Nib's InstantiateWithOwnerTopLevelObjects() not returning objects about macdriver

[progrium]

So far I haven't come across too many APIs that take an NSArray that will be written to, but I suspect that pattern is not working here because of the copying going on for converting from slices. If you were to use objc.Call to call InstantiateWithOwnerTopLevelObjects passing a constructed NSArray (maybe foundation.Array_Array()) it might work and I could look into how we might handle that in generated bindings.

[programmingkidx]

Your suggestion worked! I saw the correct output for the first time.

Here is the updated program with your suggestion implemented:

// File: main.go
// Date: 11/29/23
// Description: Uses a NIB file to display the interface
// Run directions: go run main.go


package main

import (
	"fmt"
	"os"
	"github.com/progrium/macdriver/macos/appkit"
	f "github.com/progrium/macdriver/macos/foundation"
	"github.com/progrium/macdriver/objc"
)

func main() {
	// Setup the application
	app := appkit.Application_SharedApplication()
	app.SetActivationPolicy(appkit.ApplicationActivationPolicyRegular)
	app.ActivateIgnoringOtherApps(true)
	
	// Get the NIB file's data
	godata, err := os.ReadFile("MainMenu.nib")
	if err != nil {
		fmt.Println("Failed to load nib file:", err)
		return
	}
	fmt.Println("godata length:", len(godata))
	
	// How the Nib would be obtained in Objective-C.
	// Can't use this method because InstantiateWithOwnerTopLevelObjects
	// does not accept (NS)Data object.
	nsdata := f.Data_DataWithContentsOfFile("MainMenu.nib")
	fmt.Println("nsdata length:", nsdata.Length())

	myNib := appkit.NewNibWithNibDataBundle(godata, nil)
	
	myObjects := f.Array_Array()

	fmt.Printf("address of myObjects before: %p\n", &myObjects)
	//status := myNib.InstantiateWithOwnerTopLevelObjects(nil, myObjects)
	status := objc.Call[bool](myNib, objc.Sel("instantiateWithOwner:topLevelObjects:"), nil, &myObjects)
	
	if status == false {
		fmt.Println("Error: failed to instantiate nib file")
		return
	}
	fmt.Printf("address of myObjects after: %p\n", &myObjects)
	fmt.Println("successful NIB instantiation:", status)
	fmt.Println("count:", myObjects.Count())
	
	// print out all the objects found in the NIB file
	var i uint
	for i = 0; i < myObjects.Count(); i++ {
		fmt.Printf("Index %d: %s\n", i, myObjects.ObjectAtIndex(i).Description())
	}
}

I do still like the idea of using a Go slice in place of a (NS)Array type. It more Go-friendly.

[progrium]

Yes that would be nice. I'm not even sure it's possible here. We convert/copy the Go slice to an NSArray and then because it's just passed by reference we have no way to know when to convert/copy it back to our slice, which we would have to keep track of and further complicate an already tricky memory management situation.

Glad it worked!

[programmingkidx]

Could we leave this issue open until the fix is in the repo?

[progrium]

What solution would make you want to close it?

[programmingkidx]

I think adding the rule to the bindings generator that prevents translating from an Objective-c type to a Go type when dealing with a pointer to a pointer in a parameter would fix the problem. One reason to use a pointer to a pointer is to return an object thru a parameter like an NSError.

Here are some of the methods that are probably affected by this issue:

• NSFileManager's contentsOfDirectoryAtPath:(NSString *)path error:(NSError **)error;
• NSKeyedUnarchiver's unarchivedObjectOfClass:fromData:error:
• NSString's writeToFile:atomically:encoding:error:

[progrium]

That is a great suggestion that I think should work well but can we make it a separate issue?

[programmingkidx]

I think that is a good idea. This issue probably affects more than just NSNib's InstantiateWithOwnerTopLevelObjects().

[programmingkidx]

Created issue #234 for the generator issue.