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Re: Re: Problems with ChoiceDialog inside a Dynamic: Bug

  • To: mathgroup at
  • Subject: [mg107819] [mg107819] Re: [mg107779] Re: Problems with ChoiceDialog inside a Dynamic: Bug
  • From: Adam Griffith <adamg at>
  • Date: Sat, 27 Feb 2010 03:14:28 -0500 (EST)
  • References: <hm573n$kge$> <> <>

Hi Guido,

Modality and blocking the kernel are two separate behaviors. Modal 
simply means that the user cannot access windows beneath the dialog 
while a blocking dialog holds the kernel evaluation until closed. So for 
example, the following dialog is modal and does not block:

In[9]:= CreateDialog[
  Grid[{{"Does the earth has oceans?"}, {ChoiceButtons[{DialogReturn[
        answer = True], DialogReturn[answer = False]}]}}],
  Modal -> True];

In[10]:= answer

Out[10]= False

As for the Dynamic[],

DynamicModule[{planets, x, habitantq},
 planets = {"Mercury", "Venus", "Earth"};
 x = First[planets];
 PopupMenu[Dynamic[x, {x = #;
     If[StringMatchQ[x, "Earth"],
      habitantq =
        Column[{"Do you live on earth?",
             Print["This user has selected earth as their planet of \
residence"]; DialogReturn[True]],
            CancelButton[DialogReturn[False]]}]}]]]} &,
   Evaluator -> Automatic, Method -> "Queued"], planets]]

again, adding Modal->True if desired.

Hope this helps,

Guido Tripaldi wrote:
> mmh, I've said "problem solved" too soon in the previous message! So it is NOT possible to use ChoiceDialog inside a Manipulate or more in general inside a Dynamic object, or in nested modal dialogs: very bad! This certainly limits the grade of interactivity with the user that we can put in a program, think for example in cases where it's needed to stop and alert the user before a potentially destructive operations (i.e. deleting data, etc..).
> Hoping, as usual, in the next version...
> Anyway, thank you Adam and Albert for your hints!
>    G
> Il giorno 25/feb/2010, alle ore 23.37, Albert Retey ha scritto:
>> Hi,
>>> suppose you wanna to display an alert to the user before to continue the 
>>> execution of your code when some conditions occur : probably you'll use 
>>> ChoiceDialog[], the useful function that "puts up a standard choice 
>>> dialog that displays  expr together with OK and Cancel buttons, and 
>>> returns  True if OK is clicked, and  False if Cancel is clicked.".
>>> But if you use this function inside some Dynamic[] object, it hangs the 
>>> kernel. I've tried to find in the documentation some references to this 
>>> bad combination without any luck, so I don't understand if this is a bug 
>>> or there is something missing in the code.
>>> To better explain the problem here is a very basic example:
>>> (* just a silly example *)
>>> Grid[{
>>>  {"Choose a dividend: ",
>>>   PopupMenu[Dynamic[dividend], Table[i, {i, 0, 10}]]},
>>>  {"Choose a divisor : ", PopupMenu[Dynamic[divisor], Table[i, {i, 0, 10}]]},
>>>  {"Quotient: ", Dynamic[dividend / divisor]}
>>>  }, Frame -> All]
>>> Dynamic[
>>> If[divisor == 0,
>>>   ChoiceDialog["Uh-oh, you are going to do a division by zero! Please select a different divisor.", {"Ok"}];
>>> ]];
>> It's a deficiency of how the modal dialogs behave. I have encountered
>> this about a year ago or more and reported here, but have not yet
>> received any answers. You have the same problem when you try to nest
>> modal dialogs. In the meantime I just try to avoid modal dialogs where I
>> can, which is often possible, but of course not always.
>>> Instead, if you use the MessageDialog[] function to show a message window, all works well, but of course the execution will continue without waiting for the user action (that is not what I want).
>>> Same situation if you try to use ChoiceDialog[] inside a TabView, or other kind of Views:
>>> (* another silly example *)
>>> TabView[{
>>>  "Tab1" -> Button["Show ChoiceDialog", result = ChoiceDialog["This hangs.. :-(."];],
>>>  "Tab2" -> Button["Show MessageDialog", MessageDialog["This works!"];]
>>>  }]
>> In some cases like your second example, where a modal dialog is started
>> by a button, the Method->"Queued" trick helps:
>> TabView[{
>>  "Tab1" -> Button["Show ChoiceDialog",
>>     result = ChoiceDialog["This is ok:-)."],
>>     Method->"Queued"
>>  ],
>>  "Tab2" -> Button["Show MessageDialog",
>>     MessageDialog["This works!"];
>>  ]
>> }]
>> hth,
>> albert
> ---
> Guido Tripaldi

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