On iOS use Dart API instead of memcpy.

Author: greenrobot-team

objectbox/lib/src/native/bindings/flatbuffers.dart

@@ -121,7 +121,9 @@ class ReaderWithCBuffer {
   void clear() => malloc.free(_bufferPtr);
 
   ByteData access(Pointer<Uint8> dataPtr, int size) {
-    if (size > _maxBuffer) {
+    // If memcpy is not available, instead of using Dart memcpy implementation,
+    // directly convert to view which is a little faster.
+    if (isMemcpyNotAvailable || size > _maxBuffer) {
       final uint8List = dataPtr.asTypedList(size);
       return ByteData.view(uint8List.buffer, uint8List.offsetInBytes, size);
     } else {

objectbox/lib/src/native/bindings/nativemem.dart

@@ -8,10 +8,24 @@ import 'dart:io';
 final _dart_memset memset =
     _stdlib.lookupFunction<_c_memset, _dart_memset>('memset');
 
+/// If the native memcpy function should not be used.
+///
+/// memcpy is not available to Flutter on iOS 15 simulator,
+/// so use Dart API to copy data via asTypedList (which is much slower but works).
+///
+/// https://github.com/objectbox/objectbox-dart/issues/313
+final isMemcpyNotAvailable = Platform.isIOS;
+final _dart_memcpy _memcpyDart = (dest, src, length) {
+  dest
+      .asTypedList(length)
+      .setAll(0, src.asTypedList(length).getRange(0, length));
+};
+
 /// memcpy (destination, source, num) copies the values of num bytes from the
 /// data pointed to by source to the memory block pointed to by destination.
-final _dart_memcpy memcpy =
-    _stdlib.lookupFunction<_c_memcpy, _dart_memcpy>('memcpy');
+final _dart_memcpy memcpy = isMemcpyNotAvailable
+    ? _memcpyDart
+    : _stdlib.lookupFunction<_c_memcpy, _dart_memcpy>('memcpy');
 
 // FFI signature
 typedef _dart_memset = void Function(Pointer<Uint8>, int, int);