动态创建按钮 - onclick事件不会触发

Question

我在c＃代码中创建了一个文件上传控件和一个上传按钮，如下所示：控件正在创建并显示在UI-aspx中

TableCell uploadCell = new TableCell();
uploadCell.ColumnSpan = 4;
tRow.Cells.Add(uploadCell);

FileUpload fu = new FileUpload();
fu.ID = "fu_" + BU + "_" + artifact.LookupValue + artifact.LookupId;
fu.AllowMultiple = false;     

Button btnUpload = new Button();
btnUpload.ID = "btnUpload_" + BU + "_" + artifact.LookupValue + artifact.LookupId;
btnUpload.Text = "Upload";
btnUpload.Click += new EventHandler(this.btnUpload_Click);    
PostBackTrigger trigger = new PostBackTrigger();
trigger.ControlID = btnUpload.ID;
uploadCell.Controls.Add(fu);
uploadCell.Controls.Add(btnUpload);
Up1.Triggers.Add(trigger);

private void btnUpload_Click(object sender, EventArgs e)
{
}

当我点击上传按钮时，点击事件不会被触发。我在btnUpload_Click附加了一个调试，但是没有打到。

如何触发点击事件以动态添加控件？