TreeView.TreeNodePopulate Evento
Definizione
Importante
Alcune informazioni sono relative alla release non definitiva del prodotto, che potrebbe subire modifiche significative prima della release definitiva. Microsoft non riconosce alcuna garanzia, espressa o implicita, in merito alle informazioni qui fornite.
Si verifica quando un nodo con la proprietà PopulateOnDemand impostata su true viene espanso nel controllo TreeView.
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 Tipo evento
Esempio
Nell'esempio di codice seguente viene illustrato come usare l'evento TreeNodePopulate per popolare i nodi nel controllo in TreeView modo dinamico nel server. Si noti che la EnableClientScript proprietà è impostata su false per impedire che gli eventi di espansione del nodo vengano gestiti nel 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>
Commenti
In alcuni casi, non è pratico definire in modo statico la struttura ad albero a causa delle dimensioni dei dati o del contenuto personalizzato che dipende dall'input dell'utente. Per questo motivo, il controllo supporta il TreeView popolamento di nodi dinamici. Quando la PopulateOnDemand proprietà per un nodo è impostata su true, il nodo viene popolato in fase di esecuzione quando il nodo viene espanso.
Per popolare un nodo in modo dinamico, impostare prima la PopulateOnDemand proprietà per il nodo su true. Definire quindi un metodo di gestione degli eventi per l'evento TreeNodePopulate che popola il nodo a livello di codice. Un metodo tipico di gestione degli eventi recupera i dati dei nodi da un'origine dati, inserisce i dati in una struttura di nodo e quindi aggiunge la struttura del nodo alla ChildNodes raccolta del nodo popolato. Una struttura di nodo viene creata aggiungendo TreeNode oggetti alla ChildNodes raccolta di un nodo padre.
Nota
Quando la PopulateOnDemand proprietà per un nodo è impostata su true, il nodo deve essere popolato in modo dinamico. Non è possibile annidare in modo dichiarativo un altro nodo sotto di esso; in caso contrario, si verificherà un errore nella pagina.
I browser supportati (browser compatibili con Microsoft Internet Explorer 4.0 e versioni successive) possono anche sfruttare il popolamento di nodi lato client. Se abilitata, questo consente al TreeView controllo di popolare un nodo in modo dinamico nel client quando tale nodo viene espanso, impedendo così la necessità di eseguire il postback al server. Per altre informazioni sul popolamento di nodi lato client, vedere PopulateNodesFromClient.
Per altre informazioni su come gestire gli eventi, vedere la gestione e generazione di eventi.
