csharp
/
gui-cs.Terminal.Gui
mirror of https://github.com/gui-cs/Terminal.Gui.git


			
				
					
						
						
							123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226
							<!DOCTYPE html>
<!--[if IE]><![endif]-->
<html>
  
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
    <title>Event Processing and the Application Main Loop </title>
    <meta name="viewport" content="width=device-width">
    <meta name="title" content="Event Processing and the Application Main Loop ">
    <meta name="generator" content="docfx 2.59.4.0">
    
    <link rel="shortcut icon" href="../favicon.ico">
    <link rel="stylesheet" href="../styles/docfx.vendor.css">
    <link rel="stylesheet" href="../styles/docfx.css">
    <link rel="stylesheet" href="../styles/main.css">
    <link href="https://fonts.googleapis.com/css?family=Source Sans Pro" rel="stylesheet"> 
    <link href="https://fonts.googleapis.com/css?family=Source Code Pro" rel="stylesheet"> 
    <meta property="docfx:navrel" content="../toc.html">
    <meta property="docfx:tocrel" content="../toc.html">
    
    <meta property="docfx:rel" content="../">
    
  </head>  <body data-spy="scroll" data-target="#affix" data-offset="120">
    <div id="wrapper">
      <header>
        
        <nav id="autocollapse" class="navbar navbar-inverse ng-scope" role="navigation">
          <div class="container">
            <div class="navbar-header">
              <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#navbar">
                <span class="sr-only">Toggle navigation</span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
              </button>
              
              <a class="navbar-brand" href="../index.html">
                <img id="logo" class="svg" src="../images/logo48.png" alt="">
              </a>
            </div>
            <div class="collapse navbar-collapse" id="navbar">
              <form class="navbar-form navbar-right" role="search" id="search">
                <div class="form-group">
                  <input type="text" class="form-control" id="search-query" placeholder="Search" autocomplete="off">
                </div>
              </form>
            </div>
          </div>
        </nav>
        
        <div class="subnav navbar navbar-default">
          <div class="container hide-when-search" id="breadcrumb">
            <ul class="breadcrumb">
              <li></li>
            </ul>
          </div>
        </div>
      </header>
      <div class="container body-content">
        
        <div id="search-results">
          <div class="search-list">Search Results for <span></span></div>
          <div class="sr-items">
            <p><i class="glyphicon glyphicon-refresh index-loading"></i></p>
          </div>
          <ul id="pagination" data-first="First" data-prev="Previous" data-next="Next" data-last="Last"></ul>
        </div>
      </div>
      <div role="main" class="container body-content hide-when-search">
        <div class="article row grid">
          <div class="col-md-10">
            <article class="content wrap" id="_content" data-uid="">
<h1 id="event-processing-and-the-application-main-loop">Event Processing and the Application Main Loop</h1>

<p><em>See also <a href="drivers.html">Cross-platform Driver Model</a></em></p>
<p>The method <code>Application.Run</code> that we covered before will wait for
events from either the keyboard or mouse and route those events to the
proper view.</p>
<p>The job of waiting for events and dispatching them in the
<code>Application</code> is implemented by an instance of the
<a href=""><code>MainLoop</code></a>
class.</p>
<p>Mainloops are a common idiom in many user interface toolkits so many
of the concepts will be familiar to you if you have used other
toolkits before.</p>
<p>This class provides the following capabilities:</p>
<ul>
<li>Keyboard and mouse processing</li>
<li>.NET Async support</li>
<li>Timers processing</li>
<li>Invoking of UI code from a background thread</li>
<li>Idle processing handlers</li>
<li>Possibility of integration with other mainloops.</li>
<li>On Unix systems, it can monitor file descriptors for readability or writability.</li>
</ul>
<p>The <code>MainLoop</code> property in the the
<a href="../api/Terminal.Gui/Terminal.Gui.Application.html"><code>Application</code></a>
provides access to these functions.</p>
<p>When your code invokes <code>Application.Run (Toplevel)</code>, the application
will prepare the current
<a href="../api/Terminal.Gui/Terminal.Gui.Toplevel.html"><code>Toplevel</code></a> instance by
redrawing the screen appropriately and then calling the mainloop to
run.   </p>
<p>You can configure the Mainloop before calling Application.Run, or you
can configure the MainLoop in response to events during the execution.</p>
<p>The keyboard inputs is dispatched by the application class to the
current TopLevel window this is covered in more detail in the
<a href="keyboard.html">Keyboard Event Processing</a> document.</p>
<h2 id="async-execution">Async Execution</h2>
<p>On startup, the <code>Application</code> class configured the .NET Asynchronous
machinery to allow you to use the <code>await</code> keyword to run tasks in the
background and have the execution of those tasks resume on the context
of the main thread running the main loop.</p>
<p>Once you invoke <code>Application.Main</code> the async machinery will be ready
to use, and you can merely call methods using <code>await</code> from your main
thread, and the awaited code will resume execution on the main
thread. </p>
<h2 id="timers-processing">Timers Processing</h2>
<p>You can register timers to be executed at specified intervals by
calling the <a href=""><code>AddTimeout</code></a> method, like this:</p>
<pre><code class="lang-csharp">void UpdateTimer ()
{
    time.Text = DateTime.Now.ToString ();
}

var token = Application.MainLoop.AddTimeout (TimeSpan.FromSeconds (20), UpdateTimer);
</code></pre><p>The return value from AddTimeout is a token value that you can use if
you desire to cancel the timer before it runs:</p>
<pre><code class="lang-csharup">Application.MainLoop.RemoveTimeout (token);
</code></pre><h2 id="idle-handlers">Idle Handlers</h2>
<p>You can register code to be executed when the application is idling
and there are no events to process by calling the
<a href=""><code>AddIdle</code></a>
method. This method takes as a parameter a function that will be
invoked when the application is idling. </p>
<p>Idle functions should return <code>true</code> if they should be invoked again,
and <code>false</code> if the idle invocations should stop.</p>
<p>Like the timer APIs, the return value is a token that can be used to
cancel the scheduled idle function from being executed.</p>
<h2 id="threading">Threading</h2>
<p>Like other UI toolkits, Terminal.Gui is generally not thread safe.
You should avoid calling methods in the UI classes from a background
thread as there is no guarantee that they will not corrupt the state
of the UI application. </p>
<p>Generally, as there is not much state, you will get lucky, but the
application will not behave properly.</p>
<p>You will be served better off by using C# async machinery and the
various APIs in the <code>System.Threading.Tasks.Task</code> APIs.  But if you
absolutely must work with threads on your own you should only invoke
APIs in Terminal.Gui from the main thread.</p>
<p>To make this simple, you can use the <code>Application.MainLoop.Invoke</code>
method and pass an <code>Action</code>. This action will be queued for execution
on the main thread at an appropriate time and will run your code
there.</p>
<p>For example, the following shows how to properly update a label from a
background thread:</p>
<pre><code>void BackgroundThreadUpdateProgress ()
{
    Application.MainLoop.Invoke (() =&gt; {
        progress.Text = $&quot;Progress: {bytesDownloaded/totalBytes}&quot;;
        });
}
</code></pre><h2 id="integration-with-other-main-loop-drivers">Integration With Other Main Loop Drivers</h2>
<p>It is possible to run the main loop in a way that it does not take
over control of your application, but rather in a cooperative way.</p>
<p>To do this, you must use the lower-level APIs in <code>Application</code>: the
<code>Begin</code> method to prepare a toplevel for execution, followed by calls
to <code>MainLoop.EventsPending</code> to determine whether the events must be
processed, and in that case, calling <code>RunLoop</code> method and finally
completing the process  by calling <code>End</code>.</p>
<p>The method <code>Run</code> is implemented like this:</p>
<pre><code>void Run (Toplevel top)
{
    var runToken = Begin (view);
    RunLoop (runToken);
    End (runToken);
}
</code></pre><h2 id="unix-file-descriptor-monitoring">Unix File Descriptor Monitoring</h2>
<p>On Unix, it is possible to monitor file descriptors for input being
available, or for the file descriptor being available for data to be
written without blocking the application.</p>
<p>To do this, you on Unix, you can cast the <code>MainLoop</code> instance to a
<a href=""><code>UnixMainLoop</code></a>
and use the <code>AddWatch</code> method to register an interest on a particular
condition.</p>
</article>
          </div>
          
          <div class="hidden-sm col-md-2" role="complementary">
            <div class="sideaffix">
              <div class="contribution">
                <ul class="nav">
                  <li>
                    <a href="https://github.com/gui-cs/Terminal.Gui/blob/develop/docfx/articles/mainloop.md/#L1" class="contribution-link">Improve this Doc</a>
                  </li>
                </ul>
              </div>
              <nav class="bs-docs-sidebar hidden-print hidden-xs hidden-sm affix" id="affix">
                <h5>In This Article</h5>
                <div></div>
              </nav>
            </div>
          </div>
        </div>
      </div>
      
      <footer>
        <div class="grad-bottom"></div>
        <div class="footer">
          <div class="container">
            <span class="pull-right">
              <a href="#top">Back to top</a>
            </span>
            
            <span>Generated by <strong>DocFX</strong></span>
          </div>
        </div>
      </footer>
    </div>
    
    <script type="text/javascript" src="../styles/docfx.vendor.js"></script>
    <script type="text/javascript" src="../styles/docfx.js"></script>
    <script type="text/javascript" src="../styles/main.js"></script>
  </body>
</html>