TStringGrid class

Declaration

TStringGrid = class(TCustomStringGrid)

Inheritance

1. TStringGrid
2. TCustomStringGrid
3. TCustomDrawGrid
4. TCustomGrid
5. TCustomControl
6. TWinControl
7. TControl
8. TLCLComponent
9. TComponent
10. TPersistent
11. TObject

Description

TStringGrid is a TCustomStringGrid descendant which implements a specialized grid for displaying textual content in a matrix of columns and rows.

TStringGrid is designed for use with string content stored in its cells. Internally, columns and rows in the class are mapped to TStringGridStrings instances used to store the values in the grid control. TStringGrid also allows a TObject instance to be stored for each cell in the grid using the Objects property.

TStringGrid sets the visibility for properties defined in the ancestor class. It has an overridden WSRegisterClass method to register properties (from older LCL versions) which are no longer used in LCL component streaming.

Key properties:

The ColCount and RowCount properties contain the column and row count of the grid.

The FixedCols and FixedRows properties specify the count of fixed columns or rows that are used for headings.

The column widths and row heights of the grid are accessible with the ColWidths and RowHeights properties.

The DefaultColWidth and DefaultRowHeight properties are used to specify default column widths or row heights respectively.

The colors used for the cells and other grid elements are specified in the following properties:

• AlternateColor
• BorderColor
• FixedColor
• FixedHotColor
• FocusColor
• GridLineColor

The GridWidth and GridHeight properties contain the dimension of the entire grid.

The ScrollBars controls the creation of scroll bars for the grid.

The LeftCol, TopRow, VisibleColCount and VisibleRowCount properties contain information about the visible area of the grid.

The Options controls options for the grid.

Key methods and events:

If the user highlights a cell of the grid, the SelectCell method is called that triggers the OnSelectCell event. The position of the highlighted cell is stored within the Col and Row property.

The MouseToCell method calculates a grid cell from a given screen position.

Huge changes to the grid should be encapsulated in calls to BeginUpdate and EndUpdate to speed up the application.

Component developers must override the DrawCell method in customized grid controls.

Grid cell selection

The location of the current (focused) cell (or row) can be changed using keyboard, mouse or through code. In order to change cell focus successfully to another position, we must test the target position to see if it is allowed to receive cell focus. When using keyboard, the property AutoAdvance performs part of the process by finding what should be the next focused cell. When using mouse clicks or moving by code, focus will not move from the current cell unless the target cell is permitted to receive focus.

The grid calls the SelectCell function to see if a cell is focusable: if this function returns true, then the target cell identified with arguments aCol and aRow is focusable (the current implementation of TCustomGrid simply returns true). TCustomDrawGrid and hence TDrawGrid and TStringGrid override this method to check first if cell is any wider than 0; normally you don't want a 0 width cell selected so a cell with these characteristics is skipped automatically in the process of finding a suitable cell. The other thing the overridden method SelectCell does is to call the user configurable event OnSelectCell: this event receives the cell coordinates as arguments and always returns a default result value of true.

Once a cell is known to be focusable and we are sure a movement will take place, first the method BeforeMoveSelection is called; this in turns triggers the OnBeforeSelection event. This method's arguments are the coordinates for the new focused cell. At this point any visible editor is hidden too. The "before" word means that selection is not yet changed and current focused coordinates can be accessed with grid.Col and grid.Row properties.

After that, the internal focused cell coordinates are changed and then MoveSelection method is called; this method's purpose is to trigger the OnSelection event if set (this is a notification that the focused cell has, by this time, already changed and cell coordinates are now available through grid.row and grid.col properties).

Note that is not good to use OnSelectCell event to detect cell focus changes, as this event will be triggered several times even for the same cell in the process of finding a suitable cell. Is better to use OnBeforeSelection or OnSelection events for this purpose.

Multi-selection

The Lazarus grids are able to extend the selection to multiple cells. The Option goRangeSelect must be active for this purpose: Now you can drag the mouse over a rectangle on the grid to select all the cells included or intersected by this rectangle. Or you can click on the cell in one corner, hold SHIFT down and either click on the opposite corner of the selection, or press the arrow keys to extend the selection in the corresponding direction.

In the default setting of the RangeSelectMode property, rsmSingle, only a single cell or cell range (rectangle of cells) can be selected, as described. The rsmMulti mode, however, allows selection of multiple and even discontiguous cells or ranges. After selecting the first cell/range as already described, hold the CTRL key down and click on the next cell or drag over the next range to be selected. Instead of dragging you can also select an additional range by pressing SHIFT (in addition to CTRL) and clicking on the opposite corner of the range or pressing the arrow keys.

The selected cells are highlighted by a different color. Note, however, that the currently focused cell has the default background color of the grid unless you set the Option goDrawFocusSelected.

Clicking somewhere on an unselected cell unselects the selected cell(s)/range( s).

If you need to access selections by code you can do this by using these TCustomGrid properties:

SelectedRange[AIndex: Integer]: TGridRect:

Returns the column/row coordinates of the corner cells of the selected range at the specified index (type TGridRect = TRect). A single selected cell is considered to be a block with equal Left and Right column and equal Top and Bottom row coordinates.

SelectedRangeCount: Integer:

The number of selected blocks.

Note that these are read-only properties, you can add and change selections only by user interaction. But you can call ClearSelections to unselect everything.

Your selection handling code must be prepared that a selected cell could be found in another selected block again. Normally this situation is prohibited in the user interface, but there are scenarios where a selection could be extended into another range so that the overlapping cells are "selected twice".

Additional information about grid usage is available on the Lazarus wiki in the following pages:

• Grids Reference Page
• TDrawGrid
• TStringGrid

See also

• TCustomStringGrid
• HowToUseGrids

Properties

Methods

Events

Inherited