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C# Fail to set DatagridComboboxCell value to null

I am trying to make a datagridview in which there exists a combobox column, and this column is binded a list of options. My logic is that, if the user selects the wrong option, the program could detect and deselect this wrong option(which means comboboxCell.value = null).
The psuedo code for this logic is as follows:
//use CurrentCellDirtyStateChanged and CellValueChanged as event listeners
this.DGV.CurrentCellDirtyStateChanged += DGV_CurrentCellDirtyStateChanged;
this.DGV.CellValueChanged += DGV_CellValueChanged;
//CurrentCellDirtyStateChanged event
private void DGV_CurrentCellDirtyStateChanged(object sender, EventArgs e)
{
if (DGV.IsCurrentCellDirty)
{
DGV.CommitEdit(DataGridViewDataErrorContexts.Commit);
}
}
//CellValueChanged event
private void DGV_CellValueChanged(object sender, DataGridViewCellEventArgs e)
{
if (!CheckingCorrect(DGV.CurrentCell))
{
// set selected value null
DGV.CurrentCell.Value = null
}
}
However, after the code sets currentcell value to null, the datagridview cell still kept the selected value shown.
I also tried may other ways like DGV.ClearSelection(), but none of these works.

There are two things that will make working with the DataGridViewComboBoxColumn/Cell easier...
Make a Class specifically for the combo box column
Use the proper event to help in casting the DataGridViewComboBoxCell to a
regular ComboBox.
In this example I made a simple Class called ComboValues that has two properties for the column ValueMember and DisplayMember. In this example the ValueMember is an int, however you could leave it out or use some other type that fits your needs. This class will simplify things as we will have the properties for both the ValueMember and DisplayMember for the combo box column.
This ComboValues Class may look something like…
public class ComboValues {
public int Value { get; set; }
public string Display { get; set; }
}
Then a method to get a List<ComboValues> from the DB that we will use as a DataSource for the combo box column.
private List<ComboValues> GetComboValues() {
List<ComboValues> items = new List<ComboValues>();
items.Add(new ComboValues { Value = 0, Display = null });
items.Add(new ComboValues { Value = 1, Display = "Option 1" });
items.Add(new ComboValues { Value = 2, Display = "Option 2" });
items.Add(new ComboValues { Value = 3, Display = "Option 3" });
items.Add(new ComboValues { Value = 4, Display = "Option 4" });
return items;
}
And setting up the combo box column for the grid…
private DataGridViewComboBoxColumn GetComboCol() {
DataGridViewComboBoxColumn col = new DataGridViewComboBoxColumn();
col.HeaderText = "Combo Items";
col.ValueMember = "Value";
col.DisplayMember = "Display";
col.DataSource = GetComboValues();
return col;
}
We will call the above method in the forms Load event to add the column to the Grid…
private void Form1_Load(object sender, EventArgs e) {
DGV.Columns.Add(GetComboCol());
}
Next, we want to set up the edited DataGridViewComboBoxCell to act like a REGULAR ComboBox. We can do this using the grids EditingControlShowing event. This event will fire when the user clicks into a cell and in this case if the user clicks into a combo box cell, then we want to cast that cell to a globally defined ComboBox. So, we will need a global ComboBox variable called something like… EditedComboBox.
ComboBox EditedComboBox = null;
Is what we will do is that when the grids EditingControlShowing event fires and we check to see if it is the combo box cell, then we simply cast that cell to our global EditedComboBox and wire up its SelectedIndexChanged event. Then we can capture “when” the user “changes” a value in the combo box cell. The EditingControlShowing event may look something like…
private void DGV_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e) {
if (DGV.CurrentCell.ColumnIndex == 0) {
EditedComboBox = (ComboBox)e.Control;
if (EditedComboBox != null) {
EditedComboBox.SelectedIndexChanged += new EventHandler(ComboBox_SelectedIndexChanged);
}
}
}
Above, column index 0 is the target combo box column. All we need to do is implement and wire up the SelectedIndexChanged event and wait for the user to change the combo box value.
When the user does indeed change the combo boxes value, then our SelectedIndexChanged event will fire and it is in this event where you would “CHECK” if the selected value needs adjustments on some parameters. In this example, the condition is if the user selects “Option 3”, then that is an invalid value and we will set the cells value to null. This event may look something like…
private void ComboBox_SelectedIndexChanged(object sender, EventArgs e) {
//Debug.WriteLine("CB_SelectedIndexChanged");
if (EditedComboBox != null) {
ComboValues cv = (ComboValues)EditedComboBox.SelectedItem;
if (cv != null && !CheckingCorrect(cv.Display)) {
EditedComboBox.SelectedIndexChanged -= new EventHandler(ComboBox_SelectedIndexChanged);
EditedComboBox.SelectedIndex = 0;
EditedComboBox.SelectedIndexChanged += new EventHandler(ComboBox_SelectedIndexChanged);//DGV.CurrentCell.Value = 0;
}
}
}
In this event, we grab (cast) the combo boxes SelectedItem to a ComboValues object. With it we can easily check what value is selected and in turn set its value to null if needed. Note “item” 0 in our List<ComboValues> is the null value, so we set the combo boxes SelectedIndex to zero (0) to make the grid display a null value.
Also, since we are “changing” the combo boxes Index, we do NOT want this event to re-fire.
Lastly, we need one more event to wire up to TURN OFF the SelectedIndex changed event to prevent it from firing more than we want. In this case we will wire up the grids CellLeave event. In that event, the user is leaving the cell and if the EditedComboBox is not null... then we know we need to un-wire the event. It may look something like…
private void DGV_CellLeave(object sender, DataGridViewCellEventArgs e) {
if (EditedComboBox != null) {
EditedComboBox.SelectedIndexChanged -= new EventHandler(ComboBox_SelectedIndexChanged);
EditedComboBox = null;
}
}
I altered the checking code to check for a string and not necessarily a cell. The condition checker code…
private bool CheckingCorrect(string cellValue) {
if (cellValue != null && cellValue == "Option 3") {
return false;
}
else {
return true;
}
}
I hope this helps and makes sense. If you have questions, then feel free to ask.

DataGridView with Button Control - Delete Row

I want a Delete button at the end of each row of DataGridView and by clicking that I want to remove the desired row from the binding list which is data source of my grid.
But I can't seem to do it I have created a button object in product class and instantiated it with the unique id to remove that object from list. but button is not showing in the row.
There are TextBoxes in the form and users can enter text, and when they press Add button, a new object of product is instantiated with the provided fields and then it is added to the BindingList.
Finally this list is bound to the DataGridView and details are shown in the grid. (I have done this part).
and at last by clicking save button the list is saved in the DB.
public class Product{
public string Brand { get; set; }
public int ProductPrice { get; set; }
public int Quantity { get; set; }
public product(string brand,int productPrice, int quantity){
this.Brand = brand;
this.ProductPrice = productPrice;
this.Quantity = quantity;
}
}
public partial class MainForm: Form{
.....
BindingList<Product> lProd = new BindingList<Product>();
private void btnAddProduct_Click(object sender, EventArgs e){
string Brand = txtProBrand.Text;
int Price = Convert.ToInt32(txtPrice.Text);
int Quantity = Convert.ToInt32(txtQuantity.Text);
Product pro = new Product(Brand, Price, Quantity);
lProd.Add(pro);
dataGridView1.DataSource = null;
dataGridView1.DataSource = lProd;
}
.....
}

To show a button on DataGridView rows, you should add a DataGridViewButtonColumn to columns of your grid. Here is some common tasks which you should know when using button column:
Add Button Column to DataGridView
Show Image on Button
Set Text of Button
Handle Click Event of Button
Add Button Column to DataGridView
To show a button on each row of your grid, you can add a DataGridViewButtonColumn to columns of your grid programmatically or using designer:
var deleteButton=new DataGridViewButtonColumn();
deleteButton.Name="dataGridViewDeleteButton";
deleteButton.HeaderText="Delete";
deleteButton.Text="Delete";
deleteButton.UseColumnTextForButtonValue=true;
this.dataGridView1.Columns.Add(deleteButton);
Show Image on Button
If you prefer to draw image on button, you should have an image in a resource and then handle CellPainting event of your grid:
void dataGridView1_CellPainting(object sender, DataGridViewCellPaintingEventArgs e)
{
if (e.RowIndex == dataGridView1.NewRowIndex || e.RowIndex < 0)
return;
if (e.ColumnIndex == dataGridView1.Columns["dataGridViewDeleteButton"].Index)
{
var image = Properties.Resources.DeleteImage; //An image
e.Paint(e.CellBounds, DataGridViewPaintParts.All);
var x = e.CellBounds.Left + (e.CellBounds.Width - image.Width) / 2;
var y = e.CellBounds.Top + (e.CellBounds.Height - image.Height) / 2;
e.Graphics.DrawImage(image, new Point(x, y));
e.Handled = true;
}
}
Set Text of Button
You can use either of these options:
You can set Text property of your DataGridViewButtonColumn and also set its UseColumnTextForButtonValue to true, this way the text will display on each cells of that column.
deleteButton.Text="Delete";
deleteButton.UseColumnTextForButtonValue=true;
Also you can use Value property of cell:
this.dataGridView1.Rows[1].Cells[0].Value = "Some Text";
Also as another option, you can handle CellFormatting event of your grid. This way may be useful when you want to set different texts for buttons.
void dataGridView1_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e)
{
//If this is header row or new row, do nothing
if (e.RowIndex < 0 || e.RowIndex == this.dataGridView1.NewRowIndex)
return;
//If formatting your desired column, set the value
if (e.ColumnIndex=this.dataGridView1.Columns["dataGridViewDeleteButton"].Index)
{
e.Value = "Delete";
}
}
Handle Click Event of Button
To hanlde clicks on button, you can handle CellClick or CellContentClick event of your grid. Both events fires by click and by pressing Space key.
void dataGridView_CellClick(object sender, DataGridViewCellEventArgs e)
{
//if click is on new row or header row
if( e.RowIndex == dataGridView1.NewRowIndex || e.RowIndex < 0)
return;
//Check if click is on specific column
if( e.ColumnIndex == dataGridView1.Columns["dataGridViewDeleteButton"].Index)
{
//Put some logic here, for example to remove row from your binding list.
//yourBindingList.RemoveAt(e.RowIndex);
// Or
// var data = (Product)dataGridView1.Rows[e.RowIndex].DataBoundItem;
// do something
}
}
Get data of the record on Click event
You have e.RowIndex, then you can get the data behind the row:
var data = (Product)dataGridView1.Rows[e.RowIndex].DataBoundItem;
// then you can get data.Id, data.Name, data.Price, ...
You need to cast it to the data type of the recore, for example let's say Product.
If the data binding has been setup to use a DataTable, the the type to cast is DataRowView.
You can also use dataGridView1.Rows[e.RowIndex].Cells[some cell index].Value to get value of a specific cell, however DataBoundItem makes more sense.
Note
As mentioned by Ivan in comments, when you use BindingList you don't need to set datasource of grid to null and back to binding list with every change. The BindingList itself reflects changes to your DataGridView.

Focus not setting on DataGridView on Button Preview KeyDown Event

Pressing Tab key on Button Refresh is setting focus on the dropdown list but I need to set focus on Checkbox column and first row of grid when the grid datasource is not null else the next control, however it is selecting the given cell only. I have set tabIndex property in sequence, please tell me where i am wrong, here is my code:
private void btnRefresh_PreviewKeyDown(object sender, PreviewKeyDownEventArgs e)
{
if (e.KeyCode == Keys.Tab)
{
if (grid.DataSource != null)
{
grid.Focus();
grid.CurrentCell = this.grid[1, 0];
grid.CurrentCell.Selected = true;
grid.BeginEdit(false);
}
else
{
btnCancel.Focus();
}
}
}

Have you seen this post?
Seems like your use of the index is of Grid[x,y].
Try
grid.Rows[1].Cells[0]
However, this wil select only the cell (first cell, second row by the way).
If you want to select the entire row, try
grid.Rows.First().Selected = True
Hope it helps.

How to make particular cell visible inside Gridview, not complete column?

I had a Gridview which contains 3 columns , initially during form load i only two columns will be visible one column will be having data and other having checkbox.
i want when i check a checkbox in particular cell, corresponding to that checkbox the third column cell will be visible, i don't want to complete 3rd column to get visible on checking a check box ,Gridview is hardcoded only rows are dymanic (column1,column2 are set to visible and column 3 is set to invisible)
in below inmage when i m checking checkbox complete thried column is visible,which i don't want
can any one help me in this?
i tried below code but it is making 3rd column visible not, particular cell
public form1()
{
dataGridView1.CellValueChanged += new DataGridViewCellEventHandler(dataGridView1_CellValueChanged);
}
void dataGridView1_CellValueChanged(object sender, DataGridViewCellEventArgs e)
{
dataGridView1.Columns[e.ColumnIndex + 1].Visible = true;
}

Well You can try RowCommand event for this but as i see you already have event created for checkbox ,Try to find row Index for particular row and then use Cell number (cell[2]) to find the control and assign its property as visible = false,

Here is the demo I've just tried. It seems to work OK. The whole idea is You can't hide a particular cell in DataGridView. However you can make it hidden as a normal GUI engine will use when it wants to hide any control/element (I think so). You just customize it to paint the cell with the BackgroundColor of your DataGridView. Of course, to make it work, it's not such easy. Here is the code for you:
//First, you have to be sure the whole third column is Visible.
//CellPainting event handler for your dataGridView1
private void dataGridView1_CellPainting(object sender, DataGridViewCellPaintingEventArgs e)
{
if (e.ColumnIndex == 2)//This is the Column index you want to hide.
{
object o = e.RowIndex == -1 ? null : dataGridView1[e.ColumnIndex - 1,e.RowIndex].Value;
if (o!=null &&!(bool)o || e.RowIndex == -1 || e.RowIndex == dataGridView1.RowCount - 1)
{
e.Graphics.FillRectangle(new SolidBrush(dataGridView1.BackgroundColor), e.CellBounds);
if(e.RowIndex > -1) dataGridView1[e.ColumnIndex, e.RowIndex].ReadOnly = true;
e.Handled = true;
}
if (o != null && (bool)o)
{
dataGridView1[e.ColumnIndex, e.RowIndex].ReadOnly = false;
}
}
}
//CellContentClick event handler for your dataGridView1
private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
{
UpdateThirdColumCell(e);
}
//CellContentDoubleClick event handler for your dataGridView1
private void dataGridView1_CellContentDoubleClick(object sender, DataGridViewCellEventArgs e)
{
UpdateThirdColumCell(e);
}
private void UpdateThirdColumCell(DataGridViewCellEventArgs e)
{
if (e.ColumnIndex == 1)//The column index of the CheckBox column
{
DataGridViewCheckBoxCell cell = (DataGridViewCheckBoxCell)dataGridView1[e.ColumnIndex, e.RowIndex];
cell.Value = cell.EditingCellFormattedValue;
dataGridView1.Invalidate();
if ((bool)cell.Value)
{
dataGridView1.CurrentCell = dataGridView1[e.ColumnIndex + 1, e.RowIndex];
}
}
}
//CellStateChanged event handler for your dataGridView1
private void dataGridView1_CellStateChanged(object sender, DataGridViewCellStateChangedEventArgs e)
{
if (e.Cell.ColumnIndex == 2 && e.Cell.Selected)
{
dataGridView1.BeginEdit(false);
}
}
And that's all :)

Yeah ,actually we can't make invisible but i want to give an explianation about it in simple way.using
datagridview.rows(e.rowindex).cells[your column name]=true ;
using this it won't allow the user to enter the data in the textbox.if it is false then we can modify it/enter any text.
datagridview.rows(e.rowindex).cells[your column name].backcolour=color.gray/white/black;
using this we can fill color to a particular textbox which is to be painted when checkbox is true/false;

How do I add a buttons to some (not all) of the columns in my DataGridView?

I'm trying to update this DataGridView object such that if a value == "bob" there will be a button in a column next to its name, otherwise I don't want any button to appear.
DataGridViewTextBoxColumn valueColumn = new DataGridViewTextBoxColumn();
DataGridViewButtonColumn buttonColumn = new DataGridViewButtonColumn();
buttonColumn.ReadOnly = true;
buttonColumn.Visible = false;
this.dgv.Columns.AddRange(new System.Windows.Forms.DataGridViewColumn[] {
valueColumn,
buttonColumn,
});
//elsewhere...
if(value == "bob")
{
Button button = new Button()
{
Text = "null",
};
index = dgv.Rows.Add(value, button);
DataGridViewButtonCell buttonCell = dgv.Rows[index].Cells[2] as DataGridViewButtonCell;
buttonCell.Visible = true;
}
else
{
dgv.Rows.Add(value);
}
But, since I can't set Visible on a cell, this doesn't work. Is there a way to add a button to only the rows were Value == "bob"?

Here is a neat little hack that I've used before to accomplish this:
Instead of using a DataGridViewButtonColumn, use the DataGridViewTextBoxColumn and add a DataGridViewButtonCell where appropriate.
e.g.
private void button1_Click(object sender, EventArgs e)
{
// Iterate through each of the rows.
for (int i = 0; i < dgv.RowCount - 1; i++)
{
if (dgv.Rows[i].Cells[0].Value.ToString() == "bob")
{
// Here is the trick.
var btnCell = new DataGridViewButtonCell();
dgv.Rows[i].Cells[1] = btnCell;
}
}
}
In the example above, I have two DataGridViewTextBoxColumns and iterate through each of the rows on a button click event. I check the first column to see if it contains "bob" and if it does, I add a button in the column next to it. You can use this trick however you want (i.e. button clicks, RowsAdded event, CellEndEdit event, etc.). Experiment in different ways. Hope this helps someone!

There are two possibilities here, one ugly and one from MSDN.
The Ugly: Add a button to your DGV at runtime
Do the following:
- Add an unbound DataGridViewTextBoxColumn to your DGV. Note it's index value in your DGV; this is where you'll put your button.
- Use your DGV's CellFormatting event like so:
private void dataGridView1_CellFormatting(object sender, DataGridViewCellFormattingEventArgs e) {
if (e.ColumnIndex == 0) { // Assumes column 0 has the data that determines if a button should be displayed.
if (e.Value.ToString() == "bob") { // Test if a button should be displayed on row.
// Create a Button and add it to our DGV.
Button cellButton = new Button();
// Do something to identify which row's button was clicked. Here I'm just storing the row index.
cellButton.Tag = e.RowIndex;
cellButton.Text = "Hello bob";
cellButton.Click += new EventHandler(cellButton_Click);
dataGridView1.Controls.Add(cellButton);
// Your ugly button column is shown here as having an index value of 3.
Rectangle cell = this.dataGridView1.GetCellDisplayRectangle(3, e.RowIndex, true);
cellButton.Location = cell.Location;
}
}
}
When a user clicks the button the cellButton_Click event will fire. Here's some test code:
void cellButton_Click(object sender, EventArgs e) {
Console.WriteLine("Hello from row: {0}", ((Button) sender).Tag);
}
As you can see this isn't very refined. I based it on an even uglier sample I found. I'm sure you can modify it to suit your needs.
From MSDN: Roll your own (extend) DataGridViewButtonColumn that conditionally displays a disabled button.
For this option see How to: Disable Buttons in a Button Column in the Windows Forms DataGridView Control
Of course this option doesn't actually remove any buttons, only conditionally disables them. For your application however, this might be better.

You can handle cell painting on cell painting event:
private void dgv_CellPainting(object sender, DataGridViewCellPaintingEventArgs e)
{
if(e.RowIndex>=0 && e.ColumnIndex == indexOfButtonColumn && value[e.RowIndex] != "bob")
{
e.Paint(e.ClipBounds, DataGridViewPaintParts.All & ~DataGridViewPaintParts.ContentForeground & ~DataGridViewPaintParts.ContentBackground);
e.Handled = true;
}
}