在Listbox加背景图

1.  建立一个窗体
2.  放一个ComboBox和Listbox
3.  改变Component的Style为csOwnerDrawVariable和ListBox的Style为lbOwnerDrawVariable。
4.  声明5个TBitmap的全局变量
5.  覆盖Form的OnCreate.
6.  覆盖ComboBox的OnDraw.
7.  覆盖ComboBox的OnMeasureItem.
8.  释放资源在Form的OnClose.

unit Ownerdrw;

interface

uses
  SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls,
  Forms, Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    ComboBox1: TComboBox;
    ListBox1: TListBox;
    procedure FormCreate(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure ComboBox1DrawItem(Control: TWinControl; Index: Integer;
      Rect: TRect; State: TOwnerDrawState);
    procedure ComboBox1MeasureItem(Control: TWinControl; Index: Integer;
      var Height: Integer);
    procedure ListBox1DrawItem(Control: TWinControl; Index: Integer;
      Rect: TRect; State: TOwnerDrawState);
    procedure ListBox1MeasureItem(Control: TWinControl; Index: Integer;
      var Height: Integer);

  private
    { Private declarations }

  public
    { Public declarations }

  end;

var
  Form1: TForm1;
  TheBitmap1, TheBitmap2, TheBitmap3, TheBitmap4,
  TheBitmap5 : TBitmap;
implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
  TheBitmap1 := TBitmap.Create;
  TheBitmap1.LoadFromFile(''''C:\delphi\images\buttons\globe.bmp'''');
  TheBitmap2 := TBitmap.Create;
  TheBitmap2.LoadFromFile(''''C:\delphi\images\buttons\video.bmp'''');
  TheBitmap3 := TBitmap.Create;
  TheBitmap3.LoadFromFile(''''C:\delphi\images\buttons\gears.bmp'''');
  TheBitmap4 := TBitmap.Create;
  TheBitmap4.LoadFromFile(''''C:\delphi\images\buttons\key.bmp'''');
  TheBitmap5 := TBitmap.Create;
  TheBitmap5.LoadFromFile(''''C:\delphi\images\buttons\tools.bmp'''');
  ComboBox1.Items.AddObject(''''Bitmap1: Globe'''', TheBitmap1);
  ComboBox1.Items.AddObject(''''Bitmap2: Video'''', TheBitmap2);
  ComboBox1.Items.AddObject(''''Bitmap3: Gears'''', TheBitmap3);
  ComboBox1.Items.AddObject(''''Bitmap4: Key'''', TheBitmap4);
  ComboBox1.Items.AddObject(''''Bitmap5: Tools'''', TheBitmap5);
  ListBox1.Items.AddObject(''''Bitmap1: Globe'''', TheBitmap1);
  ListBox1.Items.AddObject(''''Bitmap2: Video'''', TheBitmap2);
  ListBox1.Items.AddObject(''''Bitmap3: Gears'''', TheBitmap3);
  ListBox1.Items.AddObject(''''Bitmap4: Key'''', TheBitmap4);
  ListBox1.Items.AddObject(''''Bitmap5: Tools'''', TheBitmap5);

end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  TheBitmap1.Free;
  TheBitmap2.Free;
  TheBitmap3.Free;
  TheBitmap4.Free;
  TheBitmap5.Free;
end;

procedure TForm1.ComboBox1DrawItem(Control: TWinControl; Index: Integer;
  Rect: TRect; State: TOwnerDrawState);
var
  Bitmap: TBitmap;
  Offset: Integer;
begin
  with (Control as TComboBox).Canvas do
  begin
    FillRect(Rect);
    Bitmap := TBitmap(ComboBox1.Items.Objects[Index]);
    if Bitmap <> nil then
    begin
      BrushCopy(Bounds(Rect.Left + 2, Rect.Top + 2, Bitmap.Width,
                Bitmap.Height), Bitmap, Bounds(0, 0, Bitmap.Width,
                Bitmap.Height), clRed);
      Offset := Bitmap.width + 8;
    end;
    { display the text }
    TextOut(Rect.Left + Offset, Rect.Top, Combobox1.Items[Index])
  end;
end;

procedure TForm1.ComboBox1MeasureItem(Control: TWinControl; Index:
                                      Integer; var Height: Integer);
begin
  height:= 20;
end;

procedure TForm1.ListBox1DrawItem(Control: TWinControl; Index: Integer;
  Rect: TRect; State: TOwnerDrawState);
var
  Bitmap: TBitmap;
  Offset: Integer;
begin
  with (Control as TListBox).Canvas do
  begin
    FillRect(Rect);
    Bitmap := TBitmap(ListBox1.Items.Objects[Index]);
    if Bitmap <> nil then
    begin
      BrushCopy(Bounds(Rect.Left + 2, Rect.Top + 2, Bitmap.Width,
                Bitmap.Height), Bitmap, Bounds(0, 0, Bitmap.Width,
                Bitmap.Height), clRed);
      Offset := Bitmap.width + 8;
    end;
    { display the text }
    TextOut(Rect.Left + Offset, Rect.Top, Listbox1.Items[Index])
  end;
end;

procedure TForm1.ListBox1MeasureItem(Control: TWinControl; Index: Integer;
  var Height: Integer);
begin
  height:= 20;
end;

end.

//该窗体的DFM文件

object Form1: TForm1
  Left = 211
  Top = 155
  Width = 435
  Height = 300
  Caption = ''''Form1''''
  Font.Color = clWindowText
  Font.Height = -13
  Font.Name = ''''System''''
  Font.Style = []
  PixelsPerInch = 96
  OnClose = FormClose
  OnCreate = FormCreate
  TextHeight = 16
  object ComboBox1: TComboBox
    Left = 26
    Top = 30
    Width = 165
    Height = 22
    Style = csOwnerDrawVariable
    ItemHeight = 16
    TabOrder = 0
    OnDrawItem = ComboBox1DrawItem
    OnMeasureItem = ComboBox1MeasureItem
  end
  object ListBox1: TListBox
    Left = 216
    Top = 28
    Width = 151
    Height = 167
    ItemHeight = 16
    Style = lbOwnerDrawVariable
    TabOrder = 1
    OnDrawItem = ListBox1DrawItem
    OnMeasureItem = ListBox1MeasureItem
  end
end

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