Populating a combobox on selectedindex change of another combobox

Question

Hi,

I have created a custom dialog UI, which contains two combobox with SQL server instance & on selection of one of SQLServer instance, another combobox has to be filled with name of Databases on that server instance.

I am able to find filling combo with SQL server Instances I had written a similar CustomAction to fill the combobox with database names

[CustomAction]
    public static ActionResult FillDatabases(Session xiSession)
    {
        xiSession.Log("Begin CustomAction");
        xiSession.Log("Opening view");
        View lView = xiSession.Database.OpenView("DELETE FROM ComboBox WHERE ComboBox.Property='DBNAME'");
        lView.Execute();

        lView = xiSession.Database.OpenView("SELECT * FROM ComboBox");
        lView.Execute();

        int Index = 1;
        //bool flag = false;
        try
        {
            Microsoft.SqlServer.Management.Smo.Server svr = new Microsoft.SqlServer.Management.Smo.Server(xiSession["DBSRVR"]);
            foreach (Microsoft.SqlServer.Management.Smo.Database db in svr.Databases )
            {
                String dbName = db.Name;
                Record lRecord = xiSession.Database.CreateRecord(3);
                xiSession.Log("Setting record details");
                lRecord.SetString(1, "DBNAME");
                lRecord.SetInteger(2, Index);
                lRecord.SetString(3, db.Name);

                xiSession.Log("Adding record");
                lView.Modify(ViewModifyMode.InsertTemporary, lRecord);

                ++Index;
            }
        }
        catch (Exception ex)
        {
            //logException(xiSession, ex);
            xiSession.Log(ex.Message );
        }


        lView.Close();

        xiSession.Log("Closing view");
        lView.Close();
        return ActionResult.Success;
    }

I want to call these custom actions somewhat like shown below,

    <Binary Id="CustomActions.CA.dll" SourceFile="CustomActions.CA.dll" />
    <CustomAction Id="FillServerInstances" 
       BinaryKey="CustomActions.CA.dll" 
       DllEntry="FillServerInstances" 
       Execute="immediate" Return="check" />

<CustomAction Id="FillDatabases" 
       BinaryKey="CustomActions.CA.dll" 
       DllEntry="FillDatabases" 
       Execute="immediate" Return="check" />
    <InstallUISequence>
        <Custom Action="FillServerInstances" After="CostFinalize" />
 <Custom Action="FillDatabases" After="FillServerInstances" />
    </InstallUISequence>

I need to show this Sqlserver selection custom dialog from another custom UI, in case user clicked on a pushbutton.

1. Am I doing the right thing in the WiX code?
2. Is there a better way in which combobox custom action fire only when user click on a pushbutton?
3. "FillDatabases" custom action have to be fire whenever user select a new SQLServer instance. How do i do that?

Thanks