ListView.RetrieveVirtualItem イベント

定義

ListView が仮想モードで、ListViewItem を必要とする場合に発生します。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 

例外

Item イベントの処理時に RetrieveVirtualItem プロパティが項目に設定されていません。The Item property is not set to an item when the RetrieveVirtualItem event is handled.

このイベントのハンドラーを示すコード例を次に示します。The following code example demonstrates a handler for this event. この例では、listView1 は各 ListViewItem を使用して、インデックスの2乗を表示する必要があります。In this example, listView1 needs each ListViewItem to display the square of its index. このコード例は、VirtualMode プロパティ用に用意されている大規模な例の一部です。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

注釈

@No__t 0 のオブジェクトが仮想モードの場合、Items のコレクションを使用するのではなく、ListViewItem のオブジェクトを動的に作成します。When a ListView object is in virtual mode, it creates ListViewItem objects dynamically instead of using the Items collection. このイベントは、オブジェクトが @no__t 0 オブジェクトを作成する必要があるときに発生します。This event is raised when the object must create a ListViewItem object. このイベントのハンドラーは、適切な @no__t 0 を作成するか、キャッシュから取得し、Item プロパティを使用して再度渡す必要があります。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.

イベントの処理の詳細については、「処理とイベントの発生」を参照してください。For more information about handling events, see Handling and Raising Events.

適用対象