Log Accelerometer data to a file on Iphone IOS - ios

Question

Hi I am trying to write to a file from the accelerometer data. Here is my code:
-(void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration {
//xax.text = [NSString stringWithFormat:#"X:[%2.6f]",acceleration.x];
//yax.text = [NSString stringWithFormat:#"Y:[%2.6f]",acceleration.y];
//zax.text = [NSString stringWithFormat:#"Z:[%2.6f]",acceleration.z];
NSString *acc_x = [[NSString alloc] initWithFormat:#"X:[%2.6f]",acceleration.x];
NSString *acc_y = [[NSString alloc] initWithFormat:#"Y:[%2.6f]",acceleration.y];
NSString *acc_z = [[NSString alloc] initWithFormat:#"Z:[%2.6f]",acceleration.z];
xax.text = acc_x;
yax.text = acc_y;
zax.text = acc_z;
[acc_x release];
[acc_y release];
[acc_z release];
//wfm == 2 //Initialization of Appending to the file
if (wfm == 2)
{
NSFileManager *fileManager = [NSFileManager defaultManager];
NSString *txtFileName = [[NSString alloc] initWithFormat:#"tmp/%#.txt",txtName.text];
NSString *fileName = [NSHomeDirectory() stringByAppendingPathComponent:txtFileName];
//NSString *fileName = [NSHomeDirectory() stringByAppendingPathComponent:#"tmp/acc_w_trial2.txt"];
//Current Contents of the file
NSString *fileCurrent = [[NSString alloc] initWithContentsOfFile:fileName];
//Date and Time of each Accelerometer Data
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"yyyy-MM-dd 'at' HH:mm:ss:SSS"];
NSDate *date = [NSDate date];
NSString *formattedDateString = [dateFormatter stringFromDate:date];
NSString *msg = [[NSString alloc] initWithFormat:#"%#%# %#%#%# \n",fileCurrent,formattedDateString,xax.text,yax.text,zax.text];
//Convert NSstring to NSData
NSData* data=[msg dataUsingEncoding: [NSString defaultCStringEncoding]];
//bool fileCreationSuccess = [fileManager createFileAtPath:fileName contents:data attributes:nil];
[fileManager createFileAtPath:fileName contents:data attributes:nil];
[msg release];
[dateFormatter release];
[fileCurrent release];
[txtFileName release];
}
}
I get the warning level 1 and level 2. Is there a way I can release the NSFileManager memory to prevent this from locking up?

Answer 1

Your handler method to collect accelerometer data seems not very performant. You are allocating the resources (memory, file) everytime which can take a long time.
You should allocate the needed resources only once (i.e. use dispatch_once) and keep the file open. Use a NSFileHandle (method fileHandleForWritingAtPath) in order to append the data at the end of the file.
Furthermore NSHomeDirectory() is not where you're supposed to save user data, as iOS apps are sandboxed.
Either use NSTemporaryDirectory() or write in the Documents or Library Folder. The following is from Apple's sample code, usually in application delegate class:
- (NSString *)applicationDocumentsDirectory {
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *basePath = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;
return basePath;
}

Answer 2

You can try using an Autorelease Pool.