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Allow only specific keys on TextBox

I have a question. Examples that i find is on a "KeyPress" and they are not longer working on WPF
Can you tell me, how to allow only specified keys from keybord to be write on WPF textbox? I know about keyUp and Down functions, but how to define letters that i want to by type into it?
I think it will be easier, if i will post my code and i tell u what i want to do. What to change here?
private void textBox_KeyDown(object sender, KeyEventArgs e)
{
//something here to only allow "A" key to be pressed and displeyed into textbox
if (e.Key == Key.A)
{
stoper.Start();
}
}
private void textBox_KeyUp(object sender, KeyEventArgs e)
{
if (e.Key == Key.A)
{
//here i stop the stopwatch to count time of pressing the key
stoper.Stop();
string aS = stoper.ElapsedMilliseconds.ToString();
int aI = Convert.ToInt32(aS);
stoper.Reset();
}
}

You can use PreviewKeyDown and use e.Key to filter out what you need.
Or, in any place of your code you can use Keyboard class:
if (Keyboard.IsKeyDown(Key.E)) { /* your code */ }
UPDATE:
To forbid a key, you need to set event as handled:
if (e.Key == Key.E)
{
e.Handled = true;
MessageBox.Show($"{e.Key.ToString()} is forbidden");
}

That thing works pretty fine to me (thanks for #JohnyL):
private void textBox_KeyDown(object sender, KeyEventArgs e)
{
//something here to only allow "A" key to be pressed and displeyed into textbox
if (e.Key == Key.A)
{
stoper.Start();
}
else
e.Handled = true;
}
private void textBox_KeyUp(object sender, KeyEventArgs e)
{
if (e.Key == Key.A)
{
//here i stop the stopwatch to count time of pressing the key
stoper.Stop();
string aS = stoper.ElapsedMilliseconds.ToString();
int aI = Convert.ToInt32(aS);
stoper.Reset();
}
}

Detecting Enter key press on a button c#

This piece of code detect most keys and puts it in a messageBox, but one of the keys it doesn't is the enter key. *Note it is a key_down method
MessageBox.Show(e.KeyData.ToString());
so far I have tried so many methods to fix and searched a lot for an answer
I have tried this
private void button1_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
{
if (e.KeyCode == Keys.Enter)
{
MessageBox.Show("this is it");
e.IsInputKey = true;
}
}
it says 0 references which I know I'm not calling the method but where do I call it?
where ever I do call it, it gives an error.

you delete this line
e.IsInputKey = true;
private void button1_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
{
if (e.KeyCode == Keys.Enter)
{
MessageBox.Show("this is it");
//e.IsInputKey = true;
}
}
or
private void button1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter)
{
MessageBox.Show("this is it");
//e.IsInputKey = true;
}
}

In your Form1 Design Properties:
AcceptButton Property set dropdown to button1 or the name of your Button
KeyUp Event of your Button
private void button1_KeyUp(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter)
{
MessageBox.Show("Enter key has been pressed");
}
}
or
private void button1_KeyUp(object sender, KeyEventArgs e)
{
button1_KeyDown(sender, e);
}
private void button1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter)
{
MessageBox.Show("Enter key has been pressed");
}
}

Put this line soon after: InitializeComponents(); -->
button1.PreviewKeyDown +=new PreviewKeyDownEventHandler(button1_PreviewKeyDown);
.
The event you're trying to use will only fire when you focus on that button. The focus is passed in 2 different ways ( via user interaction ) one of which is an actual mouse click on that element and another is "tabbing" on to the control, and make sure you read about "Events" and "EventsHandlers"

Enter key in C#

I have a code like below
private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == 13)
{
if (!textBox1.AcceptsReturn)
{
button1.PerformClick();
}
}
}
After I hit Enter, it'll send a message to another textbox and begin a new line. Can anyone help me to bring the cursor back to its first line?
I tried textBox1.SelectionStart, SelectionLength and Focus but it doesn't work, is there any another way?

You can prevent that the keypress is passed on to the control by setting the KeyPressEventArgs.Handled property to true:
private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == 13)
{
if (!textBox1.AcceptsReturn)
{
button1.PerformClick();
e.Handled = true;
}
}
}
As you mentioned in a comment that you are implementing a chat app, you also might want to implement the typical behavior of Shift+Return inserting a new line:
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyValue == 13 && !e.Shift)
{
if (!textBox1.AcceptsReturn && !string.IsNullOrEmpty(textBox1.Text))
{
button1.PerformClick();
textBox1.Text = "";
e.Handled = true;
}
}
}

To set cursor position to the beginning of a textbox, use the following...
I will hazard a guess that you didn't use these in combination with each other...
textBox1.SelectionStart = 0;
textBox1.SelectionLength = 0;

Detect Enter Key C#

I have the following code which does not show the MessageBox when enter/return is pressed.
For any other key(i.e. letters/numbers) the MessageBox shows False.
private void cbServer_TextChanged(object sender, EventArgs e)
{
if (enterPressed)
{
MessageBox.Show("Enter pressed");
}
else
MessageBox.Show("False");
}
private void cbServer_Keydown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter || e.KeyCode == Keys.Return)
{
enterPressed = true;
MessageBox.Show("Enter presssed: " + enterPressed);
}
else
enterPressed = false;
}
Any ideas?
EDIT: Above code, I thought the issue was with the _Keydown even so I only posted that.

in your form designer class (formname.designer.cs) add this :
this.KeyPress += new System.Windows.Forms.KeyPressEventHandler(this.Login_KeyPress);
and add this code to backbone code (formname.cs):
void Login_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)13)
MessageBox.Show("ENTER has been pressed!");
else if (e.KeyChar == (char)27)
this.Close();
}

This is because when you press Enter TextChanged event won't fire.

private void textBox_PreviewKeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key.Enter)
{
MessageBox.Show("Enter key pressed");
}
else if (e.Key == Key.Space)
{
MessageBox.Show("Space key pressed");
}
}
Use PreviewKeyDown event to detect any key before shown in textbox or input

void cbServer_PreviewKeyDown(object sender, System.Windows.Forms.PreviewKeyDownEventArgs e)
{
// Check if User Presses Enter
if (e.KeyCode == System.Windows.Forms.Keys.Return)
{
// Here: user pressed ENTER key
}
else
{
// Here: user did not press ENTER key
}
}

Keypress To Simulate A Button Click in C#

Ok, so I'm in the process of making a Tic-Tac-Toe game to help me learn C#.
I'm attempting to add a bit of functionality to it, so I want people to be able to use the NumPad on a computer to simulate clicking the buttons.
Here is what I have but when I use the NumPad the buttons don't click.
Can any of you see a reason as to why?
//===============================
// start NumPad Simulate Clicks
// NumPad MyButtons
// 7 8 9 1 2 3
// 4 5 6 4 5 6
// 1 2 3 7 8 9
//===============================
public void myControl_NumPad7(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.NumPad7)
{
button1_Click(null, null);
}
}
public void myControl_NumPad8(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.NumPad8)
{
button2_Click(null, null);
}
}
public void myControl_NumPad9(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.NumPad9)
{
button3_Click(null, null);
}
}
public void myControl_NumPad4(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.NumPad4)
{
button4_Click(null, null);
}
}
public void myControl_NumPad5(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.NumPad5)
{
button5_Click(null, null);
}
}
public void myControl_NumPad6(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.NumPad6)
{
button6_Click(null, null);
}
}
public void myControl_NumPad1(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.NumPad1)
{
button7_Click(null, null);
}
}
public void myControl_NumPad2(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.NumPad2)
{
button8_Click(null, null);
}
}
public void myControl_NumPad3(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.NumPad3)
{
button9_Click(null, null);
}
}

EDIT
Noticed that I have to be clearer about what I mean...
From the code you posted I suspect you have 9 controls you added your key-events to. These controls will only receive key-events when they are focused.
To handle keys globally for the form, you have to set Form.KeyPreview to true. Also, I'd not handle the keys the way you do, but add a Form.KeyDown event and write something like:
switch (e.KeyCode)
{
case Keys.NumPad9:
e.Handled = true;
button3.PerformClick();
break;
case Keys.NumPad8:
e.Handled = true;
button2.PerformClick();
break;
// And so on
}
This will handle the NumPad-Keys within the form - you can then remove all the event handlers you posted in your question.
To programatically "click" a button, you should use the Button.PerformClick() method, as more than one event handler may be added to the click event, which would not be called otherwise.
EDIT 2
Syntax for the switch-statement was invalid. Of course every "case" must start with the case keyword... Now it should work.

You need to use button1.PerformClick(); for every button to invoke event correctly, here's info.