aspnetupload控件问题

对控件aspnetupload示例代码有疑问，在pageload事件下定义上传控件的局部变量upldr，为什么不将upldr定义在pageload事件之外，而且upldr.set_UploadFolder(fpath)设置上传文件夹，但在button事件下重新定义了AspnetUpload，并不能获取这个局部变量的属性，这样写究竟是什么原因呢?
protected void Page_Load(object sender, System.EventArgs e)
{
AspnetUpload upldr = new AspnetUpload();
upldr.RegisterModelessProgressBar("ProgressBar.aspx",btn_upload);
string fpath = Path.Combine(Server.MapPath("."),"Upload");
if(!Directory.Exists(fpath))
Directory.CreateDirectory(fpath);
upldr.set_UploadFolder(fpath);
}
protected void btn_upload_Click(object sender, System.EventArgs e)
{
AspnetUpload upldr = new AspnetUpload();
UploadFile file = upldr.GetUploadFile("file1");
if(file != null)
{
string fpath = Path.Combine(Server.MapPath("."),"Upload");
fpath = Path.Combine(fpath,Path.GetFileName(file.get_FileName()));
file.SaveAs(fpath);
}

}