控件编写：增强 TMEMO （一）（增加对WM_HSCROLL消息的处理）

    相信没有什么人对 MEMO 陌生了吧。尽管其组件的功能不错。但是，对它进行一些功能的改进，可以更好的使用。

     有的时候，我们想要知道，当前的坐标是什么？甚至，想要在 滚动条滚动时触发一些事件。 但，TMemo 本身并没有这样的功能。那我们就要扩展它；

     那我们现在就来作：

     file -> new -> other -> package 

     在 dpk 窗口上， Add 。

     New component 如下图：

    
     

     完整的程序源代码如下：

unit JoeMemo;


interface


uses
  Windows,Classes, Controls, StdCtrls,Messages ;

type
  TJoeMemo = class(TMemo)
  private
    { Private declarations }
    FRow : LongInt;
    FCol : LongInt;
    FOnHScroll : TNotifyEvent;
    FOnVScroll : TNotifyEvent;

    procedure WMHScroll(var msg : TWMHScroll);message WM_HSCROLL;
    procedure WMVScroll(var msg : TWMVScroll);message WM_VSCROLL;

    procedure SetRow(value : LongInt);
    procedure SetCol(value : LongInt);

    function GetRow : LongInt;
    function GetCol : LongInt;
  protected
    { Protected declarations }
    procedure HScroll; dynamic;
    procedure VScroll; dynamic;
  public
    { Public declarations }
    property Row : LongInt read GetRow write SetRow;
    property Col : LongInt read GetCol write SetCol;
  published
    { Published declarations }
    property OnHScroll : TNotifyEvent read FOnHScroll write FOnHScroll;
    property OnVScroll : TNotifyEvent read FOnVScroll write FOnVScroll;
  end;

procedure Register;

implementation

procedure Register;
begin
  RegisterComponents('JoeTools', [TJoeMemo]);
end;

{ TJoeMemo }

function TJoeMemo.GetCol: LongInt;
begin
  Result := Perform(EM_LINEINDEX,-1,0);
end;

function TJoeMemo.GetRow: LongInt;
begin
  Result := Perform(EM_LINEFROMCHAR,-1,0);
end;

procedure TJoeMemo.HScroll;
begin
  if Assigned(FOnHScroll) then FOnHScroll(Self);

end;

procedure TJoeMemo.SetCol(value: Integer);
begin
  if FCol > value  then FCol :=value;
  SelStart := Perform(EM_LINEINDEX,GetRow,0)+FCol;

end;

procedure TJoeMemo.SetRow(value: Integer);
begin
  SelStart := Perform(EM_LINEINDEX,value,0);
  FRow := SelStart;
end;

procedure TJoeMemo.VScroll;
begin
  if Assigned(FOnVScroll)  then FOnVScroll(Self);
end;

procedure TJoeMemo.WMHScroll(var msg: TWMHScroll);
begin
  inherited;
  HScroll;
end;

procedure TJoeMemo.WMVScroll(var msg: TWMVScroll);
begin
  inherited;
  VScroll;
end;

end.

http://blog.csdn.net/aroc_lo/article/details/3075814