uiInstance.close() has no effect - google-apps-script

Question

I have the following code inside a script for a Google Spreadsheet:
var uiInstance;
function displayDialog() {
uiInstance = UiApp.createApplication()
.setWidth(130)
.setHeight(130);
uiInstance.add(uiInstance.createLabel("foo"));
SpreadsheetApp.getUi().showModalDialog(uiInstance, 'bar');
}
This dialog is intended to inform the user the script is calculating something and I want to close the dialog again once the script has finished its work. If I use
uiInstance.close();
inside or outside the function nothing seems to happen though; the dialog remains opened until the user closes it. Is there any solution for my problem?

Answer 1

you have to "return" to effectively close the uiInstance, return is needed to reflect any change you made to the Ui, including closing it.
try
return uiInstance.close();
EDIT following your comment :
UiApp instances can only be closed from a handler function, I thought that was how you were using it (but I might have been wrong).
Below is a small code example :
function displayDialog() {
var uiInstance = UiApp.createApplication()
.setWidth(130)
.setHeight(130);
uiInstance.add(uiInstance.createLabel("foo"));
var handler = uiInstance.createServerHandler('closeDialog');
uiInstance.add(uiInstance.createButton('close',handler));
SpreadsheetApp.getUi().showModalDialog(uiInstance, 'bar');
}
function closeDialog(){
return UiApp.getActiveApplication().close();
}
There is also a tricky workaround that can "simulate" a user action. It uses a property of some widgets to trigger a handler function when they change value. In the example below I used a checkBox to start the process
It will close the dialog when the task in doStuf is done.
function displayDialog() {
var uiInstance = UiApp.createApplication()
.setWidth(130)
.setHeight(130);
uiInstance.add(uiInstance.createLabel("foo"));
var handler = uiInstance.createServerHandler('doStuf');
var chk = uiInstance.createCheckBox().setValue(true).setId('chk').setVisible(false);
chk.addValueChangeHandler(handler);
uiInstance.add(chk);
chk.setValue(false,true)// This actually calls the doStuf function (using the handler)
SpreadsheetApp.getUi().showModalDialog(uiInstance, 'bar');
}
function doStuf(){
Utilities.sleep(5000);// replace with something useful ...
return UiApp.getActiveApplication().close();
}

Answer 2

Use:
uiInstance = uiInstance.close();
SpreadsheetApp.getUi().showModalDialog(uiInstance, 'bar');