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Opening Event

ToolStripDropDown.Opening Event

Occurs when the ToolStripDropDown control is opening.

Namespace:  System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

public event CancelEventHandler Opening

For more information about handling events, see Handling and Raising Events.

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");

        // 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");

        // 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. 

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

        // Add the MenuStrip control last. 
        // This is important for correct placement in the z-order. 

    // 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.

        // 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.

        // Set Cancel to false.  
        // It is optimized to true based on empty entry.
        e.Cancel = false;

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1
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