ComboBox.DropDown Event

Definition

Namespace:

System.Windows.Forms

Assembly:

System.Windows.Forms.dll

Occurs when the drop-down portion of a ComboBox is shown.

public:
 event EventHandler ^ DropDown;

public event EventHandler? DropDown;

member this.DropDown : EventHandler 

Public Custom Event DropDown As EventHandler 

Event Type

EventHandler

Examples

The following code example demonstrates how to initialize a ComboBox control by setting the text property and using the AddRange method to populate the ComboBox. It also demonstrates handling the DropDown event. To run the example, paste the following code in a form and call the InitializeComboBox method in the form's constructor or Load event.

internal:
   // Declare ComboBox1
   System::Windows::Forms::ComboBox^ ComboBox1;

private:
   // Initialize ComboBox1.
   void InitializeComboBox()
   {
      this->ComboBox1 = gcnew ComboBox;
      this->ComboBox1->Location = System::Drawing::Point( 128, 48 );
      this->ComboBox1->Name = "ComboBox1";
      this->ComboBox1->Size = System::Drawing::Size( 100, 21 );
      this->ComboBox1->TabIndex = 0;
      this->ComboBox1->Text = "Typical";
      array<String^>^ installs = {"Typical","Compact","Custom"};
      ComboBox1->Items->AddRange( installs );
      this->Controls->Add( this->ComboBox1 );
      
      // Hook up the event handler.
      this->ComboBox1->DropDown += gcnew System::EventHandler(
         this, &Form1::ComboBox1_DropDown );
   }

   // Handles the ComboBox1 DropDown event. If the user expands the  
   // drop-down box, a message box will appear, recommending the
   // typical installation.
   void ComboBox1_DropDown( Object^ sender, System::EventArgs^ e )
   {
      MessageBox::Show( "Typical installation is strongly recommended.",
         "Install information", MessageBoxButtons::OK,
         MessageBoxIcon::Information );
   }

// Declare ComboBox1.
internal System.Windows.Forms.ComboBox ComboBox1;

// Initialize ComboBox1.
private void InitializeComboBox()
{
    this.ComboBox1 = new ComboBox();
    this.ComboBox1.Location = new System.Drawing.Point(128, 48);
    this.ComboBox1.Name = "ComboBox1";
    this.ComboBox1.Size = new System.Drawing.Size(100, 21);
    this.ComboBox1.TabIndex = 0;
    this.ComboBox1.Text	= "Typical";
    string[] installs = new string[]{"Typical", "Compact", "Custom"};
    ComboBox1.Items.AddRange(installs);
    this.Controls.Add(this.ComboBox1);
    
    // Hook up the event handler.
    this.ComboBox1.DropDown +=  
        new System.EventHandler(ComboBox1_DropDown);
}

// Handles the ComboBox1 DropDown event. If the user expands the  
// drop-down box, a message box will appear, recommending the
// typical installation.
private void ComboBox1_DropDown(object sender, System.EventArgs e)
{
    MessageBox.Show("Typical installation is strongly recommended.", 
    "Install information", MessageBoxButtons.OK, 
        MessageBoxIcon.Information);
}

' Declare ComboBox1.
Friend WithEvents ComboBox1 As System.Windows.Forms.ComboBox

' Initialize ComboBox1.
Private Sub InitializeComboBox()
    Me.ComboBox1 = New ComboBox
    Me.ComboBox1.Location = New System.Drawing.Point(128, 48)
    Me.ComboBox1.Name = "ComboBox1"
    Me.ComboBox1.Size = New System.Drawing.Size(100, 21)
    Me.ComboBox1.TabIndex = 0
    Me.ComboBox1.Text = "Typical"
    Dim installs() As String = New String() _
        {"Typical", "Compact", "Custom"}
    ComboBox1.Items.AddRange(installs)
    Me.Controls.Add(Me.ComboBox1)
End Sub

' Handles the ComboBox1 DropDown event. If the user expands the  
' drop-down box, a message box will appear, recommending the
' typical installation.
Private Sub ComboBox1_DropDown _ 
    (ByVal sender As Object, ByVal e As System.EventArgs) _ 
    Handles ComboBox1.DropDown
    MessageBox.Show("Typical installation is strongly recommended.", _
    "Install information", MessageBoxButtons.OK, MessageBoxIcon.Information)
End Sub

Remarks

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

See also

• DropDownClosed