Customizing scrollbars

TDBGridEh and vertical scrollbar. If you work with different types of dataset you can notice that for some types of dataset the DBGrid shows vertical scrollbar correctly, but for other dataset their vertical scrollbar has only three positions independently of record count in dataset. To adjust the vertical scrollbar accommodation the DBGrid uses RecordCount and RecNo property of DataSet component. But some dataset holds -1 in RecordCount and RecNo.DataSet function IsSequenced indicates whether the underlying database table uses record numbers to indicate the order of records. When IsSequenced returns True value, applications can safely use the RecNo property to navigate through records in the dataset and DBGrid can use RecNo property to show thumb position in vertical scrollbar. But when IsSequenced returns False value, DBGrid can not define current record position and it shows vertical scrollbar in three positions. DBGridEh component has possibility to show proportional scrollbar for no sequenced dataset. To do it we need to activate SumList and create list of record bookmars. Set SumList.Active to True and SumList.VirtualRecords to True. SumList will run through dataset and create list of records bookmarks. If you use client/sever technology to access database SumList will force dataset to fetch all records, but this operation can take much time. Keep in mind that VirtualRecords will work only for full relationship bookmarks dataset, it means that DataSet.ComapreBookmark function has to return > 0 if record1 is after record2 (i.e. record to which bookmark1 indicates has to be after record to which bookmark2 indicates). It must return 0 if bookmark1 and bookmark2 points to the same record, and value < 0 if record1 is before record2. TBDEDataSet in most cases support full relationship bookmarks.

You can control the horizontal and vertical scrolling bar using the Grid.VertScrollBar and Grid.HorzScrollBar properties of TGridScrollBarEh type. The TGridScrollBarEh class contains the following properties:

Tracking: Boolean Specifies whether or not the position in the grid to change immediately when user change the position of the slider when the user clicked the mouse and drags the slider.

Visible: Boolean Specifies permanent visibility slider bar. (The property is out of date, use VisibleMode)

SmoothStep: Boolean Sets the scroll step of the grid in which the grid is not specified on the border of the cell, and pixel-by-pixel. When SmoothStep, the grid visually scroll more smoothly, with the end of the scroll bar does not guarantee that the left-top cell of the grid will start at the border of the visible area of the grid. SmoothStep mode only works when the grid is bind to the DataSet of TMemTableEh type.

VisibleMode: TScrollBarVisibleModeEh Sets the scrollbar show mode:

sbAlwaysShowEh - the scroll bar is always displayed.

sbNeverShowEh - scroll bar is always hidden.

sbAutoShowEh - the scroll bar is displayed only if the grid is not reduced in the visible area of the client window.

Height: Integer For the horizontal scroll bar sets the height of the strip. For vertical property is not available.

Width: Integer For the vertical scroll bar sets the width of the strip. For horizontal scroll feature is not available.

ExtraPanel: TDBGridEhScrollBarPanel The property is available only for horizontal stripes. The property specifies the parameters of the additional panel that is displayed in the left part of the band. A detailed description, see the next section.

To customize scollbars you need to use subprtoperties of HorzScrollBar and VertScrollBar properties.

Tracking: Boolean This property …

SmoothStep: Boolean …

ExtScrollBar: TScrollBar; …

Visible: Boolean; …

VisibleMode: TScrollBarVisibleModeEh;sbAlwaysShowEh Always shows scrollbar.

sbNeverShowEh Never shows scrollbar.

sbAutoShowEh Shows or hides scrollbar automatically depending on visible area of grid.

If DBGridEh is connected to DataSet of TMemTableEh type then on vertical scrolling grid doesn’t change position of active record.