ListView.CacheVirtualItems 事件

定義

命名空間:

System.Windows.Forms

組件:

System.Windows.Forms.dll

來源:

ListView.cs

當虛擬模式下顯示區域 ListView 的內容發生變化，並 ListView 判斷需要新的項目範圍時。

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 

事件類型

CacheVirtualItemsEventHandler

範例

以下程式碼範例展示了此成員的使用方式。 在這個例子中，事件處理程序會檢查是否真的需要快取刷新，然後重建快取。 此程式碼範例是該物業更大 VirtualMode 範例的一部分。

//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

備註

此事件僅在 VirtualMode 為 時 true發生。 處理此事件後，可以 ListView 更新快取中所儲存的物品資訊，使其易於取得。 這能提升大型清單或計算項目昂貴清單的效能。

如需處理事件的詳細資訊，請參閱 處理和引發事件。