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Winform copy button text to textbox using universal method

So this is a fairly straightforward thing, and I am just curious if there is a better way to do it to save lines of code. For class we are making a teletype machine. Basically there is a textbox, and a series of buttons A-Z and 0-9. When you click the button it adds the corresponding letter/number to the textbox. When you click send, it adds the contents of the textbox to a label and resets the textbox. Everything works and it only took a few minutes to build. However there is a mess of redundant lines and I was curious if there is a way to clean up the code with a method.
This is my current code.
private void btn_A_Click(object sender, EventArgs e)
{
box_UserInput.Text = box_UserInput.Text + "A";
}
As you can see, it is very simplistic and straight forward. Click A, and "A" gets added to the textbox. However the Text property of the button is also just "A" and I want to know if there is a way to just copy the text property of that button and add it to the textbox string.
Something like this, except with a universal approach where instead of having to specify btn_A it just inherits which button to copy based on the button clicked. That way I can use the same line of code on every button.
private void btn_A_Click(object sender, EventArgs e)
{
box_UserInput.Text = box_UserInput.Text + btn_A.Text;
}

You can use this which is more universal as the Control class contains the Text property. Also, using the best practice $"".
private void btn_A_Click(object sender, EventArgs e)
{
box_UserInput.Text = $"{box_UserInput.Text}{((Control)sender).Text}";
}
You can also assign the same event to each button. Create an event, say addControlTextOnClick and assign the same event to each button.
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void addControlTextOnClick(object sender, EventArgs e)
{
box_UserInput.Text = $"{box_UserInput.Text}{((Control)sender).Text}";
}
}
You can even shorten this more using this C# construct:
private void addControlTextOnClick(object sender, EventArgs e) =>
box_UserInput.Text = $"{box_UserInput.Text}{((Control)sender).Text}";

C# - How to save TextBox and CheckBox in User Settings

I have a Windows Form Application, where the User can input numbers into three different TextBoxes. I want to save these numbers by checking the Checkbox next to it, so when the Application gets closed and re-opened you don't have to put in the numbers again.
I have added the Properties to the User Settings and implemented the Code below, but when I input a number and re-open the Application, nothing is shown and they aren't saved in the user.config file.
Any help is greatly appreciated as I can't find my mistake.
private void MainForm_Load(object sender, EventArgs e)
{
Text = Properties.Settings.Default.title;
chkBox1.Checked = Properties.Settings.Default.checkBox;
chkBox2.Checked = Properties.Settings.Default.checkBox;
chkBox3.Checked = Properties.Settings.Default.checkBox;
txtBox1.Text = Properties.Settings.Default.textBox;
txtBox2.Text = Properties.Settings.Default.textBox;
txtBox3.Text = Properties.Settings.Default.textBox;
this.Location = new System.Drawing.Point(Properties.Settings.Default.PX, Properties.Settings.Default.PY);
}
private void MainForm_FormClosing(object sender, FormClosingEventArgs e)
{
Properties.Settings.Default.checkBox = chkBox1.Checked;
Properties.Settings.Default.checkBox = chkBox2.Checked;
Properties.Settings.Default.checkBox = chkBox3.Checked;
Properties.Settings.Default.textBox = txtBox1.Text;
Properties.Settings.Default.textBox = txtBox2.Text;
Properties.Settings.Default.textBox = txtBox3.Text;
Properties.Settings.Default.PX = this.Location.X;
Properties.Settings.Default.PY = this.Location.Y;
Properties.Settings.Default.Save();
}
private void chkBox1_Checked(object sender, EventArgs e)
{
this.Text = txtBox1.Text;
}
private void chkBox2_Checked(object sender, EventArgs e)
{
this.Text = txtBox2.Text;
}
private void chkBox3_Checked(object sender, EventArgs e)
{
this.Text = txtBox3.Text;
}

Why not use databinding to save changes automatically. You don't need to replicate the code on form_load and form_closing events.
The best explanation I have for control data binds is that they provide two way model update between a control properties and object properties.
More Info https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.control.databindings?view=netcore-3.1
private void Form1_Load(object sender, EventArgs e)
{
chkBox1.DataBindings.Add("Checked", Properties.Settings.Default, "Checked1",true, DataSourceUpdateMode.OnPropertyChanged);
chkBox2.DataBindings.Add("Checked", Properties.Settings.Default, "Checked2",true, DataSourceUpdateMode.OnPropertyChanged);
chkBox3.DataBindings.Add("Checked", Properties.Settings.Default, "Checked3",true, DataSourceUpdateMode.OnPropertyChanged);
//you can others
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
//don't forget to call save on form closing
Properties.Settings.Default.Save();
}

The first part of my answer, regarding to the fact that nothing is saved when you close your application, is based on the assumption that when testing, you leave the third textbox empty
Why is nothing saved
First is why you are seeing nothing when opening your application, leading you to believe nothing was saved when closing it.
You are in the part of your code handling what happens when your application is closing, saving all of the textboxes (and checkboxes states) in the same setting
Which leads to the following
txtBox1 contains a
txtbox2 contains nothing (or an empty string if you prefer)
When saving, what is happening with your code is that in a first step, you are putting "a" into your textbox setting.
Then, you are replacing this vlue with the content of the second textbox, which is empty
(repeat for the third textbox)
The you are saving.... An empty value.
If you wish to fix this in a "naive" way, you would need a setting per textbox and checkbox.
Which would lead to code ressembling this in your Closing event handler
private void MainForm_FormClosing(object sender, FormClosingEventArgs e)
{
Properties.Settings.Default.checkBox1 = chkBox1.Checked;
Properties.Settings.Default.checkBox2 = chkBox2.Checked;
Properties.Settings.Default.checkBox3 = chkBox3.Checked;
Properties.Settings.Default.textBox1 = txtBox1.Text;
Properties.Settings.Default.textBox2 = txtBox2.Text;
Properties.Settings.Default.textBox3 = txtBox3.Text;
Properties.Settings.Default.PX = this.Location.X;
Properties.Settings.Default.PY = this.Location.Y;
Properties.Settings.Default.Save();
}
Why do I say "naive", because as you've surely understood, this approach is not sustainable for a huge number of controls, but this is not the scope of the question, I'll let you research a solution on your own for this particular point.
Why are the checkbox doing nothing to determine what is saved
First, with the events available on Winforms (at least with the .NET Framework 4.5 which I used to reproduce what you had) the only events available to be notified of the checkbox state change are :
CheckedChanged
CheckStateChanged
The first is used on a binary Checkbox (checked or not)
The second on a checkbox with an uncertain state added to both of the other states.
I imagine you used the first of the two (because that is the one used by default by Visual Studio when double clicking on it in the designer).
The first issue here is that it notifiesyou that the state changed not only that it went from unchecked to checked, but the other way around too.
That means if you only want an action to be done when checking, you need to add a.... check (an if block) to skip the cases you're not interest into.
Next is the actual saving.
What you are doing in your code is just copying the textbox values in a property in your class, and that will NOT persist after closing the application.
Now there is two approach you could use to save those values into the settings, the first is to do it as soon as you check the boxes.
What you would need to do then is for each event handler to copy the value of the textbox.... directly into the settings
An example for the first textbox and checkbox :
private void chkBox1_Checked(object sender, EventArgs e)
{
if(chkBox1.Checked)
{
Properties.Settings.Default.checkBox1 = chkBox1.Checked;
}
}
I'm not a huge fan though, and would prefer the second solution => to check in the closing event, before copying the value from the textbox into the settings, if the corresponding checkbox is closed.
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
if (this.chkBox1.Checked)
{
Properties.Settings.Default.textBox = txtBox1.Text;
}
[...]
}
Now that a little better, and should be working as intended.
Please note that this answer is oriented towards correcting the problem whilst using solutions that are the closest possible of your original code.

C# richBox1 text disable

I have problem with richBox1 text disabling.
I've tryed richTextBox1.readonly = true; and richTextBox1.Enabled = false;
My code:
private void richTextBox1_TextChanged(object sender, EventArgs e)
{
richTextBox1.ReadOnly = !richTextBox1.ReadOnly;
}
Its disabling after one letter.
EDIT: And if disable I can still copy text but cant write there.

Honestly, disabling expected functionality is not something you should be doing. It is not good UI design.

The event TextChanged is fired every time the text changes (including writing or removing one letter). You can use Form's Load event (by double clicking the form on design time) :
private void Form1_Load(object sender, EventArgs e)
{
richTextBox1.ReadOnly = true;
richTextBox1.Enabled = false;
}

Delete Selected Text in Richtextbox

I have a richtextbox and i want to delete not cut the selected when the user presses a button.
I have used
private void button1_Click(object sender, EventArgs e)
{
SendKeys.Send("DELETE");
}
This works but i want to know another way to do it.
I have tried
private void button1_Click(object sender, EventArgs e)
{
richTextBox1.SelectedText.Replace(richTextBox1.SelectedText, "");
}
This doesn't perform any action.
Pls what can i do?

Just do this:
private void button1_Click(object sender, EventArgs e)
{
richTextBox1.SelectedText = "";
}
Your code doesn't work because the string is immutable, you can't change the richTextBox1.SelectedText that way. All the methods (Replace, Insert, ...) performed on a string will create a new string. This new string will be used to initialize your string variable if you need.

The following line of code works for me:
SendKeys.Send("{DELETE}");
Click Link to visit the Official documentation on SendKeys methods.

Updating a textbox using no input controls

I have a windows form application which consists of a bunch of controls, but more specifically, two textBoxes. One of them is read only. The read only textBox value is supposed to be the same as the textBox that the user can type into.
So if the user types "Hello World" into textBox A, the value in textBox B should be automatically updated to "Hello World".
How do I go about doing this? I know I just need to set the text values, I'm just not sure where I place the code to get it done automatically rather than executed when a button is click or something along those lines.

TextChanged event:
private void textBox1_TextChanged(object sender, EventArgs e)
{
textBox2.Text = textBox1.Text;
}

It sounds like you want something like:
writableTextBox.TextChanged += delegate {
readonlyTextBox.Text = writableTextBox.Text;
};
In other words, whenever the text in one textbox changes, update the other. This uses the Control.TextChanged event.

If you want textBoxB to be updated as soon as the text of textBoxA is changed (i.e immediately after the user press a key in textBoxA) the event is TextChanged:
this.textBoxA.TextChanged += new System.EventHandler(this.textBoxA_TextChanged);
private void textBoxA_TextChanged(object sender, EventArgs e)
{
textBoxB.Text = textBoxA.Text;
}
If you prefer to update the text in textBoxB only after the user has finished to edit textBoxA, you should use the Leave event:
this.textBoxA.Leave += new System.EventHandler(this.textBoxA_Leave);
private void textBoxA_Leave(object sender, EventArgs e)
{
textBoxB.Text = textBoxA.Text;
}

This should do what you need:
private void textBox1_TextChanged(object sender, EventArgs e)
{
textBox2.Text = textBox1.Text;
}

Even shorter (better?) than the event approach is using winform's databinding. Just use this right after the InitializeComponents call:
readonlyTextBox.DataBindings.Add("Text", writableTextBox, "Text");