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DataGridViewCellToolTipTextNeededEventHandler Delegate

Represents the method that will handle the CellToolTipTextNeeded event of a DataGridView.

Namespace:  System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

public delegate void DataGridViewCellToolTipTextNeededEventHandler(
	Object sender,
	DataGridViewCellToolTipTextNeededEventArgs e
)

Parameters

sender
Type: System.Object

The source of the event.

e
Type: System.Windows.Forms.DataGridViewCellToolTipTextNeededEventArgs

A DataGridViewCellToolTipTextNeededEventArgs that contains the event data.

The CellToolTipTextNeeded event occurs only when the DataGridView control DataSource property is set or its VirtualMode property is true.

When you handle the CellToolTipTextNeeded event, the ToolTip text you specify in the handler is shown whenever the mouse pointer is over a cell and the control ShowCellToolTips property value is true. The CellToolTipTextNeeded event is useful when you want to display ToolTips determined by the current state or value of a cell.

The CellToolTipTextNeeded event also occurs whenever the value of the DataGridViewCell.ToolTipText property is retrieved, either programmatically or when the mouse pointer enters a cell.

You can use the DataGridViewCellEventArgs.ColumnIndex and RowIndex properties to determine the state or value of a cell, and use this information to set the ToolTipText property. This property is initialized with the value of the cell ToolTipText property, which the event value overrides.

Handle the CellToolTipTextNeeded event when working with large amounts of data to avoid the performance penalties of setting the cell ToolTipText value for multiple cells. For more information, see Best Practices for Scaling the Windows Forms DataGridView Control.

For more information about handling events, see Consuming Events.

When you create a DataGridViewCellToolTipTextNeededEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about event-handler delegates, see Events and Delegates.

The following code example uses ToolTips to display additional information about cell contents in the ReportsTo column.

private DataTable Populate(string query, bool resetUnsharedCounter)
{
    if (resetUnsharedCounter)
    {
        ResetCounter();
    }

    // Alter the data source as necessary
    SqlDataAdapter adapter = new SqlDataAdapter(query,
        new SqlConnection("Integrated Security=SSPI;Persist Security Info=False;" +
        "Initial Catalog=Northwind;Data Source=localhost"));

    DataTable table = new DataTable();
    table.Locale = System.Globalization.CultureInfo.InvariantCulture;
    adapter.Fill(table);
    return table;
}

private Label count = new Label();
private int unsharedRowCounter;

private void ResetCounter()
{
    unsharedRowCounter = 0;
    count.Text = unsharedRowCounter.ToString();
}

private void dataGridView1_CellToolTipTextNeeded(object sender,
    DataGridViewCellToolTipTextNeededEventArgs e)
{

    if (theCellImHoveringOver.ColumnIndex == dataGridView1.Columns["ReportsTo"].Index &&
        theCellImHoveringOver.RowIndex > -1)
    {

        string reportsTo = dataGridView1.Rows[theCellImHoveringOver.RowIndex].
            Cells[theCellImHoveringOver.ColumnIndex].Value.ToString();

        if (String.IsNullOrEmpty(reportsTo))
        {
            e.ToolTipText = "The buck stops here!";
        }
        else
        {
            DataTable table = Populate(
                "select firstname, lastname from employees where employeeid = '" +
                dataGridView1.Rows[theCellImHoveringOver.RowIndex].
                Cells[theCellImHoveringOver.ColumnIndex].Value.ToString() +
                "'", false);

            e.ToolTipText = "Reports to " + table.Rows[0].ItemArray[0] + " " +
                table.Rows[0].ItemArray[1];
        }
    }
}

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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