TreeView.PopulateNodesFromClient TreeView.PopulateNodesFromClient TreeView.PopulateNodesFromClient TreeView.PopulateNodesFromClient Property

Definizione

Ottiene o imposta un valore che indica se i dati del nodo sono compilati su richiesta del client.Gets or sets a value indicating whether node data is populated on demand from the client.

public:
 property bool PopulateNodesFromClient { bool get(); void set(bool value); };
public bool PopulateNodesFromClient { get; set; }
member this.PopulateNodesFromClient : bool with get, set
Public Property PopulateNodesFromClient As Boolean

Valore della proprietà

true per compilare i dati del nodo della struttura ad albero su richiesta del client; in caso contrario, false.true to populate tree node data on demand from the client; otherwise, false. Il valore predefinito è true.The default is true.

Esempi

Nell'esempio di codice riportato di seguito viene illustrato PopulateNodesFromClient come utilizzare la proprietà per abilitare il popolamento lato client dei nodi TreeView nel controllo.The following code example demonstrates how to use the PopulateNodesFromClient property to enable client-side population of the nodes in the TreeView control. Si noti che quando il popolamento del nodo lato client è abilitato, i nodi vengono popolati dinamicamente sul client, senza la necessità di eseguire il postback al server.Notice that when client-side node population is enabled, nodes are populated dynamically on the client, without the need to post back to the server.


<%@ 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>

Commenti

In alcuni casi non è pratico predefinire in modo statico la struttura ad albero a causa della dimensione dei dati o del contenuto personalizzato che dipende dall'input dell'utente.Sometimes, it is not practical to statically predefine the tree structure due to data size or custom content that depends on user input. Per questo motivo, il TreeView controllo supporta il popolamento dinamico dei nodi.Because of this, the TreeView control supports dynamic node population. Quando la PopulateOnDemand proprietà di un nodo è impostata su true, il nodo viene popolato in fase di esecuzione quando il nodo è espanso.When the PopulateOnDemand property for a node is set to true, that node gets populated at run time when the node is expanded.

Oltre a popolare i nodi su richiesta, è possibile popolare i nodi direttamente in un browser client supportato.In addition to populating nodes on demand, it is possible to populate the nodes directly on a supported client browser. Quando la PopulateNodesFromClient proprietà è impostata su true, viene chiamato un servizio dal client per popolare i nodi dell'albero, che elimina la necessità di eseguire il postback al server.When the PopulateNodesFromClient property is set to true, a service is called from the client to populate the tree nodes, which eliminates the need to post back to the server. In caso contrario TreeView , il controllo esegue il postback al server per popolare i nodi.Otherwise, the TreeView control posts back to the server to populate the nodes.

Nota

Per EnableClientScript true impostare laPopulateNodesFromClientProprietà su ,èinoltrenecessarioimpostarelaproprietàsu.trueThe EnableClientScript property must also be set to true in order for the PopulateNodesFromClient property to be set to true.

Per popolare un nodo nel client, impostare prima di tutto PopulateNodesFromClient la true proprietà su, quindi impostare PopulateOnDemand la proprietà per il nodo truesu.To populate a node on the client, first set the PopulateNodesFromClient property to true and then set the PopulateOnDemand property for the node to true. Definire quindi un metodo di gestione degli eventi per l' TreeNodePopulate evento che popola il nodo a livello di codice.Next, define an event-handling method for the TreeNodePopulate event that programmatically populates the node. Un metodo tipico di gestione degli eventi recupera i dati del nodo da un'origine dati, li inserisce in una struttura di nodi, quindi aggiunge la struttura del ChildNodes nodo alla raccolta del nodo da popolare.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. Per creare una struttura del nodo, TreeNode è necessario aggiungere oggetti alla raccoltadiunnodopadre.ChildNodesYou create a node structure by adding TreeNode objects to the ChildNodes collection of a parent node.

Nota

Quando la PopulateOnDemand proprietà di un nodo è impostata su true, il nodo deve essere popolato dinamicamente.When the PopulateOnDemand property for a node is set to true, the node must be populated dynamically. Non è possibile nidificare in modo dichiarativo un altro nodo sotto di esso; in caso contrario, si verificherà un errore nella pagina.You cannot declaratively nest another node below it; otherwise, an error will occur on the page.

Nota

La funzionalità di popolamento del nodo lato client è supportata nei browser che supportano gli script di callback.The client-side node population feature is supported in browsers that support callback scripts. Per verificare se un browser supporta l'accesso agli script SupportsCallback HttpBrowserCapabilities di callback, utilizzare la proprietà della classe.To check whether a browser supports callback scripts access, use the SupportsCallback property of the HttpBrowserCapabilities class. È possibile accedere all'istanza della HttpBrowserCapabilities classe per la richiesta corrente tramite la Browser proprietà della HttpRequest classe.You can access the instance of the HttpBrowserCapabilities class for the current request through the Browser property of the HttpRequest class.

Il valore di questa proprietà viene archiviato nello stato di visualizzazione.The value of this property is stored in view state.

Si applica a

Vedi anche