ListView.RetrieveVirtualItem Evento

Definición

Se produce cuando el control ListView está en modo virtual y requiere un objeto ListViewItem.Occurs when the ListView is in virtual mode and requires a ListViewItem.

public:
 event System::Windows::Forms::RetrieveVirtualItemEventHandler ^ RetrieveVirtualItem;
public event System.Windows.Forms.RetrieveVirtualItemEventHandler RetrieveVirtualItem;
member this.RetrieveVirtualItem : System.Windows.Forms.RetrieveVirtualItemEventHandler 
Public Custom Event RetrieveVirtualItem As RetrieveVirtualItemEventHandler 

Excepciones

La propiedad Item no se establece en un elemento cuando se controla el evento RetrieveVirtualItem.The Item property is not set to an item when the RetrieveVirtualItem event is handled.

Ejemplos

En el ejemplo de código siguiente se muestra un controlador para este evento.The following code example demonstrates a handler for this event. En este ejemplo, listView1 necesita cada ListViewItem para mostrar el cuadrado de su índice.In this example, listView1 needs each ListViewItem to display the square of its index. Este ejemplo de código forma parte de un ejemplo más extenso proporcionado para la propiedad VirtualMode.This code example is part of a larger example provided for the VirtualMode property.

//The basic VirtualMode function.  Dynamically returns a ListViewItem
//with the required properties; in this case, the square of the index.
void listView1_RetrieveVirtualItem(object sender, RetrieveVirtualItemEventArgs e)
{
    //Caching is not required but improves performance on large sets.
    //To leave out caching, don't connect the CacheVirtualItems event 
    //and make sure myCache is null.

    //check to see if the requested item is currently in the cache
    if (myCache != null && e.ItemIndex >= firstItem && e.ItemIndex < firstItem + myCache.Length)
    {
        //A cache hit, so get the ListViewItem from the cache instead of making a new one.
        e.Item = myCache[e.ItemIndex - firstItem];
    }
    else
    {
        //A cache miss, so create a new ListViewItem and pass it back.
        int x = e.ItemIndex * e.ItemIndex;
        e.Item = new ListViewItem(x.ToString());
    }
}
'The basic VirtualMode function.  Dynamically returns a ListViewItem
'with the required properties; in this case, the square of the index.
Private Sub listView1_RetrieveVirtualItem(ByVal sender As Object, ByVal e As RetrieveVirtualItemEventArgs) Handles listView1.RetrieveVirtualItem
    'Caching is not required but improves performance on large sets.
    'To leave out caching, don't connect the CacheVirtualItems event 
    'and make sure myCache is null.
    'check to see if the requested item is currently in the cache
    If Not (myCache Is Nothing) AndAlso e.ItemIndex >= firstItem AndAlso e.ItemIndex < firstItem + myCache.Length Then
        'A cache hit, so get the ListViewItem from the cache instead of making a new one.
        e.Item = myCache((e.ItemIndex - firstItem))
    Else
        'A cache miss, so create a new ListViewItem and pass it back.
        Dim x As Integer = e.ItemIndex * e.ItemIndex
        e.Item = New ListViewItem(x.ToString())
    End If


End Sub

Comentarios

Cuando un objeto ListView está en modo virtual, crea objetos de ListViewItem dinámicamente en lugar de usar la colección Items.When a ListView object is in virtual mode, it creates ListViewItem objects dynamically instead of using the Items collection. Este evento se desencadena cuando el objeto debe crear un objeto ListViewItem.This event is raised when the object must create a ListViewItem object. Un controlador para este evento debe crear el ListViewItem adecuado o recuperarlo de la memoria caché y pasarlo de nuevo por medio de la propiedad Item.A handler for this event should create the appropriate ListViewItem or retrieve it from the cache, and pass it back by way of the Item property.

Para obtener más información sobre el manejo de eventos, consulte controlar y provocar eventos.For more information about handling events, see Handling and Raising Events.

Se aplica a