objective-c - 为什么在此代码中通过另一个对象调用时 Core Motion 更新不起作用？

Question

@interface Tester()
{
    int currentAccelerationOnYaxis;
}    
@end

@implementation Tester

-(void) test
{
    CMMotionManager *motionManager = [[CMMotionManager alloc] init];
    motionManager.deviceMotionUpdateInterval = 0.01;
    [motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue mainQueue]
                                       withHandler:^(CMDeviceMotion *motion, NSError *error)
                                       {
                                           currentAccelerationOnYaxis = motion.userAcceleration.y;
                                       }
    ];
    while(1==1)
    {
        NSLog(@"current acceleration is: %f", currentAccelerationOnYaxis);
    }
}
@end

然后我像这样在后台线程上执行上述方法:
[myTester performSelectorInBackground:@selector(test) withObject:nil];

而且效果很好。

但是，以下配置不起作用，我不明白为什么:

@implementation MotionHandler

@synthesize accelerationOnYaxis; // this is an int property of the MotionHandler class

-(void) startAccelerationUpdates
{
    CMMotionManager *motionManager = [[CMMotionManager alloc] init];
    motionManager.deviceMotionUpdateInterval = 0.01;
    [motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue mainQueue]
                                       withHandler:^(CMDeviceMotion *motion, NSError *error)
                                       {
                                           self.accelerationOnYaxis = motion.userAcceleration.y;
                                       }
    ];
}

@implementation Tester

-(id)init
{
    //...
    currentMotionHandler = [[MotionHandler alloc] init];
}
-(void) test
{
    [currentMotionHandler startAccelerationUpdates];
    while(1==1)
    {
        NSLog(@"current acceleration is: %f", currentMotionHandler.accelerationOnYaxis);
    }
}
@end

然后我像这样在后台线程上执行上述方法:
[myTester performSelectorInBackground:@selector(test) withObject:nil];

它不起作用，这是为什么？

Answer 1

我想通了。在我的第二个版本中，我创建的 CMMotionManager 实例由于某种原因丢失了。因此，我将 MotionHandler 类的实现更改为:

MotionHandler.m

@interface MotionHandler()
{
   //..
   CMMotionManager *motionManager; // I now declare it here
}

@implementation MotionHandler

@synthesize accelerationOnYaxis; // this is an int property of the MotionHandler class

-(void) startAccelerationUpdates
{
    motionManager = [[CMMotionManager alloc] init]; // and then initialize it here..
    motionManager.deviceMotionUpdateInterval = 0.01;
    [motionManager startDeviceMotionUpdatesToQueue:[NSOperationQueue mainQueue]
                                       withHandler:^(CMDeviceMotion *motion, NSError *error)
                                       {
                                           self.accelerationOnYaxis = motion.userAcceleration.y;
                                       }
    ];
}
-(void)test
{
    [self startAccelerationUpdates];
    while(1==1)
    {
        NSLog(@"current acceleration on y-axis is: %f", self.accelerationOnYaxis);
    }
}

现在它似乎工作正常。