1.整个页面的判断
foreach(Control ctl in this.Controls[1].Controls)
{
if(ctl.GetType().Name=="TextBox")
{
TextBox tb =new TextBox();
tb=(TextBox)this.FindControl(ctl.ID);

if(tb.Text==string.Empty)
{
Response.Write("<script>alert(\'" + ctl.ID + "的值为空。\');</script>");
break;
}
}
}

2.指定formID里TextBox 判断

先找出你的Form的ID
protected HtmlForm yourformID;

foreach (object obj in yourformID.Controls)
{
if (obj is TextBox)
{
TextBox tb = (TextBox)obj;
if (tb.Text = string.Empty)
{
Response.Write("<script>alert(\'" + tb.ID + "的值为空。\');</script>;")
}
}
}