ComboBox | .NET Windows Forms in a Nutshell

ComboBox

marshal by reference, disposable

System. Windows .Forms (system. windows .forms.dll)

class

This control represents an edit box with a drop-down lista standard Win32 combobox. It extends the base ListControl that supports a variety of list-like controls. In addition to the standard control facilities, you can set the DropDownStyle property, which determines whether the edit box allows you to type into it and whether the list view is always visible, and set the DropDownWidth property of the drop-down list. You can set the IntegralHeight property, which can automatically adjust the height of the control to ensure that only whole items are displayed. The MaxDropDownItems property sets the maximum number of items that will be displayed in the drop-down list (without scrolling), and the MaxLength property sets the number of characters allowed in the edit field.

The selected item can be retrieved through the SelectedItem and SelectedIndex properties, which should not be confused with the SelectedText property, which gets the selected text in the edit field.

You can add and remove objects from the Items collection to alter the contents of the listbox, and the very useful members FindString() and FindStringExact() can help you locate a particular item in the list. Finally, you can select the text in the edit field using Select() or SelectAll() .

Unfortunately, the implementation of ComboBox in Version 1.0 of the framework is something of a minor fiasco. The edit control doesn't support the standard pop-up menus , and the selection and edit behavior is idiosyncratic to say the least ( especially when hosted on a TabPage ). Microsoft has indicated that this will almost certainly be improved in the next release.

 public class  ComboBox  : ListControl {  // Public Constructors  public  ComboBox  ();  // Public Instance Properties  public override Color  BackColor  {set; get; }  // overrides Control  public override Image  BackgroundImage  {set; get; }  // overrides Control  public DrawMode  DrawMode  {set; get; }    public ComboBoxStyle  DropDownStyle  {set; get; }    public int  DropDownWidth  {set; get; }    public bool  DroppedDown  {set; get; }    public override bool  Focused  {get; }  // overrides Control  public override Color  ForeColor  {set; get; }  // overrides Control  public bool  IntegralHeight  {set; get; }    public int  ItemHeight  {set; get; }    public ObjectCollection  Items  {get; }    public int  MaxDropDownItems  {set; get; }    public int  MaxLength  {set; get; }    public int  PreferredHeight  {get; }    public override int  SelectedIndex  {set; get; }  // overrides ListControl  public object  SelectedItem  {set; get; }    public string  SelectedText  {set; get; }    public int  SelectionLength  {set; get; }    public int  SelectionStart  {set; get; }    public bool  Sorted  {set; get; }    public override string  Text  {set; get; }  // overrides Control   // Protected Instance Properties  protected override CreateParams  CreateParams  {get; }  // overrides Control  protected override Size  DefaultSize  {get; }  // overrides Control   // Public Instance Methods  public void  BeginUpdate  ();    public void  EndUpdate  ();    public int  FindString  (string  s  );    public int  FindString  (string  s  , int  startIndex  );    public int  FindStringExact  (string  s  );    public int  FindStringExact  (string  s  , int  startIndex  );    public int  GetItemHeight  (int  index  );    public void  Select  (int  start  , int  length  );    public void  SelectAll  ();    public override string  ToString  ();  // overrides System.ComponentModel.Component   // Protected Instance Methods  protected virtual void  AddItemsCore  (object[ ]  value  );    protected override void  Dispose  (bool  disposing  );  // overrides Control  protected override bool  IsInputKey  (Keys  keyData  );  // overrides ListControl  protected override void  OnBackColorChanged  (EventArgs  e  );  // overrides Control  protected override void  OnDataSourceChanged  (EventArgs  e  );  // overrides ListControl  protected override void  OnDisplayMemberChanged  (EventArgs  e  );  // overrides ListControl  protected virtual void  OnDrawItem  (DrawItemEventArgs  e  );    protected virtual void  OnDropDown  (EventArgs  e  );    protected virtual void  OnDropDownStyleChanged  (EventArgs  e  );    protected override void  OnFontChanged  (EventArgs  e  );  // overrides Control  protected override void  OnForeColorChanged  (EventArgs  e  );  // overrides Control  protected override void  OnHandleCreated  (EventArgs  e  );  // overrides Control  protected override void  OnHandleDestroyed  (EventArgs  e  );  // overrides Control  protected override void  OnKeyPress  (KeyPressEventArgs  e  );  // overrides Control  protected virtual void  OnMeasureItem  (MeasureItemEventArgs  e  );    protected override void  OnParentBackColorChanged  (EventArgs  e  );  // overrides Control  protected override void  OnResize  (EventArgs  e  );  // overrides Control  protected override void  OnSelectedIndexChanged  (EventArgs  e  );  // overrides ListControl  protected virtual void  OnSelectedItemChanged  (EventArgs  e  );    protected virtual void  OnSelectionChangeCommitted  (EventArgs  e  );    protected override void  RefreshItem  (int  index  );  // overrides ListControl  protected override void  SetBoundsCore  (int  x  , int  y  , int  width  , int  height  , BoundsSpecified  specified  );  // overrides Control  protected override void  SetItemCore  (int  index  , object  value  );  // overrides ListControl  protected override void  SetItemsCore  (System.Collections.IList  value  );  // overrides ListControl  protected override void  WndProc  (ref Message  m  );  // overrides Control   // Events  public event DrawItemEventHandler  DrawItem  ;    public event EventHandler  DropDown  ;    public event EventHandler  DropDownStyleChanged  ;    public event MeasureItemEventHandler  MeasureItem  ;    public event PaintEventHandler  Paint  ;  // overrides Control  public event EventHandler  SelectedIndexChanged  ;    public event EventHandler  SelectionChangeCommitted  ; }

Hierarchy

System.Object System.MarshalByRefObject System.ComponentModel.Component(System.ComponentModel.IComponen, System.IDisposable) Control(IOleContro, IOleObject , IOleInPlaceObject , IOleInPlaceActiveObject , IOleWindow , IViewObject , IViewObject2 , IPersist , IPersistStreamInit , IPersistPropertyBag , IPersistStorage , IQuickActivate , System.ComponentModel.ISynchronizeInvoke , IWin32Window) ListControl ComboBox

Passed To

ChildAccessibleObject.ChildAccessibleObject() , ObjectCollection.ObjectCollection()