Develop Reference

Only do event after complete

How to do the event handling when the user presses the ENTER key or leaves the focus on the particular textbox? I tried for KeyChanged event, but it will keep updating the number instead of only once when complete.
private void txtNumber_TextChanged(object sender, EventArgs e)
{
txtNumber.Text = double.Parse(txtNumber.Text).ToString("F2");
}

There are a few issues with the posted code. One issue is that doing the formatting each time the user “types” a character is going to be awkward for the user. In addition, if the user presses the “Enter” key, the event txtNumber_TextChanged is not going to fire. I assume you may already know this.
Next, when getting input from users, it is imperative that you check the input for valid numbers BEFORE calling the parse method…Example, the line of code…
double.Parse(txtNumber.Text).ToString("F2");
Will FAIL and crash the program if the text in the text box… txtNumber.Text is NOT a valid double.
You should always assume the user is going to make a mistake and you don’t want your code to crash when they do.
Therefore I suggest using the double.TryPasre method to avoid these possible crashes, calling this method will NEVER throw an exception and will make validating the number easier.
To get what you want I recommend you wire up three (3) events for the text box…
The Leave event, this is used to format the text, when the user leaves the text box, like when they click on another control.
Next is the PreviewKeyDown event, this is used when the user presses the “Enter” key.
And one extra event to help the user ONLY add numbers and one dot. The KeyPressed event is wired up and will ignore any pressed keys that are not numbers or the dot (period). Also, it will only allow one period, if the user tries to add a second decimal place, it will be ignored.
Bear in mind, the key pressed event helps by preventing the user from “typing” alpha text into the text box… however, the user can still paste text. Fortunately, since we are using the TryParse method, when the pasted text is an invalid number, the try parse will simply return “0.00” and NOT crash the code.
private void txtNumber_Leave(object sender, EventArgs e) {
double.TryParse(txtNumber.Text.Trim(), out double number);
txtNumber.Text = number.ToString("F2");
}
private void txtNumber_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e) {
if (e.KeyCode == Keys.Enter) {
double.TryParse(txtNumber.Text.Trim(), out double number);
txtNumber.Text = number.ToString("F2");
}
}
private void txtNumber_KeyPress(object sender, KeyPressEventArgs e) {
if (!char.IsControl(e.KeyChar) // <- key pressed is not a control key
&& !char.IsDigit(e.KeyChar) // <- key pressed is not a digit (number)
&& e.KeyChar != '.') { // <- key pressed is not a dot (.)
e.Handled = true; // <- if its not a control key, digit or dot... then ignore it
}
// only allow one decimal point - if there is already a dot, then ignore the second one
if (e.KeyChar == '.' && txtNumber.Text.IndexOf('.') > -1) {
e.Handled = true; // <- if there is already a dot in the text... then ignore it
}
}

Formatting a text value in a TextBox must be done once the input is already done.
TextChanged, occurs when the Text property value changes. So this is not ideal.
The only event you can rely on.
LostFocus, occurs when the control loses focus. You can sheck some info when control change focus.
private void textBox1_LostFocus(object sender, System.EventArgs e)
{
// Code here
}
Sometimes we wanted the format to be changed once we click something on the keyboard, so here are the possible events for that.
The non-character keys do raise the KeyDown and KeyUp events.
KeyDown, occurs when a key is pressed while the control has focus.
KeyUp, occurs when a key is released while the control has focus.
KeyPress, occurs when a character. space or backspace key is pressed while the control has focus.
Note: When using the KeyPress you need to also consider if the Form is the one handling the input events first or not, check the Remarks here.
private void textBox1_KeyUp(object sender, System.Windows.Forms.KeyEventArgs e)
{
if (e.KeyCode == Keys.Return) // You can also use: e.KeyValue == 13
{
// Do your code here
}
};

Visual C# key detecting anomaly (D character added) while reading RFID card

I'm developing a program in Visual C# 2015 which should authenticate users through rfid cards. The device I'm using simply emulates a keyboard: let's say I open notepad, then swipe the tag or card near the reader, and I get the serial number + enter, much like most barcode readers work.
Obviously, I don't want the user to see the code, nor make him/her able to type it in a textbox, so the idea is catching the input from "that keyboard" at authentication, using KeyDown event, putting all characters in a buffer variable and then checking it against the database when enter is pressed (that is, the end of the code).
The problem is, say the card is marked as 12345678, this is what I get in notepad or in a textbox. But when I display the buffer, I get "D1D2D3D4D5D6D7D8"; I could simply avoid the problem by adding a D before each character of the database, but I really want to understand why this happens. Is it a matter of coding, or maybe the keydown events are too near to each other? Does anybody have a clue? Thank you
EDIT:
Here's the code:
XAML
<Window x:Class="myApp.MainWindow"
(...)
KeyDown="OnKeyDownHandler">
C#
private void OnKeyDownHandler(object sender, KeyEventArgs e)
{
if (!authenticated) {
if (e.Key != Key.Enter)
{
cardReadBuffer += e.Key;
}
else
{
//this returns every character preceded by a D; doesn't happen
//if I type some characters on my keyboard and then press enter
MessageBox.Show(cardReadBuffer);
cardReadBuffer = "";
}
}
}

The KeyDown event is just giving you the actual key being pressed, so try using the TextInput event to handle the string part:
private void OnKeyDownHandler(object sender, KeyEventArgs e) {
if (e.Key == Key.Enter) {
MessageBox.Show(cardReadBuffer);
cardReadBuffer = "";
e.Handled = true;
}
}
private void OnTextInput(object sender, TextCompositionEventArgs e) {
cardReadBuffer += e.Text;
}

C# type until you press enter

I have Windows Form Application with TextBox and Label and I want to type something in the textbox and then press Enter to let's say show what I've typed in Label.
Example with button:
private void button1_Click(object sender, EventArgs e)
{
this.Label1.Text = this.TextBox1.Text;
}
I need to do exactly the same but with pressing Enter not button.

private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter)
{
Label1.Text = TextBox1.Text;
}
}

I tried the code from Jan Anderssen and it works correctly. The error "Operator '==' can not be applied to operands of type 'char' and 'System.Windows.Forms.Keys" is because you are matching a character to Keys.Enter, make sure that the syntax is correct e. KeyCode.
E.KeyCode is used because in the event handler send a parameter with the value of e "KeyEventArgs e" variable and here is the key pressed.
private void txtText_KeyDown (object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter)
{
this.lblText.Text = this.txtText.Text;
}
}
Did you copy and paste the code?
If so, try doing it with the events of the properties box.
Click in the textbox -> Events ---> key down ---> double click and put the code there.
Do you have more than one form? This code may change.

you can use the text change event and check when enter pressed.
when you identify enter, then you can do what ever you want

Richtextbox deletes selected text

I have the following code:
private void richTextBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.N)
{
richTextBox1.Select(1, 3);
}
}
When I press the N key , the selected text is replaced with "n". I read this Selecting text in RichTexbox in C# deletes the text ,but it had no effects.
I am using Windows Forms.

Likely, you will need e.Handled = true; in this to stop the event.
http://msdn.microsoft.com/en-us/library/system.windows.forms.keyeventargs.handled.aspx
private void richTextBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.N)
{
richTextBox1.Select(1, 3);
e.Handled = true;
}
}

Try it yourself:
Open up the editor, type some text, mark some of this text and press N. What happens? The marked text is replaced with n.
The same thing happens in your RichTextBox. Important to understand here is, that with the event you set up, you only add some functionality and leave the default event handling (handled by the OS) intact.
So with your code, on a key press you just do
richTextBox1.Select(1, 3);
which selects some characters and afterwards the default event handling kicks in. Thus there is some marked text which gets replaced with N.
So, you simply have to mark the event as handled by yourself. Not using the Handled-property, but with the SuppressKeyPress-property.
private void richTextBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.N)
{
richTextBox1.Select(1, 3);
e.SuppressKeyPress = true;
}
}
The documentation of Handled clearly states:
If you set Handled to true on a TextBox, that control will
not pass the key press events to the underlying Win32 text
box control, but it will still display the characters that the user typed.
Here is the official documentation of SuppressKeyPress.

C# KeyEvent doesn't log the enter/return key

I've been making this login form in C# and I wanted to 'submit' all the data as soon as the user either clicks on submit or presses the enter/return key.
I've been testing a bit with KeyEvents but nothing so far worked.
void tbPassword_KeyPress(object sender, KeyPressEventArgs e)
{
MessageBox.Show(e.KeyChar.ToString());
}
The above code was to test if the event even worked in the first place.
It works perfectly, when I press 'd' it shows me 'd' when I press '8' it shows me '8' but pressing enter doesn't do anything.
So I though this was because enter isn't really bound to a character but it did show backspace, it worked just fine so it got me confused about why it didn't register my enter key.
So the question is:
How do I log the enter/return key? and why doesn't it log the key press right right now like it should?
note: I've put the event in a textbox
tbPassword.KeyPress += new KeyPressEventHandler(tbPassword_KeyPress);
So it fires when the enter button is pressed WHILE the textbox is selected (which is was the whole time of course) maybe that has something to do with the execution of the code.

Do you have a button defined as the default action?
If so then that control will gobble up the Enter key.
And maybe that is your answer. You need to set the DefaultAction property to true on your submit button.

Try the KeyDown event instead.
private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Enter)
{
MessageBox.Show("Enter");
}
}

Perhaps you should use the "AcceptButton" of the form to set it to the submit button. Think that is what you what really...

You have left out a vital bit, you must set the Handled property to true or false depending on the condition...
void tbPassword_KeyPress(object sender, KeyPressEventArgs e)
{
MessageBox.Show(e.KeyChar.ToString());
if (e.KeyCode == Keys.Enter){
// This is handled and will be removed from Windows message pump
e.Handled = true;
}
}

Try this
textBox1.KeyPress += new KeyPressEventHandler(textBox1_KeyPress);
void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == '\r')
{
MessageBox.Show("Enter Key Pressed", "Enter Key Pressed", MessageBoxButtons.OK);
}
}

go to your forms...
in the basic form change this
FormName.AcceptButton = buttonName;
this would read the key log file of enter... automatically..
you can do this if you dont want users to see accept button
buttonName.Visible = false;
FormName.AcceptButton = buttonName;
AcceptButton automatically reads the enter key from the keyboard