为什么我加入onload事件，会影响我的二级联动

Question

没加入onload事件时，我的二级联动是正确的，但是加入javascript代码后会影响二级联动，这是为什么？这两个之间应该没联系吧！应该怎么修改？
<script type="text/javascript">
            window.onload = function() {
                var a = document.getElementById("loading");
                a.parentNode.removeChild(a);
            }
            document.write('<img style="position:absolute; left:50%; top:50%;"  alt="Loading..." src="../Images/hourglass.gif"  id="loading" />');
            
        </script>

Answer 1

在一个页面里面如果多处用到了window.onload 那么后面的会覆盖掉前面的，从而导致部分js无法正常执行，因此，你需要将这些代码集中在一个方法中，然后在由window.onload调用

Answer 2

你的联动会导致页面刷新就会又执行onload

Answer 3

一级： string sqlStr = "select * from company";
                        try
                        {
                            using (SqlConnection conn = DBConn.CreateSqlConnection())
                            {
                                using (SqlCommand cmd = conn.CreateCommand())
                                {
                                    cmd.CommandType = CommandType.Text;
                                    cmd.CommandText = sqlStr;
                                    if (ConnectionState.Closed == conn.State)
                                        conn.Open();
                                    SqlDataReader sdr = cmd.ExecuteReader();
                                    ddlSystemID.DataSource = sdr;
                                    ddlProjectID.Items.Clear();
                                    ddlSystemID.DataTextField = "Company_Code";
                                    ddlSystemID.DataValueField = "Company_Code";
                                    ddlSystemID.DataBind();
                                    //ddlSystemID.Items.Insert(0, new ListItem("", ""));
                                    if (sdr.HasRows == false)
                                    {
                                        sdr.Close();
                                        conn.Close();                                    }
                                }
                            }                        }二级：
string sqlStr = "select * from system where Company_Code='" + ddlSystemID.SelectedValue + "'";
            try
            {
                using (SqlConnection conn = DBConn.CreateSqlConnection())
                {
                    using (SqlCommand cmd = conn.CreateCommand())
                    {
                        cmd.CommandType = CommandType.Text;
                        cmd.CommandText = sqlStr;
                        if (ConnectionState.Closed == conn.State)
                            conn.Open();
                        SqlDataReader dr = cmd.ExecuteReader();
                        ddlProjectID.DataSource = dr;
                        ddlProjectID.Items.Clear();
                        ddlProjectID.DataTextField = "System_ID";
                        ddlProjectID.DataValueField = "System_ID";
                        ddlProjectID.DataBind();
                        ddlProjectID.Items.Insert(0, new ListItem("", ""));
                        ddlProjectID.Visible = true;
                        txtClientID.Text = "";
                        ddlLPane.Items.Clear();
                        ddlRPane.Items.Clear();
                        if (dr.HasRows == false)
                        {
                            dr.Close();
                            conn.Close();                            
                        }
                    }
                }

Answer 4

你的联动代码是不是使用了
id="loading"
id重复了？还是缺少了？这样的问题得看代码。
正常情况下是不行影响的

Answer 5

在ddlSystemID的onchanged事件中调用那段js吧。

Answer 6

那段JS是在进入页面就调用的，刷新页面也要调用的，onchanged事件中没有调用

Answer 7

document.write('<img style="position:absolute; left:50%; top:50%;" alt="Loading..." src="../Images/hourglass.gif" id="loading" />');
删除，<img style="position:absolute; left:50%; top:50%;" alt="Loading..." src="../Images/hourglass.gif" id="loading" />放在body里面