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.
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;
}
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.
Related
I am creating an event where if someone types into a text box it will show an error using this code:
try
{
dblCostSqFt = double.Parse(txtCost.Text);
}
catch
{
MessageBox.Show("Error. You must enter valid numbers. Please correct.");
txtCost.Select();
return;
}
The issue with this is if I input a backspace it will throw that error message immediately I would like to make it to where that doesn't happen.
You're working with userinput here. Therefore i'd suggest to use Double.TryParse()
If you've got a string, and you expect it to always be a double (say, if some web service is handing you a double in string format), you'd use Double.Parse().
If you're collecting input from a user, you'd generally use Double.TryParse(), since it allows you more fine-grained control over the situation when the user enters invalid input.
With tryparse() your code will be something like this:
if (!double.TryParse(txtCost.Text, out var dblCostSqFt))
{
MessageBox.Show("Error. You must enter valid numbers. Please correct.");
txtExample.Select(0, txtCost.Text.Length);
return;
}
To make the example complete and address the issue one could simply check if the Text is not null or empty by using String.IsNullOrEmpty() making the whole code:
// makes sure your app isn't crashing upon backspaces.
if(string.IsNullOrEmpty(textCost.Text))
{
// Personally i'd indicate the user nothing is typed in (yet).
return;
}
if (!double.TryParse(txtCost.Text, out var dblCostSqFt))
{
// The user filled in something that can't be parse to doubles.
MessageBox.Show("Error. You must enter valid numbers. Please correct.");
txtExample.Select(0, txtCost.Text.Length);
return;
}
// All is great; Do stuff with dblCostSqFt.
Assuming you are using WPF for your UI without straying too far from what you have I would use something like below (as LarsTech suggested, use TryParse to test if the value can be converted). Note the if block surrounding the core code within the function, you can avoid execution entering the if block by checking if the key pressed was backspace. I also added a check for the enter key as many users would press the enter key to close the MessageBox, which would cause the event to trigger once again.
private void txtExample_KeyUp(object sender, KeyEventArgs e)
{
if (e.Key != Key.Back && e.Key != Key.Enter)
{
double dblCostSqFt = 0;
if (!double.TryParse(txtExample.Text, out dblCostSqFt))
{
MessageBox.Show("Error. You must enter valid numbers. Please correct.");
txtExample.Select(0, txtExample.Text.Length);
}
}
}
Never rely on exception handling to control the workflow of your application, exceptions have a ton of overhead and it is typically a bad practice in general.
You can accomplish the same thing in WinForms as well using the following...
private void txtExample_KeyUp(object sender, KeyEventArgs e)
{
if (e.KeyCode != Keys.Back && e.KeyCode != Keys.Enter)
{
double dblCostSqFt = 0;
if (!double.TryParse(txtExample.Text, out dblCostSqFt))
{
MessageBox.Show("Error. You must enter valid numbers. Please correct.");
txtExample.Select();
}
}
}
It looks like you are using WinForms because your textbox.Select function call does not supply any arguments, only WinForms supports an overload of the select function without any arguments.
I am very new to the programming world and recently dove into c#. I don't want to waste your time so I'll get right to it. I wanted to create a program just to test my knowledge, and thought I could attempt to execute specific blocks of code based on which key on the keyboard is pressed by the user. I tried doing this by creating an event handler that contained if statements, but then realized I didn't know how to have the event handler active in the program.
For example, and as you can see in the below snippet, after the WriteLine in Line 5 lets say I wanted to raise the EventKeyPress event so that it waits for user input and reads the key they have pressed and reacts accordingly, how would I do that?
Again, I'm almost a complete beginner and have searched around for explanations about event handlers for hours and still can't wrap my head around what I am supposed to do or if I am even using the event handler correctly. Thanks in advance!
static void Main();
{
if (search == "Ball")
{
Console.WriteLine("Press enter to exit or backspace to return to the search bar")
// RIGHT HERE
}
else
{
Console.WriteLine("Sorry, I don't recognize {0}", search);
}
void EventKeyPress(object sender, KeyPressEventArgs e)
{
for (int i = 0; i < 1;)
{
if (e.KeyChar == (char)Keys.Enter)
{
// exit app
}
else if (e.KeyChar == (char)Keys.Back)
{
// go back to search
}
else
{
i = 0; // error
}
}
}
}
So, you're asking for something that involves Threading which is not a beginner thing to accomplish at all. The best way to do this for a beginner is to ask for a prompt, then accept as an input. For example.
Console.WriteLine("Hello, what's your name?");
string nameStr = Console.ReadLine();
Console.WriteLine($"Hello, {nameStr}");
You can then use your variable and apply it to an if/while or whatever kind of conditional.
if (nameStr == "Matt"){
//Do This Code.
}
Once you have that code, add a sequential method that will ask the user to return to the main menu or whatever you want it to do.
Main.ReturnMenu(); //Or whatever you want to use.
I am trying to create some validation for a form I have. There are two text boxes and two radio buttons on the form. My logic for this validation I know is a little rusty at the moment so any suggestions would be great.
Here is the code for what I have so far:
Keep in mind that the int errors is a public variable in the class
Start Button code:
private void btnStart_Click(object sender, EventArgs e)
{
errors = validateForm();
//Here I want the user to be able to fix any errors where I am little
stuck on that logic at the moment
//validate the form
while (errors > 0)
{
validateForm();
errors = validateForm();
}
}
ValidateForm Method:
private int validateForm()
{
errors = 0;
//check the form if there are any unentered values
if (txtDest.Text == "")
{
errors++;
}
if (txtExt.Text == "")
{
errors++;
}
if (validateRadioBtns() == true)
{
errors++;
}
return errors;
}
ValidateRadioBtns Method:
private Boolean validateRadioBtns()
{
//flag - false: selected, true: none selected
Boolean blnFlag = false;
//both of the radio buttons are unchecked
if (radAll.Checked == false && radOther.Checked == false)
{
blnFlag = true;
}
//check if there is a value entered in the text box if other is checked
else if(radOther.Checked == true && txtExt.Text == "")
{
blnFlag = true;
}
return blnFlag;
}
Overall I feel like this can somehow be more stream lined which I am fairly stuck on.
Any suggestions would be greatly appreciated since I know this is such a nooby question.
Well first since you have said that you want to validate for non-entered values, did you consider white spaces as an entry? since someone can just press space and then your validation would pass.
Aside from that, you might want to indicate which textbox they did not fill out or which group they did not click, it seems like you are using web forms so here is a walkthrough http://msdn.microsoft.com/en-us/library/vstudio/a0z2h4sw(v=vs.100).aspx.
If you are using windows forms you can use this walkthrough http://msdn.microsoft.com/en-us/library/ms229603(v=vs.110).aspx.
If you need to keep the existing logic, I would suggest extracting the repeating logic into separate functions and temporary btnFlag is not necessary also as you can return true and return false at the end.
private Boolean validateRadioBtns()
{
if (radAll.Checked == false && radOther.Checked == false)
return true;
else if(radOther.Checked == true && txtExt.Text.Trim().Length == 0 ) //just a quick sample of how you can trim the spaces and check for length
return true;
return false;
}
See the documentation for the validation patterns. You have chosen the explicit validation strategy, for which you would use the ContainerControl.ValidateChildren method and either perform your "Start" action or not.
Windows Forms has dedicated events for validation that allow you to react accordingly for each of your controls. You'll use Control.Validating and Control.Validated events.
So, unless ValidateChildren returns true, you don't need to initiate your "Start" action, i.e. the logic would become trivial.
P.S. you also probably don't need the errors variable as a class member since you return it from your validation function. For showing the error, prefer the "Tell, Don't Ask" idea by separating the error visualization in a separate component.
I am writing a class to consume 'ALL' input from barcode scanner. I am using the code from http://nicholas.piasecki.name/blog/2009/02/distinguishing-barcode-scanners-from-the-keyboard-in-winforms/
I've added following lines in PreFilterMessage() for testing.
if (m.Msg != Win32.WM_INPUT)
{
// Allow any non WM_INPUT message to pass through
return false;
}
return true;
The problem is with some barcode that has "═" (Alt + Numpad: 205) in it. and it gets typed in the textbox. How can I prevent the Alt + Numpad keys from dispatching?
I am able to handle this issue by catching the keys at form level, by setting the form
keypreview=true,
and in form_keypress event setting
//if(Alt pressed && numpad keys)
e.Handled = true;
But ideally this should be handled by the class. Any ideas??
How about checking modifier keys to block Alt+Numpad keys?
E.g.
if (ModifierKeys == Keys.Alt)
return true;
I need to capture keystokes from a wedge device and prevent any controls or the form from receiving them. I also need to be able to know the value (char). I have tried overriding the ProcessCmdKey(Keys) and ProcessDialogChar(char) events. In the ProcessCmd event I can suppress the keystroke if it's one I want, but I the character isn't a parameter of the event. In the ProcessDialogChar event the character is there, but I cannot prevent the form or control with the focus from receiving the key. Suggestions?
You'll want to add this during Form load:
Application.AddMessageFilter(this);
Add this constant:
private const int WM_KEYDOWN = 0x100;
And this method:
public bool PreFilterMessage(ref Message m)
{
Keys keyCode = (Keys)(int)m.WParam & Keys.KeyCode;
bool retVal = false;
if (m.Msg == WM_KEYDOWN)
{
// Handle the keypress
retVal = true;
}
return retVal;
}
By returning true, your form and control(s) will never see the key press.
It was not how I wanted to do it, but because I needed to fix this and move on I put a hidden textbox on the form and as soon as I see the character that signals the possible start of the string of data I want to capture I set focus to that text box and respond to the TextChanged event. If I haven't seen the ending character before I timer expires I clear the textbox and start again. Kludge, but it works and got me to the next task.