Creating a Cocoa Window Using Pure C++

Tackling Integration Challenges Between C++ and Cocoa on macOS

Integrating C++ with Cocoa for macOS development presents unique opportunities and challenges. Cocoa primarily leverages Objective-C, so combining it with C++ isn’t straightforward. Here, I’ll share my journey trying to bridge these two worlds—focusing on my attempts to maintain a pure C++ environment with a .cpp extension rather than switching to an Objective-C++ .mm file.

The Initial Approach

My initial goal was to create macOS GUI applications using purely C++ without relying on Objective-C++. Although the standard practice involves using Objective-C or Swift with the Cocoa API, I was inclined to explore how far C++ could go in this realm. Cocoa provides a rich set of APIs for macOS development, typically accessed via Objective-C. To integrate these using C++, Objective-C++ (*.mm files) is usually employed as a bridge.

Trying to stick with .cpp files, however, led me down a rabbit hole of compatibility issues and linker errors. Here’s what I attempted:

1. Direct API Calls in C++: My first attempt was to directly include Cocoa headers in my C++ code and make API calls. This approach failed because Cocoa headers are not compatible with pure C++ compilers—they require Objective-C runtime support, which isn’t available in the C++ environment.

1. Static and Dynamic Libraries: I considered creating a dynamic library in Objective-C that wrapped Cocoa functionalities, which I could then link against my C++ code. Although feasible, this method required extensive boilerplate code and resulted in a complex build process without the seamless integration I was aiming for.

Transitioning to Objective-C++

Frustrations with these initial attempts led me to Objective-C++. Objective-C++ allows the use of both Objective-C and C++ in the same file (with a .mm extension), providing a more straightforward way to call Cocoa APIs from C++ classes.

I created an Objective-C++ wrapper class to encapsulate Cocoa functionalities that I could easily call from my C++ code. Here’s a simplified version of what the wrapper looked like:

// MyCocoaWrapper.mm
#import <Cocoa/Cocoa.h>

class MyCocoaWrapper {
public:
    void createWindow() {
        @autoreleasepool {
            NSWindow *window = [[NSWindow alloc] initWithContentRect:NSMakeRect(0, 0, 200, 200)
                                                          styleMask:NSTitledWindowMask
                                                            backing:NSBackingStoreBuffered
                                                              defer:NO];
            [window makeKeyAndOrderFront:nil];
        }
    }
};

And then, in my C++ code, I could create an instance of MyCocoaWrapper and call its methods:

// main.cpp
#include "MyCocoaWrapper.h"

int main() {
    MyCocoaWrapper wrapper;
    wrapper.createWindow();
    return 0;
}

Challenges and Considerations

Going this route required letting go of my initial requirement to stick purely to C++. The reality is, while it’s theoretically possible to separate concerns strictly between C++ and Objective-C code, practical implementation often leads to .mm files and Objective-C++ usage for simplicity and access to Cocoa APIs.

Regarding build configurations, Xcode handles Objective-C++ .mm files seamlessly, but integrating these within CMake or other build systems might require additional configuration to correctly handle mixed-language compilations.

Conclusion

In conclusion, while pure C++ development with Cocoa remains elusive due to language and runtime incompatibilities, Objective-C++ offers a pragmatic middle ground. By embracing .mm files, developers can effectively leverage both C++ and Cocoa APIs, thus enjoying the best of both worlds—C++’s powerful features and Cocoa’s native capabilities.