Using Query String Parameters in ASP.Net Page

You can use query string parameters in a URL request string to pass information into an aspx page. This is very common way to pass values from one page to another page. The URL query string is in the format like:

http://mypage.aspx?para1=value1¶2=value2...

I also use this mechanism to pass in additional data or flags to display some hidden values or to provide additional information from server side codes. For example, in a GridView control, normally we only display a UI table which are readable by clients, such as employee first name, last name and department. The employee ID, which is important information for server side updating, is normally a hidden column in the table.

As in this example, my codes handle some query parameters. One is "displayEmployeeID". If it is true, the employee ID then is visible:

http://mypage.aspx?para1=value1¶2=value2&displayEmployeeID=true

This parameter can be manually added the URL address text box (use & to separate parameters). If it is not available, the default value is false. Here are some codes in my aspx.cs page in the Page_Load() event:

bool display = false;
string sVal = HttpUtility.UrlDecode(Request.QueryString["displayEmployeeID"]);
if (string.IsNullOrEmpty(sVal) == false)
{
  if (!bool.TryParse(sVal, out display))
  {
    display = false;
  }
}
DataGridView.Columns[0].Visible = display;

I use the same way to display my business logic layer class's SQL string on my page so that it makes my debugging work very easy. I add a panel to the page in aspx:

<asp:Panel ID="panelDebug" runat="server" Visible="false" width="720px">
  <table width="100%"><tr align="left" ><td style="width: 110px" >
    <asp:Label ID="lblSQL" runat="server" Text="Create Object SQLs: " /></td><td>
    <asp:TextBox ID="txtSQL" runat="server" Wrap="true" Width="600px"></asp:TextBox>
    </td></tr><tr align="left"><td style="width: 25%">
    <asp:Label ID="lblUpdate" runat="server" Text="Updates: " ></asp:Label></td><td>
    <asp:TextBox ID="txtUpdate" runat="server" Width="600px" Wrap="true"></asp:TextBox>
    </td></tr>
  </table>
</asp:Panel>

Then in the event of Page_Load() and the place when my business class has retrieved data from a SQL DB:

panelDebug.Visible = GetDisplaySQL(); // method to get query parameter "displaySQL" value 
...
txtSQL.Text = bllObj.QuerySQLs; // udpate SQL by BLL class property QuerySQLs
...

Here the text box txtUpdate is as same as query SQL but for update SQL statements.

I call those query parameters as hidden parameters. They provide handy ways to get additional information about what was happened in server side, and they can also be passed in as alternative input values.