private void FetchMerkleBlockByHeight(UInt64 height, Action <ErrorCode, MerkleBlock, UInt64> handler) { GCHandle handlerHandle = GCHandle.Alloc(handler); IntPtr handlerPtr = (IntPtr)handlerHandle; ChainNative.chain_fetch_merkle_block_by_height(nativeInstance_, handlerPtr, height, internalMerkleBlockFetchHandler_); }