1.首先先创建NSStatusBarItem ,需要将item保存到属性中，否则对象会被系统的管理机制释放掉，NSStatusBar将不会出现item.
'''
NSStatusItem * item = [[NSStatusBar systemStatusBar] statusItemWithLength:NSSquareStatusItemLength];
[item.button setTarget:self];
[item.button setAction:@selector(itemClick:)];
item.button.image = [NSImage imageNamed:@"online"];
self.item = item;
'''
2.itemClick:方法，此时的item点击事件只能将处于非活动状态的应用窗口呼出到最前面，
'''
[[NSRunningApplication currentApplication]activateWithOptions:NSApplicationActivateAllWindows | NSApplicationActivateIgnoringOtherApps];
'''
3.增加通知监听window的变化，系统发出通知，创建属性记录windonw的状态，BOOL 类型isMin，发出通知时，改变属性的值，记录状态的变化.
'''
//最小化时，系统发出通知
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(minWindown:) name:NSWindowDidMiniaturizeNotification object:nil];
//处于最小化时，点击Dock区恢复
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(mainWindown:) name:NSWindowDidBecomeMainNotification object:nil];
4.在点击事件中根据属性的值，来控制如何显示windown
'''
- (void)mainWindown:(NSNotification *)noti {
self.isMin = NO;
}
- (void)minWindown:(NSNotification *)noti {
self.isMin = YES;
}
- (IBAction)itemClick:(NSButton *)sender{
if (self.isMin == YES) {
[self.window makeKeyAndOrderFront:self];
[self.window center];
}else {
self.isMin = NO;
[[NSRunningApplication currentApplication] activateWithOptions:NSApplicationActivateAllWindows | NSApplicationActivateIgnoringOtherApps];
}
}'''