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Check if combobox value is empty

I have created a ComboBox with three values. I wanted that a message box opens when no item is selected so I tried this:
if (comboBox1.SelectedItem == null)
{
MessageBox.Show("Please select a value");
return;
}
That works fine but only if I click into the field in the combobox. When I dont touch it, the program will start without message box. Whats wrong?

if (string.IsNullOrEmpty(comboBox1.Text)) or if (comboBox1.SelectedIndex == -1)

Use
if (comboBox1.SelectedIndex == -1)
{
MessageBox.Show("Please select a value");
return;
}
Note: SelectedIndex will be set to -1 when SelectedValue is blank ONLY when FormattingEnabled is true. See here.

The code should work. Although I will also set SelectedIndex as well......
if (this.comboBox1.SelectedItem == null || this.comboBox1.SelectedIndex == -1)
you mean "When I dont touch it, the program will start without message box. Whats wrong?" is there any code related with "touch it"

Check the selected index value of dropdown equals -1
if (Comboboxid.SelectedIndex == -1){
MessageBox.Show("Your message.");
}

Ithink this is the one :
if(comboBox.SelectedItems==null) //or if(comboBox.SelectedItems==-1)
{
//show no item was selected from comboBox
}
or
if(comboBox.SelectedItems.Count==0)
{
//message no items selected
}

A ComboBox displays a text box combined with a ListBox, which enables the user to select items from the list or enter a new value. Conditionally testing SelectedItem or SelectedIndex will not handle the case of the user entering a new value from another input device like a keyboard. Use string.IsNullOrEmpty(comboBox1.Text) to handle all input/selection cases.

try this is the :
if ((comboBox.SelectedValue == null) || string.IsNullOrEmpty(comboBox.Text))
{
//message no items selected
}

how to check if item is selected from a comboBox in C#

I'm pretty new here.
I have a form, and want to check if the user filled it in correctly. In the form there's a combo box; how can I build the "if" statement for checking whether the user picked an item from it ?
P.S. Sorry for my bad English, it's not my mother tongue. :)

Use:
if(comboBox.SelectedIndex > -1) //somthing was selected
To get the selected item you do:
Item m = comboBox.Items[comboBox.SelectedIndex];
As Matthew correctly states, to get the selected item you could also do
Item m = comboBox.SelectedItem;

Here is the perfect coding which checks whether the Combo Box Item is Selected or not
if (string.IsNullOrEmpty(comboBox1.Text))
{
MessageBox.Show("No Item is Selected");
}
else
{
MessageBox.Show("Item Selected is:" + comboBox1.Text);
}

You seem to be using Windows Forms. Look at the SelectedIndex or SelectedItem properties.
if (this.combo1.SelectedItem == MY_OBJECT)
{
// do stuff
}

if (comboBox1.SelectedIndex == -1)
{
//Done
}
It Works,, Try it

if (combo1.SelectedIndex > -1)
{
// do something
}
if any item is selected selected index will be greater than -1

You can try
if(combo1.Text == "")
{
}

I've found that using this null comparison works well:
if (Combobox.SelectedItem != null){
//Do something
}
else{
MessageBox.show("Please select a item");
}
This will only accept the selected item and no other value which may have been entered manually by the user which could cause validation issues.

ListView - Details View: Does 'this' belong to 'this'?

In Details View for the ListView Control, how can I do something like this, in the simplest way?
if(listView1.SelectedItem belongs to listView1.Groups["BaseballGroup"])
{
MessageBox.Show("The selected item is inside the Baseball Group");
}

Actually there's no property SelectedItem but a list of SelectedItems, then:
if(listView1.SelectedItems[0].Group == listView1.Groups["BaseballGroup"])
{
//...
}
N.B.
Check if something is selected (SelectedItems.Count > 0) to do SelectedItems[0] safely.

Perhaps you could try
listView1.Groups["BaseballGroup"].Contains(listView1.SelectedItem.ToString())

Setting default item in combo box

I have a function for setting items in a combobox and one item is to be set by default like
--SELECT LIST--
public void SetOperationDropDown()
{
int? cbSelectedValue = null;
if(cmbOperations.Items.Count == 0)
{
//This is for adding four operations with value in operation dropdown
cmbOperations.Items.Insert(0, "PrimaryKeyTables");
cmbOperations.Items.Insert(1, "NonPrimaryKeyTables");
cmbOperations.Items.Insert(2, "ForeignKeyTables");
cmbOperations.Items.Insert(3, "NonForeignKeyTables");
cmbOperations.Items.Insert(4, "UPPERCASEDTables");
cmbOperations.Items.Insert(5, "lowercasedtables");
//ByDefault the selected text in the cmbOperations will be -SELECT OPERATIONS-.
cmbOperations.Text = "-SELECT OPERATIONS-";
}
else
{
if(!string.IsNullOrEmpty("cmbOperations.SelectedValue"))
{
cbSelectedValue = Convert.ToInt32(cmbOperations.SelectedValue);
}
}
//Load the combo box cmbOperations again
if(cbSelectedValue != null)
{
cmbOperations.SelectedValue = cbSelectedValue.ToString();
}
}
Can anyone suggest a way to do this?

I've rewritten this answer to clarify some stuff.
First, the "default" text must be added as combo item as well.
Usage of combo.Text property just adds descriptive text to combobox which is "lost" first time user do something with a control.
If you like to permanently have "default" text in your combo, you must add it as an combobox item.
By the code you provided, just modify the
cmbOperations.Text = "-SELECT OPERATIONS-"; to
cmbOperations.Items.Insert(0, "-SELECT OPERATIONS-");
Note that this way you add the item "-SELECT OPERANDS-" to the 0th (read first) position in the list.
Also make sure that all your following items are increased by 1, because they are now moved by one space down in list.
Finally, put cboOperations.SelectedIndex = 0; line at the end of code. By doing so, you're telling combobox to display your "default" item initially when the form (or control) loads.
One more thing. I'm not pretty sure what do you want to achieve with the code beyond setting combo items, but if you like to check what user selected use cboOperations.SelectedIndex property which contains currently selected item in combo. You can add simple if(cboOperations.SelectedIndex == someIntValue){...}
The rest is your program logic ;)

C# How do I run some code for the selected item in a listbox?

I have a listbox of names, I want to click one of the names so that it is highlighted and then click a button that runs some code for the selected item. How do I call this selected item?
private void btnEcho_Click(object sender, EventArgs e)
{
listbox1.SelectedItem......
}
Many thanks

The listbox isn't very intuitive because it contains objects instead of something like ListItem, but if you just want the text you can do this:
string selectedText = listbox1.SelectedItem.ToString();

String s = listbox1.SelectedItem.Value.ToString();
Don't forget to do a null check, because this will throw an error if your list is empty or if no value is selected.

Listbox1.SelectedItem gets the actual selected item. You can then further call from SelectedItem to get other properties/methods such as SelectedItem.Text or SelectedItem.Value
If you wanted to make it all happen upon selection from the listbox (instead of pressing a button), you could just add a SelectedIndexChanged event for Listbox1 (and in ASP.NET make sure that AutoPostBack is set to TRUE)

string str = listbox1.SelectedValue.ToString();
here you have the what value(name) selected.
if(str == null || str == string.empty) return;
and so on. you can do whatever you want;
goodluck

You're question is not clearly to me.
Example, you have a listbox of three items: A, B and C.
You have, as you do with your example, a click-event. In that click-event you can use the switch-statement to handle some code for each item:
switch (listbox1.SelectedItem)
{
case "A":
// Code when select A
break;
case "B":
// Code when select B
break;
... (and so on).
}
Code is an example and not tested. See switch for more information.