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C# What does setting the SelectedIndex of a combobox to -1 do?

When I was working on one of my projects I was trying to write to a datasourced combobox and then write a value into the combobox like below:
//Create list for combobox
List<string> companyList= new List<string>() { "", "Company1", "Company2" };
//Datsource list to combobox
cbCompanyName.DataSource = companyList;
//If form is set to import data and the billing address is not null
if (importAddress && StaticValues.billAddress != null)
{
//Fill all fields with data from Static Values class
cbCompanyName.Text = StaticValues.billAddress.CompanyName;
cbCountry.Text = StaticValues.billAddress.Country;
}
else
{
//Set country to US
cbCountry.SelectedIndex = 0;
}
however the line cbCompanyName.Text = StaticValues.billAddress.CompanyName; ran without writing any text to the combobox, until I set the selected index of the combobox to -1. What does setting the combobox selected index to -1 do that would change this as apposed to setting the selected index to 0?

Setting the SelectedIndex on a ComboBox to -1 deselects (SelectedItem is NULL). Setting to 0 selects the first item in Items

Combobox needs to know what is my value and display member,
giving the datasource is not enough for it.
I think you can use like this or
// comboBox.DisplayMember = "Text";
// comboBox.ValueMember = "Value";
int =0;
companyList.forEach(x=> comboBox.Items.Add(new { Text = x.toString(), Value =i++ }));
comboBox1.SelectedIndex = 0;
you can look this article
similar question and answers

Two different datagridview rows getting selected when one should be selected

I am working with winform project. i have two datagridview which has same number of columns and same structure. frist column is checkbox column.
here is code to bind two datagrid with same kind of data.
List<AllGroupNames> grpDtl = GetAllGroups(Nodes);
List<AllGroupNames> grpDtl1 = GetAllGroups(Nodes); //grpDtl.GetRange(0, grpDtl.Count);
//bind two grid with all groups name
if (_grpDtl != null && _grpDtl.Count > 0)
{
dgSingleGroups.AutoGenerateColumns = false;
dgSingleGroups.DataSource = grpDtl;
dgSingleGroups.Columns[0].DataPropertyName = "Select";
dgSingleGroups.Columns[1].DataPropertyName = "GroupName";
dgSingleGroups.Columns[1].ReadOnly = true;
dgSingleGroups.Columns[0].Width = 47;
dgSingleGroups.Columns[1].Width = 346;
dgAllGroups.AutoGenerateColumns = false;
dgAllGroups.DataSource = grpDtl1;
dgAllGroups.Columns[0].DataPropertyName = "Select";
dgAllGroups.Columns[1].DataPropertyName = "GroupName";
dgAllGroups.Columns[1].ReadOnly = true;
dgAllGroups.Columns[0].Width = 47;
dgAllGroups.Columns[1].Width = 346;
}
grpDtl1 = null;
grpDtl = null;
_grpDtl = null;
GetAllGroups() iterate in treeview node collection and accumulate node name.
private List<AllGroupNames> GetAllGroups(TreeNodeCollection tnCollection)
{
//accumulate group name in recursive fashion
foreach (TreeNode tn in tnCollection)
{
if (tn.Tag != null)
{
if (((object)tn.Tag).GetType().ToString().Contains("TunerDetails"))
{
_grpDtl.Add(new AllGroupNames { Select = false, GroupName = tn.Text });
}
GetAllGroups(tn.Nodes);
}
}
return _grpDtl;
}
Now problem is when i check second grid checkbox then my first grid checkbox is getting checked invisibly means when i am reading first grid's first column value in loop then i am getting checkbox value true. where as i have not checked my first grid's any checkbox.
when i select any row of second grid that same row is getting automatically selected in first grid.
I just select one row from right side grid and same row of left side grid automatically gets selected....which is problem for me. Why two grid syncing automatically. screen shot attached.
why it is happening i am not able to capture the reason. please help me what to change in code to get rid of this problem.

Apparently every object of class AllGroupName has a Boolean property Select.
You created Column[0] such, that the checkbox is checked whenever this boolean is true, and vice versa: whenever the operator checks this checkbox, the corresponding AllGroupName.Select will become true.
You decided to use the same DataSource as object in two DataGridViews.
Operator checks the checkbox of row[4] in Dgv1
This means that DataSource[4].Select = true;
This means that all objects that have this DataSource will be notified that [4] has changed
Row[4] in Dgv1 and Dgv2 will be updated: checkbox is checked.
If you don't want that changes in Dgv1 are refelected in Dgv2, then you should make a copy of the datasource.
List<...> data1 = ...; // shouldn't this be an BindingList<...> ?
Dgv1.DataSource = data1;
List<...> data2 = new List<...>(data1); // clone data1
Dgv2.DataSource = data2;

Store elements from a ListView into a List

Since I haven't found anything that helped, I ask my question here:
I have a ListView where I select a whole row by click. Now I want to store these selected items into a List but don't know how this should work exactly.
List<String> itemSelected = new List<String>();
foreach (var selectedRow in listView1.SelectedItems)
{
itemSelected.Add(selectedRow);
}
That doesn't work because I need an index (selectedRow[?]) or something like that. How can I store the values of the first column when clicked the row?
EDIT: The problem is that the ListViewItems have the type "object"
The ListView gets populated this way:
using (SqlConnection connection = new SqlConnection(connectionQuery))
{
foreach (DataGridViewRow row in dataGridView1.SelectedRows)
{
col1 = row.Cells[col1.Text].Value.ToString();
col2 = row.Cells[col2.Text].Value.ToString();
col1Cells.Add(col1);
col2Cells.Add(col2);
}
}

You can do something like:
ListViewItem listViewItem = this.listView1.SelectedItems.Cast<ListViewItem>().FirstOrDefault();
if (listViewItem != null)
{
string firstColumn = listViewItem.Text;
string secondColumn = listViewItem.SubItems[0].Text;
// and so on with the SubItems
}
If you have more selected items and only need the values of the first columns you can use:
List<string> values = listView1.SelectedItems.Cast<ListViewItem>().Select(listViewItem => listViewItem.Text).ToList();

It's common to bind a ListView to the List of non-trivial types.
Then you can handle SelectedItemChanged or something like that. You receive the whole object (in type object) which you can cast to your custom type and retrieve any properties you want

How can i display item on itemList of devexpress LookupEdit

Hai all, Am using DevExpress LookupEdit in C#.NET project,also set both Display Member and Value member property of LookupEdit and items are not dispaying on LookupEdit list page ,but i can select items. After selecting one item the selected item dispayed on LookupEdit text. Please help
lkpReference.Properties.DataSource = _lab.selectLabReference() ;
lkpReference.Properties.DisplayMember = "refernce_name";
lkpReference.Properties.ValueMember = "lab_ref_id";
lkpReference.Properties.BestFitMode = BestFitMode.BestFit;
lkpReference.Properties.SearchMode = SearchMode.AutoComplete;
LookUpColumnInfoCollection collns = lkpReference.Properties.Columns;
collns.Add(new LookUpColumnInfo("Lab Reference", 0));
lkpReference.Properties.AutoSearchColumnIndex = 1;

lkpReference.Properties.DataSource = _lab.selectLabReference() ;
lkpReference.Properties.DisplayMember = "refernce_name";
lkpReference.Properties.ValueMember = "lab_ref_id";
lkpReference.Properties.BestFitMode = BestFitMode.BestFit;
lkpReference.Properties.SearchMode = SearchMode.AutoComplete;
// the constructor you are using accepts 2 parameters: FieldName (which is the name
// of the field from the DataTable) and Width (which is the width of the column
// displayed in the dropdown). You have set both parameters wrong.
//LookUpColumnInfoCollection collns = lkpReference.Properties.Columns;
//collns.Add(new LookUpColumnInfo("Lab Reference", 0));
// what you intended to do is this
lkpReference.Properties.Columns.Add(new LookUpColumnInfo("refernce_name", 100, "Lab Reference"));
lkpReference.Properties.AutoSearchColumnIndex = 1;

Setting dropdownlist selecteditem programmatically

I want to set the selecteditem attribute for an ASP.Net dropdownlist control programmatically.
So I want to pass a value to the dropdownlist control to set the selected item where the item is equal to the passed value.

Assuming the list is already data bound you can simply set the SelectedValue property on your dropdown list.
list.DataSource = GetListItems(); // <-- Get your data from somewhere.
list.DataValueField = "ValueProperty";
list.DataTextField = "TextProperty";
list.DataBind();
list.SelectedValue = myValue.ToString();
The value of the myValue variable would need to exist in the property specified within the DataValueField in your controls databinding.
UPDATE:
If the value of myValue doesn't exist as a value with the dropdown list options it will default to select the first option in the dropdown list.

ddlData.SelectedIndex will contain the int value To select the specific value into DropDown :
ddlData.SelectedIndex=ddlData.Items.IndexOf(ddlData.Items.FindByText("value"));
return type of ddlData.Items.IndexOf(ddlData.Items.FindByText("value")); is int.

Here is the code I was looking for :
DDL.SelectedIndex = DDL.Items.IndexOf(DDL.Items.FindByText("PassedValue"));
Or
DDL.SelectedIndex = DDL.Items.IndexOf(DDL.Items.FindByValue("PassedValue"));

Well if I understood correctly your question. The Solution for setting the value for a given dropdownlist will be:
dropdownlist1.Text="Your Value";
This will work only if the value is existing in the data-source of the dropdownlist.

If you need to select your list item based on an expression:
foreach (ListItem listItem in list.Items)
{
listItem.Selected = listItem.Value.Contains("some value");
}

Just Use this oneliner:
divisions.Items.FindByText("Some Text").Selected = true;
divisions.Items.FindByValue("some value").Selected = true;
where divisions is a dropdownlist control.
Hope it helps someone.

var index = ctx.Items.FirstOrDefault(item => Equals(item.Value, Settings.Default.Format_Encoding));
ctx.SelectedIndex = ctx.Items.IndexOf(index);
OR
foreach (var listItem in ctx.Items)
listItem.Selected = Equals(listItem.Value as Encoding, Settings.Default.Format_Encoding);
Should work.. especially when using extended RAD controls in which FindByText/Value doesn't even exist!

ddList.Items.FindByText("oldValue").Selected = false;
ddList.Items.FindByText("newValue").Selected = true;

On load of My Windows Form the comboBox will display the ClassName column of my DataTable as it's the DisplayMember also has its ValueMember (not visible to user) with it.
private void Form1_Load(object sender, EventArgs e)
{
this.comboBoxSubjectCName.DataSource = this.Student.TableClass;
this.comboBoxSubjectCName.DisplayMember = TableColumn.ClassName;//Column name that will be the DisplayMember
this.comboBoxSubjectCName.ValueMember = TableColumn.ClassID;//Column name that will be the ValueMember
}

Safety check to only select if an item is matched.
//try to find item in list.
ListItem oItem = DDL.Items.FindByValue("PassedValue"));
//if exists, select it.
if (oItem != null) oItem.Selected = true;

ddlemployee.DataSource = ds.Tables[0];
ddlemployee.DataTextField = "Employee Name";
ddlemployee.DataValueField = "RecId";
ddlemployee.DataBind();
ddlemployee.Items.Insert(0, "All");