dotnetmonitor.com

While sharing row instances saves memory, rows can easily become unshared. For example, whenever a user interacts directly with a cell, its row becomes unshared. Because this cannot be avoided, the guidelines in this topic are useful only when working with very large amounts of data and only when users will interact with a relatively small part of the data each time your program is run.

A row cannot be shared in an unbound DataGridView control if any of its cells contain values. When the DataGridView control is bound to an external data source or when you implement virtual mode and provide your own data source, the cell values are stored outside the control rather than in cell objects, allowing the rows to be shared.

A row object can only be shared if the state of all its cells can be determined from the state of the row and the states of the columns containing the cells. If you change the state of a cell so that it can no longer be deduced from the state of its row and column, the row cannot be shared.

For example, a row cannot be shared in any of the following situations:

         The row contains a single selected cell that is not in a selected column.

         The row contains a cell with its ToolTipText or ContextMenuStrip properties set.

         The row contains a DataGridViewComboBoxCell with its Items property set.

In bound mode or virtual mode, you can provide ToolTips and shortcut menus for individual cells by handling the CellToolTipTextNeeded and CellContextMenuStripNeeded events.

The DataGridView control will automatically attempt to use shared rows whenever rows are added to the DataGridViewRowCollection. Use the following guidelines to ensure that rows are shared:

         Avoid calling the Add(Object[]) overload of the Add method and the Insert(Object[]) overload of the Insert method of the Rows collection. These overloads automatically create unshared rows.

         Be sure that the row specified in the RowTemplate property can be shared in the following cases:

         When calling the Add() or Add(Int) overloads of the Add method or the Insert(Int, Int) overload of the Insert method of the Rows collection.

         When increasing the value of the RowCount property.

         When setting the DataSource property.

         Be sure that the row indicated by the indexSource parameter can be shared when calling the AddCopy, AddCopies, InsertCopy, and InsertCopies methods of the Rows collection.

         Be sure that the specified row or rows can be shared when calling the Add(DataGridViewRow) overload of the Add method, the AddRange method, the Insert(Int32,DataGridViewRow) overload of the Insert method, and the InsertRange method of the Rows collection.

To determine whether a row is shared, use the DataGridViewRowCollection.SharedRow(Int) method to retrieve the row object, and then check the object's Index property. Shared rows always have an Index property value of 1.