Managing DataBound DropDownLists Properly

So I found a tricky problem with databound DropDownLists that causes the selectedIndexChanged event to fire more than you probably intended.

Normally when you add one - you might DataBind it, and then do something like

my_ddl.Items.Add(new ListItem("Select . . . "));

This can become tricky pretty fast if your DropDownList does anything major - like add a selection to a form. The problem is that dropdownlists seem to be loaded with a SelectedIndex of -1. This means that when they are unbound (aka have no data at all), they don't want to put 0 (because that would indicate an item) - so its a -1.

So you bind your data, and then add a top level ListItem for convenience - and now the selected Index is 0 - so SelectedIndexChanged event fires!

The simple fix is to force all of your DDL's to initialize to 0 - and always have a top item! That way, if a user selects the top item, the event does not fire, but any other databound item will work fine.

So, in Page_load, do this

protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack)
return;

my_ddl.SelectedIndex = 0;
}

Note that this only needs to be done for databound controls / controls created programmatically. I have not extensively tested, so I am not 100% on what controls this affects, but I am pretty sure that ones created declaratively in the ASPX page will not have this problem

Hamy

When Databinding results in System.Byte[]

So - quite a few people seem to be having an issue with DataBinding to any sort of control (Dropdownlist, DataGrid, etc) resulting in the bound control printing out System.Byte[]. This may not be the one true answer, but it is definitely one of them.

I noticed a lot of people (like myself) were having trouble with MySql - specifically connector/net. The solution is simple, and probably affects other database storage engines just as well.

Basically - the just of it was this - here is my code to bind a DropDownList. Pretty readable stuff

----------------------------
string sql = "CALL Get_LFID_info('" + ddl_Log_Formats_1.SelectedValue + "');";
DataTable dts = ExecuteMySqlAdapter(sql);
relation1.DataSource = dts;
relation1.DataTextField = "extended_varname";
relation1.DataValueField = "variable_id";
relation1.DataBind();
----------------------------


The issue with this case was that my procedure calculated the result of "extended_varname" - which means that it was created by doing a SELECT CONCAT(name,".",id) sort of deal. Which meant there was no column type associated with it. The solution - pretty simple. Just cast the result. I did this - SELECT CAST(CONCAT(name,".",id) AS CHAR) AS extended_varname . While I believe that you might be able to so that simpler, it was the easy answer. If I figure out a better way to cast it, I will let you know - but the point is the general idea that the column needs to have a specific type associated with it before MySql Connector can correctly convert the rows to strings - any System.Byte[] result generally indicates a cast went wrong somewhere.

Hope that helps
-Hamy

References
mysql type conversion