发掘ListBox的潜力（二）：鼠标拖放插入点提示

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    ListBox1: TListBox;
    ListBox2: TListBox;
    PRocedure ListBox1DragDrop(Sender, Source: TObject; X, Y: Integer);
    procedure ListBox1DragOver(Sender, Source: TObject; X, Y: Integer;
      State: TDragState; var Accept: Boolean);
  private
    FDragOverObject: TObject;    //ListBox1DragDrop、ListBox1DragOver由多个Listbox共享，这里记录当前那个Listbox接受鼠标拖放
    FDragOverItemIndex: Integer;  //记录鼠标所在条目的Index
    procedure DrawInsertLine;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{========================================================================
  DESIGN BY :  彭国辉
  DATE:        2004-12-24
  SITE:        http://kacarton.yeah.net/
  BLOG:        http://blog.csdn.net/nhconch
  EMAIL:       kacarton#sohu.com

  文章为作者原创，转载前请先与本人联系，转载请注明文章出处、保留作者信息，谢谢支持！
=========================================================================}

procedure TForm1.ListBox1DragDrop(Sender, Source: TObject; X, Y: Integer);
var
    i: integer;
begin
  //拖放完成，将内容从原来的Listbox读到目标Listbox
  with TListBox(Source) do begin
    i := TListBox(Sender).ItemAtPos(Point(X, Y) , true);
    if i<>-1 then
      TListBox(Sender).Items.InsertObject(i, Items[ItemIndex], Items.Objects[ItemIndex])
    else
      i := TListBox(Sender).Items.AddObject(Items[ItemIndex], Items.Objects[ItemIndex]);
    if (Sender=Source) and (i>ItemIndex) then i := i-1;
    DeleteSelected;
    if (Sender=Source) then ItemIndex := i;
  end;
  FDragOverObject := nil;
  FDragOverItemIndex := -1;
end;

procedure TForm1.ListBox1DragOver(Sender, Source: TObject; X, Y: Integer;
  State: TDragState; var Accept: Boolean);
var
  Index: Integer;
begin
  Accept := (Source is TListBox) and (TListBox(Source).ItemIndex>-1);  //只接受来自Listbox的内容
  if not Accept then Exit;
  if (FDragOverObject<>nil) and (Sender<>FDragOverObject) then
    DrawInsertLine; //鼠标离开Listbox时，擦除插入位置提示线框
  Index := TListBox(Sender).ItemAtPos(Point(X, Y) , true);
  if (FDragOverObject = Sender) and (FDragOverItemIndex = Index) then Exit; //当鼠标在同一条目上移动时，只画一次即可
  if (FDragOverObject = Sender) and (FDragOverItemIndex <> Index) then
    DrawInsertLine; //鼠标移到新位置，擦除旧的插入位置提示线框
  FDragOverObject := Sender;
  FDragOverItemIndex := Index;
  DrawInsertLine;   //画出插入位置提示线框
end;

procedure TForm1.DrawInsertLine;
var
  R: TRect;
begin
  if FDragOverObject = nil then Exit;
  with TListBox(FDragOverObject) do begin
    if FDragOverItemIndex > -1 then begin
      R := ItemRect(FDragOverItemIndex);
      R.Bottom := R.Top + 4;
    end else if Items.Count>0 then begin
      R := ItemRect(Items.Count-1);
      R.Top := R.Bottom - 4;
    end else begin
      windows.GetClientRect(Handle, R);
      R.Bottom := R.Top + 4;
    end;
    DrawFocusRect(Canvas.Handle, R);
    InflateRect(R, -1, -1);
    DrawFocusRect(Canvas.Handle, R);
  end;
end;

end.