delphi 下载排队等候的问题！

Question

URL1
URL2
URL3
URL4
我用DELPHI做一个下载的工具，当用户点点URL的时候。进行下载。当用户点击另外一个连接时如果第一个没有完成下载。那么它处于等待状态。这个应该用DELHPI的什么来实现呢，刚开始学DELPHI，还不是很了解！

Answer 1

unit Unit2;interface
uses
  Windows, Classes;type
  TDownThread = class;
  TManage = class(TThread)
  private
    FDownList: TStringList;
    FLock: TRTLCriticalSection;
    J: TThreadList;
    procedure  LockList;
    procedure UnlockList;
  protected
    procedure Execute; override;
  public
    constructor Create(CreateSuspended: Boolean);
    destructor Destroy; override;
    function AddDownUrl(ADownPath: String): Boolean;
    function GetFirst: string;
  end;  TDownThread = class(TThread)
  private
    FDwonUrl: string;
  protected
    function MyDown(const ADownUrl: string): Boolean;    // 下载函数
    procedure Execute; override;
  public
    constructor Create(CreateSuspended: Boolean; ADownUrl: string);
  end;implementation
{ TManage }function TManage.AddDownUrl(ADownPath: String): Boolean;
begin
  Result := False;
  LockList;
  try
    if (FDownList.IndexOf(ADownPath) = -1) then
      Result := FDownList.Add(ADownPath) > -1
  finally
    UnlockList;
  end;
end;constructor TManage.Create(CreateSuspended: Boolean);
begin
  inherited Create(CreateSuspended);
  FDownList := TStringList.Create;
  InitializeCriticalSection(FLock);
end;destructor TManage.Destroy;
begin
  LockList;
  try
    FDownList.Free;
    inherited Destroy;
  finally
    UnlockList;
    DeleteCriticalSection(FLock);
  end;
end;procedure TManage.Execute;
var
  DownPath: string;
  DownThread: TDownThread;
begin
  FreeOnTerminate := True;
  inherited;
  while not Terminated do
  begin
    if FDownList.Count > 0 then
    begin
      LockList;
      DownPath := PChar(FDownList[0]);
      UnlockList;      DownThread := TDownThread.Create(False, DownPath);
      DownThread.WaitFor;
      DownThread.Free;      LockList;
      FDownList.Delete(0);
      UnlockList;
    end;
    Sleep(3000);
  end;  
end;function TManage.GetFirst: string;
begin
  if FDownList.Count > 0 then
    Result := FDownList[0];
end;procedure TManage.LockList;
begin
  EnterCriticalSection(FLock);
end;procedure TManage.UnlockList;
begin
  LeaveCriticalSection(FLock);
end;{ TDownThread }constructor TDownThread.Create(CreateSuspended: Boolean; ADownUrl: string);
begin
   inherited Create(CreateSuspended);
   FDwonUrl := ADownUrl;
end;procedure TDownThread.Execute;
begin
  inherited;
  while True do
  begin
    if MyDown(FDwonUrl) then
      Break;
  end;
end;function TDownThread.MyDown(const ADownUrl: string): Boolean;
begin
  Result := False;
  Result := True;
end;end.