Grid, Column, Header

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Grid, Column, Header

A grid is a “browse-in-a-read” or at least the VFP equivalent. Columns and Headers are the stuff that grids are made of.

A grid is a container object. It contains columns. Columns are also containers. They contain headers and controls. Each column has only one header, but can contain as many controls as you like. By default, each column starts out with a single text box.

Grids display table, view, or cursor contents. Each row of the grid reflects a single record. When you access the control in a column, it’s bound to the appropriate field of the current record (or an expression based on the current record).

Grid

Property	Value	Purpose
ActiveColumn, ActiveRow	Numeric	Contain the number of the column and row that have focus, respectively. Measured in absolute terms from the first row and column of the grid. Uses ColumnOrder for columns, not creation order.
ChildOrder	Character	When the grid is the "many" side of a one-to-many relation, can indicate the name of the index tag by which the table is ordered. (We say "can" because you can also do this using Data Environment properties.)
ColumnCount	Numeric	The number of columns in the grid. Set it to -1 to have one column for each field in the current RecordSource.
Columns	Collection	References to the columns in the grid.
DeleteMark	Logical	Determines whether the grid has a "delete mark" column, allowing the user to click to delete or recall a record.
GridLineColor	Numeric	The color in which the grid lines appear.
GridLines	Numeric	Determines whether the grid has horizontal or vertical grid lines, neither or both.
GridLineWidth	Numeric	The thickness of the grid lines.
HeaderHeight	Numeric	The height of the headers in the grid.
Highlight	Logical	Determines whether the contents of the cell with focus are highlighted when you tab into the cell.
HighlightRow	Logical	Determines whether the current cell is highlighted.
HighlightRowLineWidth	Numeric	New to VFP 7, this determines the width of a box highlighting the current row. Acceptable values are 0–7. HighlightRow must be .T. to use this property.
LeftColumn	Numeric	Contains the ColumnOrder of the leftmost column currently visible in the grid.
LinkMaster	Character	When the grid is the "many" side of a one-to-many relation, can indicate the alias of the "one" table.
Objects	Collection	References to the columns in the grid.
Panel	Numeric	Determines which side of a split grid has the focus.
PanelLink	Logical	Determines whether the two sides of a split grid are linked.
Partition	Numeric	Determines (in pixels) where the divider for a split grid appears. When 0, the grid isn't split.
RecordMark	Logical	Determines whether the grid has a column (on the left border) that contains a pointer for the current record.
RecordSource	Character	The table name, alias or filename of the table or query that provides the data for the grid.
RecordSourceType	Numeric	The type of object that provides the data for the grid.
RelationalExpr	Character	When the grid is the "many" side of a one-to-many relation, can indicate the expression that links the two tables.
RelativeColumn, RelativeRow	Numeric	The column and row of the cell with focus, relative to the cell visible in the upper-left corner.
RowColChange	Numeric	Contains a value indicating whether the row, column, or both changed when moving into the current cell.
RowHeight	Numeric	The height of the rows in the grid.
Scrollbars	Numeric	Determines what scrollbars, if any, the grid has.

Event	Purpose
AfterRowColChange	Fires after focus has moved to a new cell.
BeforeRowColChange	Fires when the user attempts to move focus to a new cell.
Scrolled	Fires when the user uses the scrollbars.

Method	Purpose
ActivateCell	Set focus to a particular cell in the grid.
AddColumn, RemoveColumn	Add and remove columns from the grid.
DoScroll	Scroll the grid in a specified direction.
GridHitTest	Return information about the grid element at a specified point.

Column

Property	Value	Purpose
Bound	Logical	Determines whether the controls in the column are bound to the column's ControlSource or their own.
ColumnOrder	Numeric	Determines the display position of the column within the grid.
ControlCount	Numeric	The number of controls in the column.
Controls	Collection	References to the controls in the column, including the header.
CurrentControl	Character	The name of the control in the column that is presented to the user.
DynamicAlignment	Character	An expression that evaluates to a legal Alignment value and indicates the alignment for each cell in this column at this time.
DynamicBackColor, DynamicForeColor	Character	Expressions that evaluate to color values indicating the colors used for this column at this time. Evaluated individually for each cell in the column each time the cell is redrawn.
DynamicCurrentControl	Character	An expression that evaluates to the name of one of the column's controls. Indicates which control the user should see.
DynamicFontBold, DynamicFontItalic, DynamicFontName, DynamicFontSize, DynamicFontStrikeThru, DynamicFontUnderline	Character	Expressions that evaluate to appropriate font property values. Indicate which font characteristics the column should have at this time. Like other Dynamic... properties, these are evaluated each time the grid is refreshed.
DynamicFontOutline, DynamicFontShadow	Character	Do nothing except in VFP/Mac.
DynamicInputMask	Character	An expression that evaluates to a valid input mask, indicating the mask to be used for this column at this time. Evaluated each time the grid is refreshed.
Movable	Logical	Determines whether the user can move the column.
Objects	Collection	References to the controls in the column, including the header.
Resizable	Logical	Determines whether the user can resize the column.
SelectOnEntry	Logical	Determines whether the contents of the column are highlighted when the user tabs into it.
Sparse	Logical	Determines whether the current control for the column shows all the time or only when the cell has focus.

Up until VFP 7, headers had no unique or unusual properties, events or methods, just the basic ones shared by many classes. WordWrap is perhaps one of the most heralded enhancements, allowing multi-line grid headers.

One of the trickiest issues with grids is figuring out which object in a grid receives events, especially mouse events. The grid receives these events only if nothing it contains is able to. If you click in a control of a column, the control’s Click is executed. If you click on the header of a column, the header’s Click fires. To fire the grid’s Click, you have to click on a row after the last record, or on the record mark or delete mark.

VFP 7 Service Pack 1 fixes a bug introduced in VFP 7, where the Click and other events are called only if the grid's RecordSource contains records.

Like other objects designed only to be contained in a particular container, columns and headers can’t be subclassed in the Class Designer. (See PageFrame for the consequences of this.) A good builder can be useful here, as can putting some code in the grid class’s Init method.

Aside from all other differences, you can build grids two different ways depending on the value of ColumnCount. When ColumnCount is –1, the grid contains one column for each field of the RecordSource. In this case, you can change column properties in code using the Columns collection, but you can’t do it in the property sheet. When ColumnCount is positive, you can set up each specified column ahead of time.

Example

* Set up a grid as the child side of the relation between
* the TasTrade Orders and Order_Line_Items tables.
* Assume both tables are in the Data Environment, but that
* the relation between them has been removed. Usually, you
* wouldn't do it this way - you'd use the relation in the DE.
* Set these grid properties as shown:
RecordSource = "Order_Line_Items"
ChildOrder = "Order_Id"
LinkMaster = "Orders"
RelationalExpr = "Order_Id"

* Now let's put only the columns we want to see:
ColumnCount = 3

* Now switch to column properties.
* For column1.header1:
Caption = "Product Id"

* For column1:
ControlSource = "Order_Line_Items.Product_Id"

* For column2.header1:
Caption = "Unit Price"

* For column2:
ControlSource = "Order_Line_Items.Unit_Price"

* For column3.header1:
Caption = "Quantity"

* For column3:
ControlSource = "Order_Line_Items.Quantity"

* Now set the column up to use blue for any item where quantity
* is more than 10. For column3:
DynamicForeColor = "IIF(Order_Line_Items.Quantity>10, ;
   RGB(0,0,255),RGB(0,0,0))"

* You'll want to do more cosmetic stuff like resizing the
* columns and so forth.