
      foreach (DataRow row in ResultSet.Tables[0].Rows)
      {
        
        // Create the new node. Notice that the CategoryId is stored in the Value property 
        // of the node. This will make querying for items in a specific category easier when
        // the third-level nodes are created. 
        TreeNode newNode = new TreeNode();
        newNode.Text = row["CategoryName"].ToString(); 
        newNode.Value = row["CategoryID"].ToString();        

        // Set the PopulateOnDemand property to true so that the child nodes can be 
        // dynamically populated.
        newNode.PopulateOnDemand = true;
        
        // Set additional properties for the node.
        newNode.SelectAction = TreeNodeSelectAction.Expand;
        
        // Add the new node to the ChildNodes collection of the parent node.
        node.ChildNodes.Add(newNode);
        
      }
      
    }
    
  }

  void PopulateProducts(TreeNode node)
  {

    // Query for the products of the current category. These are the values
    // for the third-level nodes.
    DataSet ResultSet = RunQuery("Select ProductName From Products Where CategoryID=" + node.Value);

    // Create the third-level nodes.
    if(ResultSet.Tables.Count > 0)
    {
    
      // Iterate through and create a new node for each row in the query results.
      // Notice that the query results are stored in the table of the DataSet.
      foreach (DataRow row in ResultSet.Tables[0].Rows)
      {
      
        // Create the new node.
        TreeNode NewNode = new TreeNode(row["ProductName"].ToString());
        
        // Set the PopulateOnDemand property to false, because these are leaf nodes and
        // do not need to be populated.
        NewNode.PopulateOnDemand = false;
        
        // Set additional properties for the node.
        NewNode.SelectAction = TreeNodeSelectAction.None;
        
        // Add the new node to the ChildNodes collection of the parent node.
        node.ChildNodes.Add(NewNode);
        
      }
      
    }

  }

  DataSet RunQuery(String QueryString)
  {

    // Declare the connection string. This example uses Microsoft SQL Server 
    // and connects to the Northwind sample database.
    String ConnectionString = "server=localhost;database=NorthWind;Integrated Security=SSPI"; 

    SqlConnection DBConnection = new SqlConnection(ConnectionString);
    SqlDataAdapter DBAdapter;
    DataSet ResultsDataSet = new DataSet();

    try
    {

      // Run the query and create a DataSet.
      DBAdapter = new SqlDataAdapter(QueryString, DBConnection);
      DBAdapter.Fill(ResultsDataSet);

      // Close the database connection.
      DBConnection.Close();

    }
    catch(Exception ex)
    {

      // Close the database connection if it is still open.
      if(DBConnection.State == ConnectionState.Open)
      {
        DBConnection.Close();
      }
      
      Message.Text = "Unable to connect to the database.";

    }

    return ResultsDataSet;

  }

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
  <head runat="server">
    <title>TreeView PopulateNodesFromClient Example</title>
</head>
<body>
    <form id="form1" runat="server">
    
      <h3>TreeView PopulateNodesFromClient Example</h3>
    
      <asp:TreeView id="LinksTreeView"
        Font-Names= "Arial"
        ForeColor="Blue"
        EnableClientScript="true"
        PopulateNodesFromClient="true"  
        OnTreeNodePopulate="PopulateNode"
        runat="server">
         
        <Nodes>
        
          <asp:TreeNode Text="Inventory" 
            SelectAction="Expand"  
            PopulateOnDemand="true"/>
        
        </Nodes>
        
      </asp:TreeView>
      
      <br /><br />
      
      <asp:Label id="Message" runat="server"/>

    </form>
  </body>
</html>


<%@ Page Language="VB" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.SqlClient" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">

  Sub PopulateNode(ByVal sender As Object, ByVal e As TreeNodeEventArgs)

    ' Call the appropriate method to populate a node at a particular level.
    Select Case e.Node.Depth

      Case 0
        ' Populate the first-level nodes.
        PopulateCategories(e.Node)

      Case 1
        ' Populate the second-level nodes.
        PopulateProducts(e.Node)

      Case Else
        ' Do nothing.

    End Select

  End Sub

  Sub PopulateCategories(ByVal node As TreeNode)

    ' Query for the product categories. These are the values
    ' for the second-level nodes.
    Dim ResultSet As DataSet = RunQuery("Select CategoryID, CategoryName From Categories")

    ' Create the second-level nodes.
    If ResultSet.Tables.Count > 0 Then

      ' Iterate through and create a new node for each row in the query results.
      ' Notice that the query results are stored in the table of the DataSet.
      Dim row As DataRow

      For Each row In ResultSet.Tables(0).Rows

        ' Create the new node. Notice that the CategoryId is stored in the Value property 
        ' of the node. This will make querying for items in a specific category easier when
        ' the third-level nodes are created. 
        Dim newNode As TreeNode = New TreeNode()
        Newnode.Text = row("CategoryName").ToString() 
        Newnode.Value = row("CategoryID").ToString()

        ' Set the PopulateOnDemand property to true so that the child nodes can be 
        ' dynamically populated.
        newNode.PopulateOnDemand = True

        ' Set additional properties for the node.
        newNode.SelectAction = TreeNodeSelectAction.Expand

        ' Add the new node to the ChildNodes collection of the parent node.
        node.ChildNodes.Add(newNode)

      Next

    End If

  End Sub

  Sub PopulateProducts(ByVal node As TreeNode)

    ' Query for the products of the current category. These are the values
    ' for the third-level nodes.
    Dim ResultSet As DataSet = RunQuery("Select ProductName From Products Where CategoryID=" & node.Value)

    ' Create the third-level nodes.
    If ResultSet.Tables.Count > 0 Then

      ' Iterate through and create a new node for each row in the query results.
      ' Notice that the query results are stored in the table of the DataSet.
      Dim row As DataRow

      For Each row In ResultSet.Tables(0).Rows

        ' Create the new node.
        Dim NewNode As TreeNode = New TreeNode(row("ProductName").ToString())

        ' Set the PopulateOnDemand property to false, because these are leaf nodes and
        ' do not need to be populated.
        NewNode.PopulateOnDemand = False

        ' Set additional properties for the node.
        NewNode.SelectAction = TreeNodeSelectAction.None

        ' Add the new node to the ChildNodes collection of the parent node.
        node.ChildNodes.Add(NewNode)

      Next

    End If

  End Sub

  Function RunQuery(ByVal QueryString As String) As DataSet

    ' Declare the connection string. This example uses Microsoft SQL Server 
    ' and connects to the Northwind sample database.
    Dim ConnectionString As String = "server=localhost;database=NorthWind;Integrated Security=SSPI"

    Dim DBConnection As SqlConnection = New SqlConnection(ConnectionString)
    Dim DBAdapter As SqlDataAdapter
    Dim ResultsDataSet As DataSet = New DataSet

    Try

      ' Run the query and create a DataSet.
      DBAdapter = New SqlDataAdapter(QueryString, DBConnection)
      DBAdapter.Fill(ResultsDataSet)

      ' Close the database connection.
      DBConnection.Close()

    Catch ex As Exception

      ' Close the database connection if it is still open.
      If DBConnection.State = ConnectionState.Open Then

        DBConnection.Close()

      End If

      Message.Text = "Unable to connect to the database."

    End Try

    Return ResultsDataSet

  End Function

</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
  <head runat="server">
    <title>TreeView PopulateNodesFromClient Example</title>
</head>
<body>
    <form id="form1" runat="server">
    
      <h3>TreeView PopulateNodesFromClient Example</h3>
    
      <asp:TreeView id="LinksTreeView"
        Font-Names= "Arial"
        ForeColor="Blue"
        EnableClientScript="true"
        PopulateNodesFromClient="true"  
        OnTreeNodePopulate="PopulateNode"
        runat="server">
         
        <Nodes>
        
          <asp:TreeNode Text="Inventory" 
            SelectAction="Expand"  
            PopulateOnDemand="true"/>
        
        </Nodes>
        
      </asp:TreeView>
      
      <br /><br />
      
      <asp:Label id="Message" runat="server"/>

    </form>
  </body>
</html>

Uwagi

Właściwość Value jest używana do uzupełniania Text właściwości przez przechowywanie wszelkich dodatkowych danych skojarzonych z węzłem. Ta wartość nie jest wyświetlana w kontrolce i jest często używana do przechowywania danych do obsługi zdarzeń po powrocie zwrotnym.

Uwaga

Value Jeśli właściwość zawiera null, get metoda dostępu zwraca wartość Text właściwości . Text Jeśli właściwość z kolei zawiera nullelement , Empty jest zwracany.

Uwaga

Węzły na tym samym poziomie muszą mieć unikatową wartość dla Value właściwości. Kontrolka TreeView nie może odróżnić różnych węzłów na tym samym poziomie, które mają tę samą wartość. W tym scenariuszu, jeśli użytkownik kliknie węzeł, który ma zduplikowaną wartość, zostanie wybrany węzeł, który zostanie wyświetlony jako pierwszy w kontrolce TreeView .

Wartość tej właściwości jest przechowywana w stanie widoku.

Wartość tej właściwości, po ustawieniu, można zapisać automatycznie w pliku zasobów przy użyciu narzędzia projektanta. Aby uzyskać więcej informacji, zobacz LocalizableAttribute Temat Globalizacja i Lokalizacja.

Dotyczy

Zobacz też