ToolStripDropDown.Opening ToolStripDropDown.Opening ToolStripDropDown.Opening ToolStripDropDown.Opening Event

定义

ToolStripDropDown 控件正打开时发生。Occurs when the ToolStripDropDown control is opening.

public:
 event System::ComponentModel::CancelEventHandler ^ Opening;
public event System.ComponentModel.CancelEventHandler Opening;
member this.Opening : System.ComponentModel.CancelEventHandler 
Public Custom Event Opening As CancelEventHandler 

示例

下面的示例演示如何处理Opening事件。The following example demonstrates how to handle the Opening event.

// This code example demonstrates how to handle the Opening event.
// It also demonstrates dynamic item addition and dynamic 
// SourceControl determination with reuse.
class Form3 : Form
{
    // Declare the ContextMenuStrip control.
    private ContextMenuStrip fruitContextMenuStrip;

    public Form3()
    {
        // Create a new ContextMenuStrip control.
        fruitContextMenuStrip = new ContextMenuStrip();

        // Attach an event handler for the 
        // ContextMenuStrip control's Opening event.
        fruitContextMenuStrip.Opening += new System.ComponentModel.CancelEventHandler(cms_Opening);

        // Create a new ToolStrip control.
        ToolStrip ts = new ToolStrip();

        // Create a ToolStripDropDownButton control and add it
        // to the ToolStrip control's Items collections.
        ToolStripDropDownButton fruitToolStripDropDownButton = new ToolStripDropDownButton("Fruit", null, null, "Fruit");
        ts.Items.Add(fruitToolStripDropDownButton);

        // Dock the ToolStrip control to the top of the form.
        ts.Dock = DockStyle.Top;

        // Assign the ContextMenuStrip control as the 
        // ToolStripDropDownButton control's DropDown menu.
        fruitToolStripDropDownButton.DropDown = fruitContextMenuStrip;

        // Create a new MenuStrip control and add a ToolStripMenuItem.
        MenuStrip ms = new MenuStrip();
        ToolStripMenuItem fruitToolStripMenuItem = new ToolStripMenuItem("Fruit", null, null, "Fruit");
        ms.Items.Add(fruitToolStripMenuItem);

        // Dock the MenuStrip control to the top of the form.
        ms.Dock = DockStyle.Top;

        // Assign the MenuStrip control as the 
        // ToolStripMenuItem's DropDown menu.
        fruitToolStripMenuItem.DropDown = fruitContextMenuStrip;

        // Assign the ContextMenuStrip to the form's 
        // ContextMenuStrip property.
        this.ContextMenuStrip = fruitContextMenuStrip;

        // Add the ToolStrip control to the Controls collection.
        this.Controls.Add(ts);

        //Add a button to the form and assign its ContextMenuStrip.
        Button b = new Button();
        b.Location = new System.Drawing.Point(60, 60);
        this.Controls.Add(b);
        b.ContextMenuStrip = fruitContextMenuStrip;

        // Add the MenuStrip control last.
        // This is important for correct placement in the z-order.
        this.Controls.Add(ms);
    }

    // This event handler is invoked when the ContextMenuStrip
    // control's Opening event is raised. It demonstrates
    // dynamic item addition and dynamic SourceControl 
    // determination with reuse.
    void cms_Opening(object sender, System.ComponentModel.CancelEventArgs e)
    {
        // Acquire references to the owning control and item.
        Control c = fruitContextMenuStrip.SourceControl as Control;
        ToolStripDropDownItem tsi = fruitContextMenuStrip.OwnerItem as ToolStripDropDownItem;

        // Clear the ContextMenuStrip control's Items collection.
        fruitContextMenuStrip.Items.Clear();

        // Check the source control first.
        if (c != null)
        {
            // Add custom item (Form)
            fruitContextMenuStrip.Items.Add("Source: " + c.GetType().ToString());
        }
        else if (tsi != null)
        {
            // Add custom item (ToolStripDropDownButton or ToolStripMenuItem)
            fruitContextMenuStrip.Items.Add("Source: " + tsi.GetType().ToString());
        }

        // Populate the ContextMenuStrip control with its default items.
        fruitContextMenuStrip.Items.Add("-");
        fruitContextMenuStrip.Items.Add("Apples");
        fruitContextMenuStrip.Items.Add("Oranges");
        fruitContextMenuStrip.Items.Add("Pears");

        // Set Cancel to false. 
        // It is optimized to true based on empty entry.
        e.Cancel = false;
    }
}
' This code example demonstrates how to handle the Opening event.
' It also demonstrates dynamic item addition and dynamic 
' SourceControl determination with reuse.
Class Form3
    Inherits Form

   ' Declare the ContextMenuStrip control.
   Private fruitContextMenuStrip As ContextMenuStrip
   
   
   Public Sub New()
      ' Create a new ContextMenuStrip control.
      fruitContextMenuStrip = New ContextMenuStrip()
      
      ' Attach an event handler for the 
      ' ContextMenuStrip control's Opening event.
      AddHandler fruitContextMenuStrip.Opening, AddressOf cms_Opening
      
      ' Create a new ToolStrip control.
      Dim ts As New ToolStrip()
      
      ' Create a ToolStripDropDownButton control and add it
      ' to the ToolStrip control's Items collections.
      Dim fruitToolStripDropDownButton As New ToolStripDropDownButton("Fruit", Nothing, Nothing, "Fruit")
      ts.Items.Add(fruitToolStripDropDownButton)
      
      ' Dock the ToolStrip control to the top of the form.
      ts.Dock = DockStyle.Top
      
      ' Assign the ContextMenuStrip control as the 
      ' ToolStripDropDownButton control's DropDown menu.
      fruitToolStripDropDownButton.DropDown = fruitContextMenuStrip
      
      ' Create a new MenuStrip control and add a ToolStripMenuItem.
      Dim ms As New MenuStrip()
      Dim fruitToolStripMenuItem As New ToolStripMenuItem("Fruit", Nothing, Nothing, "Fruit")
      ms.Items.Add(fruitToolStripMenuItem)
      
      ' Dock the MenuStrip control to the top of the form.
      ms.Dock = DockStyle.Top
      
      ' Assign the MenuStrip control as the 
      ' ToolStripMenuItem's DropDown menu.
      fruitToolStripMenuItem.DropDown = fruitContextMenuStrip
      
      ' Assign the ContextMenuStrip to the form's 
      ' ContextMenuStrip property.
      Me.ContextMenuStrip = fruitContextMenuStrip
      
      ' Add the ToolStrip control to the Controls collection.
        Me.Controls.Add(ts)

        'Add a button to the form and assign its ContextMenuStrip.
        Dim b As New Button()
        b.Location = New System.Drawing.Point(60, 60)
        Me.Controls.Add(b)
        b.ContextMenuStrip = fruitContextMenuStrip
      
      ' Add the MenuStrip control last.
      ' This is important for correct placement in the z-order.
      Me.Controls.Add(ms)
    End Sub
   
   ' This event handler is invoked when the ContextMenuStrip
   ' control's Opening event is raised. It demonstrates
   ' dynamic item addition and dynamic SourceControl 
   ' determination with reuse.
    Sub cms_Opening(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs)

        ' Acquire references to the owning control and item.
        Dim c As Control = fruitContextMenuStrip.SourceControl
        Dim tsi As ToolStripDropDownItem = fruitContextMenuStrip.OwnerItem 

        ' Clear the ContextMenuStrip control's 
        ' Items collection.
        fruitContextMenuStrip.Items.Clear()

        ' Check the source control first.
        If (c IsNot Nothing) Then
            ' Add custom item (Form)
            fruitContextMenuStrip.Items.Add(("Source: " + c.GetType().ToString()))
        ElseIf (tsi IsNot Nothing) Then
            ' Add custom item (ToolStripDropDownButton or ToolStripMenuItem)
            fruitContextMenuStrip.Items.Add(("Source: " + tsi.GetType().ToString()))
        End If

        ' Populate the ContextMenuStrip control with its default items.
        fruitContextMenuStrip.Items.Add("-")
        fruitContextMenuStrip.Items.Add("Apples")
        fruitContextMenuStrip.Items.Add("Oranges")
        fruitContextMenuStrip.Items.Add("Pears")

        ' Set Cancel to false. 
        ' It is optimized to true based on empty entry.
        e.Cancel = False
    End Sub
End Class

注解

有关处理事件的详细信息, 请参阅处理和引发事件For more information about handling events, see Handling and Raising Events.

适用于