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How to change the position of the dropdown list of a TComboBox Turn on/off line numbers in source code. Switch to Orginial background IDE or DSP color Comment or reply to this aritlce/tip for discussion. Bookmark this article to my favorite article(s). Print this article
27-Aug-02
Category
VCL-General
Language
Delphi 2.x
Views
90
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Publisher:
DSP, Administrator
Reference URL:
DKB
			Author: Tomas Rutkauskas

I have been able to find out how to increase the width of a combo box drop down so 
that it is wide enough to read the text. However if my combo box is positioned on 
the right hand side of a form when there is a particularly wide list the scroll bar 
and the list gets cut off on the edge of the screen. Is there a way to change the 
position the dropdown list?

Answer:

1   unit Unit1;
2   
3   interface
4   
5   uses
6     Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
7     Dialogs, stdctrls, Unit2;
8   
9   type
10    TForm1 = class(TForm)
11      Button1: TButton;
12      Memo1: TMemo;
13      ComboBox1: TComboBox;
14      procedure Button1Click(Sender: TObject);
15      procedure ComboBox1DropDown(Sender: TObject);
16    private
17      { Private declarations }
18      procedure WMUser(var msg: TMessage); message WM_USER;
19    public
20      { Public declarations }
21    end;
22  
23  var
24    Form1: TForm1;
25  
26  implementation
27  
28  {$R *.dfm}
29  
30  procedure TForm1.Button1Click(Sender: TObject);
31  var
32    i: Integer;
33  begin
34    for i := 0 to 20 do
35      combobox1.Items.add(StringofChar(Chr(Ord('A') + i), Random(50) + 10));
36    combobox1.Perform(CB_SETDROPPEDWIDTH, combobox1.Width * 2, 0)
37  end;
38  
39  function EnumProc(wnd: HWND; var wndresult: HWND): BOOL; stdcall;
40  var
41    classname: array[0..63] of Char;
42  begin
43    Result := True;
44    GetClassname(wnd, classname, sizeof(classname));
45    if SameText(classname, 'ComboLBox') then
46    begin
47      Result := false;
48      wndresult := wnd;
49    end;
50  end;
51  
52  procedure TForm1.ComboBox1DropDown(Sender: TObject);
53  var
54    wnd: HWND;
55    r: Trect;
56    w: Integer;
57  begin
58    wnd := 0;
59    EnumThreadWindows(GetCurrentThreadID, @EnumProc, integer(@wnd));
60    if wnd <> 0 then
61    begin
62      PostMessage(handle, WM_USER, wnd, 0);
63    end
64    else
65      memo1.lines.add('Window not found');
66  end;
67  
68  procedure TForm1.WMUser(var msg: TMessage);
69  var
70    wnd: HWND;
71    r: Trect;
72    w: Integer;
73  begin
74    wnd := msg.wparam;
75    GetWindowRect(wnd, r);
76    if r.Right > Screen.width then
77    begin
78      w := r.right - r.Left;
79      MoveWindow(wnd, Screen.Width - w, r.top, w, r.Bottom - r.Top, true);
80    end;
81    memo1.lines.add(format('Wnd: %x, r: (%d,%d,%d,%d)', [wnd, r.left, r.top, r.right, 
82  r.bottom]));
83  end;
84  
85  initialization
86    randomize;
87  end.


			
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