textview_sample.m

// https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/TextUILayer/Tasks/CreateTextViewProg.html

// To execute it, run:
// `$ clang textview_sample.m -framework Cocoa && ./a.out`

#import <Cocoa/Cocoa.h>

int main() {
  @autoreleasepool {
    NSApplication* app = [NSApplication sharedApplication];
    [app setActivationPolicy: NSApplicationActivationPolicyRegular];

    NSWindow *aWindow = [[[NSWindow alloc]
                          initWithContentRect: NSMakeRect(0, 0, 200, 200)
                                    styleMask: NSWindowStyleMaskTitled
                                      backing: NSBackingStoreBuffered
                                        defer: NO
                         ] autorelease];

    NSRect cFrame = [[aWindow contentView] frame];

    NSTextView *theTextView = [[NSTextView alloc] initWithFrame:cFrame];

    NSLog(@"%@", [theTextView markedTextAttributes]);
    NSDictionary *theAttributes =
      @{ NSBackgroundColorAttributeName: [NSColor blackColor],
         NSForegroundColorAttributeName: [NSColor whiteColor],
         NSUnderlineStyleAttributeName: @(NSUnderlineStyleDouble | NSUnderlinePatternDot) };
    [theTextView setMarkedTextAttributes:theAttributes];
    NSLog(@"%@", [theTextView markedTextAttributes]);
    
    [aWindow setContentView:theTextView];
    [aWindow cascadeTopLeftFromPoint:NSMakePoint(20,20)];
    [aWindow makeKeyAndOrderFront:nil];
    [aWindow makeFirstResponder:theTextView];
    [NSApp activateIgnoringOtherApps:YES];
    [app run];
  }
  return 0;
}