ListBox.ObjectCollection.Add(Object) 方法

定义

命名空间:

System.Windows.Forms

程序集:

System.Windows.Forms.dll

向 ListBox 的项列表添加项。

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

public int Add (object item);

member this.Add : obj -> int

Public Function Add (item As Object) As Integer

参数

item

Object

一个对象，它表示要添加到集合中的项。

返回

Int32

集合中项的从零开始的索引；如果已调用 BeginUpdate()，则为 -1。

例外

SystemException

没有足够的空间来向列表中添加新项。

ArgumentNullException

item 为 null。

示例

下面的代码示例演示如何创建一个 ListBox 控件，该控件在列中显示多个项，并且可以在控件的列表中选择多个项。 该示例的代码使用 Add 类的 ListBox.ObjectCollection 方法将 50 个项添加到 ListBox ，然后使用 方法从列表中选择SetSelected三项。 然后，代码通过属性) 显示集合 (SelectedItems的值ListBox.SelectedObjectCollection，通过属性) ListBox.SelectedIndexCollectionSelectedIndices显示 (的值。 此示例要求代码位于 中，并从 中 Form调用。

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

注解

Sorted如果 的 ListBox 属性设置为 true，则该项将按字母顺序插入列表中。 否则，该项将插入到列表的末尾。 若要将项插入列表框中的特定位置，请使用 Insert 方法。 若要在单个操作中将一组项添加到列表框，请使用 AddRange 方法。 如果要使用 Add 方法将大量项添加到列表中，请使用 BeginUpdate 和 EndUpdate 方法防止 ListBox 每次将项添加到列表中时重新绘制，直到所有项都添加到列表中。 将项添加到 时 ListBox，先对项进行排序，然后添加新项会更有效。

将对象添加到集合时，ListBox首先检查类的 ListControl 属性是否DisplayMember具有在获取项文本时指定引用的对象的成员的名称。 如果属性 DisplayMember 未指定成员， ListBox 则 调用 ToString 对象的 方法以获取要显示在列表中的文本。