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DataGridView.CellValueNeeded Event

Occurs when the VirtualMode property of the DataGridView control is true and the DataGridView requires a value for a cell in order to format and display the cell.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in system.windows.forms.dll)

public event DataGridViewCellValueEventHandler CellValueNeeded
/** @event */
public void add_CellValueNeeded (DataGridViewCellValueEventHandler value)

/** @event */
public void remove_CellValueNeeded (DataGridViewCellValueEventHandler value)

In JScript, you can handle the events defined by a class, but you cannot define your own.
Not applicable.

Use this event in virtual mode to populate cells with data from a custom data store without causing rows to become unshared. For more information about row sharing, see Best Practices for Scaling the Windows Forms DataGridView Control. For more information about virtual mode, see Virtual Mode in the Windows Forms DataGridView Control.

To add user-specified values to your custom data store, handle the CellValuePushed event.

For more information about handling events, see Consuming Events.

The following code example handles the CellValueNeeded event to populate cells with positive integers. This example is part of a larger example available in the VirtualMode reference topic.

#region "data store maintance"
const int initialValue = -1;

private void dataGridView1_CellValueNeeded(object sender,
    DataGridViewCellValueEventArgs e)
{
    if (store.ContainsKey(e.RowIndex))
    {
        // Use the store if the e value has been modified 
        // and stored.            
        e.Value = store[e.RowIndex];
    }
    else if (newRowNeeded && e.RowIndex == numberOfRows)
    {
        if (dataGridView1.IsCurrentCellInEditMode)
        {
            e.Value = initialValue;
        }
        else
        {
            // Show a blank value if the cursor is just resting
            // on the last row.
            e.Value = String.Empty;
        }
    }
    else
    {
        e.Value = e.RowIndex;
    }
}

private void dataGridView1_CellValuePushed(object sender,
    DataGridViewCellValueEventArgs e)
{
    store.Add(e.RowIndex, int.Parse(e.Value.ToString()));
}
#endregion

private Dictionary<int, int> store = new Dictionary<int, int>();

#region "data store maintance"
private final int INITIALVALUE = -1;

private void dataGridView1_CellValueNeeded(Object sender,
    DataGridViewCellValueEventArgs e)
{
    if (store.ContainsKey(e.get_RowIndex())) {
        // Use the store if the e value has been modified 
        // and stored.            
        e.set_Value((Int32)store.get_Item(e.get_RowIndex()));
    }
    else {
        if (newRowNeeded && e.get_RowIndex() == numberOfRows) {
            if (dataGridView1.get_IsCurrentCellInEditMode()) {
                e.set_Value((Int32)INITIALVALUE);
            }
            else {
                // Show a blank e if the cursor is just loitering
                // over(the)
                // last row.
                e.set_Value("");
            }
        }
        else {
            e.set_Value((Int32)e.get_RowIndex());
        }
    }
} //dataGridView1_CellValueNeeded

private void dataGridView1_CellValuePushed(Object sender,
    DataGridViewCellValueEventArgs e)
{
    store.Add(e.get_RowIndex(), Int32.Parse(e.get_Value().ToString()));
} //dataGridView1_CellValuePushed
#endregion

private Dictionary<int, int> store = new Dictionary<int, int>();

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0

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