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    <p>The simple answer is: you can't. Or, rather, you don't want (or need!) to use <code>sender()</code>. Simply capture and use <code>action</code>.</p> <pre><code>// Important! // vvvv connect(action, &amp;QAction::triggered, this, [action, this]() { // use action as you wish ... }); </code></pre> <p>The specification of <code>this</code> as the object context for the functor ensures that the functor will not get invoked if either the action or <code>this</code> (a <code>QObject</code>) cease to exist. Otherwise, the functor would try to reference dangling pointers.</p> <p>In general, the following must hold when capturing context variables for a functor passed to <code>connect</code>, in order to avoid the use of dangling pointers/references:</p> <ol> <li><p>The pointers to the source and target objects of <code>connect</code> can be captured by value, as above. It is guaranteed that if the functor is invoked, both ends of the connection exist. </p> <pre><code>connect(a, &amp;A::foo, b, [a, b]{}); </code></pre> <p>Scenarios where <code>a</code> and <code>b</code> are in different threads require special attention. It can not be guaranteed that once the functor is entered, some thread will not delete either object.</p> <p>It is idiomatic that an object is only destructed in its <code>thread()</code>, or in any thread if <code>thread() == nullptr</code>. Since a thread's event loop invokes the functor, the null thread is never a problem for <code>b</code> - without a thread the functor won't be invoked. Alas, there's no guarantee about the lifetime of <code>a</code> in <code>b</code>'s thread. It is thus safer to capture the necessary state of the action by value instead, so that <code>a</code>'s lifetime is not a concern.</p> <pre><code>// SAFE auto aName = a-&gt;objectName(); connect(a, &amp;A::foo, b, [aName, b]{ qDebug() &lt;&lt; aName; }); // UNSAFE connect(a, &amp;A::foo, b, [a,b]{ qDebug() &lt;&lt; a-&gt;objectName(); }); </code></pre></li> <li><p>Raw pointers to other objects can be captured by value if you're absolutely sure that the lifetime of the objects they point to overlaps the lifetime of the connection.</p> <pre><code>static C c; auto p = &amp;c; connect(..., [p]{}); </code></pre></li> <li><p>Ditto for references to objects:</p> <pre><code>static D d; connect(..., [&amp;d]{}); </code></pre></li> <li><p>Non-copyable objects that don't derive from <code>QObject</code> should be captured through their shared pointers by value.</p> <pre><code>std::shared_ptr&lt;E&gt; e { new E }; QSharedPointer&lt;F&gt; f { new F; } connect(..., [e,f]{}); </code></pre></li> <li><p><code>QObject</code>s living in the same thread can be captured by a <code>QPointer</code>; its value must be checked prior to use in the functor.</p> <pre><code>QPointer&lt;QObject&gt; g { this-&gt;parent(); } connect(..., [g]{ if (g) ... }); </code></pre></li> <li><p><code>QObject</code>s living in other threads must be captured by a shared pointer or a weak pointer. Their parent must be unset prior to their destruction, otherwise you'll have double deletes:</p> <pre><code>class I : public QObject { ... ~I() { setParent(nullptr); } }; std::shared_ptr&lt;I&gt; i { new I }; connect(..., [i]{ ... }); std::weak_ptr&lt;I&gt; j { i }; connect(..., [j]{ auto jp = j.lock(); if (jp) { ... } }); </code></pre></li> </ol>
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    1. COThis is beautiful and so simple! The answer was staring right at me. Thank you!
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