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<div id="content" class="content">
<h1 class="title">WXerlang simple example</h1>
<p>
wxWidgets is a graphical toolkit that ships with most erlang installs. It is object oriented, not functional and in wxErlang a module represents a class
and the object created by this class has an own type, wxCLASS().
</p>
<p>
In this blog post create a basic WX application in Erlang and present the elements wxFrame, wxButton, and wxTextCtrl
</p>
<p>
The app we’ll build looks like this:
</p>
<div id="org58edee5" class="figure">
<p><img src="./images/screenshot-simple-application-1.png" alt="simple-gui-app image" title="Action!" align="centre" />
</p>
<p><span class="figure-number">Figure 1: </span>Screenshot from application.</p>
</div>
<div id="outline-container-org9c1080e" class="outline-2">
<h2 id="org9c1080e">Creating a new applications.</h2>
<div class="outline-text-2" id="text-org9c1080e">
<p>
Let’s create a new application using rebar3, I like rebar and it seems to do things that I expect. Issue the command:
</p>
<pre class="example" id="org325f4a7">
$ rebar3 new app name="wx_simple"
===> Writing wx_simple/src/wx_simple_app.erl
===> Writing wx_simple/src/wx_simple_sup.erl
===> Writing wx_simple/src/wx_simple.app.src
===> Writing wx_simple/rebar.config
===> Writing wx_simple/.gitignore
===> Writing wx_simple/LICENSE
===> Writing wx_simple/README
</pre>
<p>
This creates the 'app' file and the a basic supervisor, there is nothing wx specific yet. The next step
is to draw a window. Now that the "App" is created along with a simple supervisor, lets make the GUI.
</p>
</div>
<div id="outline-container-orgbf49f57" class="outline-3">
<h3 id="orgbf49f57">Basics: Drawing a window.</h3>
<div class="outline-text-3" id="text-orgbf49f57">
<p>
I like my apps to fit "nicely" into the OTP style behavior, so lets make a new
file called wx_server.erl in wx_simple/src directory.
</p>
<p>
This may look familiar to existing gen_server layout, its supposed to.
</p>
<p>
The code has been simplified to provide a minimal basic example that opens a window and
nothing else.
</p>
<div class="org-src-container">
<pre class="src src-erlang">-module(wx_server).
-include_lib("wx/include/wx.hrl").
-behaviour(wx_object).
-export([start/1, start_link/0, start_link/1,
init/1, terminate/2, code_change/3,
handle_info/2, handle_call/3, handle_event/2]).
-record(state, {sb,frame }).
start(Debug) ->
wx_object:start(?MODULE, Debug, []).
start_link() ->
start_link([]).
start_link(Debug) ->
Status = wx_object:start_link(?MODULE, Debug, []),
{ok, wx_object:get_pid(Status)}.
init(Options) ->
wx:new(Options),
process_flag(trap_exit, true),
Frame = wxFrame:new(wx:null(),
?wxID_ANY,
"Simple application",
[{size,{500,500}}]),
wxFrame:show(Frame),
{Frame, #state{}}.
%%%%%%%%%%%%
%% Callbacks
%% Handled as in normal gen_server callbacks
handle_info(Msg, State) ->
io:format("handle_info callback: ~p~n",[?MODULE, Msg]),
{noreply,State}.
handle_call(Msg, _From, State) ->
io:format("~p handle_call callback: ~p~n",[?MODULE, Msg]),
{reply,ok,State}.
%% Async Events are handled in handle_event as in handle_info
handle_event(Ev,State) ->
io:format("~p Got event ~p~n",[?MODULE, Ev]),
{noreply, State}.
code_change(_, _, State) ->
{stop, not_yet_implemented, State}.
terminate(_Reason, State) ->
wx:destroy().
%%%%%%%%%%%%%%%%% Internals %%%%%%%%%%
</pre>
</div>
<p>
We need to update the supervisor (wx_simple_sup.erl) so that it can find this new worker (wx_server) to supervise it. Update "ChildSpecs"
to include the reference to the wx_server and its start function. See the example below.
</p>
<div class="org-src-container">
<pre class="src src-erlang">
ChildSpecs = [
#{id => wx_server,
start => {wx_server, start_link, []},
shutdown => brutal_kill}],
</pre>
</div>
<p>
And finally, start the application in the rebar3 shell repl.
</p>
<div class="org-src-container">
<pre class="src src-sh">$ rebar3 shell
===> Verifying dependencies...
===> Analyzing applications...
===> Compiling wx_simple
Erlang/OTP 24 [erts-12.3.2.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit]
Eshell V12.3.2.1 (abort with ^G)
1> ===> Booted wx_simple
</pre>
</div>
<p>
And a 500x500 pixel window should appear on the screen. It can be closed by clicking on
the close button (exactly how depends on which operating system you are running).
</p>
</div>
</div>
<div id="outline-container-orgf25fbc8" class="outline-3">
<h3 id="orgf25fbc8">Adding a button (wxButton)</h3>
<div class="outline-text-3" id="text-orgf25fbc8">
<p>
Our next step is to add a button, because everyone loves buttons.
</p>
<p>
The wxButton 'class/module' allows us to create buttons.
</p>
<p>
As explained in the <a href="https://www.erlang.org/doc/man/wxbutton">Docs on wx button</a>, to create button, we can write the following:
</p>
<div class="org-src-container">
<pre class="src src-erlang">Button = wxButton:new(Frame, ?wxID_ANY, [{label, "Start"},
{size, {150, 50}}]),
</pre>
</div>
<p>
The arguements to new are: new(Parent, Id, Options :: [Option]). The example above
uses the macro ?wxID_ANY a convenience function, which returns a non colliding unique ID.
</p>
<p>
The parent in this case is the "Frame", which we'll talk more about later.
</p>
<p>
We tell the button that its parent window is the frame wxobject we created earlier in
wx_server object above.
</p>
<p>
The "Options" list is a set of parameters, the ones we care about is the size.
</p>
<p>
This button has a label and size tuples in the Options list.
</p>
</div>
</div>
<div id="outline-container-org2c26463" class="outline-3">
<h3 id="org2c26463">Adding editable text label ( wxTextCtrl )</h3>
<div class="outline-text-3" id="text-org2c26463">
<p>
We’ll add text to our frame using a wxTextCtrl. As per <a href="https://www.erlang.org/doc/man/wxtextctrl">the docs:</a>
</p>
<div class="org-src-container">
<pre class="src src-erlang">TextCtrl = wxTextCtrl:new(Frame, ?wxID_ANY, [ {value, "I am error."}]).
</pre>
</div>
<p>
Which follows the very similar pattern to the previous button. The last
parameter (an empty list in the above) is any of the parameters, such as values
or location, etc.
</p>
<div class="org-src-container">
<pre class="src src-erlang">wxButton:connect(Button, command_button_clicked, [Options]
</pre>
</div>
<p>
After creating the button, you likely want to connect click events up to a function. We're going to
it via an inline callback in the "Options"
</p>
<div class="org-src-container">
<pre class="src src-erlang">wxButton:connect(Button,
command_button_clicked,
[{callback,
fun(Evt, Obj) ->
wxButton:setLabel(Button, "clicked.."),
wxButton:disable(Button)
end}]),
</pre>
</div>
<p>
In this particular callback function, we change the label and then 'disable' it, which means to
effectively disable its use.
</p>
</div>
</div>
<div id="outline-container-org3b5d5df" class="outline-3">
<h3 id="org3b5d5df">Improvement.</h3>
<div class="outline-text-3" id="text-org3b5d5df">
<p>
Not being happy with just laying out buttons, lets take it up a notch. We're going to
use a "sizer", specifically the wxBoxSizer, which is a container ainer that organizes child widgets into a single row
or column, depending on its configured orientation.
</p>
<div class="org-src-container">
<pre class="src src-erlang">MainSizer = wxBoxSizer:new(?wxVERTICAL),
</pre>
</div>
<p>
The erlang specific macro is: ?wxVERTICAL or ?wxHORIZONTAL.
</p>
<p>
After creating the sizer, you can add specific widgets to the sizer and also
configure additional layout properties of the widgets themselves.
</p>
<div class="org-src-container">
<pre class="src src-erlang">wxBoxSizer:add(MainSizer, TextCtrl, [{flag, ?wxALL}, {border, 5}]),
wxBoxSizer:add(MainSizer, Button, [{flag, ?wxALL}, {border, 5}]),
</pre>
</div>
<p>
The wxBoxSizer class inherits from <a href="https://www.erlang.org/doc/man/wxsizer">wxSizer</a> class, which means that the functions from
wxSizer apply to wxBoxSizer.
</p>
<p>
The function signature from wxSizer, looks a bit odd.
</p>
<div class="org-src-container">
<pre class="src src-erlang">wxSizer:add(This, Window, [Option])
</pre>
</div>
<p>
The second arguement is "Window", thats werid, checking out the function definition in
the <a href="https://www.erlang.org/doc/man/wxsizer#add-3">docs of add/3.</a>
</p>
<p class="verse">
This = wxSizer()<br />
Window = wxWindow:wxWindow() | wxSizer:wxSizer()<br />
Option =<br />
    {proportion, integer()} |<br />
    {flag, integer()} |<br />
    {border, integer()} |<br />
    {userData, wx:wx_object()}<br />
</p>
<p>
Ok, what is a <a href="https://www.erlang.org/doc/man/wxwindow#type-wxWindow">wxWindow()</a> ? The official docs illuminate the situation.
</p>
<p class="verse">
wxWindow is the base class for all windows and represents any visible object on screen.<br />
All controls, top level windows and so on are windows. Sizers and device contexts are<br />
not, however, as they don't appear on screen themselves.<br />
</p>
<p>
So, its pretty much any visual widget, in our example we have the button and textctrl,
widgets to add.
</p>
<p>
After that, now we can configure the main "Frame" to use this newly created Sizer.
</p>
<div class="org-src-container">
<pre class="src src-erlang">wxWindow:setSizer(Frame, MainSizer),
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<p>
Now we want wrap that up,
</p>
<p>
I should link it to a current working example, along with a current screenshot, and
make rough promises of future tutorials.
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<p>
I don't always "whoop", but when I do, there it is.
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<h2 id="org17576bc">Resources:</h2>
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<li>Idea blatently taken from <a href="https://hidnasio.github.io//elixir/wxerlang/2022/06/29/advance-wx-erlang-hello-world.html">Hello world in elixir.</a></li>
<li><a href="https://www.erlang.org/doc/man/wx.html">wx erlang man/docs</a></li>
<li>TODO: provide a link to github for this.</li>
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<div id="postamble" class="status">
<p class="author">Author: Wade Mealing</p>
<p class="date">Created: 2022-08-19 Fri 21:24</p>
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