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C# WinForms ListBox changes selection to first item

I got a problem with a ListBox in a WinForm application. I have two ListBoxes inside of a tab control and depending on the selection in the first one (lb1), the DataSource of the second one (lb2) changes. This is done in the SelectedValueChanged Event.
private void listBox_ControlUnits_SelectedValueChanged(object sender, EventArgs e)
{
ControlUnit unit = (sender as ListBox).SelectedItem as ControlUnit;
textBox_ProjectNameTab.Text = unit.ProjectName;
listBox_ControlCircuits.DataSource = null;
listBox_ControlCircuits.DataSource = unit.ControlCircuits;
}
lb1 is filled with a DataSource, too.
Now if I select a value in lb1 the selection automatically jumps back to the first item and I can not figure out why. is this some kind of UI update problem?
Even without the SelectedValueChanged event and the connection to the second listbox the issue occures.
Short gif of the problem, sorry for the blurriness
If I select one item more than once it works somehow (as seen in the gif).
Edit:
I found the problem but I do not quite understand what happens.
I have another listBox on another tab of my tab control. This listBox has the same DataSource as lb1. This seems to cause this behavior.

I finally found the problem:
I did not know that if I use the same DataSource for two ListBoxes they share the BindingContext per default.
I created a new BindingContext for the second ListBox and now the selection does no longer change.
listBox_allGroups.DataSource = null;
listBox_allGroups.DataSource = x.y;
listBox_allGroups.DisplayMember = "Name";
listBox_ControlUnits.DataSource = null;
listBox_ControlUnits.DataSource = x.y;
listBox_ControlUnits.DisplayMember = "Name";
listBox_ControlUnits.BindingContext = new BindingContext();

You can use a variable to hold the selected item
object _selecteditem=null;
and check it in ListBox click event.
prive void ListBox1_Click(object sender,EventArgs e)
{
if(ListBox1.SelectItem == _selecteditem) return;
// do ...
}

Remove something added by a particular event - c#

I have a piece of code that will add the selected item of a combobox to a listbox when a checkbox is checked. I would like to remove that selected item to be removed from the listbox when the checkbox is unchecked.
My problem is I cant simply repeat the code for removal to be the same as add because the combobox selection will different or empty when unchecked.
This is how it currently looks:
private void CBwasher_CheckedChanged(object sender, EventArgs e)
{
if (checkBox1.Checked == true)
{
listBox2.Items.Add(comboBox1.SelectedItem);
}
if (checkBox1.Checked == false)
{
listBox2.Items.Remove(comboBox1.SelectedItem);
}
So I need a way of removing whatever was added by that check change instead of removing the selected index of the combobox. Please consider that there may be multiple lines in the listbox added by multiple different checkboxes.

You simply need to store the added item and remove it.
private object addedItem;
private void CBwasher_CheckedChanged(object sender, EventArgs e)
{
if (checkBox1.Checked)
{
addedItem = comboBox1.SelectedItem;
listBox2.Items.Add(addedItem);
}
else
{
listBox2.Items.Remove(addedItem);
}
}
You may also need to check SelectedItem is null before adding/removing the item.

Focusing on the part where you said there might be multiple different checkboxes,
you need to store one item per checkbox.
You can write your own child class of the checbox control to add this feature, or simply use the Tag property.
You can also indicate which checkbox is linked to which combobox in the same way. Either child class or use the Tag property.
In my example, I'll assume you've referenced the combobox from the checkbox using the Tag property.
You can do it manually like this
checkBox1.Tag = comboBox1;
or hopefully you can automate it if you are generating these on the fly.
Here is the general idea of how the checkbox event should look.
The event is is utilising the sender argument, which means you should hook up all your checkboxes CheckedChanged events to this one handler. No need to create separate handlers for each.
private void CBwasher_CheckedChanged(object sender, EventArgs e)
{
var checkBox = (CheckBox)sender;
var comboBox = (ComboBox)checkBox.Tag;
if (checkBox.Checked && comboBox.SelectedItem != null)
{
listBox2.Items.Add(comboBox.SelectedItem);
comboBox.Tag = comboBox.SelectedItem;
}
if (!checkBox.Checked && comboBox.Tag != null)
{
listBox2.Items.Remove(comboBox.Tag);
}
}

Deselect combobox item

I have a databound combobox:
using(DataContext db = new DataContext())
{
var ds = db.Managers.Select(q=> new { q.ManagerName, q.ManagerID});
cmbbx_Managers.BindingContext = new BindingContext();
cmbbx_Managers.DataSource = ds;
cmbbx_Managers.DisplayMember = "ManagerName";
cmbbx_Managers.ValueMember = "ManagerID";
}
When the form loads neither item is selected, but when the user chooses an item it cannot be deselected. I tried to add cmbbx_Managers.items.Insert(0, "none"), but it does not solve the problem, because it is impossible to add a new item to the databound combobox.
How do I allow a user to deselect a combobox item?

To add an item to your databound ComboBox, you need to add your item to your list which is being bound to your ComboBox.
var managers = managerRepository.GetAll();
managers.Insert(0, new Manager() { ManagerID = 0, ManagerName = "(None)");
managersComboBox.DisplayMember = "ManagerName";
managersComboBox.ValueMember = "ManagerID";
managersComboBox.DataSource = managers;
So, to deselect, you now simply need to set the ComboBox.SelectedIndex = 0, or else, use the BindingSource.CurrencyManager.
Also, one needs to set the DataSource property in last line per this precision brought to us by #RamonAroujo from his comment. I updated my answer accordingly.

The way you "deselect" an item in a drop-down ComboBox is by selecting a different item.
There is no "deselect" option for a ComboBox—something always has to be selected. If you want to simulate the behavior where nothing is selected, you'll need to add a <none> item (or equivalent) to the ComboBox. The user can then select this option when they want to "deselect".
It is poor design that, by default, a ComboBox appears without any item selected, since the user can never recreate that state. You should never allow this to happen. In the control's (or parent form's) initializer, always set the ComboBox to a default value.
If you really need a widget that allows clearing the current selection, then you should use a ListView or ListBox control instead.

To deselect an item suppose the user presses the Esc key, you could subscribe to the comboxBox KeyDown event and set selected index to none.
private void cmbbx_Managers_KeyDown(object sender, KeyEventArgs e)
{
if (e.KeyCode == Keys.Escape && !this.cmbbx_Managers.DroppedDown)
{
this.cmbbx_Managers.SelectedIndex = -1;
}
}

How to add dynamic textbox in C# Combobox

I want to add "other" option in my combobox lists, and when we selected it then dynamically a text box should appear and asks for other value like other talent things.
Thanks in advance,
Vengadesh

You may need code like following :)
private void comboBox_SelectedIndexChanged(object sender, EventArgs e)
{
if (this.comboBox.Text.Equals("Other"))
this.yourTextBox.Visible = true;
else
this.yourTextBox.Visible = false;
}
Try it,

there is no way to add TextBox in a ComboBox.
instead of that we can add items in the combobox.
here the combobox is the object of ComboBox class
combobox.Items.Add(new ComboBoxItem()
{
Text="Other"
});

C# ComboBox in DropDownList style, how do I set the text?

I want to use a ComboBox with the DropDownList style (the one that makes it look like a button so you can't enter a value) to insert a value into a text box. I want the combobox to have a text label called 'Wildcards' and as I select a wildcard from the list the selected value is inserted in to a text box and the combobox text remains 'Wildcard'. My first problem is I can't seem to set a text value when the combobox is in DropDownList style. Using the properties pallet doesn't work the text value is simply cleared when you click off, adding comboBox.Text = "Wildcards"; to form_load doesn't work either. Can anyone help?

The code you specify:
comboBox.Text = "Wildcards";
...should work. The only reason it would not is that the text you specify is not an item within the comboBox's item list. When using the DropDownList style, you can only set Text to values that actually appear in the list.
If it is the case that you are trying to set the text to Wildcards and that item does not appear in the list, and an alternative solution is not acceptable, you may have to be a bit dirty with the code and add an item temporarily that is removed when the drop-down list is expanded.
For example, if you have a form containing a combobox named "comboBox1" with some items and a button named "button1" you could do something like this:
private void button1_Click(object sender, EventArgs e)
{
if (!comboBox1.Items.Contains("Wildcards"))
{
comboBox1.Items.Add("Wildcards");
}
comboBox1.Text = "Wildcards";
}
private void comboBox1_DropDown(object sender, EventArgs e)
{
if (comboBox1.Items.Contains("Wildcards"))
comboBox1.Items.Remove("Wildcards");
}
That's pretty quick and dirty but by capturing the DropDownClosed event too you could clean it up a bit, adding the "Wildcards" item back as needed.

You can select one of items on formload or in form constructor:
public MyForm()
{
InitializeComponent();
comboBox.SelectedIndex = 0;
}
or
private void MyForm_Load(object sender, EventArgs e)
{
comboBox.SelectedIndex = 0;
}

Try this
comboBox1.SelectedValue = "Wildcards";

This may be a possible solution:
comboBox1.SelectedValue = comboBox1.Items.FindByText("Wildcards").Value;