How to add observer for macOS?

[senmx]

app.pro:

macx {
    HEADERS += \
        mac.h
    OBJECTIVE_SOURCES += \
        mac.mm
    LIBS += -framework Foundation
    LIBS += -framework Cocoa
    QMAKE_INFO_PLIST=$$PWD/Info.plist
}

mac.mm:

#include "mac.h"
#include <QDebug>
#include <Foundation/Foundation.h>
#include <Cocoa/Cocoa.h>
#include <AppKit/AppKit.h>

Mac::Mac() {
}
Mac::~Mac() {
}

void Mac::workspaceChanged(NSNotification* notification) {
    qDebug() << "========================";
    qDebug() << notification;
    qDebug() << "========================";
}
void Mac::init() {
    qDebug() << "========================";
    qDebug() << (id)this; //crashed in here
    qDebug() << "========================";
    [[NSNotificationCenter defaultCenter] addObserver:(id)this
                                                     selector:@selector(workspaceChanged:)
                                                         name:NSWorkspaceActiveSpaceDidChangeNotification object:nil];
}

[mpergand]

Hi,

You must create a NSObject and pass it at the first parameter.
See this post : https://forum.qt.io/topic/103078/how-to-get-notification-of-mouse-down-in-menu-bar/5

[senmx]

Thanks. Is like this?

#include "mac.h"
#include <QDebug>
#include <Foundation/Foundation.h>
#include <Cocoa/Cocoa.h>
#include <AppKit/AppKit.h>
#include "com/util.h"

Mac::Mac() {
}
Mac::~Mac() {
}

@interface MyObserver: NSObject {
}
- (void)workspaceChanged:(NSNotification*) notification;
@end
@implementation MyObserver
- (void)workspaceChanged:(NSNotification*) notification {
    NSLog(@">>>>>>>>>>workspaceChanged %@", notification);
}
@end
void Mac::init() {
    NSLog(@"mac init");
    MyObserver *ob = [MyObserver init]; //crashed in here
    NSLog(@"ob %@", ob);
    [[NSNotificationCenter defaultCenter] addObserver:ob
                                                     selector:@selector(workspaceChanged:)
                                                         name:NSWorkspaceActiveSpaceDidChangeNotification object:nil];
}

But:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** +[MyObserver<0x107842488> init]: cannot init a class object.'

I guess there is something wrong with the objective-c code?

[mpergand]

MyObserver *ob = [[MyObserver alloc] init];

[senmx]

@mpergand Thank you very much! But I did not receive the notification of NSWorkspaceActiveSpaceDidChangeNotification, and there is no response to workspaceChanged here.

[SGaist]

Hi,

@senmx said in How to add observer for macOS?:

[[NSNotificationCenter defaultCenter]

Shouldn't you rather use the Notification Center associated to the shared workspace of your application ?

Something like:

[[[NSWorkspace sharedWorkspace] notificationCenter] addObserver:obj selector:@selector(workspaceChanged:) name:NSWorkspaceActiveSpaceDidChangeNotification  object:nil];

[mpergand]

@SGaist good point !
You're right, (have checked with some old code of mine)

[senmx]

@SGaist Thank you very much, it worked!