ListViewGroupCollection.Clear 方法

public:
 virtual void Clear();

public void Clear();

abstract member Clear : unit -> unit
override this.Clear : unit -> unit

Public Sub Clear ()

下列範例示範如何在 Clear 依詳細資料檢視中的子專案值來組織 ListView 專案的應用程式中使用 方法。 這種群組形式類似于 Windows 檔案總管中使用的群組。 在此範例中，會動態建立群組。 針對每個子專案資料行，會為每個唯一子專案值建立一個群組。 針對父專案資料行，會為每個唯一的初始字母建立一個群組。 針對每個資料行建立的群組會儲存在雜湊表中，以及子專案文字或初始字母。 按一下資料行標頭時，會 ListViewGroupCollection 清除 。 接著會擷取對應至所按一下資料行的雜湊表，並將每個專案指派給適當的群組。 最後，雜湊表中群組的已排序陣列會新增至 ListViewGroupCollection 。

如需完整的範例，請參閱 ListViewGroupCollection 概觀參考主題。

   // Sets myListView to the groups created for the specified column.
private:
   void SetGroups(int column)
   {
      // Remove the current groups.
      myListView->Groups->Clear();

      // Retrieve the hash table corresponding to the column.
      Hashtable^ groups = dynamic_cast<Hashtable^>(groupTables[column]);

      // Copy the groups for the column to an array.
      array<ListViewGroup^>^ groupsArray = gcnew array<ListViewGroup^>(groups->Count);
      groups->Values->CopyTo(groupsArray, 0);

      // Sort the groups and add them to myListView.
      Array::Sort(groupsArray, gcnew ListViewGroupSorter(myListView->Sorting));
      myListView->Groups->AddRange(groupsArray);

      // Iterate through the items in myListView, assigning each 
      // one to the appropriate group.
      IEnumerator^ myEnum = myListView->Items->GetEnumerator();
      while (myEnum->MoveNext())
      {
         ListViewItem^ item = safe_cast<ListViewItem^>(myEnum->Current);
         // Retrieve the subitem text corresponding to the column.
         String^ subItemText = item->SubItems[column]->Text;

         // For the Title column, use only the first letter.
         if (column == 0) 
         {
            subItemText = subItemText->Substring(0, 1);
         }

         // Assign the item to the matching group.
         item->Group = dynamic_cast<ListViewGroup^>(groups[subItemText]);
      }
   }

// Sets myListView to the groups created for the specified column.
private void SetGroups(int column)
{
    // Remove the current groups.
    myListView.Groups.Clear();

    // Retrieve the hash table corresponding to the column.
    Hashtable groups = (Hashtable)groupTables[column];

    // Copy the groups for the column to an array.
    ListViewGroup[] groupsArray = new ListViewGroup[groups.Count];
    groups.Values.CopyTo(groupsArray, 0);

    // Sort the groups and add them to myListView.
    Array.Sort(groupsArray, new ListViewGroupSorter(myListView.Sorting));
    myListView.Groups.AddRange(groupsArray);

    // Iterate through the items in myListView, assigning each 
    // one to the appropriate group.
    foreach (ListViewItem item in myListView.Items)
    {
        // Retrieve the subitem text corresponding to the column.
        string subItemText = item.SubItems[column].Text;

        // For the Title column, use only the first letter.
        if (column == 0) 
        {
            subItemText = subItemText.Substring(0, 1);
        }

        // Assign the item to the matching group.
        item.Group = (ListViewGroup)groups[subItemText];
    }
}

' Sets myListView to the groups created for the specified column.
Private Sub SetGroups(column As Integer)
    ' Remove the current groups.
    myListView.Groups.Clear()
    
    ' Retrieve the hash table corresponding to the column.
    Dim groups As Hashtable = CType(groupTables(column), Hashtable)
    
    ' Copy the groups for the column to an array.
    Dim groupsArray(groups.Count - 1) As ListViewGroup
    groups.Values.CopyTo(groupsArray, 0)
    
    ' Sort the groups and add them to myListView.
    Array.Sort(groupsArray, New ListViewGroupSorter(myListView.Sorting))
    myListView.Groups.AddRange(groupsArray)
    
    ' Iterate through the items in myListView, assigning each 
    ' one to the appropriate group.
    Dim item As ListViewItem
    For Each item In myListView.Items
        ' Retrieve the subitem text corresponding to the column.
        Dim subItemText As String = item.SubItems(column).Text
        
        ' For the Title column, use only the first letter.
        If column = 0 Then
            subItemText = subItemText.Substring(0, 1)
        End If 

        ' Assign the item to the matching group.
        item.Group = CType(groups(subItemText), ListViewGroup)
    Next item
End Sub

使用這個方法可從集合中移除所有群組。 請注意，從 ListView.Groups 集合中移除群組並不會從 ListView 控制項中移除專案。

這個方法適用于停用群組功能。 當控制項中 ListView 沒有群組時，專案通常會顯示。 若要從集合中移除個別群組，請使用 Remove 或 RemoveAt 方法。

當您想要提供多種方式來群組專案時，此方法也很有用。 若要變更群組，請先使用 Clear 方法從集合中移除所有群組，然後使用 AddRange 方法新增不同的群組陣列。