To completely comprehend the way Objective Grid draws, let's take a look at how it implements and manipulates the controls for each cell.

Each composed style object for a cell contains an identifier for a control. Like any other style attribute, this identifier can be changed at run time allowing the developer maximum flexibility. The CGXGridCore class maintains a map of registered control types and identifiers. In the CGXGridCore::OnGridInitialUpdate() member function, the developer can register any additional control types with their identifiers by calling RegisterControl().

Another interesting facet of the control implementation is the concept of the current cell. Objective Grid manages the current cell as the user navigates through the grid by clicking or using arrow keys. When the user changes the current cell, the grid resets the attributes of the control bound to the previous current cell and initializes the control of the new current cell. Finally, Objective Grid passes all other events to the control so the end user can interact directly with the control. When the user changes the current cell, the grid object takes over again and the current cell process starts over.

2.4.1 Current Cell Interface

SetCurrentCell()

Selects the current cell at the given coordinates.

GetCurrentCell()

Returns TRUE if a current cell exists and retrieves the cell coordinates of the current cell.

IsCurrentCell()

Returns TRUE if a current cell exists or is the specified cell.

MoveCurrentCell()

Selects a new current cell based on an offset from the existing current cell in a specified direction.

TransferCurrentCell()

2.4.2 Current Cell Notifications

There are many notification methods the developer can override in a CGXGridCore-derived class. Many of the notification methods have related virtual methods in the CGXControl class. You can choose whether you want to override the method for all cells in the grid or only for specific controls.

CanSelectCurrentCell()

Called to determine if the specified cell can be selected or deselected. If the cell is deselected, CanSelectCurrentCell() calls OnValidateCell(); otherwise it returns TRUE.

OnCanceledEditing()

Called after the current cell's content is canceled and the control has been reinitialized with the previous cell's data.

OnCancelEditing()

Called when the user presses <ESC> on the current cell. You should return TRUE if the control can be deactivated. If you return FALSE, the control cannot be deactivated.

OnClickedButtonRowCol()

Called when the user presses some sort of button (e.g. a pushbutton, hotspot, or radio button) inside of a grid cell.

OnDeleteCell()

Called when the user presses <DELETE> in the inactive current cell. Returns TRUE if the cell's data can be deleted.

OnEndEditing()

Called when the user confirms the contents of the current cell and they are valid. You should return TRUE if the data can be accepted. If you return FALSE, the data will not be accepted, and the cell will remain in edit mode.

OnInitCurrentCell()

Called when current cell is initialized. CGXControl::Init() fires this event.

DoLButtonDown()

Delegates the standard MFC OnLButtonDown() event from (CGXGridWnd and CGXGridView) to the correct spot of the grid.

OnLButtonClickedRowCol()

Called when the user clicks and releases the left mouse button in a cell.

OnLButtonDblClkRowCol()

Called when the user double-clicks the left mouse button in a cell.

OnLButtonHitRowCol()

Called when the user clicks the left mouse button in a cell. Subsequent calls occur when the mouse is dragged and when the user releases the mouse button.

OnLeftCell()

Called after the grid has deselected the old current cell. You may override this method and redraw the cell or row. If you return FALSE, the cell will not be redrawn by the grid. If you return TRUE (default), the grid will refresh the cell itself.

OnMButtonClickedRowCol()

Called when the user clicks and releases the middle mouse button in a cell.

OnMButtonDblClkRowCol()

Called when the user double-clicks the middle mouse button in a cell.

OnMButtonHitRowCol()

Called when the user clicks the middle mouse button in a cell. Subsequent calls occur when the mouse is dragged and when the user releases the mouse button.

OnModifyCell()

Called when the user changes text in the current cell.

OnMovedCurrentCell()

Called when a new current cell has been selected, but the change is not yet visible.

DoRButtonDown()

Delegates the standard MFC OnRButtonDown() event from (CGXGridWnd and CGXGridView) to the correct spot of the grid.

OnRButtonClickedRowCol()

Called when the user clicks and releases the right mouse button in a cell.

OnRButtonDblClkRowCol()

Called when the user double-clicks the right mouse button in a cell.

OnRButtonHitRowCol()

Called when the user clicks the right mouse button in a cell. Subsequent calls occur when the mouse is dragged and when the user releases the mouse button.

OnStartEditing()

Called when the user presses a key or the mouse on the current cell. Returns TRUE if the control can be activated for editing.

OnValidateCell()

Called after the user has left a modified cell and before another cell is selected. OnValidateCell() can be overridden to perform cell-level validation.

ProcessKeys()

Interprets keystrokes sent either from the current cell's control or the grid-window.

2.4.3 Predefined Controls

The following control IDs are predefined in Objective Grid. You can use one of the following control IDs in a call to a SetStyleRange() command, without explicitly registering them. Objective Grid will register the control automatically as needed.

Table 2: Predefined control IDs

Here is an example of using these settings:

// Assign a combo box to a cell SetStyleRange(CGXRange(3,3), CGXStyle() .SetControl(GX_IDS_CTRL_COMBOBOX) .SetChoiceList("one\ntwo\nthree\n") );