Develop Reference

C# Key Events - KeyDown

I have a Windows Form Application. I want some functions to work with the space key. But when I press the space key, the function I want is not working and it goes to the next form. (I did KeyPreview = true)
private void Form7_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Space)
{
IEyeTracker eyeTracker = EyeTrackingOperations.FindAllEyeTrackers().FirstOrDefault();
GazeDataStop(eyeTracker);
}
}

Because:
1- If you have buttons, ... keydown won't work as form won't have focus anymore
2-you must handle the keydown so that it is not passed to ohter controls
Solution for 1:
set KeyPreview property of your form to true
Solution for 2:
set e.Handled = true:
private void Form7_KeyDown(object sender, KeyEventArgs e)
{
e.Handled = true;
if (e.KeyCode == Keys.Space)
{
IEyeTracker eyeTracker = EyeTrackingOperations.FindAllEyeTrackers().FirstOrDefault();
GazeDataStop(eyeTracker);
}
}

c# detect and send f13-f24 keys

I need an application that can detect the keypress of F13-F24. I tried making a form and setting keydown and Keypress events and printing in a messagebox the key pressed but when i press F13-F24, i don't get a messagebox
private void Form1_KeyDown(object sender, KeyEventArgs e)
{
MessageBox.Show(e.KeyCode.ToString());
}
private void Form1_KeyPress(object sender, KeyPressEventArgs e)
{
MessageBox.Show(e.KeyChar.ToString());
}
This didn't seem to work. How can I do this?

You can capture this using System.Windows.Forms.KeyEventHandler.
The KeyEventHandler will provide a KeyEventArgs object that includes a KeyCode property. KeyCode is a System.Windows.Forms.Keys enumeration and supports F1-F24.
private void KeyDownHandler(object sender, System.Windows.Forms.KeyEventArgs e) {
if (e.KeyCode == Keys.F13) {
//F13
} else if (e.KeyCode == Keys.F14) {
//F14
} else if (e.KeyCode == Keys.F15) {
//F15
}
// etc
}
If you don't have a keyboard capable of sending higher F-keys, the F13-F24 keys are the equivilent of SHIFT-F1-SHIFT-F12. You can capture this sequence using the KeyCode and Modifiers (Modifiers == Keys.Shift) properties together.

Windows 10 doesn't recognize the higher Function keys 13-24. You can test this by turning on the Windows Narrator functionality, and then press Shift -F1. The narrator just says "Shift F1", not "F13"
So, instead I recommend that you just detect Shift -F1 to Shift -F12 instead.
private void Form1_PreviewKeyDown(object sender, KeyPressEventArgs e)
{
if(e.KeyCode == Keys.F1 && e.Modifiers == Keys.Shift)
{
MessageBox.Show("Shift-F1 pressed");
}
}
As MstfAsan commented, you need to use the PreviewKeyDown eventhandler and set the form's KeyPreview property to True for this to work

Focus selected controls by pressing Enter Key

In C# windows application to navigate all control of a Form (using Enter Key) I am using the below code:
private void Form1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyData == System.Windows.Forms.Keys.Enter)
{
SendKeys.Send("{TAB}");
}
}
N.B.: Form Property KeyPreview = True;
The above code works fine but when I am going to navigate between two dateTimePicker (dateTimePicker1, dateTimePicker2) pressing Enter Key.
When Form open Focus on dateTimePicker1 and press Enter Key then Focus dateTimePicker2 and press Enter Key Focus dateTimePicker1.
The below code works fine without the above code. What is the best way to navigate the two dateTimePicker using the above code or any other way?
private void dateTimePicker1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter) {
dateTimePicker2.Focus();
}
}
private void dateTimePicker2_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter) {
dateTimePicker1.Focus();
}
}
Anybody please help me.

You can subscribe your two DateTimePickers to the same event handler instead of using two events, and use the sender object:
private void dateTimePicker_KeyDown(object sender, KeyEventArgs e)
{
var dtp = sender as DateTimePicker;
if (e.KeyCode == Keys.Enter)
{
if (dtp?.Name[dtp.Name.Length - 1] == '1')
dateTimePicker2.Focus();
else dateTimePicker1.Focus();
}
}
Just don't forget to change the value of the KeyDown event in the properties window of the both DateTimePickrs to point to this event.

How do I tell when the enter key is pressed in a TextBox?

Basically, I want to be able to trigger an event when the ENTER key is pressed. I tried this already:
private void input_KeyDown(object sender, KeyEventArgs e)
{
if (e.Equals("{ENTER}"))
{
MessageBox.Show("Pressed enter.");
}
}
But the MessageBox never shows up. How can I do this?

Give this a shot...
private void input_KeyDown(object sender, KeyEventArgs e)
{
if(e.KeyData == Keys.Enter)
{
MessageBox.Show("Pressed enter.");
}
}

To add to #Willy David Jr answer: you also can use actual Key codes.
private void input_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyChar == 13)
{
MessageBox.Show("Pressed enter.");
}
}

You can actually just say
private void input_KeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key.Enter)
{
MessageBox.Show("Pressed enter.");
}
}

You can use the Keypress event. If you are just looking for the "Enter" keypress, then you probably don't care about modifier keys (such as Shift and/or Ctrl), which is why most would use KeyDown instead of Keypress. A second benefit is to answer the question that is almost always asked after implementing any of the other answers: "When I use the referenced code, why does pressing "Enter" cause a beep?" It is because the Keypress event needs to be handled. By using Keypress, you solve both in one place:
private void input_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.Enter)
{
// Your logic here....
e.Handled = true; //Handle the Keypress event (suppress the Beep)
}
}

If your Form has AcceptButton defined, you won't be able to use KeyDown to capture the Enter.
What you should do is to catch it at the Form level. Add this code to the Form:
protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
{
if ((this.ActiveControl == myTextBox) && (keyData == Keys.Return))
{
//do something
return true;
}
else
{
return base.ProcessCmdKey(ref msg, keyData);
}
}

You can also do this:
private void input_KeyDown(object sender, KeyEventArgs e)
{
if(e.KeyCode== Keys.Enter)
{
//Your business logic here.
}
}
The only difference with KeyCode vs KeyData is that KeyCode can detect modifiers combination with KeyCode (e.g. CTRL, Shift + A) which you don't need here.

Fast forward 2022, the following statement above is completely other way around.
"The only difference with KeyCode vs KeyData is that KeyCode can detect modifiers combination with KeyCode (e.g. CTRL, Shift + A) which you don't need here."
the KeyDown event e.KeyCode does not trigger Keys.Enter

how to make a multiline textbox not accept Enter and Backspace

I have a multiline textbox which shouldn't accept alphabets, numbers, newline(enter key) and backspace. In short, the textbox.Text shouldn't be editable. But I do want the textbox to accept two shortcut keys - control and control+R. One way I can make the textbox un-editable is by making it read-only. But then the textbox wont accept any keystroke at all. In short, my shortcuts ( control and control+R) wont work( Control + R) with read-only method.
Can anyone help in this regard. That's all I have to do.
One thing I could do here is not to make the textbox read-only and then restrict the characters(alphabets and digits) that could be inputted in the textbox. With this code:
private void txtResult_KeyPress(object sender, KeyPressEventArgs e)
{
// only modifier keys, escape, enter, backspace etc is accepted now
e.Handled = !char.IsControl(e.KeyChar);
}
private void txtResult_KeyDown(object sender, KeyEventArgs e)
{
if (e.Control == true)
{
if (e.KeyCode == Keys.R)
{
// do something
}
else
{
//do something
}
}
if (e.KeyCode == Keys.Escape)
{
//do something
}
}
With this technique I can get the shortcuts(control and control+R) working. But the trouble with this method is that Enter and Backspace keys work as well making it possible to edit the text of textbox. How can I specifically restrict Enter and Backspace key being registered from the textbox, but let Control and Escape??

did you try SuppressKeyPress = true ?
private void textBox2_KeyDown(object sender, KeyEventArgs e)
{
if (e.Control == true)
{
if (e.KeyCode == Keys.R)
{
// do something
}
else
{
//do something
}
}
else
e.SuppressKeyPress = true;
}

Since you are handling the keys in the KeyDown event handler, why not have your KeyPress handler return that all keystrokes are handled?
So just set e.Handled = true no matter what. I believe the backspace and enter would be interpreted as control characters, also.

The Enter and Backspace keys won't work if the textbox is set to ReadOnly, as you suggested early on in the question that you had done. Make sure the property is still set to true. You can either set it in the Properties window, or through code like so:
myTextBox.ReadOnly = true;
Then, you need to handle the KeyDown event for the textbox control, and watch for the specific keys that you're interested in. Something like this:
private void myTextBox_KeyDown(object sender, KeyEventArgs e)
{
if (e.Control)
{
if (e.KeyCode == Keys.R)
{
MessageBox.Show("Pressed Ctrl+R");
}
else
{
MessageBox.Show("Pressed Ctrl");
}
}
else if (e.KeyCode == Keys.Escape)
{
MessageBox.Show("Pressed Esc");
}
}
This works exactly as expected, as long as the textbox is set to read-only. No other keys are recognized, and the user cannot change or modify any of the text in the textbox. You don't need to suppress the keypresses, as the control is already doing that when you set it to read-only. You also don't need to handle both the KeyDown and KeyPress events. KeyPress won't work for you anyway, as it doesn't let you handle control characters.