[SOLVED] DBGrid - Center selected row.

[pcurtis]

I have a DBGrid that can show 7 rows. The dataset has 1000 rows.

How can I center the selected row in the center of the grid?
(If RecNo > 3 and RecNo < 997)

[Zvoni]

Maybe with some math using TopRow-Property?
along the lines of
Grid.TopRow:=IndexOfSelectedRow - 3

You would have to catch the Edge-cases of course (SelectedRow Index is 2, 2-3 is -1, setting TopRow to -1 = KABOOM)

Nota Bene: No idea if my proposal works, since i have no clue to how TopRow works, but it was the one Property catching my eye

[pcurtis]

TopRow is not a property of TDBGrid

or after a

Code: Pascal  [Select][+][-]

1.   iTemp := ZQuery1['fnIDX'];
2.   MyQuery.ExecSQL; // update recordset
3.   ZQuery1.Close;
4.   ZQuery1.Open;
5.   ZQuery1.Locate('fnIDX', iTemp, []);
6.  

put the DBGrid back to the same place / position as before the update.

[Zvoni]

TopRow is not a property of TDBGrid

Argg... missed that.
It's protected in TCustomGrid.
No idea how to make a protected Property in Ancestor to public in the Grandkid

[Handoko]

If you meant you want the DBGrid to scroll to certain position showing certain record number, then this maybe is what you want:

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, dbf, Forms, Controls, Dialogs, DBGrids, StdCtrls, Spin, DB;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     Button1: TButton;
16.     Dbf1: TDbf;
17.     DBGrid1: TDBGrid;
18.     Label1: TLabel;
19.     speGoto: TSpinEdit;
20.     speTop: TSpinEdit;
21.     procedure Button1Click(Sender: TObject);
22.     procedure FormCreate(Sender: TObject);
23.   private
24.     function  RandomChars(Count: Integer): string;
25.     procedure GenerateDataFile;
26.     procedure GotoRow(RowNo, TopPadding: Integer);
27.   end;
28.  
29. var
30.   Form1: TForm1;
31.  
32. implementation
33.  
34. Const
35.   DataFileName = 'Data.dbf';
36.  
37. {$R *.lfm}
38.  
39. { TForm1 }
40.  
41. procedure TForm1.FormCreate(Sender: TObject);
42. var
43.   aDataSource: TDataSource;
44. begin
45.  
46.   // Connection and data
47.   aDataSource         := TDataSource.Create(Self);
48.   aDataSource.DataSet := Dbf1;
49.   Dbf1.FilePathFull   := ExtractFileDir(ParamStr(0));
50.   Dbf1.TableName      := DataFileName;
51.   if not(FileExists(DataFileName)) then
52.     GenerateDataFile;
53.   Dbf1.Active        := True;
54.   DBGrid1.DataSource := aDataSource;
55.  
56.   // Appearance
57.   Constraints.MinHeight := 240;
58.   Constraints.MinWidth  := 320;
59.   DBGrid1.Anchors       := [akLeft, akRight, akTop, akBottom];
60.   Button1.Anchors       := [akLeft, akBottom];
61.   speGoto.MaxValue      := Dbf1.ExactRecordCount;
62.   speGoto.Anchors       := [akLeft, akBottom];
63.   speTop.MaxValue       := Dbf1.ExactRecordCount;
64.   speTop.Anchors        := [akLeft, akBottom];
65.  
66. end;
67.  
68. procedure TForm1.Button1Click(Sender: TObject);
69. begin
70.   GotoRow(speGoto.Value, speTop.Value);
71. end;
72.  
73. function TForm1.RandomChars(Count: Integer): string;
74. var
75.   S: string;
76.   i: Integer;
77. begin
78.   if Count < 1  then Count := 1;
79.   if Count > 20 then Count := 20;
80.   S := '';
81.   for i := 1 to Count do
82.     S := S + chr(Ord('a')+Random(26));
83.   Result := S;
84. end;
85.  
86. procedure TForm1.GenerateDataFile;
87. const
88.   TotalItems = 1000;
89. var
90.   i: Integer;
91. begin
92.   with Dbf1 do
93.   begin
94.     FieldDefs.Add('ID', ftInteger, 0, True);
95.     FieldDefs.Add('DATA', ftString, 8, True);
96.     CreateTable;
97.     Open;
98.       for i := 1 to TotalItems do
99.       begin
100.         Append;
101.         FieldByName('ID').AsInteger  := i;
102.         FieldByName('DATA').AsString := RandomChars(8);
103.         Post;
104.       end;
105.     Close;
106.   end;
107. end;
108.  
109. procedure TForm1.GotoRow(RowNo, TopPadding: Integer);
110. var
111.   Total:       Integer;
112.   VisibleRows: Integer;
113.   Key:         Word;
114.   Adjust:      Integer;
115.   i:           Integer;
116. begin
117.  
118.   Total := Dbf1.ExactRecordCount;
119.   if Total <= 0 then Exit;
120.  
121.   // Get visible row count
122.   VisibleRows := 0;
123.   for i := 1 to Total do
124.     if DBGrid1.IsCellVisible(1, i) then
125.       Inc(VisibleRows);
126.   if VisibleRows <= 0 then Exit;
127.  
128.   // Send Ctrl+Home keyboard signal to the grid
129.   Key := 36;
130.   DBGrid1.EditorKeyDown(Self, Key, [ssCtrl]);
131.  
132.   // Send Arrow_Down keyboard signal to the grid
133.   for i := 1 to RowNo-1 do
134.   begin
135.     Key := 40;
136.     DBGrid1.EditorKeyDown(Self, Key, []);
137.   end;
138.  
139.   // Send arrow up and down signals to get position for the top padding
140.   if TopPadding >= VisibleRows + 1 then Exit;
141.   Adjust := VisibleRows - TopPadding - 1;
142.   if RowNo + Adjust > Total then
143.     Adjust := Total - RowNo;
144.   for i := 1 to Adjust do
145.   begin
146.     Key := 40;
147.     DBGrid1.EditorKeyDown(Self, Key, []);
148.   end;
149.   for i := 1 to Adjust do
150.   begin
151.     Key := 38;
152.     DBGrid1.EditorKeyDown(Self, Key, []);
153.   end;
154.  
155. end;
156.  
157. end.

• First time running the program, a dbf with 1000 records will be created, see line #86
• The grid will try to scroll to position the RecNo to have the top padding as the value provided but it may fail on some cases
• TopPadding = 0 means to show the wanted RecNo on the first row in the grid
• The trick to make the grid to scroll automatically is in the GotoRow procedure, see line #109

Warning:
Tested on Lazarus 2.0.10 GTK2 Linux, it may or may not work on future versions of Lazarus and it is may not work on other OSes.

[Handoko]

TopRow is not a property of TDBGrid

It's protected in TCustomGrid.

Not a problem, we can force a protected property to be used on its descendants.

Code: Pascal  [Select][+][-]

1. type
2.   TMyGrid = class(TCustomGrid)
3.     public
4.       property TopRow;
5.   end;
6.  
7. procedure TForm1.Button1Click(Sender: TObject);
8. begin
9.   TMyGrid(DBGrid1).TopRow := 5;
10. end;

Only warning but compile-able. Unfortunately, due to some unknown reason it does not work.

[Zvoni]

Not a problem, we can force a protected property to be used on its descendants.

Code: Pascal  [Select][+][-]

1. type
2.   TMyGrid = class(TCustomGrid)
3.     public
4.       property TopRow;
5.   end;
6.  
7. procedure TForm1.Button1Click(Sender: TObject);
8. begin
9.   TMyGrid(DBGrid1).TopRow := 5;
10. end;

Only warning but compile-able. Unfortunately, due to some unknown reason it does not work.

In Singlestep-Mode, when assigning (your Line 9), can you step into the (protected) setter of the Property?

[Handoko]

Just tried it, yes I can step into it. Unfortunately the code is too advanced, I am not able to digest it.

Code: Pascal  [Select][+][-]

1. procedure TCustomGrid.TryScrollTo(aCol, aRow: Integer; ClearColOff,
2.   ClearRowOff: Boolean);
3. var
4.   TryTL: TPoint;
5.   NewCol,NewRow: Integer;
6.   TLChange: Boolean;
7. begin
8.   TryTL:=ScrollGrid(False,aCol, aRow);
9.   TLChange := not PointIgual(TryTL, FTopLeft);
10.   if TLChange
11.   or (not PointIgual(TryTL, Point(aCol, aRow)) and (goSmoothScroll in Options))
12.   or (ClearColOff and (FGCache.TLColOff<>0))
13.   or (ClearRowOff and (FGCache.TLRowOff<>0)) then
14.   begin
15.     NewCol := TryTL.X - FTopLeft.X + Col;
16.     NewRow := TryTL.Y - FTopLeft.Y + Row;
17.     FTopLeft:=TryTL;
18.     if ClearColOff then
19.       FGCache.TLColOff := 0;
20.     if ClearRowOff then
21.       FGCache.TLRowOff := 0;
22.     if (aCol>TryTL.X) and (goSmoothScroll in Options) then
23.       FGCache.TLColOff := FGCache.MaxTLOffset.X;
24.     if (aRow>TryTL.Y) and (goSmoothScroll in Options) then
25.       FGCache.TLRowOff := FGCache.MaxTLOffset.Y;
26.     {$ifdef dbgscroll}
27.     DebugLn('TryScrollTo: TopLeft=%s NewCol=%d NewRow=%d',
28.       [dbgs(FTopLeft), NewCol, NewRow]);
29.     {$endif}
30.     // To-Do: move rect with ScrollBy_WS and invalidate only new (not scrolled) rects
31.     if TLChange then
32.       doTopleftChange(False)
33.     else
34.       VisualChange;
35.     if goScrollKeepVisible in Options then
36.       MoveNextSelectable(False, NewCol, NewRow);
37.   end;
38. end;

[pcurtis]

@Handoko PERFECT

[pcurtis]

I made this custom DBGrid based on your supplied code

Code: Pascal  [Select][+][-]

1. unit MyDBGrid;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, LResources, Forms, Windows, Controls, Graphics, StdCtrls, ExtCtrls,
9.   Dialogs, DBGrids, Grids;
10.  
11. type
12.   TMyHackedGrid = class(TDBGrid);
13.   TMyDBGrid = class(TDBGrid)
14.   private
15.  
16.   protected
17.  
18.   public
19.     function GetSelectedRow : Integer;
20.     function GetVisibleRowCount : Integer;
21.     procedure ScrollTo(aIndexField : String; aValue : Integer; aOffset : Integer);
22.     constructor Create(AOwner : TComponent); override;
23.     destructor Destroy; override;
24.   published
25.  
26.   end;
27.  
28. procedure Register;
29.  
30. implementation
31.  
32. {$R mydbgrid.res}
33.  
34. constructor TMyDBGrid.Create(AOwner : TComponent);
35. begin
36.   inherited Create(AOwner);
37.   AlternateColor := clMoneyGreen;
38.   Color := clCream;
39.   Options := Options + [dgRowSelect];
40.   Options := Options - [dgEditing];
41.   AutoFillColumns := true;
42. end;
43.  
44. destructor TMyDBGrid.Destroy;
45. begin
46.   inherited Destroy;
47. end;
48.  
49. function TMyDBGrid.GetSelectedRow : Integer;
50. begin
51.   Result := TMyHackedGrid(Self).Row;
52. end;
53.  
54. function TMyDBGrid.GetVisibleRowCount : Integer;
55. begin
56.   Result := TMyHackedGrid(Self).VisibleRowCount;
57. end;
58.  
59. procedure TMyDBGrid.ScrollTo(aIndexField : String; aValue : Integer; aOffset : Integer);
60. var
61.   iTemp : Integer;
62. begin
63.   if (not Assigned(DataSource)) or
64.      (DataSource.DataSet.Active = False) or
65.      (DataSource.DataSet.RecordCount = 0) then
66.        exit;
67.  
68.   DataSource.DataSet.First;
69.   DataSource.DataSet.Locate(aIndexField, aValue, []);
70.  
71.   for iTemp := 1 to aOffset do
72.   begin
73.     PostMessage(Self.Handle, WM_KEYDOWN, VK_UP, 0);
74.   end;
75.  
76.   for iTemp := 1 to aOffset do
77.   begin
78.     PostMessage(Self.Handle, WM_KEYDOWN, VK_DOWN, 0);
79.   end;
80. end;
81.  
82. procedure Register;
83. begin
84.   RegisterComponents('Misc',[TMyDBGrid]);
85. end;
86.  
87. end.
88.  

[Handoko]

That looks good. Unfortunately, I cannot test it because it depends on Windows unit.

[lainz]

Windows unit can not be replaced with LCLType, at some extent?

[wp]

That looks good. Unfortunately, I cannot test it because it depends on Windows unit.

Replace unit Windows by LCLType and LCLIntf. And replace WM_KEYDOWN/WM_KEYUP by LM_KEYDOWN/LM_KEYUP.

[Sieben]

Based on this here idea by 'Soner' I ended up with that little sketch included below that seems to do quite a good job in keeping the selected row of a DBGrid centered. Of course that has to be supended when the user clicks a certain record, but snaps in again asap. And I could not get the grid to agree that the 'natural' center position with an even number of data rows ist the last line of the upper half instead of the first one of the lower. Solution is to make sure that your grid is odd...