Develop Reference

How to prevent user from deleting item by pressing "backspace"?

Users will usually expand the ComboBox, pick the desired option and the ComboBox will hide other options. Now user can delete the chosen option by pressing backspace button. May I know how to prevent it?

This could be avoided by handling the PreviewKeyDown event and marking any use of the backspace key as handled
void OnComboPreviewKeyDown(object sender, KeyEventArgs e) {
if (e.Key == Key.Back) {
e.Handled = true;
}
}

You could set its DropDownStyle to DropDownList if you don't want it to be editable at all.

C# prevent default action on a listbox control when the right or left arrow keys are pressed

I have a listbox control in a windows app and I want to disable the default right and left arrow keydown event triggers. Currently when you press right or left arrows the selected item travels up and down the listbox. I want to add my own actions.

Try adding an event handler to the ListBox.KeyDown event. If the key pressed is an arrow key, set the Handled flag of the KeyPressEventArgs to true to prevent further processing.
A code example, based on an MSDN Forum post
private void listBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
If (e.KeyCode == Keys.Right || e.KeyCode == Keys.Left)
e.Handled = true;
}

You have to override the ProcessCmdKey method in the listbox control. Create a new class, derive it from listbox, then override the ProcessCmdKey.

How to ignore a checkbox change in listview?

I have a listview with a the property checkbox = true.
When the user clicks on the checkbox and changes its state (checked -> unchecked or unchecked -> checked), I catch the ItemCheck event and do some DB implementation.
I want to ask the user for confirmation before working with the DB.
When I the user cancel it's command, I want that the checkbox will return to it's status.
How can I tell the listview to ignore the state change of the checkbox?
Thank,
Mattan

In the ItemCheck event, set the NewValue to the CurrentValue:
private void listView1_ItemCheck(object sender, ItemCheckEventArgs e)
{
if (MessageBox.Show(this, "Change?", "Test", MessageBoxButtons.YesNo) == System.Windows.Forms.DialogResult.No)
e.NewValue = e.CurrentValue;
}

Check out the OnClientClick attribute of the checkBox:
http://www.dotnetcurry.com/ShowArticle.aspx?ID=93&AspxAutoDetectCookieSupport=1
Using this you can cancel the postback, as well as set the value of the checkbox back to what it was before. If you use a templatefield instead of the checkbox=true property, you can add the OnClientClick attribute to the checkbox there; otherwise you need to add it dynamically in the ListView ItemDataBound event.
EDIT Oops, didn't see the "winforms" tag; thought this was ASP.Net (which also has a ListView control). Kindly disregard.

I used the OnChecked event instead of OnCheck.
To cancel, I just set the value to the !value.

create textbox one by one on enter keypress event

am using c# vs-2005
am on project to create textbox one by one on form1 and am success on button click event my code is below.
// declare location point of textbox on Global Area.
private point txtboxstartpoint=new point(10,10);
private void button_click (Object sender,EventArgs)
{
Textbox tbx = new TextBox();
tbx.Location= txtboxstartpoint;
tbx.size=new size (200,20);
this.panel1.control.add(tbx);
txtboxstartpoint.y += 25;
}
this works fine on button click event but problem is on keypress event like on enter
i wants to create textbox on enter one by one. and for that i assume that any method have
to create and call enter keypress event on newly created control like textbox to create
another new textbox below the previous one.
Kindly help me. suggest proper code for the same.

It's very hard to understand your question, but let's try some guessing:
You have a form, and if a user presses some specific key, you'd like to create a new TextBox and show it on your form regardless which control has currently the focus in your form.
If this statement is true, you can set Form.KeyPreview to true. And add an event handler to Form.KeyDown.
Due to the fact, that you set the preview to true you'll get every keyboard hit before it will be give further to the control that has currently the focus. So here you can check if the key that was pressed is the one you're listening for. And if yes, just call your TextBoxFactory and set the e.Handled to true to prevent that this key stroke will additionally reach the currently focused control.

I use the KeyDown event, to intercept the 'F1' key to provide my small help in a very small programm. Here is the code:
private void MainForm_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.F1)
{
//Your Code here
}
}

Press Escape key to call method

Is there a way to start a method in C# if a key is pressed? For example, Esc?

use the OnKeyPress Event of your textbox and in the event
if(e.KeyCode==Keys.Escape)
{
yourTextBox.Text = string.Empty;
}

As others have mentioned, handle the KeyDown or KeyUp event of the appropriate control. The KeyPress event would work for the Escape key as well, though it will not trigger for some keys, such as Shift, Ctrl or ALt.
If you want to execute this function anytime the user presses the Escape key, then you probably want to handle the event on the Form. If you do this, you will probably also want to set the Form's KeyPreview property to true. This will allow the Form control to receive the event even if the focus is currently inside of one of the child controls.
If you want the behavior to be specific to a control, such as clearing the text within a textbox that currently has focus, then you should handle the KeyDown or KeyUp event of the TextBox control. This way, your event handler will not be triggered if the user presses the escape key outside of the textbox.
In some situations you might want to prevent child controls from handling the same event that you've just handled. You can use the SuppressKeyPress property on the KeyEventArgs class to control this behavior:
private void Form1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Escape)
{
MessageBox.Show("Escape key pressed");
// prevent child controls from handling this event as well
e.SuppressKeyPress = true;
}
}

In case someone is looking for how to do this in a console application
if (Console.ReadKey().Key == ConsoleKey.Escape)
{
return;
}

I am writing WinForms application. User fills the textbox and if he wants to delete everything, he just clicks esc key on keyboard
I think you need to handle the KeyDown event.

You have to switch the form property "KeyPreview" to true or your events will not be fired. Handling these events alone will not do anything even though the events are correct. It will look to you like nothing really happens even though you have subscribed the proper event handlers.

First in Properties do > KeyPreview : True
Then :
private void Form1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Escape)
{
//call your method here
}
}

Are you writing a Console application, a WinForms application or something else? Are you trying to capture the ESC key at all times (regardless of the focused window/application) or something else?
More context required.
If you're writing a Console app, then you should start looking at things like Console.ReadKey...
http://msdn.microsoft.com/en-us/library/system.console.readkey.aspx

With Event KeyPress...
//Escape
if (e.KeyChar == '')
{
this.DialogResult = DialogResult.Cancel;
e.Handled = true;
}

You can use KeyUp event too. I prefer it though.
private void Window_KeyUp(object sender, System.Windows.Input.KeyEventArgs e) {
if (e.Key == Key.Escape) {
//WHAT WILL HAPPEN INSERT HERE
}
}

The basic answer is listed here several time
Implement Form_KeyDown
Private Sub frmCustomerSearch_KeyDown(sender As Object, e As KeyEventArgs) Handles Me.KeyDown
Try
If e.KeyCode = Keys.Escape Then
ClearFindForm()
End If
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
Set form.keyPreview
form.KeyPreview = true
The additional thing you need to check is whether you have a button capturing ESC so it can be the form.cancelButton
to be sure ...
form.CancelButton = nothing
This is sneaky. If you have set that and forgot about it, the Escape key will not trigger the KeyDown event.
I was led to this because a button set to be the form.CancelButton does not seem to fire if it is invisible or on a non visible tab,so KEYDOWN is your only option.