UIAlertView Delegate

[jayden]

Hi,

Im following Brian Long's video on accessing iOS API's but trying to implement it in C++. Managed to get my head around it until he implemented a Delegate for UIAlertView. This is what I have so far:

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#pragma region UIAlertView - Using Delegate
class TAlertViewDelegate : public TOCLocal, public UIAlertViewDelegate
{
   //Virtual in .hpp I believe means that its going to be defined somewhere else
   public:
      void __cdecl alertView(_di_UIAlertView alertView, int clickedButtonAtIndex);
      void __cdecl alertViewCancel(_di_UIAlertView alertView);
};
_di_UIAlertViewDelegate Delegate;
#pragma region Helper Function - Returns A ObjC Pointer To An NSString From A Unicode String
void * PNSSTR(const String str)
{
   return ((_di_ILocalObject)StrToNSStr(str))->GetObjectID();
}
#pragma end_region

void __cdecl TAlertViewDelegate::alertView(_di_UIAlertView alertView, int clickedButtonAtIndex)
{
   //Could Use Log::d again but will use NSlog
   Iosapi::Foundation::NSLog(PNSSTR("UIAlertView Button Pressed!"));
   switch(clickedButtonAtIndex)
   {
      case 0:
         Log::d("You Clicked Cancel");
         break;
      case 1:
         Log::d("You clicked Yes");
         break;
      case 2:
         Log::d("You clicked No");
         break;
      case 3:
         Log::d("You clicked Maybe");
         break;
   }
   alertView->setDelegate(nil);
   Delegate = nil;
}

void __cdecl TAlertViewDelegate::alertViewCancel(_di_UIAlertView alertView)
{
   Log::d("Alert View Was Cancelled");
   alertView->setDelegate(nil);
   Delegate = nil;
}
void __fastcall TForm1::ListBoxItem6Click(TObject *Sender)
{
   _di_UIAlertView alertView;
   Delegate = TAlertViewDelegate();  ----> COMPILER ERROR: See Below
   alertView = TUIAlertView::Alloc();
   __try
   {
      alertView = TUIAlertView::Wrap(alertView->initWithTitle(
         StrToNSStr("A Very Important Question"),             //Title
         StrToNSStr("Do you like me? :)"),               //Message
         ((_di_ILocalObject)Delegate)->GetObjectID(),    //Delegate
         StrToNSStr("Cancel"),                           //Cancel Button Caption
         nil                                             //Other Button Caption
      ));
      /*Add Some More Buttons....*/
      alertView->addButtonWithTitle(StrToNSStr("Absolutley!"));
      alertView->addButtonWithTitle(StrToNSStr("Nope."));
      alertView->addButtonWithTitle(StrToNSStr("Meh :|"));
      alertView->show();
   }
   __finally
   {
      alertView->release();
   }
}
#pragma end_region


However I am not sure if I have created the delegate correctly - but I am getting a compiler error saying "allocating an object of abstract class type 'TAlertViewDelegate'. Looking at the source the TOCLocal has a constructor so therefor as I am subclassing it do I call TAlertViewDelegate::TOCLocal()?

Any help would be appreciated!

FYI The UIAlertViewDelegate interface from iOSapi.UIKit.hpp

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__interface  INTERFACE_UUID("{A52A64A0-AA7E-422E-B7A4-8EFCF2C20A49}") UIAlertViewDelegate  : public Macapi::Objectivec::IObjectiveC
{
#ifndef __aarch64__
   virtual void __cdecl alertView(_di_UIAlertView alertView, int clickedButtonAtIndex) = 0 /* overload */;
#else /* __aarch64__ */
   virtual void __cdecl alertView(_di_UIAlertView alertView, long clickedButtonAtIndex) = 0 /* overload */;
#endif /* __aarch64__ */
   virtual void __cdecl alertViewCancel(_di_UIAlertView alertView) = 0 ;
   virtual void __cdecl didPresentAlertView(_di_UIAlertView alertView) = 0 ;
#ifndef __aarch64__
   virtual void __cdecl alertViewDidDismissWithButtonIndex(_di_UIAlertView alertView, int didDismissWithButtonIndex) = 0 ;
#else /* __aarch64__ */
   virtual void __cdecl alertViewDidDismissWithButtonIndex(_di_UIAlertView alertView, long didDismissWithButtonIndex) = 0 ;
#endif /* __aarch64__ */
};


[rlebeau]

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class TAlertViewDelegate : public TOCLocal, public UIAlertViewDelegate
{
   //Virtual in .hpp I believe means that its going to be defined somewhere else
   public:
      void __cdecl alertView(_di_UIAlertView alertView, int clickedButtonAtIndex);
      void __cdecl alertViewCancel(_di_UIAlertView alertView);
};


They are not just virtual, they are "pure" virtual (they all have "= 0" on their declarations), aka they are "abstract" methods. Which means you MUST override them. UIAlertViewDelegate defines 4 abstract methods (2 of which are wrapped in #ifdef's to account for iOS64), but your class is only overriding 2 of them. You need to overriding all 4 of them, or else your class will be abstract and cannot be instantiated directly (which is exactly what the compiler is complaining about):

Code: Select all

class TAlertViewDelegate : public TOCLocal, public UIAlertViewDelegate
{
public:
    #ifndef __aarch64__
    virtual void __cdecl alertView(_di_UIAlertView alertView, int clickedButtonAtIndex);
    #else
    virtual void __cdecl alertView(_di_UIAlertView alertView, long clickedButtonAtIndex);
    #endif

    virtual void __cdecl alertViewCancel(_di_UIAlertView alertView);
    virtual void __cdecl didPresentAlertView(_di_UIAlertView alertView);

    #ifndef __aarch64__
    virtual void __cdecl alertViewDidDismissWithButtonIndex(_di_UIAlertView alertView, int didDismissWithButtonIndex);
    #else
    virtual void __cdecl alertViewDidDismissWithButtonIndex(_di_UIAlertView alertView, long didDismissWithButtonIndex);
    #endif
};

#ifndef __aarch64__
void __cdecl TAlertViewDelegate::alertView(_di_UIAlertView alertView, int clickedButtonAtIndex)
#else
void __cdecl TAlertViewDelegate::alertView(_di_UIAlertView alertView, long clickedButtonAtIndex)
#endif
{
    //...
}

void __cdecl TAlertViewDelegate::alertViewCancel(_di_UIAlertView alertView)
{
    //...
}

void __cdecl TAlertViewDelegate::didPresentAlertView(_di_UIAlertView alertView)
{
    //...
}

#ifndef __aarch64__
void __cdecl TAlertViewDelegate::alertViewDidDismissWithButtonIndex(_di_UIAlertView alertView, int didDismissWithButtonIndex)
#else
void __cdecl ::alertViewDidDismissWithButtonIndex(_di_UIAlertView alertView, long didDismissWithButtonIndex)
#endif
{
    //...
}


Alternatively, use a custom #define to clean up the #ifdef's:

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#ifndef __aarch64__
#define aarch_int_t int
#else
#define aarch_int_t long
#endif

class TAlertViewDelegate : public TOCLocal, public UIAlertViewDelegate
{
public:
    virtual void __cdecl alertView(_di_UIAlertView alertView, aarch_int_t clickedButtonAtIndex);
    virtual void __cdecl alertViewCancel(_di_UIAlertView alertView);
    virtual void __cdecl didPresentAlertView(_di_UIAlertView alertView);
    virtual void __cdecl alertViewDidDismissWithButtonIndex(_di_UIAlertView alertView, aarch_int_t didDismissWithButtonIndex);
};

void __cdecl TAlertViewDelegate::alertView(_di_UIAlertView alertView, aarch_int_t clickedButtonAtIndex)
{
    //...
}

void __cdecl TAlertViewDelegate::alertViewCancel(_di_UIAlertView alertView)
{
    //...
}

void __cdecl TAlertViewDelegate::didPresentAlertView(_di_UIAlertView alertView)
{
    //...
}

void __cdecl TAlertViewDelegate::alertViewDidDismissWithButtonIndex(_di_UIAlertView alertView, aarch_int_t didDismissWithButtonIndex)
{
    //...
}


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alertView->setDelegate(nil);
Delegate = nil;


FYI, you need to use NULL or nullptr in C++. nil is a Delphi keyword.

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Delegate = TAlertViewDelegate();  ----> COMPILER ERROR: See Below


Even if that could compile, it would not work. You need to allocate the class on the heap instead of the stack:

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Delegate = (UIAlertViewDelegate*) new TAlertViewDelegate();


[jayden]

Hi Remy,

Thanks a ton, I understand why they all need to be implemented makes perfect sense. I am however still getting a compiler issue (same as before) as it is telling me that:

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[bcciosarm Error] Unit1.cpp(208): allocating an object of abstract class type 'TAlertViewDelegate'
  sysmac.h(329): unimplemented pure virtual method 'Release' in 'TAlertViewDelegate'
  sysmac.h(327): unimplemented pure virtual method 'QueryInterface' in 'TAlertViewDelegate'
  sysmac.h(328): unimplemented pure virtual method 'AddRef' in 'TAlertViewDelegate'


Surely for these methods I would want to leave the implementation to that defined in TOCLocal for updating the reference counts?
Thanks,
Jayden

[rlebeau]

Thanks a ton, I understand why they all need to be implemented makes perfect sense. I am however still getting a compiler issue (same as before) as it is telling me that:

Code: Select all

[bcciosarm Error] Unit1.cpp(208): allocating an object of abstract class type 'TAlertViewDelegate'
  sysmac.h(329): unimplemented pure virtual method 'Release' in 'TAlertViewDelegate'
  sysmac.h(327): unimplemented pure virtual method 'QueryInterface' in 'TAlertViewDelegate'
  sysmac.h(328): unimplemented pure virtual method 'AddRef' in 'TAlertViewDelegate'


Those are IUnknown methods. Delphi interfaces derive from IInterface instead, which is Delphi's equivalent to IUnknown. They are similar but have subtle differences. Delphi's TInterfacedObject base class implements IInterface, not IUnknown.

Surely for these methods I would want to leave the implementation to that defined in TOCLocal for updating the reference counts?

Yes, but you have to implement the IUnknown methods in your class and have them call TOCLocal's IInterface methods. There is a section on this issue in the Embarcadero DocWiki:

IUnknown and IInterface

Creating classes that support IUnknown

[jayden]

Great, thanks I will give this a shot tomorrow!

[jayden]

Hi Remy,

Gave this a try, looking at the link you gave me I implemented INTFOBJECT_IMPL_IUNKOWN(TOCLocal); after my class declaration and the program then compiled.

However on when clicking the item that constructs the UIAlertView with a delegate I got an exception:
First chance exception at $00188DF5. Exception class EObjectiveC with message 'RTTI for type UIAlertViewDelegate was not found. Perhaps missing {$M+}?'. Process Project5 (1145233)

I then tried changing my class declaration to:

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class __declspec(TAlertViewDelegate) TAlertViewDelegate : public TOCLocal, public UIAlertViewDelegate
{
 //....
}

However this yielded a result no different - I got the exact same exception as before.
and

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class __declspec(delphirtti) TAlertViewDelegate  : public TOLocal, public UIAlertViewDelegate
{
 //...
}

This caused a different exception - it came up on runtime slightly different to the one before:
Project Project5 raised exception class EObjectiveC with message 'RTTI for type NSObject was not found. Perhaps missing {$M+}?'.

I have had a look at the documentation here, but any help to figure out what this is and how to access the delegate would be greatly appreciated. I must confess at this point I have little idea how or what the Delphi RTTI is - all that I know is from what is available from the wiki that I can understand

Thanks!

[rlebeau]

However on when clicking the item that constructs the UIAlertView with a delegate I got an exception:
First chance exception at $00188DF5. Exception class EObjectiveC with message 'RTTI for type UIAlertViewDelegate was not found. Perhaps missing {$M+}?'. Process Project5 (1145233)

Sorry, I can't help with that error. You will likely have to contact Embarcadero directly for help.

I then tried changing my class declaration to:

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class __declspec(TAlertViewDelegate) TAlertViewDelegate : public TOCLocal, public UIAlertViewDelegate


TAlertViewDelegate is not a valid parameter value for __declspec(). You might try using __declspec(delphiclass), though.