Develop Reference

Catch and process KeyPress/KeyDown without modifying text in TextBox

I currently have the following event handler which catches the Ctrl+Enter key combo in my Form code:
private void Form1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter && e.Control)
{
// Stuff
}
}
I also have two non-ReadOnly TextBoxes in the form, one of which is multiline, while the other one isn't. Whenever I hit Ctrl+Enter, the event does get handled, but it also registers as an Enter keypress when the focus is in either TextBox. What I want to do is register the key combo without the Enter keypress modifying the text in either box. Is there any way I could go about doing this?

Your best choice is use ProcessCmdKey: Just add this to your Form add it will work:
protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
{
if (keyData == (Keys.Control | Keys.Enter))
{
// Stuff
return true;
}
return base.ProcessCmdKey(ref msg, keyData);
}

You should use the PreviewKeyDown event instead and set the IsInputKey property accordingly:
private void Form1_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
{
if (e.KeyCode == Keys.Enter && e.Control)
{
// Stuff
e.IsInputKey = false;
}
}
UPDATE: From the name of your handler, I guess you added it to the Form's KeyPress/KeyDown/PreviewKeyDown event. Instead you should register the method I showed above with each TextBox's PreviewKeyDown event.
To not destroy what already works for you, you may leave your code as it is and just add a handler to the TextBox's PreviewKeyDown event where you set IsInputKey to false for the specified keys, but don't do your // Stuff.

How to enable a WinForm button in time to receive focus by tabbing

Visual Studio 2010, C#
I have a ComboBox with a DropDown, AutoComplete set to SuggestAppend and the AutoCompleteSource is from the ListItems. The user keys data into it until the have the correct entry. Utill the data matches one of the list items, a button next to the combobox is disabled.
If the user hits the tab key the autocomplete feature accepts current suggestion. It also moves on to the next control in tab sequence that is enabled. Of course since I want it to go to the disbabled button I need to enable it as soon as I validate the entry.
The problem is that none of the events I've tried, PreviewKeyDown, LostFocus, SelectedIndexChanged allow me to enable the button in time for it to be proccessed and receive the focus. It always goes to the next button in tab order which is always enabled.
I am about ready to leave the button enabled and have it give an error if pressed too soon but I don't want to do it that way. I also don't want to get into have special mode flags to keep track of when these controls receive focus. Validation seems to be a normal thing, but I'm stuck.
If the SelectedIndexChanged worked when the user made a match this would be easy. It doesn't fire when the box clears nor when a typed match is found.

You could create your own ComboBox class to encapsulate this behavior. Something like this:
using System;
using System.Windows.Forms;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
this.myComboBox1.TheButton = this.button1;
this.myComboBox1.Items.AddRange( new string[] {
"Monday",
"Tuesday",
"Wednesday",
"Thursday",
"Friday",
"Saturday",
"Sunday"
} );
button1.Enabled = false;
}
}
public class MyComboBox : ComboBox
{
public Control TheButton { get; set; }
public MyComboBox()
{
}
bool IsValidItemSelected
{
get { return null != this.SelectedItem; }
}
protected override void OnValidated( EventArgs e )
{
if ( null != TheButton )
{
TheButton.Enabled = this.IsValidItemSelected;
TheButton.Focus();
}
base.OnValidated( e );
}
protected override void OnTextChanged( EventArgs e )
{
if ( null != TheButton )
{
TheButton.Enabled = this.IsValidItemSelected;
}
base.OnTextChanged( e );
}
}
}

try this :
key_press event :
if (e.KeyData == Keys.Enter)
{
button2.Enabled = true;
button2.Focus();
}

Instead of the event hanlders you mentioned, (LostFocus, SelectedIndexChanged and PreviewKeyDown) use the "Validated" event of your combobox to set the enabled state of the button.
You may need to also manually focus on the button to force the focus to move to it though.
e.g.
private void comboBox1_Validated(object sender, EventArgs e)
{
button1.Enabled = true;
button1.Focus();
}

With some thought to the other answers here I came up with a partial senario that works without using AutoComplete. A side effect is that the PreviewKeyDown event is called a second time and therefore validation is called twice. I wonder why... maybe I should ask another question.
private void comboBox1_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e) {
if (e.KeyData == Keys.Tab) {
if (ValidationRoutine()) {
e.IsInputKey = true; //If Validated, signals KeyDown to examine this key
} //Side effect - This event is called twice when IsInputKey is set to true
}
}
private void comboBox1_KeyDown(object sender, KeyEventArgs e) {
if (e.KeyData == Keys.Tab) {
e.SuppressKeyPress = true; //Stops further processing of the TAB key
btnEdit.Enabled = true;
btnEdit.Focus();
}
}
Once you turn on AutoCompleteMode with any setting other than None, the KeyDown event doesn't fire for Tab anymore the key is silently eaten.

C# keypress doesn't capture 'delete' key

I have added a keyPress event on a ListView. With a breakpoint on my event, I can see that most of the keys trigger the event. However, a few among which, the one I'm interested in (delete), just won't trigger my event.
Is that weird ? And no, there's no broken keys on my keyboard :D
private void listView1_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)Keys.Delete)
{
ListView target = (ListView)sender;
if (target.SelectedIndices != null && target.SelectedIndices.Count > 0)
{
string ric = target.SelectedItems[0].SubItems[0].Text;
//target.Items.RemoveAt(target.SelectedIndices[0]);
ListModels.getInstance().getModel("Vols").removeRic(ric);
}
}
}

The reason for this is that the KeyPress event sends a character to the control based upon the character-key you press. However, as you'd expect, the delete key does not represent a character and is thus a non-character key.
Therefore using the KeyPress event will do nothing as you have noticed. You should use the KeyDown or KeyUp Events, either of which will work absolutely fine. The nuance being whether you want your event to fire upon pressing, or letting go of a key.

You'll want to use the KeyDown event for this.

In KeyDown use the condition as follows,
if (e.KeyCode == Keys.Delete)
{
// Your Logic....
}

Use keyDown instead; keyPress is something like a full keyDown + keyUp

The problem is that if you set EditMode property to EditOnEnter it won't fire. If you use EditOnKeyStrokeOfF2 it will fire the event

If you are looking for a solution where the user should only be able to choose from the defined items, then I believe you can do it with this:
private void DropDownRank_KeyDown(object sender, KeyEventArgs e)
{
e.SuppressKeyPress = true;
}

See this code:
private void Form1_Load(object sender, EventArgs e)
{
listView1.KeyUp += new KeyEventHandler(ListView_KeyUp);
}
/// <summary>鍵盤觸發 ListView 清單</summary>
private void ListView_KeyUp(object sender, KeyEventArgs e)
{
ListView ListViewControl = sender as ListView;
if (e.KeyCode == Keys.Delete)
{
foreach (ListViewItem eachItem in ListViewControl.SelectedItems)
{
ListViewControl.Items.Remove(eachItem);
}
}
}

I tried all the stuff mentioned above but nothing worked for me, so im posting what i actually did and worked, in the hopes of helping others with the same problem as me:
Add an event handler in the constructor:
public partial class Test
{
public Test()
{
this.RemoveHandler(KeyDownEvent, new KeyEventHandler(Test_KeyDown));
// im not sure if the above line is needed (or if the GC takes care of it
// anyway) , im adding it just to be safe
this.AddHandler(KeyDownEvent, new KeyEventHandler(Test_KeyDown), true);
InitializeComponent();
}
//....
private void Test_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Delete)
{
//your logic
}
}
}

DataGridView keydown event not working in C#

DataGridView keydown event is not working when I am editing text inside a cell.
I am assigning shortcut Alt+S to save the data, it works when cell is not in edit mode, but if it is in edit mode below code is not working
private void dataGridView1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyData == (Keys.Alt | Keys.S))
{
//save data
}
}

Whenever a cell is in edit mode, its hosted control is receiving the KeyDown event instead of the parent DataGridView that contains it. That's why your keyboard shortcut is working whenever a cell is not in edit mode (even if it is selected), because your DataGridView control itself receives the KeyDown event. However, when you are in edit mode, the edit control contained by the cell is receiving the event, and nothing happens because it doesn't have your custom handler routine attached to it.
I have spent way too much time tweaking the standard DataGridView control to handle edit commits the way I want it to, and I found that the easiest way to get around this phenomenon is by subclassing the existing DataGridView control and overriding its ProcessCmdKey function. Whatever custom code that you put in here will run whenever a key is pressed on top of the DataGridView, regardless of whether or not it is in edit mode.
For example, you could do something like this:
class MyDataGridView : System.Windows.Forms.DataGridView
{
protected override bool ProcessCmdKey(ref System.Windows.Forms.Message msg, System.Windows.Forms.Keys keyData)
{
MessageBox.Show("Key Press Detected");
if ((keyData == (Keys.Alt | Keys.S)))
{
//Save data
}
return base.ProcessCmdKey(ref msg, keyData);
}
}
Also see related, though somewhat older, article: How to trap keystrokes in controls by using Visual C#

Another way of doing it is by using the EditingControlShowing event to redirect the event handling to a custom event handler as below:
private void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
if (e.Control is DataGridViewTextBoxEditingControl tb)
{
tb.KeyDown -= dataGridView1_KeyDown;
tb.KeyDown += dataGridView1_KeyDown;
}
}
//then in your keydown event handler, execute your code
private void dataGridView1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyData == (Keys.Alt | Keys.S))
{
//save data
}
}

This is true that EditingControlShowing can help, but not if you wants to catch the Enter key. In that case, one should use the following method:
private void dataGridView_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
if (e.Control is DataGridViewTextBoxEditingControl)
{
DataGridViewTextBoxEditingControl tb = e.Control as DataGridViewTextBoxEditingControl;
tb.KeyDown -= dataGridView_KeyDown;
tb.PreviewKeyDown -= dataGridView_PreviewKeyDown;
tb.KeyDown += dataGridView_KeyDown;
tb.PreviewKeyDown += dataGridView_PreviewKeyDown;
}
}
void dataGridView_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
{
if (e.KeyData == Keys.Enter)
{
<your logic goes here>
}
}

A simpler way I just tried out is as follows:
Set the KeyPreview property of the Form to true.
Instead of catching the KeyDown event on Grid, catch the KeyDown event on Form.
Code as follows:
Private Sub form1_KeyDown(sender As Object, e As KeyEventArgs) Handles Me.KeyDown
If grd.Focused Then
'Do your work
End If
End Sub

I worked with this
private void grdViewOrderDetail_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
grdViewOrderDetail_KeyDown(null,null);
}
private void grdViewOrderDetail_KeyDown(object sender, KeyEventArgs e)
{
//Code
}

The solution
class MyDataGridView : System.Windows.Forms.DataGridView {
protected override bool ProcessCmdKey(ref System.Windows.Forms.Message msg, System.Windows.Forms.Keys keyData) {
if ( keyData == Keys.Enter ) {
.
Process Enter Key
.
}
return base.ProcessCmdKey(ref msg, keyData);
}
}
Worked perfectly for me

use PreviewKeyDown event
private void dataGridView1_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
{
}

C# trying to capture the KeyDown event on a form

I am creating a small game, the game is printed onto a panel on a windows form. Now i want to capture the keydown event to see if its the arrow keys that has been pressed, the problem however is that i can't seem to capture it.
Let me explain, on the form i have 4 buttons and various other controls and if the user for instance press one of the buttons (to trigger a game event) then the button has focus and i can't capture the movements with the arrow keys.
I tried something like
private void KeyDown(KeyEventArgs e)
{
if (e.KeyCode == Keys.Left)
{
game.MovePlayer(DonutWarsLibrary.GameObjects.Direction.E);
game.DrawObjects(panel1.CreateGraphics());
}
else if (e.KeyCode == Keys.Right)
{
game.MovePlayer(DonutWarsLibrary.GameObjects.Direction.W);
game.DrawObjects(panel1.CreateGraphics());
}
else if (e.KeyCode == Keys.Up)
{
game.MovePlayer(DonutWarsLibrary.GameObjects.Direction.N);
game.DrawObjects(panel1.CreateGraphics());
}
else if (e.KeyCode == Keys.Down)
{
game.MovePlayer(DonutWarsLibrary.GameObjects.Direction.S);
game.DrawObjects(panel1.CreateGraphics());
}
}
and then when the form key down event was pressed, i used this
private void MainForm_KeyDown(object sender, KeyEventArgs e)
{
KeyDown(e);
}
I also added keydown for the buttons and the various other controls on the windows form, but i am not getting any response back. I have setup a breakpoint inside the function to see if it's being called, but that breakpoint never triggers?
Any ideas?
The most optimal was to have a general KeyDown event that triggers (regardless of what control that currently has focus) and then calls the KeyDown method.

Have you set the KeyPreview property of the form to true? That will cause the form to get a "first look" at key events.
Update: getting this to work properly when a Button has focus seems to be a bit tricky. The Button control intercepts the arrow key presses and moves focus to the next or previous control in the tab order in a manner so that the KeyDown, KeyUp and KeyPress events are not raised. However, the PreviewKeyDown event is raised, so that can be used:
private void Form_KeyDown(object sender, KeyEventArgs e)
{
e.Handled = ProcessKeyDown(e.KeyCode);
}
// event handler for the PreViewKeyDown event for the buttons
private void ArrowButton_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
{
ProcessKeyDown(e.KeyCode);
}
private bool ProcessKeyDown(Keys keyCode)
{
switch (keyCode)
{
case Keys.Up:
{
// act on up arrow
return true;
}
case Keys.Down:
{
// act on down arrow
return true;
}
case Keys.Left:
{
// act on left arrow
return true;
}
case Keys.Right:
{
// act on right arrow
return true;
}
}
return false;
}
Still, the focus moves around in a rather ugly manner...

I believe the easiest way of solving this problem is through overriding the ProcessCmdKey() method of the form. That way, your key handling logic gets executed no matter what control has focus at the time of keypress. Beside that, you even get to choose whether the focused control gets the key after you processed it (return false) or not (return true).
Your little game example could be rewritten like this:
protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
{
if (keyData == Keys.Left)
{
MoveLeft(); DrawGame(); DoWhatever();
return true; //for the active control to see the keypress, return false
}
else if (keyData == Keys.Right)
{
MoveRight(); DrawGame(); DoWhatever();
return true; //for the active control to see the keypress, return false
}
else if (keyData == Keys.Up)
{
MoveUp(); DrawGame(); DoWhatever();
return true; //for the active control to see the keypress, return false
}
else if (keyData == Keys.Down)
{
MoveDown(); DrawGame(); DoWhatever();
return true; //for the active control to see the keypress, return false
}
else
return base.ProcessCmdKey(ref msg, keyData);
}

Override IsInputKey behaviour
You must override the IsInputKey behavior to inform that you want the Right Arrow key to be treated as an InputKey and not as a special behavior key.
For that you must override the method for each of your controls.
I would advise you to create your won Buttons, let's say MyButton
The class below creates a custom Button that overrides the IsInputKey method so that the right arrow key is not treated as a special key. From there you can easily make it for the other arrow keys or anything else.
public partial class MyButton : Button
{
protected override bool IsInputKey(Keys keyData)
{
if (keyData == Keys.Right)
{
return true;
}
else
{
return base.IsInputKey(keyData);
}
}
}
Afterwards, you can treat your keyDown event event in each different Button or in the form itself:
In the Buttons' KeyDown Method try to set these properties:
private void myButton1_KeyDown(object sender, KeyEventArgs e)
{
e.Handled = true;
//DoSomething();
}
-- OR --
handle the common behaviour in the form: (do not set e.Handled = true; in the buttons)
private void Form1_KeyDown(object sender, KeyEventArgs e)
{
//DoSomething();
}

public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
KeyPreview = true;
KeyDown += new KeyEventHandler(Form1_KeyDown);
}
void Form1_KeyDown(object sender, KeyEventArgs e)
{
System.Diagnostics.Debug.Write(e.KeyCode);
}
}