blob 与memory的问题

Question

大家帮忙看看错在那？(d6 develeper's guide's instance)
 提示说：invalid class typecast  procedure TMainForm.sbPlayClick(Sender: TObject);
var
  B: TBlobStream;
  M: TMemoryStream;
begin
  B:= TBlobStream.Create(adotable1Wave, bmRead); // create blob stream
  Screen.Cursor := crHourGlass;                   // wait hourglass
  try
    M := TMemoryStream.Create;                    // create memory stream
    try
      M.CopyFrom(B, B.Size);             // copy from blob to memory stream
      // Attempt to play sound.  Raise exception if something goes wrong
      Win32Check(PlaySound(M.Memory, 0, SND_SYNC or SND_MEMORY));
    finally
      M.Free;
    end;
  finally
    Screen.Cursor := crDefault;
    B.Free;                                       // clean up
  end;
end;

Answer 1

adotable1wave字段是保存的是*。wav文件，sbPlayClick是播放按钮

Answer 2

一般采用sndPlaySound播放wav文件,同时你也要引用uses MMSystem才可以播放,你把Win32Check(PlaySound(M.Memory, 0, SND_SYNC or SND_MEMORY))改为Win32Check(PlaySound(M.Memory, 0, SND_ASYNC));看看

Answer 3

还是不行，原程序如下，是不是blobstream 与memorystream 类型转换的问题？
unit Main;interfaceuses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  ExtCtrls, DBCtrls, DB, DBTables, StdCtrls, Mask, Buttons, ComCtrls, ADODB;type
  TMainForm = class(TForm)
    dsSounds: TDataSource;
    edTitle: TDBEdit;
    edFileName: TDBEdit;
    Label1: TLabel;
    Label2: TLabel;
    OpenDialog: TOpenDialog;
    SaveDialog: TSaveDialog;
    pnlToobar: TPanel;
    sbPlay: TSpeedButton;
    sbAdd: TSpeedButton;
    sbSave: TSpeedButton;
    sbExit: TSpeedButton;
    Bevel1: TBevel;
    dbnNavigator: TDBNavigator;
    stbStatus: TStatusBar;
    ADOTable1: TADOTable;
    ADOTable1Wavetitle: TWideStringField;
    ADOTable1Filename: TWideStringField;
    ADOTable1id: TAutoIncField;
    ADOTable1wave: TBlobField;
    procedure sbPlayClick(Sender: TObject);
    procedure sbAddClick(Sender: TObject);
    procedure sbSaveClick(Sender: TObject);
    procedure sbExitClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
  private
    procedure OnAppHint(Sender: TObject);
  end;var
  MainForm: TMainForm;implementation{$R *.DFM}uses MMSystem;procedure TMainForm.sbPlayClick(Sender: TObject);
var
  B: TBlobStream;
  M: TMemoryStream;
begin
  B:= TBlobStream.Create(adotable1Wave, bmRead); // create blob stream
  Screen.Cursor := crHourGlass;                   // wait hourglass
  try
    M := TMemoryStream.Create;                    // create memory stream
    try
      M.CopyFrom(B, B.Size);             // copy from blob to memory stream
      // Attempt to play sound.  Raise exception if something goes wrong
      Win32Check(PlaySound(M.Memory, 0, SND_ASYNC));//or SND_MEMORY));//试过了，不行
    finally
      M.Free;
    end;
  finally
    Screen.Cursor := crDefault;
    B.Free;                                       // clean up
  end;
end;procedure TMainForm.sbAddClick(Sender: TObject);
begin
  if OpenDialog.Execute then
  begin
    adotable1.Append;
    adotable1['FileName'] := ExtractFileName(OpenDialog.FileName);
    adotable1Wave.LoadFromFile(OpenDialog.FileName);
    edTitle.SetFocus;
  end;
end;procedure TMainForm.sbSaveClick(Sender: TObject);
begin
  with SaveDialog do
  begin
    FileName := adotable1['FileName'];    // initialize file name
    if Execute then                       // execute dialog
      adotable1Wave.SaveToFile(FileName); // save blob to file
  end;
end;procedure TMainForm.sbExitClick(Sender: TObject);
begin
  Close;
end;procedure TMainForm.FormCreate(Sender: TObject);
begin
  Application.OnHint := OnAppHint;
  adotable1.Open;
end;procedure TMainForm.OnAppHint(Sender: TObject);
begin
  stbStatus.SimpleText := Application.Hint;
end;procedure TMainForm.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  adotable1.Close;
end;end.