AU: Reset plug-in host callbacks in prepareToPlay() in case they were removed when uninitialising or resetting the audio unit

modules/juce_audio_processors/format_types/juce_AudioUnitPluginFormat.mm

@@ -598,11 +598,7 @@ public:
     void cleanup()
     {
        #if JUCE_MAC
-        if (eventListenerRef != nullptr)
-        {
-            AUListenerDispose (eventListenerRef);
-            eventListenerRef = nullptr;
-        }
+        disposeEventListener();
        #endif
 
         if (prepared)
@@ -618,7 +614,11 @@ public:
         setRateAndBufferSizeDetails (rate, blockSize);
         setLatencySamples (0);
         refreshParameterList();
-        createPluginCallbacks();
+        setPluginCallbacks();
+
+       #if JUCE_MAC
+        createEventListener();
+       #endif
 
         return true;
     }
@@ -1001,6 +1001,8 @@ public:
                 if (! haveParameterList)
                     refreshParameterList();
 
+                setPluginCallbacks();
+
                 if (! syncBusLayouts (getBusesLayout(), true, ignore))
                 {
                     prepared = false;
@@ -1666,7 +1668,7 @@ private:
     bool lastProcessBlockCallWasBypass = false, auSupportsBypass = false;
     bool haveParameterList = false;
 
-    void createPluginCallbacks()
+    void setPluginCallbacks()
     {
         if (audioUnit != nullptr)
         {
@@ -1684,52 +1686,65 @@ private:
             }
            #endif
 
-            {
-                HostCallbackInfo info;
-                zerostruct (info);
+            HostCallbackInfo info;
+            zerostruct (info);
 
-                info.hostUserData = this;
-                info.beatAndTempoProc = getBeatAndTempoCallback;
-                info.musicalTimeLocationProc = getMusicalTimeLocationCallback;
-                info.transportStateProc = getTransportStateCallback;
+            info.hostUserData = this;
+            info.beatAndTempoProc = getBeatAndTempoCallback;
+            info.musicalTimeLocationProc = getMusicalTimeLocationCallback;
+            info.transportStateProc = getTransportStateCallback;
 
-                AudioUnitSetProperty (audioUnit, kAudioUnitProperty_HostCallbacks,
-                                      kAudioUnitScope_Global, 0, &info, sizeof (info));
-            }
-           #if JUCE_MAC
-            AUEventListenerCreate (eventListenerCallback, this, CFRunLoopGetMain(),
-                                   kCFRunLoopDefaultMode, 0, 0, &eventListenerRef);
+            AudioUnitSetProperty (audioUnit, kAudioUnitProperty_HostCallbacks,
+                                  kAudioUnitScope_Global, 0, &info, sizeof (info));
+        }
+    }
 
-            for (auto* param : getParameters())
-            {
-                if (auto* auParam = dynamic_cast<AUInstanceParameter*> (param))
-                {
-                    AudioUnitEvent event;
-                    event.mArgument.mParameter.mAudioUnit = audioUnit;
-                    event.mArgument.mParameter.mParameterID = auParam->paramID;
-                    event.mArgument.mParameter.mScope = kAudioUnitScope_Global;
-                    event.mArgument.mParameter.mElement = 0;
+   #if JUCE_MAC
+    void disposeEventListener()
+    {
+        if (eventListenerRef != nullptr)
+        {
+            AUListenerDispose (eventListenerRef);
+            eventListenerRef = nullptr;
+        }
+    }
 
-                    event.mEventType = kAudioUnitEvent_ParameterValueChange;
-                    AUEventListenerAddEventType (eventListenerRef, nullptr, &event);
+    void createEventListener()
+    {
+        if (audioUnit == nullptr)
+            return;
 
-                    event.mEventType = kAudioUnitEvent_BeginParameterChangeGesture;
-                    AUEventListenerAddEventType (eventListenerRef, nullptr, &event);
+        disposeEventListener();
 
-                    event.mEventType = kAudioUnitEvent_EndParameterChangeGesture;
-                    AUEventListenerAddEventType (eventListenerRef, nullptr, &event);
-                }
-            }
+        AUEventListenerCreate (eventListenerCallback, this, CFRunLoopGetMain(),
+                               kCFRunLoopDefaultMode, 0, 0, &eventListenerRef);
 
-            addPropertyChangeListener (kAudioUnitProperty_PresentPreset);
-            addPropertyChangeListener (kAudioUnitProperty_ParameterList);
-            addPropertyChangeListener (kAudioUnitProperty_Latency);
-            addPropertyChangeListener (kAudioUnitProperty_BypassEffect);
-           #endif
+        for (auto* param : getParameters())
+        {
+            jassert (dynamic_cast<AUInstanceParameter*> (param) != nullptr);
+
+            AudioUnitEvent event;
+            event.mArgument.mParameter.mAudioUnit = audioUnit;
+            event.mArgument.mParameter.mParameterID = static_cast<AUInstanceParameter*> (param)->paramID;
+            event.mArgument.mParameter.mScope = kAudioUnitScope_Global;
+            event.mArgument.mParameter.mElement = 0;
+
+            event.mEventType = kAudioUnitEvent_ParameterValueChange;
+            AUEventListenerAddEventType (eventListenerRef, nullptr, &event);
+
+            event.mEventType = kAudioUnitEvent_BeginParameterChangeGesture;
+            AUEventListenerAddEventType (eventListenerRef, nullptr, &event);
+
+            event.mEventType = kAudioUnitEvent_EndParameterChangeGesture;
+            AUEventListenerAddEventType (eventListenerRef, nullptr, &event);
         }
+
+        addPropertyChangeListener (kAudioUnitProperty_PresentPreset);
+        addPropertyChangeListener (kAudioUnitProperty_ParameterList);
+        addPropertyChangeListener (kAudioUnitProperty_Latency);
+        addPropertyChangeListener (kAudioUnitProperty_BypassEffect);
     }
 
-   #if JUCE_MAC
     void addPropertyChangeListener (AudioUnitPropertyID type) const
     {
         AudioUnitEvent event;