How to obtain CFStringRef value from iOS API function in Delphi 10.3 Rio

Question

Cannot obtain CFStringRef value from iOS API function (framework) in Delphi 10.3 Rio

// external call bridge function to iOS:
function MIDIObjectGetStringProperty(obj: MIDIObjectRef;
            propertyID: CFStringRef;
            out str: CFStringRef):OSStatus; cdecl; external libCoreMidi name _PU + 'MIDIObjectGetStringProperty';

Function MIDIObjectGetStringProperty (iOS CoreMIDI function) return in str:CFStringRef name of MIDI ports ...

How can I obtain value of CFString variable in Delphi? In this example str:CFStringRef value?

I try it in my func.:

function getDisplayName(obj: MIDIEndpointRef):string;
var 
    EndPointName: CFStringRef;
    i:integer;
begin
    //EndPointName:= nil; // when I assign nil value, function return i=-50 otherwise raise Access Violation error ...

    i := MIDIObjectGetStringProperty(obj, kMIDIPropertyDisplayName , EndPointName); --> AV error !!!

    //in EndPointName should be returned CFStringRef value from iOS 

    getDisplayName :=  CFToDelphiString(EndPointName); // convert to string
end;

Probably EndPointName need to be allocated ... else I give AV error. Please got someone solution how obtain ANY CFStringRef value from iOS framework and convert to string? Thanx.

Adds:

I build crossplatform (iOS, Android, W64) app in Delphi Rio via FireMonkey frameforks api - for CoreMIDI I use this interface https://github.com/FMXExpress/ios-object-pascal-wrapper/blob/master/iOSapi.CoreMIDI.pas

So the externall call and constants are defined in iOSapi.CoreMIDI there:

function MIDIObjectGetStringProperty (obj: MIDIObjectRef; propertyID: CFStringRef; str: CFStringRef) : OSStatus; cdecl; external libCoreMIDI name _PU + 'MIDIObjectGetStringProperty';

and iOS pointer const:

function kMIDIPropertyDisplayName: Pointer;
begin
  Result := CocoaPointerConst(libCoreMIDI, 'kMIDIPropertyDisplayName');
end;

Otherwies compiled app work on real iOS (iPad) very well (reading MIDI message from connected MIDI keyboard) based on this solution https://pjstrnad.com/reading-data-midi-keyboard-ios-probably-also-mac/

obj: MIDIObjectRef is source pointer from source:= MIDIGetSource(ci);

Problem is calling API function MIDIObjectGetStringProperty. In pointer str: CFStringRef (EndPointName) should be VALUE of MIDIportNAME. I cannot obtain this value and parse to delphi string ...

I tried declared this poiter CFStringRef as:

var
EndPointName: pointer;
EndPointName1: array of Byte;
EndPointName2: TBytes;
EndPointName3: TPtrWrapper;
M: TMarshaller;

and construction as:

SetLength(EndPointName1, 255);
GetMem(EndPointName2,255);
EndPointName3 := M.AllocMem(255);

i := MIDIObjectGetStringProperty(obj, kMIDIPropertyDisplayName , @EndPointNameX);

--> nothing works, AV error !!!

I thing it must be solution how to obtain CFStringRef and convert to delphi string ...

How are obj and kMIDIPropertyDisplayName obtained? It's important to show all code that we cannot determine for ourselves. — Dave Nottage
Please stop referring to XE. That version of Delphi predates mobile support. You are using 10.3 Rio. Please correct the text. — David Heffernan

Hans Hans · Accepted Answer · 2020-01-15T12:51:56

The kMIDIPropertyDisplayName is broken on iOS, but you can replace it with CFSTR('displayName'). It works for me. So your function looks like this:

function getDisplayName(aEndPointRef: MIDIEndpointRef):string;
var 
  LEndPointName: CFStringRef;
  i:integer;
begin
  getDisplayName := 'MIDI endpoint';
  LEndPointName:= nil; 
  i := MIDIObjectGetStringProperty(aEndPointRef, CFSTR('displayName'), LEndPointName);
  if (i=0) and (LEndPointName<>nil) then
    getDisplayName := CFStringRefToStr(LEndPointName);
end;

Add Macapi.CoreFoundation and Macapi.Helpers to your USES clause to get access to CFSTR and CFStringRefToStr

How to obtain CFStringRef value from iOS API function in Delphi 10.3 Rio

1 Answers