A trivial inches-to-mm converter application for OS X Tiger.

main.m

//
//  main.m
//  Project1
//
//  Created by Mac User on 12/22/22.
//  Copyright __MyCompanyName__ 2022. All rights reserved.
//

#import <Cocoa/Cocoa.h>

#define NSViewLeftMargin (NSViewMinXMargin)
#define NSViewRightMargin (NSViewMaxXMargin)
#define NSViewTopMargin (NSViewMaxYMargin)
#define NSViewBottomMargin (NSViewMinYMargin)

@class MainView;


// MARK: - MainController

#define INCHES_FIELD (1)
#define MM_FIELD (2)

@interface MainController: NSObject {
	MainView* _mainView;
	int _lastEdited;
}
@end

@implementation MainController

- (id)initWithView:(MainView*)mainView {
	self = [super init];
	if (self != nil) {
		_mainView = mainView;
		[[_mainView inchesField] setDelegate:self];
		[[_mainView mmField] setDelegate:self];
		[[_mainView convertButton] setTarget:self];
		[[_mainView convertButton] setAction:@selector(convertDidGetClicked:)];
		_lastEdited = INCHES_FIELD;
	}
	return self;
}

- (void)convertDidGetClicked:(id)sender {
	NSLog(@"Convert did get clicked!");
	if (_lastEdited == INCHES_FIELD) {
		float inches = [[_mainView inchesField] floatValue];
		float mm = inches * 25.4;
		[[_mainView mmField] setFloatValue:mm];
	} else if (_lastEdited == MM_FIELD) {
		float mm = [[_mainView mmField] floatValue];
		float inches = mm / 25.4;
		[[_mainView inchesField] setFloatValue:inches];
	}
}

- (void)controlTextDidBeginEditing:(NSNotification *)aNotification {
	if ([[aNotification object] isEqual:[_mainView inchesField]]) {
		NSLog(@"textDidBeginEditing (inchesField)");
		_lastEdited = INCHES_FIELD;
	} else if ([[aNotification object] isEqual:[_mainView mmField]]) {
		NSLog(@"textDidBeginEditing (mmField)");
		_lastEdited = MM_FIELD;
	}
}

@end


// MARK: - MainView

@interface MainView: NSView {
	NSButton* _convertButton;
	NSTextField* _inchesField;
	NSTextField* _inchesLabel;
	NSTextField* _mmField;
	NSTextField* _mmLabel;
}
- (NSButton*)convertButton;
- (NSTextField*)inchesField;
- (NSTextField*)mmField;
@end

@implementation MainView

- (NSButton*)convertButton {
	return _convertButton;
}

- (NSTextField*)inchesField {
	return _inchesField;
}

- (NSTextField*)mmField {
	return _mmField;
}

- (id) initWithFrame:(NSRect)frame {
	self = [super initWithFrame:frame];
	NSLog(@"MainView.initWithFrame: %fx%f, %fx%f", frame.origin.x, frame.origin.y, frame.size.width, frame.size.height);
	if (self != nil) {
		[self _setupSubviews];
		[self setAutoresizesSubviews:true];
	}
	return self;
}

- (void)setBounds:(NSRect)boundsRect {
	NSLog(@"MainView.setBounds: %@", boundsRect);
	[self _layoutSubviews];
	[super setBounds:boundsRect];
}

- (void)setFrame:(NSRect)frameRect {
	NSLog(@"MainView.setFrame: %fx%f, %fx%f", frameRect.origin.x, frameRect.origin.y, frameRect.size.width, frameRect.size.height);
	[self _layoutSubviews];
	[super setFrame:frameRect];
}

- (void)_setupSubviews {
	NSSize size = [self bounds].size;
	NSLog(@"MainView._setupSubviews, size: %fx%f", size.width, size.height);

	_inchesField = [[NSTextField alloc] init];
	[_inchesField setAutoresizingMask:NSViewBottomMargin];
	[self addSubview:_inchesField];

	_inchesLabel = [[NSTextField alloc] init];
	[_inchesLabel setAutoresizingMask:NSViewBottomMargin];
	[self addSubview:_inchesLabel];
	[_inchesLabel setBordered:false];
	[_inchesLabel setBezeled:false];
	[_inchesLabel setDrawsBackground:false];
	[_inchesLabel setStringValue:@"inches"];

	_mmField = [[NSTextField alloc] init];
	[_mmField setAutoresizingMask:NSViewBottomMargin];
	[self addSubview:_mmField];

	_mmLabel = [[NSTextField alloc] init];
	[_mmLabel setAutoresizingMask:NSViewBottomMargin];
	[self addSubview:_mmLabel];
	[_mmLabel setBordered:false];
	[_mmLabel setBezeled:false];
	[_mmLabel setDrawsBackground:false];
	[_mmLabel setStringValue:@"mm"];

	_convertButton = [[NSButton alloc] init];
	[_convertButton setButtonType:NSMomentaryPushInButton];
	[_convertButton setBezelStyle:NSRoundedBezelStyle];
	[_convertButton setTitle:@"Convert"];
	[_convertButton setAutoresizingMask:NSViewRightMargin|NSViewBottomMargin];
	[self addSubview:_convertButton];
}

- (void)_layoutSubviews {
	NSSize size = [self bounds].size;
	NSLog(@"MainView._layoutSubviews, size: %fx%f", size.width, size.height);

	[_inchesField setFrameSize:NSMakeSize(96,22)];
	[_inchesField setFrameOrigin:NSMakePoint(16, size.height-16-22)];

	[_inchesLabel sizeToFit];
	[_inchesLabel setFrameOrigin:NSMakePoint(16+96+4, size.height-16-22)];

	[_mmField setFrameSize:NSMakeSize(96,22)];
	[_mmField setFrameOrigin:NSMakePoint(16, size.height-16-22-16-22)];

	[_mmLabel sizeToFit];
	[_mmLabel setFrameOrigin:NSMakePoint(16+96+4, size.height-16-22-16-22)];

	[_convertButton sizeToFit];
	NSSize bsize = [_convertButton bounds].size;
	[_convertButton setFrameOrigin:NSMakePoint(16+96+64, size.height-bsize.height-31)];
}

@end


// MARK: - AppDelegate

@interface AppDelegate: NSObject {
	MainController* _mainController;
}
- (void)applicationWillFinishLaunching:(NSNotification *)aNotification;
- (void)applicationDidFinishLaunching:(NSNotification*)aNotification;
@end

@implementation AppDelegate

- (void) applicationWillFinishLaunching:(NSNotification *)aNotification {
	NSLog(@"AppDelegate.applicationDidFinishLaunching");
	NSWindow* window = [[[NSApplication sharedApplication] windows] objectAtIndex:0];
	NSRect wframe = [window frame];
	[window setFrame:NSMakeRect(wframe.origin.x,wframe.origin.y,260,116) display:true];
	NSView* mainView = [[MainView alloc] initWithFrame:NSMakeRect(0,0,640,480)];
	_mainController = [[MainController alloc] initWithView:mainView];
	[window setContentView:mainView];
}

- (void)applicationDidFinishLaunching:(NSNotification*)aNotification {
	NSLog(@"AppDelegate.applicationWillFinishLaunching");
}

@end


// MARK: - main

int main(int argc, char *argv[]) {
	NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
	AppDelegate* appDelegate = [[AppDelegate alloc] init];
	[[NSApplication sharedApplication] setDelegate:appDelegate];
    int ret = NSApplicationMain(argc,  (const char **) argv);
	[pool release];
	NSLog(@"main exiting!");
	return ret;
}