ListViewGroupCollection.Clear 方法

public:
 virtual void Clear();

public void Clear();

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

Public Sub Clear ()

實作

範例

以下範例展示了該方法如何在 Clear 應用程式中依子項目值組織 ListView 細節檢視。 這種分組方式類似於 Windows 檔案總管中使用的分組方式。 在範例中，群組是動態建立的。 每個子項目欄位，為每個獨特子項目值建立一個群組。 對於父項目欄位，每個唯一字母首字母會建立一個群組。 每欄建立的群組會與子項目文字或首字母一同儲存在雜湊表中。 當點擊欄位標頭時，該欄位 ListViewGroupCollection 會被清除。 接著取出對應點擊欄位的雜湊表，並將每個項目分配到相應的群組。 最後，雜湊表中群組的排序陣列會加入 ListViewGroupCollection。

完整範例請參閱 ListViewGroupCollection 概述參考主題。

   // 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

備註

使用此方法將所有群組從集合中移除。 請注意，從集合中移除群組 ListView.Groups 並不代表控制項 ListView 也被移除。

此方法有助於停用分組功能。 當控制組中沒有群組 ListView 時，項目會正常出現。 若要從集合中移除個別群組，請使用 Remove or RemoveAt 方法。

當你想提供多種分組方式時，這個方法也很有用。 要更改分組，先使用 Clear 移除所有群組的方法，然後再用該 AddRange 方法新增不同的群組陣列。