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How to overwrite ctrl + a select all from list box?

I was hoping that this code below would overwrite it, since I am assigning new stuff. But instead it executes both, selecting all and my message box
private void EventSetter_OnHandler(object sender, KeyEventArgs e)
{
if (e.Key == Key.A && (Keyboard.IsKeyDown(Key.LeftCtrl) || Keyboard.IsKeyDown(Key.RightCtrl)))
{
System.Windows.MessageBox.Show("ctrl a");
}
}
please help thanks

If you handle the PreviewKeyDown event for the ListBox, you should be able to mark the event as handled, and the Ctrl+A should be ignored:
private void OnListBoxKeyDown(object sender, KeyEventArgs e)
{
if (e.Key == Key.A && (Keyboard.IsKeyDown(Key.LeftCtrl) || Keyboard.IsKeyDown(Key.RightCtrl)))
{
e.Handled = true;
}
}

C# - How can I block the typing of a letter on a key press?

I have a textbox with a OnKeyPress event. In this textbox I wish to input only numbers, and for some specific letters like t or m, I would want to execute a code without that letter being typed in the textbox. Small sample of what I am trying to do:
//OnKeyPressed:
void TextBox1KeyDown(object sender, KeyEventArgs e)
{
if(e.KeyCode == Keys.T || e.KeyCode == Keys.M) Button1Click(this, EventArgs.Empty);
}
This unfortunately does not prevent the input of the letter..

Set the SuppressKeyPress property from KeyEventArgs to true, like below:
private void TextBox1KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.T || e.KeyCode == Keys.M)
{
e.SuppressKeyPress = true;
Button1Click(this, EventArgs.Empty);
}
}

You could always run the TryParse on the keyDown event so as to validate as the data gets entered. It saves the user an additional UI interaction.
private void TextBox1KeyDown(object sender, KeyEventArgs e)
{
int i;
string s = string.Empty;
s += (char)e.KeyValue;
if (!(int.TryParse(s, out i)))
{
e.SuppressKeyPress = true;
}
else if(e.KeyCode == Keys.T || e.KeyCode == Keys.M)
{
e.SuppressKeyPress = true;
Button1Click(this, EventArgs.Empty);
}
}

Using KeyDown event for single action

I am trying to use the KeyDown-Event (because I like to use KeyCode) to make a single action happen. For this purpose I am using a bool variable to stop continuous actions.
Can't figure out what's wrong with my code though, and haven't found a comparable problem/solution yet...
There are 2 tabs on my tabcontrol and i want to be able to switch between them using CTRL+TAB.
The switching should happen ONCE on keydown of tab.
bool tabSwitchPossible = true;
void Form1_KeyUp(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Tab)
tabSwitchPossible = true; //Reset boolean
}
void Form1_KeyDown(object sender, KeyEventArgs e)
{
if (tabSwitchPossible && e.KeyCode == Keys.Tab && e.Modifiers == Keys.Control)
{
tabSwitchPossible = false; //Set boolean to prevent further action
if (mainTabControl.SelectedIndex >= mainTabControl.TabCount - 1)
mainTabControl.SelectedIndex = 0;
else
mainTabControl.SelectedIndex++;
return;
}
}
Is there an automatic KeyUp event fired, even when i don't release the key?!
Thanks, in advance guys...

You don't need to handle Form1_KeyUp and tabSwitchPossible varible, remove it and just copy the following code:
void Form1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Tab && e.Modifiers == Keys.Control)
{
if (mainTabControl.SelectedIndex >= mainTabControl.TabCount - 1)
mainTabControl.SelectedIndex = 0;
else
mainTabControl.SelectedIndex++;
}
}

How can I determine in KeyDown that Shift + Tab was pressed

How can I determine in KeyDown that ⇧ + Tab was pressed.
private void DateTimePicker_BirthDate_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Tab && e.Modifiers == Keys.Shift)
{
//do stuff
}
}
can't work, because never both keys are pressed exactly in the same second. You always to at first the Shift and then the other one..

It can't work, because never both keys are pressed exactly in the same second.
You're right that your code doesn't work, but your reason is wrong. The problem is that the Tab key has a special meaning - it causes the focus to change. Your event handler is not called.
If you use a different key instead of Tab, then your code will work fine.
If you really want to change the behaviour of Shift + Tab for one specific control, it can be done by overriding ProcessCmdKey but remember that many users use the Tab key to navigate around the form and changing the behaviour of this key may annoy those users.
protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
{
if (DateTimePicker_BirthDate.Focused && keyData == (Keys.Tab | Keys.Shift))
{
MessageBox.Show("shift + tab pressed");
return true;
}
else
{
return base.ProcessCmdKey(ref msg, keyData);
}
}

If you are looking for a key press combination (Tab, then Shift) like Ctrl K + D you will have to use this modified example which was taken from MSDN social.
private StringBuilder _pressedKeys = new StringBuilder();
private void DateTimePicker_BirthDate_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Tab)
{
_pressedKeys.Append("Tab");
return;
}
if (e.Modifiers == Keys.Shift)
{
_pressedKeys.Append("Shift");
return;
}
if (_pressedKeys.ToString()."TabShift")
{
MessageBox.Show("It works!");
_pressedKeys.Clear();
}
else
{
_pressedKeys.Clear();
}
base.OnKeyDown(e);
}

First hook the Tab keypress event, then during the event, check the state of the Shift key. Keep in mind that there are two shift keys; make sure you check both of them.
This very related post shows how to check the state of modifier keys:
How to detect the currently pressed key?
Edit: an insight provided by another answerer who justly deserves an upvote is that the default behavior of the tab key (to change control focus) must be suppressed.

You can find your answer in
this post

It's Simple.
You can do that using KeyUp Event in the TextBox
private void txtBox1_KeyUp(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Tab && e.Shift == false) // TAB Key Pressed
{
}
if (e.KeyCode == Keys.Tab && e.Shift == true) // TAB + SHIFT Key Pressed
{
}
}
Or
Using this you can identify Any Key is press inside the form
//Add This code inside the Form_Load Event
private void Form1_Load(object sender, EventArgs e)
{
this.KeyUp += new System.Windows.Forms.KeyEventHandler(KeyPressEvent);
this.KeyPreview = true;
}
//Create this Custom Event
private void KeyPressEvent(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Tab && e.Shift == false) // TAB Key Pressed
{
}
if (e.KeyCode == Keys.Tab && e.Shift == true) // TAB + SHIFT Key Pressed
{
}
}

It's Simple.
Using this you can identify Any Key is press inside the form
//Add This code inside the Form_Load Event
private void Form1_Load(object sender, EventArgs e)
{
this.KeyUp += new System.Windows.Forms.KeyEventHandler(KeyPressEvent);
this.KeyPreview = true;
}
//Create this Custom Event
private void KeyPressEvent(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Tab && e.Shift == false) // TAB Key Pressed
{
}
if (e.KeyCode == Keys.Tab && e.Shift == true) // TAB + SHIFT Key Pressed
{
}
}

How to detect multiple keys entered in c# keydown event of textbox?

I want to design a numeric textbox in silverlight.
I have added keydown event of TextBox to handle the keypress.
Inside event I validate the key entered in the textbox.
event as follows
private void TextBox_KeyDown(object sender, KeyEventArgs e)
{
if (!this.Validate(sender,e))
e.Handled = true;
}
function Validate as follows
private bool Validate(object sender, KeyEventArgs e)
{
if (e.Key == Key.Enter) //accept enter and tab
{
return true;
}
if (e.Key == Key.Tab)
{
return true;
}
if (e.Key < Key.D0 || e.Key > Key.D9) //accept number on alphnumeric key
if (e.Key < Key.NumPad0 || e.Key > Key.NumPad9) //accept number fomr NumPad
if (e.Key != Key.Back) //accept backspace
return false;
return true;
}
I am not able to detect shift and Key.D0 to Key.D1 i.e.
SHIFT + 1 which returns "!"
SHIFT + 3 returns "#" like wise any other special keys.
I dont want user to enter special character in to textbox.
How do i handle this keys event??

In Silverlight, I don't think there are any Modifiers in the KeyEventArgs class but instead in Keyboard:
public void KeyDown(KeyEventArgs e)
{
if (Keyboard.Modifiers == ModifierKeys.Control && e.Key == Key.D0)
{
ControlZero();
}
}

e should have a property on it that will tell you if Shift, Control or Alt are pressed. e.Modifiers can also give you additional information about which additional modifier keys have been pressed.
To cancel the character you can set e.Handled to True, which will cause the control to ignore the keypress.

textBox2.Text = string.Empty;
textBox2.Text = e.Modifiers.ToString() + " + " + e.KeyCode.ToString();