Develop Reference

Get long combination key (password) entered in WPF Window

I'm having a bit of confusion regarding my post here. How to get combination key about 5-10 keys? I'm intended to capture "!qaz$esz" key without double quotes.
My application is a full screen application that prevent access to desktop before entering a right key to enable desktop access. I have kill explorer.exe and disable the Task Manager when the program start and enable it back after combination password is correct:-
private void Window_Loaded(object sender, RoutedEventArgs e)
{
/**
* 1. KILL EXPLORER
* 2. DISABLE KEY TO TERMINATE
* = Alt + F4
* = Win + Tab
* = Win + D
* = etc
* 3. ACCEPT SPECIFIC KEY ONLY TO UNLOCK TO MINIMIZE AND SET TOP = FALSE
*
*
* **/
RegistryKey regkey = SetKey(TaskManager.Disabled);
regkey.Close();
}
public static RegistryKey SetKey(TaskManager command)
{
RegistryKey mKey;
string subKey = "Software\\Microsoft\\Windows\\CurrentVersion\\Policies\\System";
mKey = Registry.CurrentUser.CreateSubKey(subKey);
switch (command)
{
case TaskManager.Enabled:
mKey.SetValue("DisableTaskMgr", 0);
break;
case TaskManager.Disabled:
mKey.SetValue("DisableTaskMgr", 1);
break;
}
return mKey;
}
But something must be lack on my code where I cannot detect the combination code that more to password.
Below code are what I'm testing to see if my entered key is captured.
public MainWindow()
{
InitializeComponent();
AddHandler(Keyboard.KeyDownEvent, (KeyEventHandler)HandleKeyDownEvent);
}
private void HandleKeyDownEvent(object sender, KeyEventArgs e)
{
if (e.Key == Key.Tab && (Keyboard.Modifiers & (ModifierKeys.Control | ModifierKeys.Shift)) == (ModifierKeys.Control | ModifierKeys.Shift))
{
MessageBox.Show("CTRL + SHIFT + TAB trapped"); // Working
}
if (e.Key == Key.Tab && (Keyboard.Modifiers & ModifierKeys.Control) == ModifierKeys.Control)
{
MessageBox.Show("CTRL + TAB trapped"); // Working
}
if (e.Key == Key.F4 && Keyboard.Modifiers.HasFlag(ModifierKeys.Alt))
{
MessageBox.Show("ALT + F4 trapped"); // Not working
}
if (e.Key == Key.D && Keyboard.Modifiers.HasFlag(ModifierKeys.Windows))
{
MessageBox.Show("WIN + D trapped"); // Not working
}
if ((Keyboard.IsKeyDown(Key.LeftShift) && e.Key == Key.D1) && e.Key ==Key.Q && e.Key == Key.A && e.Key == Key.Z && e.Key == Key.D4 && e.Key == Key.E && e.Key == Key.S && e.Key == Key.Z)
{
MessageBox.Show("COMBOKEY"); // Not working
// RUN EXPLORER
// ENABLE TASK MANAGER
}
}
What is not settle is WINLOGO + D, ALT + TAB, ALT + F4 and LONG COMBINATION KEY.
I have try some of the code from here:-
https://stackoverflow.com/a/5750757/3436326
https://stackoverflow.com/a/17088823/3436326
I have see some discussion/posting/article on writing to LowLevelAPI. I'm not familiar accessing low level API and apply it on WPF application:-
http://www.tamas.io/c-disable-ctrl-alt-del-alt-tab-alt-f4-start-menu-and-so-on/
https://www.codeproject.com/articles/14485/low-level-windows-api-hooks-from-c-to-stop-unwante

e.Key == Key.Q && e.Key == Key.A
If e.Key is equal to Key.Q, it cannot be equal to Key.A at the same time. That’s why it’s not working. What you want to detect is the sequence of those keys, and since you only have a key listener, you have to take care of managing the state yourself:
private int passwordState = 0;
private void HandleKeyDownEvent(object sender, KeyEventArgs e)
{
// other checks
else if (Keyboard.IsKeyDown(Key.LeftShift) && e.Key == Key.D1)
passwordState = 1; // first key of the password
else if (passwordState == 1 && e.Key == Key.Q)
passwordState = 2;
else if (passwordState == 2 && e.Key == Key.A)
passwordState = 3;
else if (passwordState == 3 && e.Key == Key.Z)
passwordState = 4;
else if (passwordState == 4 && e.Key == Key.D4)
passwordState = 5;
else if (passwordState == 5 && e.Key == Key.E)
passwordState = 6;
else if (passwordState == 6 && e.Key == Key.S)
passwordState = 7;
else if (passwordState == 7 && e.Key == Key.Z)
{
passwordState = 0;
// correct password
MessageBox.Show("COMBOKEY");
}
else
passwordState = 0; // some other/unexpected key: reset password state
}
But that is really annoying to maintain, so why don’t you have a special key combination instead that simply shows a modal prompt for the user to enter the password? Yes, you would show the user a clear password prompt then that they could accidentally discover, but what’s the problem with that?

WPF Key is digit or number

I have previewKeyDown method in my window, and I'd like to know that pressed key is only A-Z letter or 1-0 number (without anyF1..12, enter, ctrl, alt etc - just letter or number).
I've tried Char.IsLetter, but i need to give the char, so e.key.ToString()[0] doesn't work, because it is almost everytime a letter.

Something like this will do:
if ((e.Key >= Key.A && e.Key <= Key.Z) || (e.Key >= Key.D0 && e.Key <= Key.D9) || (e.Key >= Key.NumPad0 && e.Key <= Key.NumPad9))
Of course you will also have to check that no modifier keys like CTRL are pressed according to your requirements.

e.Key is giving you a member of the enum System.Windows.Input.Key
You should be able to do the following to determine whether it is a letter or a number:
var isNumber = e.Key >= Key.D0 && e.Key <= Key.D9;
var isLetter = e.Key >= Key.A && e.Key <= Key.Z;

In your specific case the answer provided by Jon and Jeffery is probably best, however if you need to test your string for some other letter/number logic then you can use the KeyConverter class to convert a System.Windows.Input.Key to a string
var strKey = new KeyConverter().ConvertToString(e.Key);
You'll still need to check to see if any modifier keys are being held down (Shift, Ctrl, and Alt), and it should also be noted that this only works for Letters and Numbers. Special characters (such as commas, quotes, etc) will get displayed the same as e.Key.ToString()

try this, it works.
private void txbNumber_KeyDown(object sender, KeyEventArgs e)
{
if (e.Key >= Key.D0 && e.Key <= Key.D9) ; // it`s number
else if (e.Key >= Key.NumPad0 && e.Key <= Key.NumPad9) ; // it`s number
else if (e.Key == Key.Escape || e.Key == Key.Tab || e.Key == Key.CapsLock || e.Key == Key.LeftShift || e.Key == Key.LeftCtrl ||
e.Key == Key.LWin || e.Key == Key.LeftAlt || e.Key == Key.RightAlt || e.Key == Key.RightCtrl || e.Key == Key.RightShift ||
e.Key == Key.Left || e.Key == Key.Up || e.Key == Key.Down || e.Key == Key.Right || e.Key == Key.Return || e.Key == Key.Delete ||
e.Key == Key.System) ; // it`s a system key (add other key here if you want to allow)
else
e.Handled = true; // the key will sappressed
}

Add a reference to Microsoft.VisualBasic and use the VB IsNumeric function, combined with char.IsLetter().

bit of a cludge but it works :)
private void TextBox_KeyDown(object sender, KeyEventArgs e)
{
Regex R = new Regex("^([A-Z]|[0-9]){1}$");
var strKey = new KeyConverter().ConvertToString(e.Key);
if(strKey.Length > 1 )
{
strKey = strKey.Replace("NumPad", "").Replace("D", "");
}
if (strKey.Length == 1)
{
if (!R.IsMatch(strKey))
{
e.Handled = true;
}
}
else
{
e.Handled = true;
}
}

Can you put some code to show what you intend? Shouldn't this work for you
if(e.key.ToString().Length==1)
`Char.IsLetter(e.key.ToString()[0])`
else
//

Setting an attribute to only allow doubles in a textbox

I remember using some attribute on the getter/setter that would limit the input to a certain datatype, length etc. IE [Attribute something something].
Any ideas?
Thanks

Did you mean the ValidateInput attribute available in System.Web.Mvc?
Also, you could probably use a MaskedTextBox if you're doing WinForms.

One way to do it (if you want to keep using a standard text box) would be to make an event for the text changed event of the text box, and in that, read the text to make sure that it contains only numbers (and an optional period in the case of a double)

Winforms? Have you considered using masked Textbox control?
http://msdn.microsoft.com/en-us/library/system.windows.forms.maskedtextbox.aspx

Winforms? Why not use a NumericUpDown?
http://msdn.microsoft.com/en-us/library/57dy4d56.aspx
http://msdn.microsoft.com/en-us/library/system.windows.forms.numericupdown.aspx
If you need scientific notation you can do :
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
TextBox tBox = (TextBox)sender;
if (!((e.KeyCode >= Keys.D0 && e.KeyCode <= Keys.D9)
|| (e.KeyCode >= Keys.NumPad0 && e.KeyCode <= Keys.NumPad9)
|| (e.KeyCode == Keys.Decimal && !(tBox.Text.Contains('.'))
&& !(tBox.Text.Length == 0)
&& !((tBox.Text.Length == 1)
&& (tBox.Text.Contains('-') || tBox.Text.Contains('+'))))
|| (e.KeyCode == Keys.OemPeriod && !(tBox.Text.Contains('.'))
&& !(tBox.Text.Length == 0)
&& !((tBox.Text.Length == 1)
&& (tBox.Text.Contains('-') || tBox.Text.Contains('+'))))
|| (e.KeyCode == Keys.Subtract && ((tBox.Text.Length == 0) ||
tBox.Text.EndsWith("e") || tBox.Text.EndsWith("E")))
|| (e.KeyCode == Keys.OemMinus && ((tBox.Text.Length == 0) ||
tBox.Text.EndsWith("e") || tBox.Text.EndsWith("E")))
|| (e.KeyCode == Keys.Add && ((tBox.Text.Length == 0) ||
tBox.Text.EndsWith("e") || tBox.Text.EndsWith("E")))
|| (e.KeyCode == Keys.Oemplus && ((tBox.Text.Length == 0) ||
tBox.Text.EndsWith("e") || tBox.Text.EndsWith("E")))
|| e.KeyCode == Keys.Delete
|| e.KeyCode == Keys.Back
|| e.KeyCode == Keys.Left
|| e.KeyCode == Keys.Right
|| (e.KeyCode == Keys.E) && !(tBox.Text.Contains('e')) &&
(tBox.Text.Contains('.') && !tBox.Text.EndsWith("."))))
{
e.SuppressKeyPress = true;
}
}
This will deny input of any pattern which is not consistent with a numeric value. Minus signs are only allowed at the beginning of the string (to indicate a negative number) and after an e or E to indicate a negative exponent. Plus signs follow the same rule as minus. Only one decimal point is allowed and it must follow at least one number. Only one e or E is allowed and it must follow a decimal point and at least one number after the decimal point.
You could also allow things like the Help, Tab, etc, keys if it would interfere with other aspects of your program function.
Note that this does not prevent incomplete numbers (ie: 1.37E- or -13. from being entered so you would probably want to check the string in any case. This at least denies any immediately invalid entries.
You might do something like (in the same handler, before the other logic):
if (e.KeyCode == Keys.Enter)
{
textBox1_Validating(sender, new CancelEventArgs());
return;
}
The above only gives the enter key the normal 'feel' for input (force validation). Leaving the textbox (going out of focus) will also trigger validation where you might do something like :
private void textBox1_Validating(object sender, CancelEventArgs e)
{
TextBox tBox = (TextBox)sender;
double tstDbl;
if (!double.TryParse(tBox.Text, out tstDbl))
{
//handle bad input
}
else
{
//double value OK
doSomething(tstDbl);
}
}

More efficient way of screening KeyCodes on KeyDown Event

I'm trying to fire an event perform some work when the user tries to enter only useful data into a form-field using the KeyDown event. But, I keep getting false alarms because the KeyDown event works for just any key!
I'm trying not to make the event fire for buttons such as "Alt, Control, Shift, Esc, the F-keys, etc." What's the best way of doing this?
What I have so far is this:
private void formControl_KeyModified(object sender, KeyEventArgs e)
{
if (e.KeyCode != Keys.Shift && e.KeyCode != Keys.CapsLock && e.KeyCode != Keys.Tab && e.KeyCode != Keys.Escape &&
e.KeyCode != Keys.Insert && e.KeyCode != Keys.Home && e.KeyCode != Keys.End && e.KeyCode != Keys.PageUp &&
e.KeyCode != Keys.PageDown && e.KeyCode != Keys.Up && e.KeyCode != Keys.Down && e.KeyCode != Keys.Left &&
e.KeyCode != Keys.Right && e.KeyCode != Keys.Control && e.KeyCode != Keys.Alt && e.KeyCode != Keys.NumLock &&
e.KeyCode != Keys.Insert && e.KeyCode != Keys.None && e.KeyCode != Keys.PrintScreen && e.KeyCode != Keys.Help &&
e.KeyCode != Keys.ControlKey && e.KeyCode != Keys.ShiftKey && e.KeyCode != Keys.Sleep && e.KeyCode != Keys.LWin &&
e.KeyCode != Keys.RWin && e.KeyCode != Keys.RMenu && e.KeyCode != Keys.LMenu && e.KeyCode != Keys.LShiftKey &&
e.KeyCode != Keys.RShiftKey && e.KeyCode != Keys.Pause && e.KeyCode != Keys.F1 && e.KeyCode != Keys.F2 &&
e.KeyCode != Keys.F3 && e.KeyCode != Keys.F4 && e.KeyCode != Keys.F5 && e.KeyCode != Keys.F6 && e.KeyCode != Keys.F7 &&
e.KeyCode != Keys.F8 && e.KeyCode != Keys.F9 && e.KeyCode != Keys.F10 && e.KeyCode != Keys.F11 && e.KeyCode != Keys.F12 &&
e.KeyCode != Keys.L)
{
// Do some work...
}
}
However, that doesn't quite seem like the best way to handle this to me. Again, I'm just trying to get keys for the characters that could be entered into a textbox (such as 213135udf!##%#!###%15nfaosdf~!#}{:?>, and so on)! Any help at all will be appreciated, thanks!
Sincerely,
Isaac D.
(Edited for clarity and quality)

You could throw all values into a HashSet<T> and check if the KeyCode is in the set.
var invalidKeys = new HashSet<Keys> { Keys.Shift, Keys.CapsLock, Keys.Tab, ... Keys.L };
if (!invalidKeys.Contains(e.KeyCode))
{
// Do some work...
}
Or alternatively, since you're checking for equality, you could just throw all that into a switch statement.
switch (e.KeyCode)
{
case Keys.Shift:
case Keys.CapsLock:
case Keys.Tab:
// ...
case Keys.L:
break;
default:
// Do some work...
break;
}

you can for example (there are many good attempts) check this page for help on the Char class where you can use methods like IsLetterOrDigit or other functions. Now I could not recognise if you are using Windows Forms? If so, use a simple cast like (char)e.KeyCode to get the char.
Example:
private void formControl_KeyModified(object sender, KeyEventArgs e)
{
char c = (char)e.KeyCode;
if (Char.IsLetterOrDigit(c)) {
// useful
}
// might add more checks
// else if (Char.IsPunctuation(c)) ...
}

You can handle the KeyPress event of the form. The mentioned event take a KeyPressEventArgs as its arguments parameter.
Use the Char.IsLetterOrDigit function to check the value of the KeyPressEventArgs.KeyChar property.
private void form_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
if (char.IsLetterOrDigit(e.KeyChar)) {}
else { e.Handled = false; }
}
EDIT:
You can also try to make a list of your accepted Char values, then check if the preseed character is included in it:
private void form_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
List<Char> charList = new List<Char>;
charList.AddRange(new Char[] { 'a', 'b' ... });
if (charList.Contains(e.KeyChar)) {}
else { e.Handled = false; }
}
You may need to consider combining both ways or even more to fulfill your requirements.

If you are concerned with the execution time of the if statement, create a SortedList of the Key values and check if the SortedList contains your key.
A possibly better solution is to use the Forms TextBox "TextChanged" event rather than using the KeyDown event.

Like #Daniel states in his comment, perhaps white-listing the valid keys is preferable than black-listing all those that are of no interest to you. So if, let's say, you are interested only in letter keys and numbers, you could do it just like it is described in the msdn Keys example
if(e.KeyCode > Keys.NumPad0 && e.KeyCode < Keys.NumPad9 ||
e.KeyCode > Keys.D0 && e.KeyCode < Keys.D9 ||
e.KeyCode > Keys.A && e.KeyCode < Keys.Z) {
//do useful stuff here
}

Keystroke combinations in c# winforms app

does anyone know how i can setup an event handler so that if the keystrokes Alt + Shift + Ctrl + a letter will do something?

override void OnKeyDown( object sender, KeyEventArgs e )
{
bool myKeysPressed = (e.KeyCode == Keys.A) &&
((e.Modifiers & Keys.Alt) == Keys.Alt) &&
((e.Modifiers & Keys.Shift) == Keys.Shift) &&
((e.Modifiers & Keys.Control) == Keys.Control);
}

Sames as Ed's, but shorter and more readable ;)
override void OnKeyDown( object sender, KeyEventArgs e )
{
bool myKeysPressed = (e.KeyCode == Keys.A) &&
e.Alt &&
e.Shift &&
e.Control;
}