TreeView.TreeNodePopulate Ereignis

Definition

Tritt ein, wenn ein Knoten, dessen PopulateOnDemand-Eigenschaft auf true festgelegt ist, im TreeView-Steuerelement erweitert wird.Occurs when a node with its PopulateOnDemand property set to true is expanded in the TreeView control.

public:
 event System::Web::UI::WebControls::TreeNodeEventHandler ^ TreeNodePopulate;
public event System.Web.UI.WebControls.TreeNodeEventHandler TreeNodePopulate;
member this.TreeNodePopulate : System.Web.UI.WebControls.TreeNodeEventHandler 
Public Custom Event TreeNodePopulate As TreeNodeEventHandler 

Beispiele

Im folgenden Codebeispiel wird veranschaulicht, wie das TreeNodePopulate -Ereignis verwendet wird, um die Knoten TreeView im-Steuerelement dynamisch auf dem Server aufzufüllen.The following code example demonstrates how to use the TreeNodePopulate event to populate the nodes in the TreeView control dynamically on the server. Beachten Sie, EnableClientScript dass die-Eigenschaft false auf festgelegt ist, um zu verhindern, dass erweiternde Knoten Ereignisse auf dem Client behandelt werden.Notice that the EnableClientScript property is set to false to prevent expanding-node events from being handled on the client.


<%@ 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(row["CategoryName"].ToString(), 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 TreeNodePopulate Example</title>
</head>
<body>
    <form id="form1" runat="server">
    
      <h3>TreeView TreeNodePopulate Example</h3>
    
      <asp:TreeView id="LinksTreeView"
        Font-Names= "Arial"
        ForeColor="Blue"
        EnableClientScript="false" 
        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(row("CategoryName").ToString(), 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 TreeNodePopulate Example</title>
</head>
<body>
    <form id="form1" runat="server">
    
      <h3>TreeView TreeNodePopulate Example</h3>
    
      <asp:TreeView id="LinksTreeView"
        Font-Names= "Arial"
        ForeColor="Blue"
        EnableClientScript="false" 
        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>

Hinweise

In manchen Fällen ist es nicht praktikabel, die Struktur durch die Datengröße oder den benutzerdefinierten Inhalt, der von Benutzereingaben abhängt, statisch vorzudefinieren.Sometimes, it is not practical to statically predefine the tree structure due to data size or custom content that depends on user input. Aus diesem Grund unterstützt TreeView das-Steuerelement die dynamische Knoten Auffüllung.Because of this, the TreeView control supports dynamic node population. Wenn die PopulateOnDemand -Eigenschaft für einen Knoten auf truefestgelegt ist, wird dieser Knoten zur Laufzeit aufgefüllt, wenn der Knoten erweitert wird.When the PopulateOnDemand property for a node is set to true, that node gets populated at run time when the node is expanded.

Um einen Knoten dynamisch aufzufüllen, legen Sie zuerst PopulateOnDemand die-Eigenschaft für den trueKnoten auf fest.To populate a node dynamically, first set the PopulateOnDemand property for the node to true. Definieren Sie als nächstes eine Ereignis Behandlungsmethode für TreeNodePopulate das Ereignis, das den Knotenprogramm gesteuert füllt.Next, define an event-handling method for the TreeNodePopulate event that populates the node programmatically. Eine typische Ereignis Behandlungsmethode ruft Knoten Daten aus einer Datenquelle ab, platziert die Daten in einer Knoten Struktur und fügt dann die Knoten Struktur ChildNodes der Auflistung des Knotens hinzu, der aufgefüllt wird.A typical event-handling method retrieves node data from a data source, places the data into a node structure, and then adds the node structure to the ChildNodes collection of the node being populated. Eine Knoten Struktur wird erstellt, indem TreeNode der ChildNodes -Auflistung eines übergeordneten Knotens-Objekte hinzugefügt werden.A node structure is created by adding TreeNode objects to the ChildNodes collection of a parent node.

Hinweis

Wenn die PopulateOnDemand -Eigenschaft für einen Knoten auf truefestgelegt ist, muss der Knoten dynamisch aufgefüllt werden.When the PopulateOnDemand property for a node is set to true, the node must be populated dynamically. Es ist nicht möglich, einen anderen untergeordneten Knoten deklarativ zu schachteln. Andernfalls tritt ein Fehler auf der Seite auf.You cannot declaratively nest another node below it; otherwise, an error will occur on the page.

Unterstützte Browser (Microsoft Internet Explorer 4,0-kompatible Browser und höher) können auch die Client seitige Knoten Population nutzen.Supported browsers (Microsoft Internet Explorer 4.0-compatible browsers and later) can also take advantage of client-side node population. Wenn diese Option aktiviert ist, TreeView kann das Steuerelement einen Knoten dynamisch auf dem Client auffüllen, wenn dieser Knoten erweitert wird. Dadurch wird verhindert, dass ein Postback an den Server erfolgt.When enabled, this allows the TreeView control to populate a node dynamically on the client when that node is expanded, which prevents the need to post back to the server. Weitere Informationen zur Client seitigen Knoten Population finden PopulateNodesFromClientSie unter.For more information on client-side node population, see PopulateNodesFromClient.

Weitere Informationen zum Behandeln von Ereignissen finden Sie unter behandeln und Auslösen von Ereignissen.For more information about how to handle events, see Handling and Raising Events.

Gilt für:

Siehe auch