ListView.CacheVirtualItems ListView.CacheVirtualItems ListView.CacheVirtualItems ListView.CacheVirtualItems Event

Définition

Se produit lorsque le contenu de la zone d’affichage pour un ListView en mode virtuel a changé et le ListView détermine qu’une nouvelle plage d’éléments est nécessaire.Occurs when the contents of the display area for a ListView in virtual mode has changed, and the ListView determines that a new range of items is needed.

public:
 event System::Windows::Forms::CacheVirtualItemsEventHandler ^ CacheVirtualItems;
public event System.Windows.Forms.CacheVirtualItemsEventHandler CacheVirtualItems;
member this.CacheVirtualItems : System.Windows.Forms.CacheVirtualItemsEventHandler 
Public Custom Event CacheVirtualItems As CacheVirtualItemsEventHandler 

Exemples

L’exemple de code suivant illustre l’utilisation de ce membre.The following code example demonstrates the use of this member. Dans l’exemple, le Gestionnaire d’événements vérifie qu’une actualisation du cache est vraiment nécessaire, puis reconstruit le cache.In the example, the event handler checks to make sure a cache refresh is really necessary, and then rebuilds the cache. Cet exemple de code fait partie d’un exemple plus complet fourni pour le VirtualMode propriété.This code example is part of a larger example provided for the VirtualMode property.

//Manages the cache.  ListView calls this when it might need a 
//cache refresh.
void listView1_CacheVirtualItems(object sender, CacheVirtualItemsEventArgs e)
{
    //We've gotten a request to refresh the cache.
    //First check if it's really neccesary.
    if (myCache != null && e.StartIndex >= firstItem && e.EndIndex <= firstItem + myCache.Length)
    {
        //If the newly requested cache is a subset of the old cache, 
        //no need to rebuild everything, so do nothing.
        return;
    }

    //Now we need to rebuild the cache.
    firstItem = e.StartIndex;
    int length = e.EndIndex - e.StartIndex + 1; //indexes are inclusive
    myCache = new ListViewItem[length];
    
    //Fill the cache with the appropriate ListViewItems.
    int x = 0;
    for (int i = 0; i < length; i++)
    {
        x = (i + firstItem) * (i + firstItem);
        myCache[i] = new ListViewItem(x.ToString());
    }

}
'Manages the cache.  ListView calls this when it might need a 
'cache refresh.
Private Sub listView1_CacheVirtualItems(ByVal sender As Object, ByVal e As CacheVirtualItemsEventArgs) Handles listView1.CacheVirtualItems
    'We've gotten a request to refresh the cache.
    'First check if it's really neccesary.
    If Not (myCache Is Nothing) AndAlso e.StartIndex >= firstItem AndAlso e.EndIndex <= firstItem + myCache.Length Then
        'If the newly requested cache is a subset of the old cache, 
        'no need to rebuild everything, so do nothing.
        Return
    End If

    'Now we need to rebuild the cache.
    firstItem = e.StartIndex
    Dim length As Integer = e.EndIndex - e.StartIndex + 1 'indexes are inclusive
    myCache = New ListViewItem(length) {}

    'Fill the cache with the appropriate ListViewItems.
    Dim x As Integer = 0
    Dim i As Integer
    For i = 0 To length
        x = (i + firstItem) * (i + firstItem)
        myCache(i) = New ListViewItem(x.ToString())
    Next i

End Sub

Remarques

Cet événement se produit uniquement lorsque VirtualMode est true.This event only occurs when VirtualMode is true. La gestion de cet événement permet le ListView pour mettre à jour les informations d’élément contenues dans le cache afin qu’il soit facilement disponible.Handling this event allows the ListView to update the item information held in the cache so that it is readily available. Cela peut améliorer les performances sur les grandes listes ou des listes dont les éléments sont coûteuses à calculer.This can improve performance on large lists, or lists whose items are expensive to calculate.

Pour plus d'informations sur la gestion des événements, voir gestion et déclenchement d’événements.For more information about handling events, see Handling and Raising Events.

S’applique à