Develop Reference

c# Populate datagridview based on ComboBox Item Selected

I have this datagrid where Combobox is populated from Db.
What I'm trying to achieve is that when I select something in the column "Esercizio", the cell of "Video" column auto populate with respective value from the "link_video" column of Db.
So if I select "kickback", I need to see the link video of kickback from db in the textbox cell.
Here's the code that i use to populate the combobox on form load:
private void Myform_Load(object sender, EventArgs e)
{
con = new SqlConnection("Data Source=(LocalDB)\\etc");
cmd = new SqlCommand();
con.Open();
cmd.Connection = con;
cmd.CommandText = "SELECT * FROM Esercizi";
dr = cmd.ExecuteReader();
while (dr.Read())
{
//populate Column1 combobox with "nome" column from Esercizi db table
Column1.Items.Add(dr["nome"]);
}
con.Close();
}
datagridview
EDIT
I've figured out with 2 new problems.
I'm trying to load a saved workout from db but when I do this, no video link populate the dgv as the grid event doesn't fire.
What I've tried is to add a foreach loop to a new selectionindexchanged function and to fire it at the end of the Load Button code like this:
private void curCombo_LoadedValues(object sender, EventArgs e)
{
foreach (DataGridViewRow row in dataGridView1.Rows)
{
foreach (DataGridViewCell cell in row.Cells)
{
if (curCombo != null && curCombo.SelectedValue != null)
{
ExerciseAndVideo selectedExercise = (ExerciseAndVideo)curCombo.SelectedItem;
dataGridView1.CurrentRow.Cells["Video"].Value = selectedExercise.Video;
}
}
}
}
private void button9_Click(object sender, EventArgs e){
string connectionString = "Data Source=(LocalDB)\\etc";
string sql = "SELECT * FROM Schede WHERE Id = 6 AND dgv = 'dataGridView1'";
SqlConnection connection = new SqlConnection(connectionString);
SqlDataAdapter dataadapter = new SqlDataAdapter(sql, connection);using (DataTable dt = new DataTable())
{
dataadapter.Fill(dt);
//Set AutoGenerateColumns False
dataGridView1.AutoGenerateColumns = false;
//Set Columns Count
dataGridView1.ColumnCount = 6;
//Add Columns
dataGridView1.Columns[0].Name = "Esercizio";
dataGridView1.Columns[0].HeaderText = "Esercizio";
dataGridView1.Columns[0].DataPropertyName = "Esercizio";
dataGridView1.Columns[1].Name = "Serie";
dataGridView1.Columns[1].HeaderText = "Serie";
dataGridView1.Columns[1].DataPropertyName = "Serie";
dataGridView1.Columns[2].HeaderText = "Ripetizioni";
dataGridView1.Columns[2].Name = "Ripetizioni";
dataGridView1.Columns[2].DataPropertyName = "Ripetizioni";
dataGridView1.Columns[3].Name = "Recupero";
dataGridView1.Columns[3].HeaderText = "Recupero";
dataGridView1.Columns[3].DataPropertyName = "Recupero";
dataGridView1.Columns[4].Name = "Time Under Tension";
dataGridView1.Columns[4].HeaderText = "Time Under Tension";
dataGridView1.Columns[4].DataPropertyName = "Time_Under_Tension";
dataGridView1.DataSource = dt;
connection.Close();
}
curCombo_LoadedValues();
}
But I get this error "the are no arguments for the obligatory parameter sender...
How I can call it correctly?
The second Issue is that when I populate some dgv columns like this, combos stops working correctly and I get an error exception on the combobox :
dataGridView1.Rows.Add(7);
Random rnd = new Random();
dataGridView1.Rows[0].Cells[1].Value = 3;
dataGridView1.Rows[0].Cells[2].Value = rnd.Next(1, 13);
dataGridView1.Rows[0].Cells[3].Value = 1;
dataGridView1.Rows[0].Cells[4].Value = 201;
dataGridView1.Rows[1].Cells[1].Value = 2;
dataGridView1.Rows[1].Cells[2].Value = rnd.Next(1, 13);
dataGridView1.Rows[1].Cells[3].Value = 1;
dataGridView1.Rows[1].Cells[4].Value = 201;
dataGridView1.Rows[2].Cells[1].Value = 3;
dataGridView1.Rows[2].Cells[2].Value = rnd.Next(1, 13);
dataGridView1.Rows[2].Cells[3].Value = 1;
dataGridView1.Rows[2].Cells[4].Value = 201;
dataGridView1.Rows[3].Cells[1].Value = 4;
dataGridView1.Rows[3].Cells[2].Value = rnd.Next(1, 13);
dataGridView1.Rows[3].Cells[3].Value = 1;
dataGridView1.Rows[3].Cells[4].Value = 201;
dataGridView1.Rows[4].Cells[1].Value = 5;
dataGridView1.Rows[4].Cells[2].Value = rnd.Next(1, 13);
dataGridView1.Rows[4].Cells[3].Value = 1;
dataGridView1.Rows[4].Cells[4].Value = 201;
dataGridView1.Rows[5].Cells[1].Value = 6;
dataGridView1.Rows[5].Cells[2].Value = rnd.Next(1, 13);
dataGridView1.Rows[5].Cells[3].Value = 1;
dataGridView1.Rows[5].Cells[4].Value = 201;
dataGridView1.Rows[6].Cells[1].Value = 7;
dataGridView1.Rows[6].Cells[2].Value = rnd.Next(1, 13);
dataGridView1.Rows[6].Cells[3].Value = 1;
dataGridView1.Rows[6].Cells[4].Value = 201;
This is the look of the dgv now:
dgv
And this is the error the i get after combos stop working correctly (I click and no dropdown appear or if I click 2-3 times, a random item get selected but no video link appear in the other column):
error

In the posted code, it shows a query to a DB to get the exercise names and adds those names as the items to display in “each” combo box cell in that column. This is fine, however, there is zero (0) information about “which video” belongs to each of the items in the combo boxes list of items. I will assume the “relation” to which video is related to which exercise would involve another query to the DB.
If this is the case, then it is easy to see that when a combo box in the grid is changed, that you could simply query the DB for which video to use for the selected exercise. This would certainly work; however, it creates a redundancy issue. Example, let’s say the user selected “kicks” in the combo box in row 1 in the gird. The code queries the DB and gets the location of the “kicks” video and sets the “video” cell to this videos path. Then later, the user selects “kicks” again for some other row. This will re-query the DB for the SAME data we previously got. You want to avoid querying the DB unnecessarily.
So given this, it appears a better approach to avoid re-querying the DB unnecessarily, is that we somehow “combine” the exercise with the particular video that the exercise uses. You could do this ONCE when the form loads. Once you have the exercises, then loop though each exercise and query the DB for that exercises video and combine this with the exercise. Once we have the video link, we “save” this info. With this approach, you will not have to re-query the DB for any given exercise since we have saved that info for all exercises.
There are a myriad number of ways to “combine” the exercise with the video. One possible solution is to create a Class that has these two properties. Let’s call this Class ExerciseAndVideo… it has two properties, a string Exercise that is the exercise text and a string Video that defines the path to the video for that Exercise. This simple class may look something like…
public class ExerciseAndVideo {
public string Exercise { get; set; }
public string Video { get; set; }
}
This is one approach to “combine” an Exercise with a particular Video. We could then make a list of ExerciseAndVideo objects like…
List<ExerciseAndVideo> ExerciseList;
Then we cannot only use this list as a DataSource to the combo box column, but we could also use this list as a way to easily tell “which” video belongs to “which” exercise. The example below uses this strategy.
How to implement this in the DataGridView…
One thing to keep in mind is that a DataGridViewComboBoxCell is “different monster” than a “regular” ComboBox. Example; for a regular combo box, there is an event called… SelectedIndexChanged event. This event fires when the user “changes” the combo boxes currently selected index. On the other hand, a DataGridViewComboBoxCell does NOT have a SelectedIndexChanged event, which I assume you may be aware of. The grid’s absence of this event makes sense, because the grid’s combo box “column” may have MANY combo boxes in it.
Fortunately, even though the DataGridViewComboBoxCell does not have a SelectedIndexChanged event, we CAN cast an “individual” combo box cell to a ComboBox (in this case the combo box cell being edited), THEN we CAN subscribe to that ComboBoxes SelectedIndexChanged event. Then we could simply wait until the SelectedIndexChanged event fires then update the video cell data with the appropriate video link.
The DataGridView provides a special event for this called… EditingControlShowing. This event will fire when the user starts to “edit” a cell in the grid. In this particular case, this event would fire when the user clicks into a combo box cell and “starts” to change the cells value. Is what we want to do in this event is simply cast that combo box cell to a regular ComboBox…, THEN, subscribe to that ComboBoxes SelectedIndexChanged event which we will implement below.
The strategy goes like this… we will make a “global” ComboBox variable we will call curCombo. When the grids EditingControlShowing event fires and we see that the edited cell is an “Exercise” cell… Then we will cast THAT combo box cell in the grid to the global curCombo variable. Then we will subscribe to that combo boxes SelectedIndexChanged event. When the user “leaves” the cell we will unsubscribe from the global variables curCombo SelectedIndexChanged event to keep things clean.
Therefore, given this, the grids EditingControlShowing event may look something like below...
private void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e) {
if (dataGridView1.Columns[dataGridView1.CurrentCell.ColumnIndex].Name == "Exercise") {
curCombo = e.Control as ComboBox;
if (curCombo != null) {
curCombo.SelectedIndexChanged -= new EventHandler(curCombo_SelectedIndexChanged);
curCombo.SelectedIndexChanged += new EventHandler(curCombo_SelectedIndexChanged);
}
}
}
Obviously we need to implement the event handler curCombo_SelectedIndexChanged. In this event, we would know that previously, the user selected a combo box cell and has changed the value in that cell to some other value. Since the Exercise changed, we know we need to change the “Video” cell.
Again there are numerous ways you could do this, however, if we set the grid’s “Exercise” combo box column’s DataSource as a List of ExerciseAndVideo objects, then we should be able to get that particular ExerciseAndVideo object directly from the global ComboBox curCombo. This will tell us “which” video to place in the “Video” cell. This may look something like…
private void curCombo_SelectedIndexChanged(object sender, EventArgs e) {
if (curCombo != null && curCombo.SelectedValue != null) {
ExerciseAndVideo selectedExercise = (ExerciseAndVideo)curCombo.SelectedItem;
dataGridView1.CurrentRow.Cells["Video"].Value = selectedExercise.Video;
}
}
private void dataGridView1_CellLeave(object sender, DataGridViewCellEventArgs e) {
if (dataGridView1.Columns[e.ColumnIndex].Name == "Exercise") {
if (curCombo != null) {
curCombo.SelectedIndexChanged -= new EventHandler(curCombo_SelectedIndexChanged);
}
}
}
To complete the example and putting all this together may produce something like below…
List<ExerciseAndVideo> ExerciseList;
ComboBox curCombo;
public Form2() {
InitializeComponent();
}
private void Form2_Load(object sender, EventArgs e) {
ExerciseList = GetExerciseVideoComboBoxListFromDB();
dataGridView1.Columns.Add(GetExcerciseComboBoxColumn(ExerciseList));
dataGridView1.Columns.Add(GetLinkColumn());
dataGridView1.CellLeave += new DataGridViewCellEventHandler(dataGridView1_CellLeave);
dataGridView1.EditingControlShowing += new DataGridViewEditingControlShowingEventHandler(dataGridView1_EditingControlShowing);
}
private DataGridViewComboBoxColumn GetExcerciseComboBoxColumn(List<ExerciseAndVideo> exerciseData) {
DataGridViewComboBoxColumn cbCol = new DataGridViewComboBoxColumn();
cbCol.HeaderText = "Exercise";
cbCol.Name = "Exercise";
cbCol.DisplayMember = "Exercise";
cbCol.DataSource = exerciseData;
return cbCol;
}
private DataGridViewLinkColumn GetLinkColumn() {
DataGridViewLinkColumn col = new DataGridViewLinkColumn();
col.HeaderText = "Video";
col.Name = "Video";
col.AutoSizeMode = DataGridViewAutoSizeColumnMode.Fill;
return col;
}
private List<ExerciseAndVideo> GetExerciseVideoComboBoxListFromDB() {
List<ExerciseAndVideo> exerciseList = new List<ExerciseAndVideo>();
exerciseList.Add(new ExerciseAndVideo { Exercise = "Crosses", Video = #"C:/somepath/Crosses.htm/" });
exerciseList.Add(new ExerciseAndVideo { Exercise = "Kickback", Video = #"C:/somepath/Kickback.htm" });
exerciseList.Add(new ExerciseAndVideo { Exercise = "Leg Extensions", Video = #"C:/somepath/LegExtensions.htm" });
exerciseList.Add(new ExerciseAndVideo { Exercise = "Crunches", Video = #"C:/somepath/Crunches.htm" });
exerciseList.Add(new ExerciseAndVideo { Exercise = "Pushups", Video = #"C:/somepath/Pushups.htm" });
return exerciseList;
}
What if the grid has a data source?
This works as expected when the grid has no data source. However, if the grid has a data source and one of the columns/properties in the data source is bound to our “Exercise” combo box column, then, is what will happen… is that after the data is loaded, the combo boxes should display the proper exercise, however, all the video cells will remain empty. This is obviously because the grid events are not fired when the data is loaded.
So, in that case, you will want a method that loops through all the rows in the grid, checks what the exercise value is for that row, then set the video cell value to the correct video link. Since you do not say if the grid does or does not have a data source, I will assume this is all you need. If there is a data source, I recommend you check each “Exercise” to make sure the “Exercises” in the data are in the combo boxes list of items, if one or more “Exercises” are in the data that are not in the combo box columns list of items, then you will get the grids DataError when you attempt to set the grids data source.
I hope this makes sense.
Edit... An example of setting the video cell after the data has been loaded into the grid.
private void SetVideoCellsAfterDataLoad() {
foreach (DataGridViewRow row in dataGridView1.Rows) {
if (!row.IsNewRow && row.Cells["Exercise"].Value != null) {
foreach (ExerciseAndVideo eav in ExerciseList) {
if (row.Cells["Exercise"].Value.ToString() == eav.Exercise) {
row.Cells["Video"].Value = eav.Video;
break;
}
}
}
}
}

I mixed ComboBox with DatagridViewComboboxColumn.
It's partly your fault :).
Here you have a form with events. Since CellValueChanged fires on cell exit, I added a Dirty StateEvent to update the Video column.
From the designer, just put the datagrid in the form and make sure the name is the same.
IMHO, these 3 events are crucial
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
Init();
}
private void Init()
{
var list = new List<Exercise>() {
new Exercise (){Name="Name1", Link= "Link1" },
new Exercise (){Name="Name3", Link= "Link3" },
new Exercise (){Name="Name4", Link= "Link4" },
};
var comboColumn = new DataGridViewComboBoxColumn() { Name = "ExerciseName", CellTemplate = new DataGridViewComboBoxCell() };
comboColumn.DisplayMember = nameof(Exercise.Name);
comboColumn.ValueMember = nameof(Exercise.Link);
comboColumn.DataSource = list;
dataGridView1.Columns.Add(comboColumn);
dataGridView1.Columns.Add(new DataGridViewTextBoxColumn() { Name = "Video" });
dataGridView1.CellContentClick += DataGridView1_CellContentClick;
dataGridView1.CellValueChanged += DataGridView1_CellValueChanged;
dataGridView1.CurrentCellDirtyStateChanged += DataGridView1_CurrentCellDirtyStateChanged;
}
private void DataGridView1_CurrentCellDirtyStateChanged(object sender, EventArgs e)
{
var currentCell = (sender as DataGridView).CurrentCell;
if(currentCell.ColumnIndex == 0)
dataGridView1.CommitEdit(DataGridViewDataErrorContexts.Commit);
}
private void DataGridView1_CellValueChanged(object sender, DataGridViewCellEventArgs e)
{
if (e.ColumnIndex != 0)
return;
var comboCell = (dataGridView1.Rows[e.RowIndex].Cells[0] as DataGridViewComboBoxCell);
var value = comboCell.Value;
dataGridView1.Rows[e.RowIndex].Cells["Video"].Value = value;
}
private void DataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
{
}
}
public class Exercise
{
public string Name { get; set; }
public string Link { get; set; }
}

add tooltip to datagrid column filled from sqlite query

I am trying to add a tooltip to a specific column that may or may not be present, depending on the results of an sqlite query. The columnheaders are filled in from the query results.
I have this code to fill the datagrid:
SQLiteCommand command = new SQLiteCommand(sql, m_dbConnection);
SQLiteDataAdapter sda = new SQLiteDataAdapter(command);
sda.Fill(dt);
MainDataGrid.ItemsSource = dt.DefaultView;
I would like to do something like:
if(ColumnHeader == "Gauge")
{Column.Tooltip.Text = "Double click Gauge # to view details";} //Tooltip shows for entire column
But, I can't imagine it's that easy. I am completely self taught in c# and wpf, so a lot of my problems come from not knowing how to word the question properly.
I am not looking for a copy-paste answer. Just a link(s) and an explanation.

I used the following code:
void MainDataGrid_AutoGeneratingColumn(object sender, DataGridAutoGeneratingColumnEventArgs e)
{
string tooltip = null;
switch (e.Column.Header.ToString())
{
case "Gauge":
tooltip = "Double click Gauge ID to view its details";
break;
}
if (tooltip != null)
{
var style = new Style(typeof(DataGridCell));
style.Setters.Add(new Setter(ToolTipService.ToolTipProperty, tooltip));
e.Column.CellStyle = style;
}
}
I got it here: Setting ToolTip for DataGridView automatically created columns
Thanks #Sinatr for getting me started in the right path.

Progmatically Checking "CheckBoxCell" in DataGridView

Currently my application will load items from the SQL database that the user can select from, they can then use the checkboxes to select which of these items are applicable to themselves, then can then save these selections and exit the window; this works fine.
I need to make my application fetch the user's previously saved selection, and then check the relevant boxes once the grid has been populated with all of the options (so just showing their selection).
I have the following code so far:
private void LoadUserSelection()
{
using (SqlConnection conn = new SqlConnection(sys.gvConnectionString))
{
using (SqlCommand cmd = new SqlCommand(qry.SelectUsersSelections(), conn))
{
cmd.Parameters.AddWithValue("#SiteID", sys.gvSiteID);
using (SqlDataAdapter da = new SqlDataAdapter())
{
da.SelectCommand = cmd;
using (DataTable dt = new DataTable())
{
conn.Open();
da.Fill(dt);
conn.Close();
foreach (DataGridViewRow row in grdQueues.Rows)
{
foreach (DataRow dr in dt.Rows)
{
if (dr["ID"].ToString() == row.Cells["ID"].Value.ToString())
{
DataGridViewCheckBoxCell chk = (DataGridViewCheckBoxCell)row.Cells[0];
chk.Value = 1;
}
}
}
}
}
}
}
}
Hopefully this code make sense, it runs without issue, however even though the code does in fact hit the section to mark the checkbox as true it does not.
I have tried the following alternatives for chk.Value = 1
chk.Value = TrueValue;
chk.Selected = true;
chk.Value = true;
As this is a multi-user database, I cannot simply store boolean values against the pre-determined list, hence why the pre-determined list is fetched and populated first, and then I'm trying to action their previous selections.
Note: I'm not too sure what I'm doing above is even the best way to go around this, so as a bonus, if anyone has any tips on how I've nested the using statements or how I'm approaching this, it would be appreciated.

Your code is correct using either of the two following options:
chk.Value = 1; // Or...
chk.Value = true;
The only way I could duplicate this problem was if the DataGridViewCheckBoxColumn was manually added in the form constructor. Otherwise, when that column was also part of the original DataTable your code always worked in my tests. So assuming your workflow in that constructor is:
DataGridViewCheckBoxColumn col = new DataGridViewCheckBoxColumn();
// any col Properties manually set
dataGridView1.Columns.Add(col);
dataGridView1.AllowUserToAddRows = false;
dataGridView1.DataSource = LoadAllData();
LoadUserSelection();
You will see that LoadUserSelection correctly runs as expected, but due to binding behavior during construction you are not seeing the results. If you were to call your method anywhere else (like a Button.Click event) you'd probably see the results. If you want this behavior once the data is loaded, the following worked for me:
this.dataGridView1.DataBindingComplete += DataGridView1_DataBindingComplete;
private void DataGridView1_DataBindingComplete(object sender, DataGridViewBindingCompleteEventArgs e)
{
this.LoadUserSelection();
}

How do i set a default comboBox Text?

How do i set a default text for my combobox on loadup, such as "Select Something". I tried this on the Form Load
comboBox1.Text = "Select Something";
But that didnt work. Any help?

Your code is working for me, so you must be setting the text before binding the combobox to your data source. In the following test code it works if you have the cb.Text = "Test"; running after the databinding of the combobox, and displaying the same symptoms you are seeing if you are setting prior to the databind.
Consider the following code where there is just a combobox defined on the form (cb). If you move the last line to the top, it will display the symptoms you are seeing.
private void Form1_Load(object sender, EventArgs e)
{
DataTable tb = new DataTable();
tb.Columns.Add("Value");
tb.Rows.Add("Combo Box Item");
cb.DisplayMember = "Value";
cb.ValueMember = "Value";
cb.DataSource = tb;
cb.Text = "Select Something";
}

How to create an Auto-complete combo-box or text box to filter text containing a string

How do I create an Auto-complete ComboBox or TextBox that filters text based on a string?
For example: if I type an "a" in a TextBox, I only get to see all strings containing an "a".

If you mean show suggestions then it's a simple matter of changing a property when you have the TextBox selected in your IDE of choice:
The options shown in the picture allow you to change the rules for autocompleting text in the text box as well as the source for the suggestions. (Visual Studio 2010)
You can go to the following link to learn more about the TextBox control.
MSDN Text Box Control

Windows Forms's autocomplete implementation uses Shell's autocomplete object, which can only do a "BeginWith" match until Windows Vista.
If you can demand your users to upgrade to Windows Vista, you can use IAutoComplete2::SetOptions to specify ACO_NOPREFIXFILTERING. Otherwise I am afraid you need to write your own.

Here is how I auto-complete for a specific value in a comboDropDown box.
void comboBox_Leave(object sender, EventArgs e)
{
ComboBox cbo = (sender as ComboBox);
if (cbo.Text.Length > 0)
{
Int32 rowIndex = cbo.FindString(cbo.Text.Trim());
if (rowIndex != -1)
{
cbo.SelectedIndex = rowIndex;
}
else
{
cbo.SelectedIndex = -1;
}
}
else
{
cbo.SelectedIndex = -1;
}
}

This filters results based on user input. Optimizing for large lists, populating your own data and error handling left out for you to complete:
public partial class Form1 : Form
{
List<String> data;
ListView lst = new ListView();
TextBox txt = new TextBox();
public Form1()
{
InitializeComponent();
data = new List<string>("Lorem ipsum dolor sit amet consectetur adipiscing elit Suspendisse vel".Split());
}
private void Form1_Load(object sender, EventArgs e)
{
this.Controls.Add(txt);
lst.Top = 20;
txt.TextChanged += new EventHandler(txt_TextChanged);
lst.View = View.List;
this.Controls.Add(lst);
list_items("");
}
void txt_TextChanged(object sender, EventArgs e)
{
list_items(txt.Text);
}
void list_items(string filter)
{
lst.Items.Clear();
List<string> results = (from d in data where d.Contains(filter) select d).ToList();
foreach (string s in results)
{
lst.Items.Add(s);
}
}
}
To get the combobox to auto complete, set the AutoCompleteSource and AutoCompleteMode properties:
cbo.AutoCompleteSource = AutoCompleteSource.ListItems;
cbo.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
The ListItems source tells the combo to use it's items collection as the auto complete source.

I know this is an old topic but i tried so hard to find a solution for c# autocomplete filtering too and couldn't find any so i came up with my own simple and easy way so i'll just share it for those who may think it's useful and wanna use in their projects. It does not use the control's autocomplete features. What it does just simply get the text entered from the combobox, search it in the source then display only the matching ones from the source as the combobox' new source. I implemented it in the combobox' KeyUp event.
Let's say (actually this is what i do for almost all the cases when i want autocompleting) we have a globally assigned DataTable called dt_source to be the combobox' source and it has two columns: id(int) and name(string).
DataTable dt_source = new DataTable("table");
dt_source.Columns.Add("id", typeof(int));
dt_source.Columns.Add("name", typeof(string));
And this is what my KeyUp method looks like:
private void cmb_box_KeyUp(object sender, KeyEventArgs e)
{
string srch = cmb_box.Text;
string srch_str = "ABackCDeleteEFGHIJKLMNOPQRSpaceTUVWXYZD1D2D3D4D5D6D7D8D9D0";
if (srch_str.IndexOf(e.KeyCode.ToString()) >= 0)
{
cmb_box.DisplayMember = "name"; // we want name list in the datatable to be shown
cmb_box.ValueMember = "id"; // we want id field in the datatable to be the value
DataView dv_source = new DataView(dt_source); // make a DataView from DataTable so ...
dv_source.RowFilter = "name LIKE '%"+ srch +"%'"; // ... we can filter it
cmb_box.DataSource = dv_source; // append this DataView as a new source to the combobox
/* The 3 lines below is the tricky part. If you repopulate a combobox, the first
item in it will be automatically selected so let's unselect it*/
cmb_box.SelectedIndex = -1; // unselection
/* Again when a combobox repopulated the text region will be reset but we have the
srch variable to rewrite what's written before */
cmb_box.Text = srch;
/* And since we're rewriting the text region let's make the cursor appear at the
end of the text - assuming 100 chars is enough*/
cmb_box.Select(100,0);
cmb_box.DroppedDown = true; // Showing the dropdownlist
}
}

I think your best bet is to override the OnKeyDown(KeyEventArgs e) event, and use the value to filter the ComboBox.AutoCompleteCustomSource. Then as noted above, change the AutoCompleteSource to AutoCompleteSource.ListItems.