App.alert parameters on ios device

Hi there!

I'm working on a form that needs to be used on ios (iPad specifically).

I added a button that turns a group of fields to read only.

The code is:

if(app.alert("Document vergendelen?",2,2)==4)
{
this.getField("Group1").readonly = true;
}

This works perfectly on desktop, but on ios it doesn't give me the Yes/No option, only an "OK" button which cancels the action (tried on Acrobat and PDF Viewer).

I also tried it on PDF Expert which does give the Yes/No option, but then the app freezes and nothing happens.

We would prefer to stick to Acrobat or PDF Viewer though for ease of use.

Any help would be greatly appreciated!