wxerlang workups

A solution to the mid-run exit issue

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Category: Erlang

Published on Sunday, 05 June 2016 14:49

Written by Doug Edmunds

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On the page Coding the wx window Part 3, I mention that an unresolved issue was being able to exit (cancel) the GUIi mid-run, because my code for the Exit button did not function until the run had ended.  I received an email from Alan Gingras that provides a solution to this.  The code below is a modification of the final code version (wxcd08.erl), which is in the module wxcd08a.erl.  

-module(wxcd08a).
-author("Doug Edmunds").
%% updated version of wxcd08, by Alan Gingras
%% resolves exiting during mid-run
-compile(export_all).
-include_lib("wx/include/wx.hrl").
 
start() ->
    State = make_window(),
    loop (State),
    wx:destroy().
 
make_window() ->
    Server = wx:new(),
    Frame = wxFrame:new(Server, -1, "Countdown", [{size,{250, 150}}]),
    Panel  = wxPanel:new(Frame),
 
%% create widgets
%% the order entered here does not control appearance
    T1001 = wxTextCtrl:new(Panel, 1001,[{value, "10"}]), %set default value
    ST2001 = wxStaticText:new(Panel, 2001,"Output Area",[]),
    B101  = wxButton:new(Panel, 101, [{label, "&Countdown"}]),
    B102  = wxButton:new(Panel, ?wxID_EXIT, [{label, "E&xit"}]),
 
%%You can create sizers before or after the widgets that will go into them, but
%%the widgets have to exist before they are added to sizer.
    OuterSizer  = wxBoxSizer:new(?wxHORIZONTAL),
    MainSizer   = wxBoxSizer:new(?wxVERTICAL),
    InputSizer  = wxStaticBoxSizer:new(?wxHORIZONTAL, Panel, [{label, "Enter an integer"}]),
    ButtonSizer = wxBoxSizer:new(?wxHORIZONTAL),
 
%% Note that the widget is added using the VARIABLE, not the ID.
%% The order they are added here controls appearance.
 
    wxSizer:add(InputSizer, T1001, []),
    wxSizer:add(InputSizer, 40, 0, []),
 
    wxSizer:addSpacer(MainSizer, 10),  %spacer
    wxSizer:add(MainSizer, InputSizer,[]),
    wxSizer:addSpacer(MainSizer, 5),  %spacer
 
    wxSizer:add(MainSizer, ST2001, []),
    wxSizer:addSpacer(MainSizer, 10),  %spacer
 
    wxSizer:add(ButtonSizer, B101,  []),
    wxSizer:add(ButtonSizer, B102,  []),
    wxSizer:add(MainSizer, ButtonSizer, []),
 
    wxSizer:addSpacer(OuterSizer, 20), % spacer
    wxSizer:add(OuterSizer, MainSizer, []),
 
%% Now 'set' OuterSizer into the Panel
    wxPanel:setSizer(Panel, OuterSizer),
 
    wxFrame:show(Frame),
 
% create two listeners
    wxFrame:connect( Frame, close_window),
    wxPanel:connect(Panel, command_button_clicked),
 
%% the return value, which is stored in State
    {Frame, T1001, ST2001, self()}.
 
loop(State) ->
    {Frame, T1001, ST2001, Pid} = State,  % break State back down into its components
    io:format("--waiting in the loop--~n", []), % optional, feedback to the shell
    receive
 
        % a connection get the close_window signal
        % and sends this message to the server
        #wx{event=#wxClose{}} ->
                                                if
                                                                Pid /= self() -> Pid ! { -1 };
                                                                true -> ok
                                                end,
            io:format("~p Closing window ~n",[self()]), %optional, goes to shell
            %now we use the reference to Frame
         wxWindow:destroy(Frame),  %closes the window
         ok;  % we exit the loop
 
        #wx{id = ?wxID_EXIT, event=#wxCommand{type = command_button_clicked} } ->
    %%     {wx, ?wxID_EXIT, _,_,_} ->
           %this message is sent when the exit button (ID 102) is clicked
            %the other fields in the tuple are not important to us.
                                                if
                                                                Pid /= self() -> Pid ! { -1 };
                                                                true -> ok
                                                end,
            io:format("~p Closing window ~n",[self()]), %optional, goes to shell
         wxWindow:destroy(Frame),
         ok;  % we exit the loop
 
        #wx{id = 101, event=#wxCommand{type = command_button_clicked}} ->
            %this message is sent when the Countdown button (ID 101) is clicked
            T1001_val = wxTextCtrl:getValue(T1001),
            case is_valid_list_to_integer(T1001_val) of
                true ->
                    T1001_int = list_to_integer(T1001_val),
                                                                                MyPid = self(),
                                                                                CntdwnPid = spawn( fun() -> cntdwn( T1001_int, MyPid ) end );
                _ ->
                    wxStaticText:setLabel(ST2001, "Only integers are allowed"),
                                                                                CntdwnPid = Pid
            end,
            loop( {Frame, T1001, ST2001, CntdwnPid } );
                                { 0 } ->
                                                OutputStr = "ZERO",
                                                wxStaticText:setLabel(ST2001, OutputStr),
                                                loop( State );
                                               
                                { N } ->
                                                OutputStr = integer_to_list(N),
                                                wxStaticText:setLabel(ST2001, OutputStr),
                                                loop( State );
 
        Msg ->
            %everything else ends up here
            io:format("loop default triggered: Got ~n ~p ~n", [Msg]),
            loop(State)
 
    end.
 
cntdwn( N, Pid ) when N > 0 ->
    % assumes N is an integer
    io:format("~w~n", [N]),
                Pid ! { N },
    receive
                                { -1 } -> io:format( "Cancelled~n" ),
                                                ok
        after 1000 ->
                                                cntdwn(N-1, Pid)
     end;
cntdwn(_, Pid) ->
    io:format("ZERO~n"),
                Pid ! { 0 },
    ok.
 
is_valid_list_to_integer(Input) ->
    try list_to_integer(Input) of
        _An_integer -> true
    catch
        error: _Reason -> false  %Reason is badarg
    end.

Thank you very much, Alan!