为TListBox添加水平滚动条
实例说明
TListBox组件是一个较为常用的列表组件，在默认情况下该组件是没有水平滚动条的，所以文字过长会显示不完全，在文字较短的情况下还可以，但是如果一行的文字很长的话也不行。本例为TListBox添加了一个水平的滚动条，运行本程序单击【添加滚动条】按钮在TListBox组件中就会增加一个水平滚动条，运行效果如图1所示。
图1 为TListBox添加水平滚动条
思路与技术
在Windows中大部分窗口都具有滚动条，如果窗口被建立时没有让它具有滚动条特性的话，滚动条就不会被显示出来。Windows提供的消息LB_SETHORIZONTALEXTEND可以设置窗体的滚动条。因为TListBox也属于一种窗体，所以通过使用该消息同样可以设置TListBox的水平滚动条。
向TListBox组件发送该消息应使用SendMessage函数，当向TListBox组件发送LB_SETHORI ZONTALEXTEND消息时，SendMessage函数的参数wParam是水平滚动条的宽度。
SendMessage(listbox1.Handle
,lb_sethorizontalextent,100,0);
{ Listbox messages }
const
{$EXTERNALSYM
LB_ADDSTRING}
LB_ADDSTRING = $0180;
{$EXTERNALSYM
LB_INSERTSTRING}
LB_INSERTSTRING = $0181;
{$EXTERNALSYM
LB_DELETESTRING}
LB_DELETESTRING = $0182;
{$EXTERNALSYM
LB_SELITEMRANGEEX}
LB_SELITEMRANGEEX = $0183;
{$EXTERNALSYM
LB_RESETCONTENT}
LB_RESETCONTENT = $0184;
{$EXTERNALSYM
LB_SETSEL}
LB_SETSEL = $0185;
{$EXTERNALSYM
LB_SETCURSEL}
LB_SETCURSEL = $0186;
{$EXTERNALSYM
LB_GETSEL}
LB_GETSEL = $0187;
{$EXTERNALSYM
LB_GETCURSEL}
LB_GETCURSEL = $0188;
{$EXTERNALSYM
LB_GETTEXT}
LB_GETTEXT = $0189;
{$EXTERNALSYM
LB_GETTEXTLEN}
LB_GETTEXTLEN = $018A;
{$EXTERNALSYM
LB_GETCOUNT}
LB_GETCOUNT = $018B;
{$EXTERNALSYM
LB_SELECTSTRING}
LB_SELECTSTRING = $018C;
{$EXTERNALSYM
LB_DIR}
LB_DIR = $018D;
{$EXTERNALSYM
LB_GETTOPINDEX}
LB_GETTOPINDEX = $018E;
{$EXTERNALSYM
LB_FINDSTRING}
LB_FINDSTRING = $018F;
{$EXTERNALSYM
LB_GETSELCOUNT}
LB_GETSELCOUNT = $0190;
{$EXTERNALSYM
LB_GETSELITEMS}
LB_GETSELITEMS = $0191;
{$EXTERNALSYM
LB_SETTABSTOPS}
LB_SETTABSTOPS = $0192;
{$EXTERNALSYM
LB_GETHORIZONTALEXTENT}
LB_GETHORIZONTALEXTENT = $0193;
{$EXTERNALSYM LB_SETHORIZONTALEXTENT}
LB_SETHORIZONTALEXTENT = $0194;
{$EXTERNALSYM
LB_SETCOLUMNWIDTH}
LB_SETCOLUMNWIDTH = $0195;
{$EXTERNALSYM
LB_ADDFILE}
LB_ADDFILE = $0196;
{$EXTERNALSYM
LB_SETTOPINDEX}
LB_SETTOPINDEX = $0197;
{$EXTERNALSYM
LB_GETITEMRECT}
LB_GETITEMRECT = $0198;
{$EXTERNALSYM
LB_GETITEMDATA}
LB_GETITEMDATA = $0199;
{$EXTERNALSYM
LB_SETITEMDATA}
LB_SETITEMDATA = $019A;
{$EXTERNALSYM
LB_SELITEMRANGE}
LB_SELITEMRANGE = $019B;
{$EXTERNALSYM
LB_SETANCHORINDEX}
LB_SETANCHORINDEX = $019C;
{$EXTERNALSYM
LB_GETANCHORINDEX}
LB_GETANCHORINDEX = $019D;
{$EXTERNALSYM
LB_SETCARETINDEX}
LB_SETCARETINDEX = $019E;
{$EXTERNALSYM
LB_GETCARETINDEX}
LB_GETCARETINDEX = $019F;
{$EXTERNALSYM
LB_SETITEMHEIGHT}
LB_SETITEMHEIGHT = $01A0;
{$EXTERNALSYM
LB_GETITEMHEIGHT}
LB_GETITEMHEIGHT = $01A1;
{$EXTERNALSYM
LB_FINDSTRINGEXACT}
LB_FINDSTRINGEXACT = $01A2;
{$EXTERNALSYM
LB_SETLOCALE}
LB_SETLOCALE = $01A5;
{$EXTERNALSYM
LB_GETLOCALE}
LB_GETLOCALE = $01A6;
{$EXTERNALSYM
LB_SETCOUNT}
LB_SETCOUNT = $01A7;
{$EXTERNALSYM
LB_INITSTORAGE}
LB_INITSTORAGE = $01A8;
{$EXTERNALSYM
LB_ITEMFROMPOINT}
LB_ITEMFROMPOINT = $01A9;
{$EXTERNALSYM
LB_MSGMAX}
LB_MSGMAX = 432;
开发步骤
（1）新建一个标准工程，创建一个新窗体，默认主窗体的Name属性为Form1。
（2）在窗体中添加TGroupBox、TListBox和TButton组件。
（3）程序完整代码如下：
procedure TForm1.FormCreate(Sender:
TObject);
begin
ListBox1.Items.Add('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa');
end;
procedure TForm1.Button1Click(Sender:
TObject);
var
i,ItemWith:
integer;
begin
ItemWith:= 0;
for i := 0 to listbox1.Items.Count
- 1 do
if ItemWith <
listbox1.Canvas.TextWidth(listbox1.Items[i])then
ItemWith
:=
listbox1.Canvas.Textwidth(listbox1.Items[i]);
SendMessage(listbox1.Handle
,lb_sethorizontalextent,ItemWith,0);
end;