delphi自动调整combobox下拉列表宽度，PostMessage CB_SETDROPPEDWIDTH

在combobox所在的窗口的Formshow事件里调用即可

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1. procedure SetComboBoxListWidth( AComboBox: TComboBox );
2. var
3. i: Integer;
4. nMaxLen, nMinWidth: integer;
5. nFontWidth: Integer;
6. nCboLeft: integer;
7. ctlCustom: TControl;
8. begin
9. nCboLeft := AComboBox.Left;
10. ctlCustom := AComboBox;
11. with AComboBox do
12. begin
13. nFontWidth := Round( Abs(Font.Height / 2 ) );
14. nMaxLen:= 0;
15. for i:=0 to Items.Count-1 do
16. begin
17. if length(Items[i])* nFontWidth > nMaxLen then
18. nMaxlen:= length(Items[i])* nFontWidth+5;
19. end;
20. if Items.Count > DropDownCount then
21. nMaxLen := nMaxLen + 20;
22. if nMaxLen > Width then
23. begin
24. if Items.Count>DropDownCount then
25. begin
26. SendMessage( Handle, CB_SETHORIZONTALEXTENT, nMaxLen+5, 0 );
27. {解决分辨率小导致的ComboboxList的宽度超出屏幕}
28. //while 部分是用来取出combobox控件相对与窗体的横坐标
29. while not (ctlCustom.Parent is TForm) do
30. begin
31. nCboLeft := nCboLeft + ctlCustom.Parent.Left;
32. ctlCustom := ctlCustom.Parent;
33. end;
34. nMinWidth := Min(400, nMaxLen); // 使用不大于nMaxLen的数做比较
35. if (nCboLeft + nMinWidth) > Screen.Width-25 then // 不超出屏幕，并保留窗口滚动条宽度，约25
36. nMinWidth := Screen.Width-25-nCboLeft;
37. nMinWidth := Max(nMinWidth, Width); // 不小于控件自身宽度
38. PostMessage(Handle, CB_SETDROPPEDWIDTH, nMinWidth, 0);
39. end
40. else
41. PostMessage(Handle, CB_SETDROPPEDWIDTH, nMaxLen , 0);
42. ShowHint := True;
43. end
44. else
45. begin
46. SendMessage( Handle, CB_SETHORIZONTALEXTENT, 0, 0 );
47. PostMessage(Handle, CB_SETDROPPEDWIDTH, Width , 0);
48. end;
49. end;
50. end;

http://blog.csdn.net/youthon/article/details/8179348