ListBox.ObjectCollection.Add(Object) 方法

定義

命名空間:

System.Windows.Forms

組件:

System.Windows.Forms.dll

將項目加入至 ListBox 的項目清單。

public:
 int Add(System::Object ^ item);

public int Add (object item);

member this.Add : obj -> int

Public Function Add (item As Object) As Integer

參數

item

Object

物件，表示要加入至集合中的項目。

傳回

Int32

集合中項目之以零起始的索引；如果已呼叫 BeginUpdate() 則為 -1。

例外狀況

SystemException

空間不足，無法將新項目加入至清單中。

ArgumentNullException

item 為 null。

範例

下列程式碼範例示範如何建立 ListBox 控制項，以在資料行中顯示多個專案，而且可以在控制項清單中選取多個專案。 此範例的程式碼會使用 Add 類別的 ListBox.ObjectCollection 方法，將 50 個專案新增至 ListBox ，然後使用 方法從清單中 SetSelected 選取三個專案。 然後，程式碼會透過 SelectedItems 屬性) (SelectedIndices 和 ListBox.SelectedIndexCollection 屬性) ，顯示集合 (的值 ListBox.SelectedObjectCollection 。 此範例要求程式碼位於 ，並從 呼叫 Form 。

void button1_Click( Object^ /*sender*/, System::EventArgs^ /*e*/ )
{
   
   // Create an instance of the ListBox.
   ListBox^ listBox1 = gcnew ListBox;
   
   // Set the size and location of the ListBox.
   listBox1->Size = System::Drawing::Size( 200, 100 );
   listBox1->Location = System::Drawing::Point( 10, 10 );
   
   // Add the ListBox to the form.
   this->Controls->Add( listBox1 );
   
   // Set the ListBox to display items in multiple columns.
   listBox1->MultiColumn = true;
   
   // Set the selection mode to multiple and extended.
   listBox1->SelectionMode = SelectionMode::MultiExtended;
   
   // Shutdown the painting of the ListBox as items are added.
   listBox1->BeginUpdate();
   
   // Loop through and add 50 items to the ListBox.
   for ( int x = 1; x <= 50; x++ )
   {
      listBox1->Items->Add( String::Format( "Item {0}", x ) );

   }
   listBox1->EndUpdate();
   
   // Select three items from the ListBox.
   listBox1->SetSelected( 1, true );
   listBox1->SetSelected( 3, true );
   listBox1->SetSelected( 5, true );
   
   #if defined(DEBUG)
   // Display the second selected item in the ListBox to the console.
   System::Diagnostics::Debug::WriteLine( listBox1->SelectedItems[ 1 ] );
   
   // Display the index of the first selected item in the ListBox.
   System::Diagnostics::Debug::WriteLine( listBox1->SelectedIndices[ 0 ] );
   #endif
}

private void button1_Click(object sender, System.EventArgs e)
{
   // Create an instance of the ListBox.
   ListBox listBox1 = new ListBox();
   // Set the size and location of the ListBox.
   listBox1.Size = new System.Drawing.Size(200, 100);
   listBox1.Location = new System.Drawing.Point(10,10);
   // Add the ListBox to the form.
   this.Controls.Add(listBox1);
   // Set the ListBox to display items in multiple columns.
   listBox1.MultiColumn = true;
   // Set the selection mode to multiple and extended.
   listBox1.SelectionMode = SelectionMode.MultiExtended;
 
   // Shutdown the painting of the ListBox as items are added.
   listBox1.BeginUpdate();
   // Loop through and add 50 items to the ListBox.
   for (int x = 1; x <= 50; x++)
   {
      listBox1.Items.Add("Item " + x.ToString());
   }
   // Allow the ListBox to repaint and display the new items.
   listBox1.EndUpdate();
      
   // Select three items from the ListBox.
   listBox1.SetSelected(1, true);
   listBox1.SetSelected(3, true);
   listBox1.SetSelected(5, true);

   // Display the second selected item in the ListBox to the console.
   System.Diagnostics.Debug.WriteLine(listBox1.SelectedItems[1].ToString());
   // Display the index of the first selected item in the ListBox.
   System.Diagnostics.Debug.WriteLine(listBox1.SelectedIndices[0].ToString());             
}

Private Sub button1_Click(sender As Object, e As System.EventArgs)
    ' Create an instance of the ListBox.
    Dim listBox1 As New ListBox()
    ' Set the size and location of the ListBox.
    listBox1.Size = New System.Drawing.Size(200, 100)
    listBox1.Location = New System.Drawing.Point(10, 10)
    ' Add the ListBox to the form.
    Me.Controls.Add(listBox1)
    ' Set the ListBox to display items in multiple columns.
    listBox1.MultiColumn = True
    ' Set the selection mode to multiple and extended.
    listBox1.SelectionMode = SelectionMode.MultiExtended
    
    ' Shutdown the painting of the ListBox as items are added.
    listBox1.BeginUpdate()
    ' Loop through and add 50 items to the ListBox.
    Dim x As Integer
    For x = 1 To 50
        listBox1.Items.Add("Item " & x.ToString())
    Next x
    ' Allow the ListBox to repaint and display the new items.
    listBox1.EndUpdate()
    
    ' Select three items from the ListBox.
    listBox1.SetSelected(1, True)
    listBox1.SetSelected(3, True)
    listBox1.SetSelected(5, True)
       
    ' Display the second selected item in the ListBox to the console.
    System.Diagnostics.Debug.WriteLine(listBox1.SelectedItems(1).ToString())
    ' Display the index of the first selected item in the ListBox.
    System.Diagnostics.Debug.WriteLine(listBox1.SelectedIndices(0).ToString())
End Sub

備註

如果 的 SortedListBox 屬性設定 true 為 ，專案會依字母順序插入清單中。 否則，專案會插入清單結尾。 若要在特定位置將專案插入清單方塊中，請使用 Insert 方法。 若要在單一作業中將一組專案新增至清單方塊，請使用 AddRange 方法。 如果您想要使用 Add 方法將大量專案新增至清單，請使用 BeginUpdate 和 EndUpdate 方法來防止 ListBox 每次將專案新增至清單時重新繪製，直到所有專案加入清單為止。 將專案新增至 ListBox 時，先排序專案，然後新增專案會更有效率。

當物件加入至集合時， ListBox 第一次會檢查 類別的 ListControl 屬性是否 DisplayMember 具有指定之物件的成員名稱，以在取得專案文字時參考。 DisplayMember如果屬性沒有指定成員， ListBox 則 會呼叫 ToString 物件的 方法，以取得要顯示在清單中的文字。