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<tr><th colspan="3" align="center">Appendix C. Creating your own signals</th></tr>
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<div class="appendix">
<div class="titlepage"><div><div><h1 class="title">
<a name="chapter-custom-signals"></a>Appendix C. Creating your own signals</h1></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<ul class="toc"><li><span class="section"><a href="chapter-custom-signals.html#chapter-custom-signals-example">Example</a></span></li></ul>
</div>
<p>
Now that you've seen signals and signal handlers in <span class="application">gtkmm</span>, you
might like to use the same technique to allow interaction between your
own classes. That's actually very simple by using the
<span class="application">libsigc++</span> library directly.
</p>
<p>
This isn't purely a <span class="application">gtkmm</span> or GUI issue. <span class="application">gtkmm</span> uses
<span class="application">libsigc++</span> to implement its proxy wrappers for the
<span class="application">GTK</span> signal system, but for new,
non-GTK signals, you can create pure C++ signals, using the
<code class="classname">sigc::signal<></code> template.
</p>
<p>
For instance, to create a signal that sends 2 parameters, a <span class="type">bool</span>
and an <span class="type">int</span>, just declare a <code class="classname">sigc::signal</code>,
like so:
</p>
<pre class="programlisting"><code class="code">sigc::signal<void(bool, int)> signal_something;
</code></pre>
<p>
You could just declare that signal as a public member variable, but
some people find that distasteful and prefer to make it available via
an accessor method, like so:
</p>
<pre class="programlisting"><code class="code">class Server
{
public:
//signal accessor:
using type_signal_something = sigc::signal<void(bool, int)>;
type_signal_something signal_something();
protected:
type_signal_something m_signal_something;
};
Server::type_signal_something Server::signal_something()
{
return m_signal_something;
}
</code></pre>
<p>
You can then connect to the signal using the same syntax used when
connecting to <span class="application">gtkmm</span> signals. For instance,
</p>
<pre class="programlisting"><code class="code">server.signal_something().connect(
sigc::mem_fun(client, &Client::on_server_something) );
</code></pre>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="chapter-custom-signals-example"></a>Example</h2></div></div></div>
<p>
This is a full working example that defines and uses custom signals.
</p>
<p><a class="ulink" href="https://gitlab.gnome.org/GNOME/gtkmm-documentation/tree/master/examples/book/signals/custom/" target="_top">Source Code</a></p>
<p>File: <code class="filename">client.h</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#ifndef GTKMM_EXAMPLE_CLIENT_H
#define GTKMM_EXAMPLE_CLIENT_H
#include <sigc++/sigc++.h>
//Client must inherit from sigc::trackable.
//because libsigc++ needs to keep track of the lifetime of signal handlers.
class Client : public sigc::trackable
{
public:
Client();
virtual ~Client();
//Signal handler:
void on_server_something(bool a, int b);
};
#endif //GTKMM_EXAMPLE_CLIENT_H
</code></pre>
<p>File: <code class="filename">server.h</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#ifndef GTKMM_EXAMPLE_SERVER_H
#define GTKMM_EXAMPLE_SERVER_H
#include <sigc++/sigc++.h>
class Server
{
public:
Server();
virtual ~Server();
void do_something();
//signal accessor:
using type_signal_something = sigc::signal<void(bool, int)>;
type_signal_something signal_something();
protected:
type_signal_something m_signal_something;
};
#endif //GTKMM_EXAMPLE_SERVER_H
</code></pre>
<p>File: <code class="filename">client.cc</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#include "client.h"
#include <iostream>
Client::Client()
{
}
Client::~Client()
{
}
void Client::on_server_something(bool a, int b)
{
std::cout << "Client::on_server_something() called with these parameters: "
<< a << ", " << b << std::endl;
}
</code></pre>
<p>File: <code class="filename">main.cc</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#include "server.h"
#include "client.h"
#include <iostream>
int main(int, char**)
{
Server server;
Client client;
//Connect a Server signal to the signal handler in Client.
server.signal_something().connect(sigc::mem_fun(client,
&Client::on_server_something) );
std::cout << "Before Server::do_something()" << std::endl;
//Tell the server to do something that will eventually cause it to emit the
//"something" signal.
server.do_something(); // Client::on_server_something() will run before
// Server::do_something() has completed.
std::cout << "After Server::do_something()" << std::endl;
return 0;
}
</code></pre>
<p>File: <code class="filename">server.cc</code> (For use with gtkmm 4)</p>
<pre class="programlisting"><code class="code">#include "server.h"
#include <iostream>
Server::Server()
{
}
Server::~Server()
{
}
Server::type_signal_something Server::signal_something()
{
return m_signal_something;
}
void Server::do_something()
{
m_signal_something.emit(false, 5);
}
</code></pre>
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