CODEWITHSUNDEEP
c#winformskeypressonkeydown
vexe
vexe

Reputation: 5615

how to detect the (Shift+Delete) key press?

I'm making a custom Terminal in a C# winform. When the user presses a key in the TextBox that I'm using I have to make sure that it's a valid key. I need to prevent them from being able to delete stuff and do whatever they want. I managed to handle the backspace and delete and others via the KeyPress and KeyDown events. I had a problem with the user pressing shift + delete. It deletes stuff just like backspace. I don't know what the integer equivalent of it is. I made a C++ program to detect it, it was simple:

char c = _getch();
cout << (int)c << endl;

I got a -32. It didn't work in C#.

After so many tries to encircle its value, I found that it was 0. It worked, at least for yesterday, but now it doesn't. I'm also able to delete stuff with the shift+delete.

Here's my key validation method:

private bool IsInvalidKey(char key)
{
  bool condition1 = !IsAsciiKey(key) && !IsNavigatingKey(key); // by navigation I mean: left, right, end and home keys.
  bool condition2 = (GetCaretPosition() == CaretPosition.OutsideCommandLine && !IsNavigatingKey(key));
  bool condition3 = ((key == (char)Keys.Back) && GetCaretPosition() == CaretPosition.BeginningOfCommandLine);
  return (condition1 || condition2 || condition3);
}

private bool IsAsciiKey(char key)
{
  return ((int)key > 0 && (int)key <= 127); // char(0) should be shift+delete
}

How can I detect this key and where (in which event, KeyPress or KeyDown?)

I'm using a normal TextBox control, not a RichTextBox.

Upvotes: 3

Views: 4723

Answers (2)

Servy
Servy

Reputation: 203830

Rather than trying to look at each individual key through the use of the KeyDown event, what you really need to do is do all of your validation in the TextChanged event, and you need to validate the entire entry (not just the last character) every time anything changes. This is the only way to support everything that the user could possibly do. As an example, the user could use the mouse to cut or paste text in the textbox, and that doesn't trigger any key press events at all.

If you want, you can handle the key press event as well so that you can prevent invalid characters/key from changing the text in the first place (and causing a full validation) but that's basically like performing client side validation of a field on a webpage; it's nice to do, but since you can get around it you can't only use it.

Upvotes: 4

Jens Granlund
Jens Granlund

Reputation: 5070

You could try something like this in the KeyDown event.

private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Shift && e.KeyCode == Keys.Delete) e.Handled = true;
}

Upvotes: 4

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