ListView.CacheVirtualItems イベント

定義

仮想モードで ListView の表示領域の内容が変化し、ListView によって項目の新しい範囲が必要であると判断された場合に発生します。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 

このメンバーの使用例を次のコード例に示します。The following code example demonstrates the use of this member. この例では、イベントハンドラーはキャッシュの更新が本当に必要であることを確認し、キャッシュを再構築します。In the example, the event handler checks to make sure a cache refresh is really necessary, and then rebuilds the cache. 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.

//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

注釈

このイベントは、VirtualModetrue場合にのみ発生します。This event only occurs when VirtualMode is true. このイベントを処理することにより、ListView はキャッシュに保持されている項目情報を更新してすぐに使用できるようになります。Handling this event allows the ListView to update the item information held in the cache so that it is readily available. これにより、サイズの大きいリストや、計算に負荷のかかる項目を含むリストのパフォーマンスが向上します。This can improve performance on large lists, or lists whose items are expensive to calculate.

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