Virtual Mode in the Windows Forms DataGridView Control

With virtual mode, you can manage the interaction between the DataGridView control and a custom data cache. To implement virtual mode, set the VirtualMode property to true and handle one or more of the events described in this topic. You will typically handle at least the CellValueNeeded event, which enables the control look up values in the data cache.

Virtual mode is necessary only when you need to supplement or replace bound mode. In bound mode, you set the DataSource property and the control automatically loads the data from the specified source and submits user changes back to it. You can control which of the bound columns are displayed, and the data source itself typically handles operations such as sorting.

You can supplement bound mode by displaying unbound columns along with the bound columns. This is sometimes called "mixed mode" and is useful for displaying things like calculated values or user-interface (UI) controls.

Because unbound columns are outside the data source, they are ignored by the data source's sorting operations. Therefore, when you enable sorting in mixed mode, you must manage the unbound data in a local cache and implement virtual mode to let the DataGridView control interact with it.

For more information about using virtual mode to maintain the values in unbound columns, see the examples in the DataGridViewCheckBoxColumn.ThreeState property and System.Windows.Forms.DataGridViewComboBoxColumn class reference topics.

If bound mode does not meet your performance needs, you can manage all your data in a custom cache through virtual-mode event handlers. For example, you can use virtual mode to implement a just-in-time data loading mechanism that retrieves only as much data from a networked database as is necessary for optimal performance. This scenario is particularly useful when working with large amounts of data over a slow network connection or with client machines that have a limited amount of RAM or storage space.

For more information about using virtual mode in a just-in-time scenario, see Implementing Virtual Mode with Just-In-Time Data Loading in the Windows Forms DataGridView Control.

If your data is read-only, the CellValueNeeded event may be the only event you will need to handle. Additional virtual-mode events let you enable specific functionality like user edits, row addition and deletion, and row-level transactions.

Some standard DataGridView events (such as events that occur when users add or delete rows, or when cell values are edited, parsed, validated, or formatted) are useful in virtual mode, as well. You can also handle events that let you maintain values not typically stored in a bound data source, such as cell ToolTip text, cell and row error text, cell and row shortcut menu data, and row height data.

For more information about implementing virtual mode to manage read/write data with a row-level commit scope, see Walkthrough: Implementing Virtual Mode in the Windows Forms DataGridView Control.

For an example that implements virtual mode with a cell-level commit scope, see the VirtualMode property reference topic.

The following events occur only when the VirtualMode property is set to true.

The following events are useful in virtual mode, but can be used regardless of the VirtualMode property setting.

If you are implementing virtual mode in order to work efficiently with large amounts of data, you will also want to ensure that you are working efficiently with the DataGridView control itself. For more information about the efficient use of cell styles, automatic sizing, selections, and row sharing, see Best Practices for Scaling the Windows Forms DataGridView Control.

• DataGridView
• VirtualMode
• Performance Tuning in the Windows Forms DataGridView Control
• Best Practices for Scaling the Windows Forms DataGridView Control
• Walkthrough: Implementing Virtual Mode in the Windows Forms DataGridView Control
• Implementing Virtual Mode with Just-In-Time Data Loading in the Windows Forms DataGridView Control