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The General Winforms Interview Questions consists the most frequently
asked questions in Winforms. This list of 100+ questions guage your familiarity
with the Winforms platform. The q&a have been collected over a period
of time from various blogs, forums and other similar Winforms sites
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9.Windows Forms Menus
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| 9.1 How do I add a
context menu to a control?
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| 9.2 When using the
ContextMenu on multiple Controls, how do I know on which Control the right
click was performed?
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| 9.3 How do menu shortcuts
work?
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| 9.4 How do I make the
context menu appear only when clicked at certain portions of the Control?
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| 9.5 How do I prevent the
context menu from showing up on certain keyboard keys (like Keys.Apps)?
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| 9.6 How do I know when a
menu is closed/started so that I can refresh my status bar?
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| 9.7 Is there an Idle
event which will get fired from which I could update my menu item's enabled
state?
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| 9.8 How do I cancel a
context menu programatically?
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| 9.9 Is there an easy way
to create the "Window" menu that shows the list of child forms open?
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| 9.10 How can I work
around my menu shortcuts from showing up incorrectly when I use Ctrl+Number?
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| 9.11 How do I control
the position of the context menu when it is invoked via the keyboard?
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| 9.12 How do I disable
the default context menu of a textbox?
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| 9.13 How can I make the
context menu to close after a set time interval?
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| 9.14 How can I add an
icon to my menu items?
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| 9.15 How to add a
Separator in a menu?
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| 9.16 How can I enable
the mnemonics (underline) to show when my application is launched?
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9.1 How do I add a context menu to a control?
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The frame will manage a context menu for you if you set the control's
ContextMenu property. Here is some code adding a context menu to a Label.
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//Add Menus in your form's constructor...
this.pictureContextMenu = new ContextMenu();
this.pictureContextMenu.MenuItems.Add("&Color",
new EventHandler(Color_Clicked));
this.pictureContextMenu.MenuItems.Add("&Font",
new EventHandler(Font_Clicked));
label1.ContextMenu = this.pictureContextMenu;
//
// TODO: Add any constructor code after InitializeComponent call
//
}
private void Font_Clicked(object sender, System.EventArgs e)
{ . . . }
private void Color_Clicked(object sender, System.EventArgs e)
{ ... }
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9.2 When using the ContextMenu on multiple Controls, how do I know on which
Control the right click was performed?
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The ContextMenu.SourceControl property will specify the latest Control on which
the context menu was shown.
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9.3 How do menu shortcuts work?
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The focused control's ProcessCmdKey will be called first.
1) The Control class implementation of this method will check if there is a
ContextMenu associated with the Control and if so let the context menu handle
the shortcut.
2) If not handled, the ProcessCmdKey of the parent will be called recursively
until the Form is reached.
3) When the Form is reached it's MainMenu will be requested to handle the key.
You can override ProcessCmdKey of any Control and interrupt the normal
processing. Note that you can also override the ProcessCmdKey method is the
MainMenu and ContextMenu classes (this is not documented) to override default
processing.
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9.4 I How do I make the context menu appear only when clicked at certain
portions of the Control?
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You can listen to the Popup event, determine where the mouse was clicked and
selectively make the menu items visible in the menu as follows:
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// In C#
private void contextMenu1_Popup(object sender, System.EventArgs e)
{
// Get current mouse click position in the control (assuming pictureBox1 is the
control):
Point ptClick = this.pictureBox1.PointToClient(Control.MousePosition);
// Get the rectangle where you want to show the context menu.
Rectangle preferredClickRect = new Rectangle(0, 0, 50, 50);
if(preferredClickRect.Contains(ptClick))
{
// Show all the menu items so that the menu will appear
foreach(MenuItem item in this.contextMenu1.MenuItems)
item.Visible = true;
}
else
{
// Hide all the menu items so that the menu will not appear
foreach(MenuItem item in this.contextMenu1.MenuItems)
item.Visible = false;
}
}
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' In VB.Net
Private Sub contextMenu1_Popup(ByVal sender As Object, ByVal e As
System.EventArgs)
' Get current mouse click position in the control (assuming pictureBox1 is the
control):
Dim ptClick As Point = Me.pictureBox1.PointToClient(Control.MousePosition)
' Get the rectangle where you want to show the context menu.
Dim preferredClickRect As Rectangle = New Rectangle(0,0,50,50)
If preferredClickRect.Contains(ptClick) Then
' Show all the menu items so that the menu will appear
Dim item As MenuItem
For Each item In Me.contextMenu1.MenuItems
item.Visible = True
Next
Else
' Hide all the menu items so that the menu will not appear
Dim item As MenuItem
For Each item In Me.contextMenu1.MenuItems
item.Visible = False
Next
End If
End Sub
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9.5 How do I prevent the context menu from showing up on certain keyboard keys
(like Keys.Apps)?
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Override WndProc in your Control and do the following. You should then listen
to keyup and show the context menu yourself.
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[C#]
protected override void WndProc(ref Message m)
{
if(m.Msg == 0x7b /*WM_CONTEXTMENU*/ )
{
return;
}
if(m.Msg == 0x101 /*WM_KEYUP*/)
{
Keys keys = (Keys)m.WParam.ToInt32();
// Prevent this key from being processed.
if(keys == Keys.Apps)
return;
}
base.WndProc(ref m);
}
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[VB.Net]
Protected Overrides Sub WndProc(ByRef m As Message)
If m.Msg = 0x7b Then 'WM_CONTEXTMENU
Return
End If
If m.Msg = 0x101 Then 'WM_KEYUP
Dim keys As Keys = CType(m.WParam.ToInt32(), Keys)
' Prevent this key from being processed.
If keys = Keys.Apps Then
Return
End If
End If
MyBase.WndProc( m)
End Sub
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9.6 How do I know when a menu is closed/started so that I can refresh my status
bar?
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There are MenuComplete and MenuStart events in the Form that will inform you of
the corresponding menu events in the Form.
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9.7 Is there an Idle event which will get fired from which I could update my
menu item's enabled state?
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This used to be a very useful feature in MFC. You can do something similar with
the System.Windows.Forms.Application.Idle event which will get fired when the
app becomes Idle. Where you could parse through all the menu items and update
their states.
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9.8 How do I cancel a context menu programatically?
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First keep track of which control is showing the ContextMenu by listening to
the menu's Popup event and querying for the SourceControl.
Then when you are ready to cancel the popup, do as follows:
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[C#]
[DllImport("user32.dll", CharSet=CharSet.Auto)]
extern internal static IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wParam,
IntPtr lParam);
private void Timer_Tick(object sender, EventArgs e)
{
if(menuSourceControl != null)
SendMessage(menuSourceControl.Handle, 0x001F/*WM_CANCELMODE*/, IntPtr.Zero,
IntPtr.Zero);
}
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[VB.Net]
_ extern internal static IntPtr SendMessage(IntPtr hWnd, Integer msg, IntPtr
wParam, IntPtr lParam)
Private Sub Timer_Tick(ByVal sender As Object, ByVal e As EventArgs)
If Not menuSourceControl Is Nothing Then
SendMessage(menuSourceControl.Handle, 0x001F, IntPtr.Zero, IntPtr.Zero)
End If
End Sub
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9.9 Is there an easy way to create the "Window" menu that shows the list of
child forms open?
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Create a "Window" menu in you mdi parent form's menu and then drop another
MenuItem into it, setting it's MdiList property to true. It will then expand to
show all the available mdi children during runtime.
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9.10 How can I work around my menu shortcuts from showing up incorrectly when I
use Ctrl+Number?
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When you assign Ctrl1, Ctrl2 etc as shortcuts for menuitems they show up as
Ctrl+D1, Ctrl+D2. This can be worked around by creating and adding the menuitem
through code as demonstrated below:
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[C#]
//Create the menuitem
MenuItem mymenuItem = new MenuItem();
//ShortCut
mymenuItem.Shortcut = System.Windows.Forms.Shortcut.Ctrl1;
//Add Event Handler for the menuitem
mymenuItem.Click +=new EventHandler(this.mymenuItem_Click);
//ShortCut Text to be displayed
mymenuItem.Text = "My MenuItem" +"\t"+ "Ctrl+1";
//hide shortcut
mymenuItem.ShowShortcut = false;
//Add it to the bottom of the first menu
this.mainMenu1.MenuItems[0].MenuItems.Add(mymenuItem);
[VB.NET]
'Create the menuitem
Dim mymenuItem As MenuItem = New MenuItem()
'ShortCut
mymenuItem.Shortcut = System.Windows.Forms.Shortcut.Ctrl1
'Add Event Handler for the menuitem
mymenuItem.Click +=New EventHandler(Me.mymenuItem_Click)
'ShortCut Text to be displayed
mymenuItem.Text = "My MenuItem" +"\t"+ "Ctrl+1"
'hide shortcut
mymenuItem.ShowShortcut = False
'Add it to the bottom of the first menu
Me.mainMenu1.MenuItems(0).MenuItems.Add(mymenuItem)
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9.11 How do I control the position of the context menu when it is invoked via
the keyboard?
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Normally, the context menu will be shown at the center of the control when the
keyboard is used to invoke the context menu of a control (Shift+F10, for
example). You can customize the location as follows.
1. Override WndProc in the grid and check if the Message.Msg is WM_CONTEXTMENU
(0x007b)
2. If so, check if the Message.LParam is -1, which means this was due to a
keyboard message as opposed to the user right-clicking the mouse.
3. Now, call the associated ContextMenu's Show method explicitly at the
selected row position.
4. Make sure NOT to call the base class after showing the menu explicitly.
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protected override void WndProc(ref Message m)
{
if(m.Msg == 0x007B /*WM_CONTEXTMENU*/)
{
// LParam == -1 means that this is due to a keyboard message
if((int)m.LParam == -1)
{
this.contextMenu.Show();
return;
}
}
}
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[VB.Net]
Protected Overrides Sub WndProc(ByRef m As Message)
If m.Msg = 0x007B Then 'WM_CONTEXTMENU
' LParam == -1 means that this is due to a keyboard message
If (CType(m.LParam,Integer)) = -1 Then
Me.contextMenu.Show()
Return
End If
End If
End Sub
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9.12 How do I disable the default context menu of a textbox?
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To prevent the default context menu of a TextBox from showing up, assign a
empty context menu as shown below:
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[C#]
textBox1.ContextMenu = new ContextMenu();
[VB.Net]
textBox1.ContextMenu = New ContextMenu()
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9.13 How can I make the context menu to close after a set time interval?
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To automatically close the context menu after a set time interval, you can use
a Timer and send a ESC key stroke after the desired time interval as shown:
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[C#]
private void timer1_Tick(object sender, System.EventArgs e)
{
SendKeys.Send("{ESC}");
timer1.Stop();
}
private void contextMenu1_Popup(object sender, System.EventArgs e)
{
//set interval to 5 seconds
timer1.Interval = 5000;
timer1.Start();
}
[VB.Net]
Private Sub timer1_Tick(ByVal sender As Object, ByVal e As System.EventArgs)
SendKeys.Send("{ESC}")
timer1.Stop()
End Sub
Private Sub contextMenu1_Popup(ByVal sender As Object, ByVal e As
System.EventArgs)
'set interval to 5 seconds
timer1.Interval = 5000
timer1.Start()
End Sub
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9.14 How can I add an icon to my menu items?
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You need to implement an owner drawn menu to add icons to it. Take a look at
the sample on .netPlus.
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9.15 How to add a Separator in a menu?
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contextmenu.MenuItems.Add("-");
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9.16 How can I enable the mnemonics (underline) to show when my application is
launched?
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Usually the underline appears only after you press the ALT Key, but you can
enable it by changing the Operating System Settings. On Windows XP, Right Click
Desktop to bring up the Display Properties Dialog and then choose Appearance
tab and then the Effects Button and uncheck the checkbox "Hide Underlined
letters for keyboard navigation until I press the ALT Key".
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