Author: Peter Johnson
It's often useful to remember the size and state of your program's window (or
sometimes of dialogue boxes) between executions. This article discusses how.
Answer:
The method we're going to use is to save the position in the registry.
First of all, decide where you're going to keep the information. It's customary for
apps to place information that varies between users in
HKEY_CURRENT_USER\Software\MyCompany\MyProgram\X.X
(X.X is the version number of the program). We'll use such a key in this article.
You can save the window's current position and size when the program is closing
down - the OnDestroy form event handler is a good place for this. The program then
restores it's position from the registry (if it's been written yet) when opening -
we use the form's OnCreate handler for that code.
There are complications when saving and restoring the window state because of when
the window is minimised, Delphi doesn't minimise the form - it hides it and
displays the Application window in the taskbar. The method I've used causes a
previously minimised window to flash on-screen briefly. I'd welcome ideas on any
alternative approaches. (This has now been fixed -- see the component available for
download).
Another complication is that when a window is maximised Delphi updates the Width,
Height, Left and Top properties of the form to the window's maximised size and
position. This means that closing a maximised window stores the maximised size in
the registry. When the program is run again it appears maximised, but when the user
restores it they expect it to go to the previous normal size and position, but if
we reloaded the Left, Top, Height and Width properties, the form won't shrink when
restored. We get round this by using the Windows API to get the non-maximised size.
Here's the code - the comments should explain what's happening.
1 const
2 CRegKey = 'Software\Demos\WdwStateDemo\1.0';
3
4 // Helper function to read registry values, and deal with
5 // cases where no values exist
6
7 function ReadIntFromReg(Reg: TRegistry; Name: string;
8 Def: Integer): Integer;
9 {Reads integer with given name from registry and returns it
10 If no such value exists, returns Def default value}
11 begin
12 if Reg.ValueExists(Name) then
13 Result := Reg.ReadInteger(Name)
14 else
15 Result := Def;
16 end;
17
18 procedure TForm1.FormDestroy(Sender: TObject);
19 var
20 Reg: TRegistry; // the registry
21 State: Integer; // state of wdw
22 Pl: TWindowPlacement; // used for API call
23 R: TRect; // used for wdw pos
24 begin
25 {Calculate window's normal size and position using
26 Windows API call - the form's Width, Height, Top and
27 Left properties will give maximized window size if
28 form is maximised, which is not what we want here}
29 Pl.Length := SizeOf(TWindowPlacement);
30 GetWindowPlacement(Self.Handle, @Pl);
31 R := Pl.rcNormalPosition;
32 Reg := TRegistry.Create;
33 try
34 // Open required key - and create it if it doesn't exist
35 Reg.RootKey := HKEY_CURRENT_USER;
36 Reg.OpenKey(CRegKey, True);
37 // Write window size and position
38 Reg.WriteInteger('Width', R.Right - R.Left);
39 Reg.WriteInteger('Height', R.Bottom - R.Top);
40 Reg.WriteInteger('Left', R.Left);
41 Reg.WriteInteger('Top', R.Top);
42 // Write out state of window
43 {Record window state (maximised, minimised or normal)
44 - special case when minimized since form window is simply
45 hidden when minimised, and application window is actually
46 the one minimised - so we check to see if application
47 window *is* minimized and act accordingly}
48 if IsIconic(Application.Handle) then
49 {minimized - write that state}
50 State := Ord(wsMinimized)
51 else
52 {not mimimized - we can rely on window state of form}
53 State := Ord(Self.WindowState);
54 Reg.WriteInteger('State', State);
55 finally
56 Reg.Free;
57 end;
58 end;
59
60 procedure TForm1.FormCreate(Sender: TObject);
61 var
62 Reg: TRegistry; // the registry
63 State: Integer; // state of wdw
64 begin
65 Reg := TRegistry.Create;
66 try
67 // Open required key - and exit if it doesn't exist
68 Reg.RootKey := HKEY_CURRENT_USER;
69 if not Reg.OpenKey(CRegKey, False) then
70 Exit;
71 // Read the window size and position
72 // - designed form sizes are defaults
73 Self.Width := ReadIntFromReg(Reg, 'Width', Self.Width);
74 Self.Height := ReadIntFromReg(Reg, 'Height', Self.Height);
75 Self.Left := ReadIntFromReg(Reg, 'Left', Self.Left);
76 Self.Top := ReadIntFromReg(Reg, 'Top', Self.Top);
77 // Now get window state and restore
78 State := ReadIntFromReg(Reg, 'State', Ord(wsNormal));
79 {check if window was minimised - we have special
80 processing for minimized state since Delphi doesn't
81 minimize windows - it uses application window
82 instead}
83 if State = Ord(wsMinimized) then
84 begin
85 {we need to set visible true else form won't restore
86 properly - but this causes a brief display of form
87 any ideas on how to stop this?}
88 Self.Visible := True;
89 Application.Minimize;
90 end
91 else
92 Self.WindowState := TWindowState(State);
93 finally
94 Reg.Free;
95 end;
96 end;
A component that wraps up all this functionality on behalf of the form it lives on
is available for download. There's also a sister component included that works with
ini files rather than the registry.
Component Download: http://www.delphidabbler.com/download.php?file=pjwdwstate.zip
|
