Delphi用TActionList实现下载文件的方法

Delphi中的TActionList有个标准动作TDownLoadURL，内部是使用的URLDownloadToFile，它下载文件时会定时产生OnDownloadProgress 事件，这样就可以用进度条显示。

本文讲述了Delphi用TActionList实现下载文件的方法，实现代码如下所示：

uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms, Dialogs, ExtActns, ActnList, StdCtrls, ComCtrls;
 
type
 TForm1 = class(TForm)
  Button1: TButton;
  ActionList1: TActionList;
  ProgressBar1: TProgressBar;
  procedure Button1Click(Sender: TObject);
 private
  { Private declarations }
  procedure URL_OnDownloadProgress
       (Sender: TDownLoadURL;
       Progress, ProgressMax: Cardinal;
       StatusCode: TURLDownloadStatus;
       StatusText: String; var Cancel: Boolean) ;
 public
  { Public declarations }
 end;
 
var
 Form1: TForm1;
 
implementation
 
{$R *.dfm}
 
procedure Tform1.URL_OnDownloadProgress;
begin
  ProgressBar1.Max:= ProgressMax;
  ProgressBar1.Position:= Progress;
end;
 
procedure TForm1.Button1Click(Sender: TObject);
begin
  with TDownloadURL.Create(self) do
  try
   URL:='//www.jb51.net/images/logo.gif';
   FileName := 'logo.gif';
   OnDownloadProgress := URL_OnDownloadProgress;
   ExecuteTarget(nil) ;
  finally
   Free;
  end;
  showMessage('OK');
  ProgressBar1.Max := 0;
end;