Accelerometer must be in a specific orientation for a given time interval before next action

问题

I am trying to execute a method in my application, but only after the phone was been in the correct accelerometer orientation for a given time interval. The problem I am having is each time the accelerometer is updated, the timer resets. I have not been able to figure out how to trigger the time to start only once and not each time the accelerometer is updated.

// In ViewController.h

#import <UIKit/UIKit.h>
#import <CoreMotion/CoreMotion.h>

@interface ViewController : UIViewController
{
    float timeTest;
}

@property (nonatomic, strong) CMMotionManager *motionManager;
@property (nonatomic, strong) NSTimer *timerObject;

- (void) testMethod;

- (void) addTime;

- (void) startTimer;

@end

// In ViewController.m

#import "ViewController.h"

@implementation ViewController

@synthesize motionManager;
@synthesize timerObject;

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    self.motionManager = [[CMMotionManager alloc]init];
    [self testMethod];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void) testMethod
{
    if ([self.motionManager isAccelerometerAvailable])
    {
        NSOperationQueue *queue = [[NSOperationQueue alloc]init];
        [self.motionManager startAccelerometerUpdatesToQueue:queue withHandler:^(CMAccelerometerData *accelerometerData,NSError *error)
         {
             if (ABS(accelerometerData.acceleration.x) < 0.30 && ABS(accelerometerData.acceleration.y) < 0.30 && ABS(accelerometerData.acceleration.z) > 0.70) // Phone is flat and screen faces up
             {
                 NSLog(@"Correct position.");  
                 [self startTimer]; // Problem here.  This just continually resets the timer for each accelerometer update.
             }
             else
             {
                 NSLog(@"Incorrect position.");
                 [timerObject invalidate];
                 timeTest = 0.0;
            }

         }];
    }
    else
    {
        NSLog(@"Accelerometer is not available.");
    }
}


- (void) addTime
{
    timeTest = timeTest + 0.1;
    if (timeTest == 3.0)
    {
        [timerObject invalidate];

        // Where code for next action would go.  For feedback, just simply set the screen to green.
        self.view.backgroundColor = [UIColor greenColor];
    }
}

- (void) startTimer
{
    timeTest = 0.0;
    timerObject = [NSTimer scheduledTimerWithTimeInterval:0.1f target:self selector:@selector(addTime) userInfo:nil repeats:YES];
}

@end

Any assistance would be great!

回答1:

One way would be to insert a BOOL flag to indicate the timer has started, to prevent it constantly being unnecessarily re-started. You'd then reset the flag when the timer is invalidated. So you'd have something like this (not tested but I'm sure you'll get the gist):

- (void) testMethod
{
    BOOL timerStarted = NO;
    if ([self.motionManager isAccelerometerAvailable])
    {
        NSOperationQueue *queue = [[NSOperationQueue alloc]init];
        [self.motionManager startAccelerometerUpdatesToQueue:queue withHandler:^(CMAccelerometerData *accelerometerData,NSError *error)
         {
             if (ABS(accelerometerData.acceleration.x) < 0.30 && ABS(accelerometerData.acceleration.y) < 0.30 && ABS(accelerometerData.acceleration.z) > 0.70) // Phone is flat and screen faces up
             {
                 NSLog(@"Correct position."); 
                 if(timerStarted == NO){//Only start the timer if it's not already running
                     [self startTimer]; 
                     timerStarted = YES;
                 }
             }
             else
             {
                 NSLog(@"Incorrect position.");
                 [timerObject invalidate];
                 timerStarted = NO;
                 timeTest = 0.0;
            }

         }];
    }
    else
    {
        NSLog(@"Accelerometer is not available.");
    }
}

EDIT You're also calling your startTimer method from a block, which mean the timer isn't being added to the main runloop. Try this instead:

- (void) startTimer
{
    timeTest = 0.0;
    self.timerObject = [NSTimer timerWithTimeInterval:0.1f target:self selector:@selector(addTime) userInfo:nil repeats:YES];
    [[NSRunLoop mainRunLoop] addTimer:self.timerObject forMode:NSDefaultRunLoopMode];
}

Your addTime method should now get called correctly.

来源：https://stackoverflow.com/questions/17999375/accelerometer-must-be-in-a-specific-orientation-for-a-given-time-interval-before

标签

objective-c

nstimer