Nib's InstantiateWithOwnerTopLevelObjects() not returning objects

[programmingkidx]

I am trying to port this Objective-c program to Go. What is does is loads a NIB file and uses it to display the interface. To run this program copy and paste it to a file called main.m, then run this command: clear ; clang -framework foundation -framework appkit main.m && ./a.out Download the included MainMenu.nib.zip file is included here, unzip it, and place the MenuMenu.nib file in the same folder as the a.out program. MainMenu.nib.zip

//Description: Finds and sets up a button on a window in a nib file
// Build directions: clang -framework foundation -framework appkit main.m
// Run directions: clear ; clang -framework foundation -framework appkit main.m && ./a.out

#import <Cocoa/Cocoa.h>

@interface MyClass : NSObject {
    NSTextField *textField;
}
- (void) doButton:(id) sender;
- (void) setTextField: (NSTextField *) newTextField;
@end

@implementation MyClass
- (void) doButton:(id) sender {
    NSLog(@"I'M ALIVE!!!");
    [textField setStringValue: @"OUCH!"];
}

- (void) setTextField: (NSTextField *) newTextField {
    textField = newTextField;
}

- (void) dealloc {
    [super dealloc];
    NSLog(@"Freeing MyClass object");
}
@end

int main(int argc, const char * argv[]) {
    NSData *data = [NSData dataWithContentsOfFile: @"MainMenu.nib"];
    if (data == nil) {
        NSLog(@"Failed to create data object");
        return -2;
    }
    NSLog(@"nsdata length: %lu", [data length]);

    NSNib *myNib = [[NSNib alloc] initWithNibData: data bundle: nil];
    if (myNib == nil) {
        NSLog(@"Error: failed to create nib object");
        return -1;
    }

    NSArray *myObjects = nil;
    NSLog(@"address of myObjects before: %p", myObjects);
    BOOL status;
    status = [myNib instantiateWithOwner: nil topLevelObjects:&myObjects];
    if (status == NO) {
        NSLog(@"Error: failed to instantiate nib file");
        return -6;
    }
    NSLog(@"address of myObjects after: %p", myObjects);
    NSLog(@"successful NIB instantiation: %d", status);
    NSLog(@"count: %lu", [myObjects count]);

    // print out all the objects found in the NIB file
    for(int i = 0; i < [myObjects count]; i++) {
        NSLog(@"Index %d: %@", i, myObjects[i]);
    }

    MyClass *myObj = [[MyClass alloc] init];
    BOOL foundWindow = NO;
    for(int i = 0; i < [myObjects count]; i++) {
        id theObject = [myObjects objectAtIndex: i];
        if ([theObject isKindOfClass: [NSWindow class]]) {
            [theObject orderFront: nil];
            foundWindow = YES;
            NSButton *aButton = [[theObject contentView] viewWithTag:1];
            if (aButton == nil) {
                NSLog(@"Failed to find button with tag 1");
                return -4;
            }
            [aButton setTarget: myObj];
            [aButton setAction: @selector(doButton:)];

            NSTextField *textField = [[theObject contentView] viewWithTag:2];
            if (textField == nil) {
                NSLog(@"Failed to find textfield with tag 2");
                return -5;
            }
            [myObj setTextField: textField];
            break;
        }
    }

    if (foundWindow == NO) {
        NSLog(@"Failed to find window in nib file");
        return -3;
    }
    return NSApplicationMain(argc, argv);
}

This is most of the Go version of the above program:

// 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)

    var myObjects []objc.IObject
    myObjects = nil                            // runs but no objects
    //myObjects = make([]objc.IObject, 0, 0)   // runs but no objects
    //myObjects = make([]objc.IObject, 0, 10)  // runs but no objects
    //myObjects = make([]objc.IObject, 10, 10) // causes panic

    fmt.Printf("address of myObjects before: %p\n", myObjects)
    status := myNib.InstantiateWithOwnerTopLevelObjects(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:", len(myObjects))

    // print out all the objects found in the NIB file
    for i := 0; i < len(myObjects); i++ {
        fmt.Printf("Index %d: %s", i, myObjects[i].Description())
    }
}

This Go program should do the same things as the Objective-c version. The issue appears to be that Nib's InstantiateWithOwnerTopLevelObjects() does not return the objects in the slice that is used as an argument to the method. I believe this could be a bug with DarwinKit.

Here is the output for the Objective-c program:

2023-12-06 11:03:09.211 a.out[1918:38326] nsdata length: 35871
2023-12-06 11:03:09.212 a.out[1918:38326] address of myObjects before: 0x0
2023-12-06 11:03:09.311 a.out[1918:38326] address of myObjects after: 0x6000007a4a50
2023-12-06 11:03:09.311 a.out[1918:38326] successful NIB instantiation: 1
2023-12-06 11:03:09.311 a.out[1918:38326] count: 5
2023-12-06 11:03:09.311 a.out[1918:38326] Index 0: <NSMenu: 0x600001c850c0>
    Title: Main Menu
    Supermenu: 0x0 (None), autoenable: YES
    Items:     (
        "<NSMenuItem: 0x6000022b8380 erase, submenu: 0x600001c84a40 (erase)>",
        "<NSMenuItem: 0x6000022b83f0 File, submenu: 0x600001c84f40 (File)>",
        "<NSMenuItem: 0x6000022b8460 Edit, submenu: 0x600001c84c40 (Edit)>",
        "<NSMenuItem: 0x6000022b84d0 Format, submenu: 0x600001c851c0 (Format)>",
        "<NSMenuItem: 0x6000022b8620 View, submenu: 0x600001c84840 (View)>",
        "<NSMenuItem: 0x6000022b8690 Window, submenu: 0x600001c85040 (Window)>",
        "<NSMenuItem: 0x6000022b8700 Help, submenu: 0x600001c84fc0 (Help)>"
    )
2023-12-06 11:03:09.311 a.out[1918:38326] Index 1: <NSObject: 0x600000bac010>
2023-12-06 11:03:09.311 a.out[1918:38326] Index 2: <NSFontManager: 0x600002aaefd0>
2023-12-06 11:03:09.311 a.out[1918:38326] Index 3: <NSWindow: 0x14b80f0f0>
2023-12-06 11:03:09.311 a.out[1918:38326] Index 4: <NSApplication: 0x14b82efe0>

Here is the output of the Go program:

godata length: 35871
nsdata length: 35871
address of myObjects before: 0x0
address of myObjects after: 0x1400000e0f0
successful NIB instantiation: true
count: 0

The Go program does correctly display the length of the NIB file. But it returns zero objects in the slice.

[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 https://github.com/progrium/macdriver/issues/234 for the generator issue.