DataGridView.VirtualMode Proprietà
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.
Ottiene o imposta un valore che indica se sono state fornite operazioni di gestione dati personalizzate per il controllo DataGridView.
public:
property bool VirtualMode { bool get(); void set(bool value); };public bool VirtualMode { get; set; }member this.VirtualMode : bool with get, setPublic Property VirtualMode As BooleanValore della proprietà
true se DataGridView usa operazioni di gestione dati fornite dall'utente; in caso contrario, false. Il valore predefinito è false.
Esempio
Il codice di esempio di codice seguente usa la modalità virtuale per creare una tabella di numeri interi positivi.
using System.IO;
using System.Collections.Generic;
using System.Windows.Forms;
using System.Drawing;
using System;
public class VirtualModeDemo : Form
{
DataGridView dataGridView1 = new DataGridView();
public VirtualModeDemo()
: base()
{
Text = "DataGridView virtual-mode demo (cell-level commit scope)";
dataGridView1.NewRowNeeded +=
new DataGridViewRowEventHandler(dataGridView1_NewRowNeeded);
dataGridView1.RowsAdded +=
new DataGridViewRowsAddedEventHandler(dataGridView1_RowsAdded);
dataGridView1.CellValidating +=
new DataGridViewCellValidatingEventHandler(dataGridView1_CellValidating);
dataGridView1.CellValueNeeded +=
new DataGridViewCellValueEventHandler(dataGridView1_CellValueNeeded);
dataGridView1.CellValuePushed +=
new DataGridViewCellValueEventHandler(dataGridView1_CellValuePushed);
Controls.Add(dataGridView1);
dataGridView1.VirtualMode = true;
dataGridView1.AllowUserToDeleteRows = false;
dataGridView1.Columns.Add("Numbers", "Positive Numbers");
dataGridView1.Rows.AddCopies(0, initialSize);
}
bool newRowNeeded;
private void dataGridView1_NewRowNeeded(object sender,
DataGridViewRowEventArgs e)
{
newRowNeeded = true;
}
const int initialSize = 5000000;
int numberOfRows = initialSize;
private void dataGridView1_RowsAdded(object sender,
DataGridViewRowsAddedEventArgs e)
{
if (newRowNeeded)
{
newRowNeeded = false;
numberOfRows = numberOfRows + 1;
}
}
#region "data store maintance"
const int initialValue = -1;
private void dataGridView1_CellValueNeeded(object sender,
DataGridViewCellValueEventArgs e)
{
if (store.ContainsKey(e.RowIndex))
{
// Use the store if the e value has been modified
// and stored.
e.Value = store[e.RowIndex];
}
else if (newRowNeeded && e.RowIndex == numberOfRows)
{
if (dataGridView1.IsCurrentCellInEditMode)
{
e.Value = initialValue;
}
else
{
// Show a blank value if the cursor is just resting
// on the last row.
e.Value = String.Empty;
}
}
else
{
e.Value = e.RowIndex;
}
}
private void dataGridView1_CellValuePushed(object sender,
DataGridViewCellValueEventArgs e)
{
store.Add(e.RowIndex, int.Parse(e.Value.ToString()));
}
#endregion
private Dictionary<int, int> store = new Dictionary<int, int>();
private void dataGridView1_CellValidating(object sender,
DataGridViewCellValidatingEventArgs e)
{
dataGridView1.Rows[e.RowIndex].ErrorText = "";
int newInteger;
// Don't try to validate the 'new row' until finished
// editing since there
// is not any point in validating its initial value.
if (dataGridView1.Rows[e.RowIndex].IsNewRow) { return; }
if (!int.TryParse(e.FormattedValue.ToString(),
out newInteger) || newInteger < 0)
{
e.Cancel = true;
dataGridView1.Rows[e.RowIndex].ErrorText = "the value must be a non-negative integer";
}
}
[STAThreadAttribute()]
public static void Main()
{
Application.Run(new VirtualModeDemo());
}
}
Imports System.IO
Imports System.Collections.Generic
Imports System.Windows.Forms
Public Class VirtualModeDemo
Inherits System.Windows.Forms.Form
Dim WithEvents dataGridView1 As New DataGridView
Public Sub New()
MyBase.New()
Text = "DataGridView virtual-mode demo (cell-level commit scope)"
Controls.Add(dataGridView1)
dataGridView1.VirtualMode = True
dataGridView1.AllowUserToDeleteRows = False
dataGridView1.Columns.Add("Numbers", "Positive Numbers")
dataGridView1.Rows.AddCopies(0, initialSize)
End Sub
Dim newRowNeeded As Boolean
Private Sub dataGridView1_NewRowNeeded(ByVal sender As Object, _
ByVal e As DataGridViewRowEventArgs) _
Handles dataGridView1.NewRowNeeded
newRowNeeded = True
End Sub
Const initialSize As Integer = 5000000
Dim numberOfRows As Integer = initialSize
Private Sub dataGridView1_RowsAdded(ByVal sender As Object, _
ByVal e As DataGridViewRowsAddedEventArgs) _
Handles dataGridView1.RowsAdded
If newRowNeeded Then
newRowNeeded = False
numberOfRows = numberOfRows + 1
End If
End Sub
#Region "data store maintance"
Const initialValue As Integer = -1
Private Sub dataGridView1_CellValueNeeded(ByVal sender As Object, _
ByVal e As DataGridViewCellValueEventArgs) _
Handles dataGridView1.CellValueNeeded
If store.ContainsKey(e.RowIndex) Then
' Use the store if the e value has been modified
' and stored.
e.Value = store(e.RowIndex)
ElseIf newRowNeeded AndAlso e.RowIndex = numberOfRows Then
If dataGridView1.IsCurrentCellInEditMode Then
e.Value = initialValue
Else
' Show a blank value if the cursor is just resting
' on the last row.
e.Value = String.Empty
End If
Else
e.Value = e.RowIndex
End If
End Sub
Private Sub dataGridView1_CellValuePushed(ByVal sender As Object, _
ByVal e As DataGridViewCellValueEventArgs) _
Handles dataGridView1.CellValuePushed
store.Add(e.RowIndex, CInt(e.Value))
End Sub
#End Region
Dim store As System.Collections.Generic.Dictionary(Of Integer, Integer) = _
New Dictionary(Of Integer, Integer)
Private Sub dataGridView1_CellValidating(ByVal sender As Object, _
ByVal e _
As DataGridViewCellValidatingEventArgs) _
Handles dataGridView1.CellValidating
Me.dataGridView1.Rows(e.RowIndex).ErrorText = ""
Dim newInteger As Integer
' Don't try to validate the 'new row' until finished
' editing since there
' is not any point in validating its initial value.
If dataGridView1.Rows(e.RowIndex).IsNewRow Then Return
If Not Integer.TryParse(e.FormattedValue.ToString(), newInteger) _
OrElse newInteger < 0 Then
e.Cancel = True
Me.dataGridView1.Rows(e.RowIndex).ErrorText = "the value must be a non-negative integer"
End If
End Sub
<STAThreadAttribute()> _
Public Shared Sub Main()
Application.Run(New VirtualModeDemo())
End Sub
End Class
Commenti
La modalità virtuale è progettata per l'uso con archivi di dati molto grandi. Quando la VirtualMode proprietà è true, si crea un DataGridView oggetto con un numero impostato di righe e colonne e quindi si gestisce l'evento CellValueNeeded per popolare le celle. La modalità virtuale richiede l'implementazione di una cache di dati sottostante per gestire il popolamento, la modifica e l'eliminazione di DataGridView celle in base alle azioni dell'utente. Per altre informazioni sull'implementazione della modalità virtuale, vedere Procedura: Implementare la modalità virtuale nel controllo DataGridView Windows Forms.
È necessario utilizzare la modalità virtuale per mantenere i valori delle colonne non associate quando il DataGridView controllo è in modalità associata. L'ordinamento in base alle colonne non associate in modalità associata non è supportato.
