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Merge pull request #6199 from livecodeali/feature-objc_protocol_proxy
[[ ObjcDelegates ]] Enable creation of objc delegates implementing protocol methods
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‎docs/lcb/notes/feature-objc_delegates.md‎

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# LiveCode Builder Language
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## Objective-C delegate support
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Handlers `CreateObjcDelegate` and `CreateObjcDelegateWithContext` have
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been added to the objc module which allow the creation of custom
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delegate objects with LCB implementations of protocol methods.
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In order to create a delegate to handle a particular protocol method,
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pass in the protocol name as the first argument and the mapping from
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method names to LCB handlers as the second argument. For example, to
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create a selectionChanged message for an `NSTextView`, we need to create
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a handler
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private handler DidChangeSelection(in pNotification as ObjcObject) returns nothing
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post "selectionChanged"
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end handler
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and create a `NSTextViewDelegate`:
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variable tDelegate as optional ObjcObject
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put CreateObjcDelegate( \
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"NSTextViewDelegate", \
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{"textViewDidChangeSelection:": DidChangeSelection}, \
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) into tDelegate
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if tDelegate is not nothing then
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put tDelegate into mTextViewDelegate
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end if
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Optionally, a context parameter can be passed in at delegate creation
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time:
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put CreateObjcDelegateWithContext( \
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"NSTextViewDelegate", \
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{"textViewDidChangeSelection:": DidChangeSelectionContext}, \
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tContext) into tDelegate
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if tDelegate is not nothing then
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put tDelegate into mTextViewDelegate
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end if
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In this case the context variable will be passed as first argument of
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the corresponding LCB callback:
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private handler DidChangeSelectionContext(in pContext, in pNotification as ObjcObject) returns nothing
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post "selectionChanged" with [pContext]
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end handler
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Some protocols consist of purely optional methods. In this case the
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information about the protocol's methods are not available from the
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objective-c runtime API. For this eventuality there are also handlers
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`CreateObjcInformalDelegate` and `CreateObjcInformalDelegateWithContext`.
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These handlers take a list of foreign handlers as their first argument
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instead of a protocol name. The foreign handlers' information is used to
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resolve incoming selectors so that the desired LCB callback is called.
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For example the `NSSoundDelegate` protocol has only one method, and it
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is optional,
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- (void)sound:(NSSound *)sound didFinishPlaying:(BOOL)aBool;
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So in order to create an `NSSoundDelegate`, we need to create a list of
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foreign handlers, in this case just the following:
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foreign handler NSSoundDidFinishPlaying(in pSound as ObjcId, in pDidFinish as CSChar) binds to "objc:.-sound:didFinishPlaying:"
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and create the informal delegate
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handler DidSoundFinish(in pSound as ObjcId, in pDidFinish as Boolean) returns nothing
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if pDidFinish then
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post "soundFinished"
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end if
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end handler
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foreign handler Objc_SetSoundDelegate(in pSound as ObjcId, in pDelegate as ObjcId) returns nothing \
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binds to "objc:NSSound.-setDelegate:"
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...
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variable tDelegate as optional ObjcObject
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put CreateObjcInformalDelegate( \
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[NSSoundDidFinishPlaying], \
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{"textViewDidChangeSelection:": DidChangeSelection}) \
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into tDelegate
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end if
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if tDelegate is not nothing then
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put tDelegate into mSoundDelegate
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Objc_SetSoundDelegate(tSound, tDelegate)
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end if
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> *Note:* Delegate properties are usually 'assigned' rather than
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> 'retained', so it is necessary to store them in module variables
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> until they are no longer needed. Generally the pattern required is
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> as follows:
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handler OnOpen()
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-- Create native view and set native layer
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-- Set native view delegate property
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-- Store view and delegate in module vars
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end handler
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handler OnClose()
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-- Set native view delegate property to nothing
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-- Put nothing into view and delegate module vars
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-- Set native layer to nothing
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end handler

‎libfoundation/include/foundation-objc.h‎

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NSData *MCDataConvertToAutoreleasedNSData(MCDataRef data);
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#endif
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extern MCTypeInfoRef kMCObjcDelegateCallbackSignatureErrorTypeInfo;
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extern MCTypeInfoRef kMCObjcDelegateMappingErrorTypeInfo;
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#endif

‎libfoundation/include/foundation.h‎

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// HANDLER DEFINITIONS
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//
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enum MCHandlerQueryType
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{
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kMCHandlerQueryTypeNone,
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kMCHandlerQueryTypeObjcSelector,
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};
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struct MCHandlerCallbacks
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{
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size_t size;
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void (*release)(void *context);
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bool (*invoke)(void *context, MCValueRef *arguments, uindex_t argument_count, MCValueRef& r_value);
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bool (*describe)(void *context, MCStringRef& r_desc);
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bool (*query)(void *context, MCHandlerQueryType type, void *r_info);
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};
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MC_DLLEXPORT bool MCHandlerCreate(MCTypeInfoRef typeinfo, const MCHandlerCallbacks *callbacks, void *context, MCHandlerRef& r_handler);
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* an ObjcObject. The id is autoreleased before being returned. */
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MC_DLLEXPORT void *MCObjcObjectGetAutoreleasedId(MCObjcObjectRef obj);
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/* Create an ObjcObject containing an instance of the com_livecode_MCObjcFormalDelegate class,
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* mapping protocol methods to MCHandlerRefs, with
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* a context parameter. */
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MC_DLLEXPORT bool MCObjcCreateDelegateWithContext(MCStringRef p_protocol_name, MCArrayRef p_handler_mapping, MCValueRef p_context, MCObjcObjectRef& r_object);
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/* Create an ObjcObject containing an instance of the com_livecode_MCObjcFormalDelegate class,
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* mapping protocol methods to MCHandlerRefs. */
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MC_DLLEXPORT bool MCObjcCreateDelegate(MCStringRef p_protocol_name, MCArrayRef p_handler_mapping, MCObjcObjectRef& r_object);
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/* Create an ObjcObject containing an instance of the com_livecode_MCObjcInformalDelegate class,
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* mapping informal protocol methods specified as a list of foreign handler to MCHandlerRefs, with
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* a context parameter. */
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MC_DLLEXPORT bool MCObjcCreateInformalDelegateWithContext(MCProperListRef p_foreign_handlers, MCArrayRef p_handler_mapping, MCValueRef p_context, MCObjcObjectRef& r_object);
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/* Create an ObjcObject containing an instance of the com_livecode_MCObjcInformalDelegate class,
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* mapping informal protocol methods specified as a list of foreign handler to MCHandlerRefs. */
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MC_DLLEXPORT bool MCObjcCreateInformalDelegate(MCProperListRef p_foreign_handlers, MCArrayRef p_handler_mapping, MCObjcObjectRef& r_object);
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////////////////////////////////////////////////////////////////////////////////
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enum MCPickleFieldType

‎libfoundation/src/foundation-objc-dummy.cpp‎

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////////////////////////////////////////////////////////////////////////////////
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extern "C" MC_DLLEXPORT_DEF
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bool MCObjcCreateDelegateWithContext(MCStringRef p_protocol_name, MCArrayRef p_handler_mapping, MCValueRef p_context, MCObjcObjectRef& r_object)
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{
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return false;
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}
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extern "C" MC_DLLEXPORT_DEF
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bool MCObjcCreateDelegate(MCStringRef p_protocol_name, MCArrayRef p_handler_mapping, MCObjcObjectRef& r_object)
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{
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return false;
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}
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extern "C" MC_DLLEXPORT_DEF
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bool MCObjcCreateInformalDelegateWithContext(MCProperListRef p_foreign_handlers, MCArrayRef p_handler_mapping, MCValueRef p_context, MCObjcObjectRef& r_object)
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{
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return false;
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}
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extern "C" MC_DLLEXPORT_DEF
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bool MCObjcCreateInformalDelegate(MCProperListRef p_foreign_handlers, MCArrayRef p_handler_mapping, MCObjcObjectRef& r_object)
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{
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return false;
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}
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////////////////////////////////////////////////////////////////////////////////
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bool __MCObjcInitialize(void)
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{
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if (!MCNamedCustomTypeInfoCreate(MCNAME("com.livecode.objc.ObjcObject"),

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