NSButton Failing to Reflect a Change of its Image

What happens if, instead of calling setNeedsDisplay, you directly set the image of the NSButton ? Does it work better ?

If so, problem could be that there is already a redraw in the queue for the button.

https://www.hackingwithswift.com/example-code/uikit/how-to-force-a-uiview-to-redraw-setneedsdisplay

I found a work around to the problem. In the example code below, in response to a color change the action message, newColor:, changes the color of the image and calls the button's setImage: message. This actually is the same NSImage object already in the Button. In this case the API ignores the setNeedsDisplay message.

If a new NSImage object is created, as in the line commented out, and sent to the Button, the Button is redrawn with the new image.

I still think it is a bug that the in the first instance the setNeedsDisplay message is ignored.

//  AppDelegate.m
//  TestUI
//
//  Created by Bruce D MacKenzie on 11/20/22.
//

#import "AppDelegate.h"

@interface AppDelegate ()
{
}

@property (strong) IBOutlet NSWindow *window;
@property (assign) IBOutlet NSButton *theButton;

@end

@implementation AppDelegate
{
    NSImage     *image;
}

@synthesize theButton;

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    // Insert code here to initialize your application
}


- (void)applicationWillTerminate:(NSNotification *)aNotification {
    // Insert code here to tear down your application
}

-(void)awakeFromNib
{

    image = [[NSImage alloc] initWithSize: NSMakeSize( 32 , 32 )];
    [image lockFocus];
    [[NSColor redColor] drawSwatchInRect: NSMakeRect(0, 0, 32, 32)];
    [image unlockFocus];

    [[self theButton] setImage: image];
}

- (BOOL)applicationSupportsSecureRestorableState:(NSApplication *)app {
    return YES;
}

-(IBAction)newColor: (NSColorWell *)sender
{
    NSColor     *newColor;

    newColor = [sender color];


//    image = [[NSImage alloc] initWithSize: NSMakeSize( 32 , 32 )];

    [image lockFocus];
    [newColor drawSwatchInRect: NSMakeRect( 0, 0, 32, 32)];
    [image unlockFocus];

    [[self theButton] setImage: image];
    [[self theButton] setNeedsDisplay: YES];
}
code-block

Not sure it is a bug but maybe a side effect on how the rendering engine (NSRunLoop) works, by "stacking" changes.

There was a very interesting TN by Quinn here: https://developer.apple.com/forums/thread/717392

There may be a simple way to work around the issue.

Change the color inside a dispatch asyncAfter (did not try it yet); that should give time to the system to proceed before it takes the color change into consideration:

  DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 0.1)  { 
    [[self theButton] setImage: image];
   }