ListViewGroupCollection.Clear 方法

定义

命名空间:

System.Windows.Forms

程序集:

System.Windows.Forms.dll

从集合中移除所有组。

public:
 virtual void Clear();

public void Clear ();

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

Public Sub Clear ()

实现

Clear()

示例

以下示例演示如何 Clear 在按子项值在详细信息视图中组织 ListView 项的应用程序中使用该方法。 这种分组形式类似于Windows资源管理器中使用的分组。 在此示例中，会动态创建组。 对于每个子项列，为每个唯一子项值创建一个组。 对于父项列，为每个唯一的初始字母创建一个组。 为每个列创建的组存储在哈希表中，以及子项文本或首字母。 单击列标题时，将清除列 ListViewGroupCollection 标题。 然后检索与单击列对应的哈希表，并将每个项分配给相应的组。 最后，哈希表中组的排序数组将添加到 ListViewGroupCollection该数组中。

有关完整示例，请参阅 ListViewGroupCollection 概述参考主题。

   // 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

注解

使用此方法从集合中删除所有组。 请注意，从 ListView.Groups 集合中删除组不会从 ListView 控件中删除项。

此方法可用于禁用分组功能。 当控件中 ListView 没有组时，这些项将正常显示。 若要从集合中删除单个组，请使用 Remove 或 RemoveAt 方法。

如果想要提供对项进行分组的多种方法，此方法也很有用。 若要更改分组，请先使用 Clear 该方法从集合中删除所有组，然后使用 AddRange 该方法添加不同的组数组。