Added a class EventHandler, for adding lambda callbacks to components

modules/juce_events/broadcasters/juce_EventHandler.h

@@ -0,0 +1,78 @@
+/*
+  ==============================================================================
+
+   This file is part of the JUCE library.
+   Copyright (c) 2017 - ROLI Ltd.
+
+   JUCE is an open source library subject to commercial or open-source
+   licensing.
+
+   The code included in this file is provided under the terms of the ISC license
+   http://www.isc.org/downloads/software-support-policy/isc-license. Permission
+   To use, copy, modify, and/or distribute this software for any purpose with or
+   without fee is hereby granted provided that the above copyright notice and
+   this permission notice appear in all copies.
+
+   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
+   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
+   DISCLAIMED.
+
+  ==============================================================================
+*/
+
+namespace juce
+{
+
+//==============================================================================
+/**
+    Helper class for dispatching callbacks to a lambda function.
+
+    This class probably isn't something many users will use in their own code, but
+    some juce classes use it as a helper to allow lambdas to be assigned to callback
+    hooks - e.g. see its use in Button::onClick
+*/
+template <typename OwnerClass>
+struct EventHandler
+{
+    EventHandler() {}
+    ~EventHandler() {}
+
+    /** Assigns a void std::function to this callback.
+        Note that this will replace any existing function that was previously assigned.
+    */
+    void operator= (std::function<void()> callbackToAttach)
+    {
+        callback = [=](OwnerClass&) { callbackToAttach(); };
+    }
+
+    /** Assigns a std::function to this callback which takes a reference to the
+        source object that's making the callback.
+        In the example of this class being used inside, e.g. a Button, then the
+        callback parameter would be the Button that is doing the calling.
+        Note that this will replace any existing function that was previously assigned.
+    */
+    void operator= (std::function<void(OwnerClass&)> callbackToAttach)
+    {
+        callback = static_cast<std::function<void(OwnerClass&)>&&> (callbackToAttach);
+    }
+
+    /** Removes any existing function that was previously assigned to the callback. */
+    void reset() noexcept
+    {
+        callback = {};
+    }
+
+    /** @internal */
+    void invoke (OwnerClass& owner)
+    {
+        if (callback != nullptr)
+            callback (owner);
+    }
+
+private:
+    std::function<void(OwnerClass&)> callback;
+
+    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (EventHandler)
+};
+
+} // namespace juce

modules/juce_events/juce_events.h

@@ -76,6 +76,7 @@
 #include "broadcasters/juce_AsyncUpdater.h"
 #include "broadcasters/juce_ChangeListener.h"
 #include "broadcasters/juce_ChangeBroadcaster.h"
+#include "broadcasters/juce_EventHandler.h"
 #include "timers/juce_Timer.h"
 #include "timers/juce_MultiTimer.h"
 #include "interprocess/juce_InterprocessConnection.h"