Dynamically updating UI (binding, maybe?)

Question

So I am writing an export plugin for lightroom. I need to update the export UI dynamically after getting a result from Lrhttp.post. The code is underlined below. Basically, how can I display to the user that their login is successful by dynamically updating the export UI after they click the submit button (I want the last row to display whether the login was a success or not)? I could not find a UI refresh function in the LR API.
I tried looking at Lr.Binding to try to bind resultlogin but that did not work as intended. Any suggestions? Thanks!
ExportDialogSections = {}
function ExportDialogSections.sectionsForTopOfDialog(f, propertyTable)
           return {
                              title = "...",
                              f:row {
                                        spacing = f:control_spacing(),
                                        f:static_text {
                                                  title =  "Username",
                                                  width = share 'labelWidth',
                                                  alignment = 'right',
                                        f:edit_field {
                                                  value = bind 'Username',
                                                  width_in_chars = 40
                              f:row {
                                        spacing = f:control_spacing(),
                                        f:static_text {
                                                  title = "Password",
                                                  width = share 'labelWidth',
                                                  alignment = 'right',
                                        f:password_field {
                                                  value = bind 'Password',
                                                  width_in_chars = 40
                              f:push_button{
                                        title="Submit",
                                        action = function( button )
                                                  import "LrTasks".startAsyncTask( function()
                                                            resultlogin = LrHttp.post(...)
                                                  end )
                                                  if resultlogin == "success" then
                                                            --send username to exporttask and display username is valid
                                                            sendUsername(...)
                                                  else
                                                            sendUsername(...)
                                                  end
                                        end,
                              f:row {
                                        spacing = f:control_spacing(),
                                        f:static_text {
                                                  title = resultlogin,
                                                  width = share 'labelWidth',
                                                  alignment = 'right',
end
return ExportDialogSections

Answer 1

You have to assign resultLogin as a member of a (observable) property table, then bind to that member by name, for example:
f:static_text {
    title = LrView.bind( 'resultlogin' ),
    width = share 'labelWidth',
    alignment = 'right',
In the case of export dialog box, the export settings themselves are a usable property table. In other cases, you may need to create one yourself - see LrFunctionContext, in which case the only trick is to make sure that the property table is specified as bind_to_object.
There are examples galore in my plugin's source code:
http://www.robcole.com/Rob/ProductsAndServices
Rob