I'm using djinni to create cross platform code between c++, java and objective c because I'm currently moving a lot of code to a cross platform c++ implementation.
The problem is, that I have an interface that is a protocol in objective c. Another interface, that is implemented in c++ gets hte implementation of this protocol as a parameter and then calles the method. But this method is not called at all in objective c. (Better swift, but I tried also to implement this protocol in objective c, does not work). I have investigated into a bit more, but first my code.
To see if my issue are caused from the existing code, I created a test project, but it still like that:
So this is my idl file for djinni:
DataProvider = interface +j +o {
const getContentForUrl(url: string): string;
}
DataUser = interface +c {
static create(url: string, dataProvider: DataProvider): DataUser;
getContent(): string;
}
This are the created c++ files:
DataProvider.hpp:
// AUTOGENERATED FILE - DO NOT MODIFY!
// This file generated by Djinni from htmlparser.djinni
#pragma once
#include <string>
namespace testdjinni {
class DataProvider {
public:
virtual ~DataProvider() {}
virtual std::string getContentForUrl(const std::string & url) = 0;
};
} // namespace testdjinni
DataUser.hpp:
// AUTOGENERATED FILE - DO NOT MODIFY!
// This file generated by Djinni from htmlparser.djinni
#pragma once
#include <memory>
#include <string>
#include <vector>
namespace testdjinni {
class DataProvider;
class DataUser {
public:
virtual ~DataUser() {}
static std::shared_ptr<DataUser> create(const std::string & url, const std::shared_ptr<DataProvider> & dataProvider);
virtual std::string getContent() = 0;
};
} // namespace destdjinni
This is my DataUser interface and implementation in C++:
DataUserImpl.h:
#ifndef TESTDJINNI_DATAUSER_H
#define TESTDJINNI_DATAUSER_H
#include <string>
#include "generated-src/cpp/DataUser.hpp"
using namespace std;
class DataUserImpl : public testdjinni::DataUser{
private:
string *content;
testdjinni::DataUser *dataUser;
public:
DataUserImpl(const string &url, testdjinni::DataProvider *dataProvider);
virtual string getContent();
};
#endif //TESTDJINNI_DATAUSER
DataUserImpl.cpp:
#include <iostream>
#include "DataUserImpl.h"
#include "generated-src/cpp/DataProvider.hpp"
DataUserImpl::DataUserImpl(const string &url, testdjinni::DataProvider *dataProvider): dataProvider(dataProvider) {
this->url = new string(url);
}
HtmlDocumentImpl::~HtmlDocumentImpl() {
delete url;
}
std::shared_ptr<testdjinni::DataUser> testdjinni::DataUser::create(const std::string & url, const std::shared_ptr<testdjinni::DataProvider> & dataProvider) {
return std::shared_ptr<testdjinni::DataUser>(new DataUserImpl(url, dataProvider.get()));
}
string DataUserImpl::getContent() {
if (this->content == NULL || *this->content == "")
this->content = new string(this->getDataProvider()->getContentForUrl(*this->url));
return *this->content;
};
Now I have this code in swift (I also tried the same in Objective C, but did not work):
class Provider: HPDataProvider {
func getContentForUrl(_ url: String) -> String {
return "Testcontent und so"
}
}
class ViewController: UIViewController {
let provider = Provider()
override func viewDidLoad() {
super.viewDidLoad()
let user = HPDataUser.create("http://www.testurl.com", dataProvider: provider)
print(user?.getContent())
}
}
The problem is, that the pethod getContentForUrl in the implemented protocol is not called at all. I get a crash:
Assertion failed: (string), function toCpp, file /Path/to/my/project/deps/djinni/support-lib/objc/DJIMarshal+Private.h, line 119.
So what I can say now is, that the string seems to be null and my protocol implementation was not called.
Ok, so I got down to see what happens at all:
In the generated file for DataProvider+Private.mm that looks like this:
// AUTOGENERATED FILE - DO NOT MODIFY!
// This file generated by Djinni from htmlparser.djinni
#import "HPDataProvider+Private.h"
#import "HPDataProvider.h"
#import "DJIMarshal+Private.h"
#import "DJIObjcWrapperCache+Private.h"
#include <stdexcept>
static_assert(__has_feature(objc_arc), "Djinni requires ARC to be enabled for this file");
namespace djinni_generated {
class DataProvider::ObjcProxy final
: public ::htmlparser::DataProvider
, private ::djinni::ObjcProxyBase<ObjcType>
{
friend class ::djinni_generated::DataProvider;
public:
using ObjcProxyBase::ObjcProxyBase;
std::string getContentForUrl(const std::string & c_url) override
{
@autoreleasepool {
// Here, the objcpp_result is null, even if the object was not null, but my implementation of the protocol was never called.
auto objcpp_result_ = [djinni_private_get_proxied_objc_object() getContentForUrl:(::djinni::String::fromCpp(c_url))];
return ::djinni::String::toCpp(objcpp_result_);
}
}
};
} // namespace djinni_generated
namespace djinni_generated {
auto DataProvider::toCpp(ObjcType objc) -> CppType
{
if (!objc) {
return nullptr;
}
return ::djinni::get_objc_proxy<ObjcProxy>(objc);
}
auto DataProvider::fromCppOpt(const CppOptType& cpp) -> ObjcType
{
if (!cpp) {
return nil;
}
return dynamic_cast<ObjcProxy&>(*cpp).djinni_private_get_proxied_objc_object();
}
} // namespace djinni_generated
I am clueless what I can do here... I mean, this is just basic code...
Errors that you experiencing are due to improper use of shared_ptr.
std::shared_ptr<testdjinni::DataUser> testdjinni::DataUser::create(const std::string & url, const std::shared_ptr<testdjinni::DataProvider> & dataProvider) {
return std::shared_ptr<testdjinni::DataUser>(new DataUserImpl(url, dataProvider.get()));
}
You pass DataProvider raw pointer (dataProvider.get()) to DataUserImpl. The object that you are pointing with the raw pointer will be destroyed when all shared_ptrs holding it will go.
Since you do not save shared_ptr anywhere, with the end of it, your DataProvider object is destructed too and you are pointing to invalid memory.
The solution would be to save shared_ptr as a field of DataUserImpl instead of the raw pointer. In this way, the lifetime of your object will be prolongated to the lifetime of DataUserImpl.