ListView.CacheVirtualItems 事件

定义

当处于虚拟模式下的 ListView 的显示区域的内容发生更改时发生,ListView 决定需要的项的新范围。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 

示例

下面的代码示例演示如何使用此成员。The following code example demonstrates the use of this member. 在此示例中,事件处理程序将进行检查以确保确实需要缓存刷新,然后重新生成缓存。In the example, the event handler checks to make sure a cache refresh is really necessary, and then rebuilds the cache. 此代码示例是为 VirtualMode 属性提供的更大示例的一部分。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

注解

此事件仅在 VirtualMode @no__t 时发生。This event only occurs when VirtualMode is true. 处理此事件将允许 ListView 更新缓存中保存的项信息,使其随时可用。Handling this event allows the ListView to update the item information held in the cache so that it is readily available. 这可以提高大型列表或其项计算成本高昂的列表的性能。This can improve performance on large lists, or lists whose items are expensive to calculate.

有关处理事件的详细信息,请参阅处理和引发事件For more information about handling events, see Handling and Raising Events.

适用于