How do I compare a constant value to a continuously-updated Accelerometer value each time round a loop? - objective-c

Question

As it was suggested to me in a previous post of mine, the following code takes the data coming from the accelerometer the "minute" the assignment : CMAccelerometerData* data = [manager accelerometerData]; is performed, and then extracts from that data the acceleration exercised on the x-Axis and stores its value in a double (double x) :
CMMotionManager* manager = [[CMMotionManager alloc] init];
CMAccelerometerData* data = [manager accelerometerData];
double x = [data acceleration].x;
Suppose the value stored is 0.03 and suppose that I want to use it in a while loop as follows :
while (x > 0)
{
// do something
}
the above loop will obviously run forever
However, what if I used the following code instead :
CMMotionManager* manager = [[CMMotionManager alloc] init];
while([[manager accelerometerData] acceleration].x > 0)
{
// do something
}
wouldn't I be now comparing zero to a different value each time round the loop?
(which is what I'm going for in my project anyway..)
any thoughts?
the reason I'm asking this is the following :
I want to check the values coming from the x-Axis over a certain period of time, rather than keep checking them at regular intervals, so I basically want to write a loop that would look something like this :
if ([[manager accelerometerData] acceleration].x > 0 )
{
// initialiseTimer
}
while ([[manager accelerometerData] acceleration].x > 0 )
{
if( checkTimer >=250ms )
{
stopTimer;
printOut("X-Axis acceleration was greater than zero for at least 250ms");
breakFromLoop;
}
}
I know the code in my 2nd if-block isn't valid Objective-C..This was just to give you an idea of what I'm going for..

Answer 1

This has a simple solution.
1)Declare an instance variable x that you update each time the accelerometer tell you to.
2)Compare this x to whatever value you need in the loop .
Hope this helps.
Regards,
George