iOS,KVO:Observer无法跟踪对myObject.myCALayer.center的更改

我看到了。这个视图中间有一个轮子。它还支持IAD和自动旋转。因此,每当广告弹出顶部,或设备旋转,轮子自动重新定位到开放空间的中心。

现在我有一个类来检测用户是否在旋转轮子。它源于uiadvancedprocesse,但要使它正确工作,它需要知道车轮的中心。不断变化。如何修复?

我想“观察”myObject.myCALayer.center,每次它改变时,都会将新值发送到我的touchinput processing类中。

所以我做到了:

- (id) initWithFrame: (CGRect) theFrame
              target: (id) p_target
     actionPlayChord: (SEL) p_actionPlayChord
      actionSettings: (SEL) p_actionSettingsClick
{
    target = p_target;
    actionPlayChord = p_actionPlayChord;

    self = [super initWithFrame: theFrame];

    if ( ! self )
        return nil;

    CGPoint centre = CGPointMake(theFrame.size.width / 2.0, theFrame.size.height / 2.0);

    WheelTouchHandler * wheelTouchHandler = [WheelTouchHandler alloc];
    [wheelTouchHandler initWithTarget: self 
                       activateAction: @selector(engaged:)
                         moveCWAction: @selector(movedCW:)
                        moveACWAction: @selector(movedACW:)
     ] ;

    [self addGestureRecognizer: wheelTouchHandler];

    [self setMultipleTouchEnabled: NO];


    self.wheel = [Wheel alloc];

    NSUserDefaults * prefs = [NSUserDefaults standardUserDefaults];
    NSString *symbol = [prefs stringForKey: @"sharpsOrFlats"];

    [self.wheel init_rMax: WHEEL_R_MAX
                     rMin: WHEEL_R_MIN
                   rGap01: WHEEL_R_RATIO_GAP_TO_DISC
                   rRatio: WHEEL_R_RATIO_OUTER_TO_INNER
              sharpsFlats: symbol
               bitmapSize: theFrame.size 
     ] ;

    [self.layer addSublayer:  [self.wheel wheelLayer] ];

    [self.wheel.wheelLayer setPosition: centre ];


    [self.layer addSublayer:  [self.wheel labelLayer] ];
    [self.wheel.labelLayer setPosition: centre ];

    // "center" fails too...
    [self.wheel.wheelLayer addObserver:self forKeyPath:@"position" options:0 context:nil];


    return self;
}

- (void)observeValueForKeyPath:(NSString *)keyPath 
                      ofObject:(id)object 
                        change:(NSDictionary *)change 
                       context:(void *)context
{
    NSLog(@"Changed!"); <--  this line does not get hit - why?
}

但是,没有任何记录。我做错什么了?显然轮子的加莱尔在屏幕上重新定位。但是观察者没有观察到这种变化。如何修复?

更新: 显然,KVO在CALayer属性上存在一些问题。

我尝试过将CALayer子类化,如下所示:

@实现监视层

+(BOOL) automaticallyNotifiesObserversForKey: (NSString *) key
{

    //, if key is @"position" return YES, otherwise return [super automatically...]

    if ([key isEqual: @"position"])
        return YES; // doesn't get hit

    if ([key isEqual: @"center"])
        return YES; // <-- gets hit

    return [super automaticallyNotifiesObserversForKey: key];
}

- (void) setValue: (id) value 
           forKey: (NSString *) key
{
    // method doesn't get hit


    if ([key isEqual: @"position"])
    {
        NSLog(@"POSHIT");
    }

    [super setValue: value 
             forKey: key];
}

@end

但仍然没有快乐