如何在C＃中的Winform应用程序中设置combobox第一个元素

Question

I am new in Winform application, here i am using Entity framework, when i binding values to a combobox from sql table, i need to set first combobox item as "Please select", how can i set this..?

var qry = context.Tbl_EmployeeDetails.Where(x => x.IsDeleted == false).ToList();          
            if(qry!=null)
            {                
                drpname.ValueMember = "RecordId";
                drpname.DisplayMember = "Name";              
                drpname.DataSource = qry;                          
            }

how can i set this first item as "please select" and value '0'

another suggestion in winform that.. how can i set value in a datagridview linkbutton column when i set 'Edit', 'Delete' columns are as linkbutton

Answer 1

You can insert that item in the beginning of the list.

Code:

var items = db.Tbl_EmployeeDetails.Where(x => x.IsDeleted == false).ToList();
items.Insert(0,new Tbl_EmployeeDetail() { RecordId= 0, Name = "[Please Select an Item]" });

drpname.DropDownStyle = ComboBoxStyle.DropDownList; //optional
drpname.ValueMember = "RecordId";
drpname.DisplayMember = "Name";
drpname.DataSource = items;
drpname.SelectedIndex = 0;

Screenshot:

Note

To have a hint in ComboBox without adding an item, take a look at following post:

• Set hint or watermark or default text for ComboBox without adding it as item :

Answer 2

After you load your var qry which will be a List<string> you want to do the following

var qry = context.Tbl_EmployeeDetails.Where(x => x.IsDeleted == false).ToList();   

if(qry!=null)
{                
    drpname.ValueMember = "RecordId";
    drpname.DisplayMember = "Name";              
    drpname.DataSource = qry;  
    drpname.Items.Insert(0, "--Please Select--");   
    drpname.SelectedIndex = 0;                     
}

Or you could have easily added it to qry since you are returning the data ToList()

for example

var qry = context.Tbl_EmployeeDetails.Where(x => x.IsDeleted == false).ToList();   
qry.Insert(0, "--Please Select--");

if(qry!=null)
{                
    drpname.ValueMember = "RecordId";
    drpname.DisplayMember = "Name";              
    drpname.DataSource = qry; 
    drpname.SelectedIndex = 0; 
}

Answer 3

Your combobox cannot contain additional items if you are binding it to a data source. You have a few options here:

1. Don't bind it to a data source, ie populate it manually from your data set by looping through the items in your query and adding them individually to the combobox; this will allow you the opportunity to first add your "Please Select" item. This can be complicated because you will actually have to add the string names as the items in the combobox, and then you can set the item's Tag property to the actual query row to reference it later.

2. Include a fake item returned from your query that has a display member of "please select". Note, I don't recommend this approach because you're allowing your presentation logic to leak into your data/business layer.

3. Use a third-party control instead of the win forms combobox. I've used Infragistics and they have the ability to display a "suggestion" that's not actually in the list when nothing is selected.