Read / write / create data files

[Xavier]

Hi,

I just started to develop applications for iPhone, and I'm actually trying to access files in order to read or write data.
I can successfully read a raw data file, but I'm having some problems about writing.
Here is the small piece of code I wrote:

	char *saves = "abcd";
	NSData *data = [[NSData alloc] initWithBytes:saves length:4]; 
	BOOL test = [self writeToFile:data:@"data":@"iph"];

- (BOOL)writeToFile:(NSData *)data:(NSString *)fileName:(NSString *)extension 
{
	NSFileManager *fm = [NSFileManager defaultManager];
	NSString *appFile = [[NSBundle mainBundle] pathForResource:fileName ofType:extension];
	
	if (!appFile)  // if file doesn't exist, create it
	{
		printf("File %s doesn't exist, so we create it", appFile);
		return ([fm createFileAtPath:appFile contents:data attributes:nil]);
	}
	else
		return ([data writeToFile:appFile atomically:YES]); 	
}

The writeToFile method returns a YES, but nothing is written into my file.
(By the way the file creation isn't working too).

Did you already managed to write into a file this way ?

Thanks !

[jrgalan]

i believe the following code:

NSString *appFile = [[NSBundle mainBundle] pathForResource:fileName ofType:extension];

only searches the app dir for a resource that ALREADY exists.

this is how i write files:

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
	
// the path to write file
NSString *appFile = [documentsDirectory stringByAppendingPathComponent:@"myFile"];

[data writeToFile:appFile atomically:YES];

[Xavier]

It seems that I have no permission to write in the App bundle.
I tried in the Documents directory and it's working fine.

Thanks.

[ghost]

Originally Posted by jrgalan

i believe the following code:

NSString *appFile = [[NSBundle mainBundle] pathForResource:fileName ofType:extension];

only searches the app dir for a resource that ALREADY exists.

this is how i write files:

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
	
// the path to write file
NSString *appFile = [documentsDirectory stringByAppendingPathComponent:@"myFile"];

[data writeToFile:appFile atomically:YES];

I'm trying to save GPS data so I'm using your code like this:

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
		NSString *documentsDirectory = [paths objectAtIndex:0];
		
		// the path to write file
		NSString *appFile = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@,%@",latitude,longitude]];
		
		[data writeToFile:appFile atomically:YES];

How would I retrieve that file and save the lat and lon into 2 separate variables?

Thanks!

[jgoemat]

How would I retrieve that file and save the lat and lon into 2 separate variables?

Thanks!

You could use the NSMutableDictionary's writeToFile methods instead, I find that handy for simple data. It can basically read/write any type you can use in your plist files (Dictionary, Array, Boolean, Data, Date, Number, String).

I use a static method to return the full path to the data file so I don't have to write it twice:

+ (NSString *)dataFilePath {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(
        NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *docDirectory = [paths objectAtIndex:0];
    return [docDirectory stringByAppendingPathComponent:@"GPS.dat"];
}

Save values:

NSMutableDictionary *dict = [[NSMutableDictionary alloc]  init];
[dict setValue:[NSNumber numberWithFloat:43.3] forKey:@"latitude"];
[dict setValue:[NSNumber numberWithFloat:-85.7] forKey:@"longitude"];
[dict writeToFile:[classname dataFilePath]];

Load and log values:

NSMutableDictionary *dict = [[NSMutableDictionary alloc] 
        initWithContentsOfFile:[classname dataFilePath]];
NSLog("%f, %f", 
        [dict valueForKey:@"latitude"], 
        [dict valueForKey:@"longitude"]);

[aanupaul]

can read music files stored in iphone to my apps.

if anybody know pls reply as soon as possible.....
Thanks...

[fulvio]

Originally Posted by jgoemat

You could use the NSMutableDictionary's writeToFile methods instead, I find that handy for simple data. It can basically read/write any type you can use in your plist files (Dictionary, Array, Boolean, Data, Date, Number, String).

I use a static method to return the full path to the data file so I don't have to write it twice:

+ (NSString *)dataFilePath {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(
        NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *docDirectory = [paths objectAtIndex:0];
    return [docDirectory stringByAppendingPathComponent:@"GPS.dat"];
}

Save values:

NSMutableDictionary *dict = [[NSMutableDictionary alloc]  init];
[dict setValue:[NSNumber numberWithFloat:43.3] forKey:@"latitude"];
[dict setValue:[NSNumber numberWithFloat:-85.7] forKey:@"longitude"];
[dict writeToFile:[classname dataFilePath]];

Load and log values:

NSMutableDictionary *dict = [[NSMutableDictionary alloc] 
        initWithContentsOfFile:[classname dataFilePath]];
NSLog("%f, %f", 
        [dict valueForKey:@"latitude"], 
        [dict valueForKey:@"longitude"]);

I implemented your code because I wanted to save the value of a UISwitch.

Here is my code:

I'm not sure whether this is the correct way of saving UISwitch values to a file. Unfortunately this doesn't work.

- (IBAction)switchChanged:(id)sender {
	soundEffectsMode = (UISwitch*) sender;
	
	NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
	
	BOOL currentValue = (BOOL)soundEffectsMode.isOn;
	
	if (currentValue) {
		[dict setValue:[NSNumber numberWithInt:1] forKey:@"soundEffects"];
	} else {
		[dict setValue:[NSNumber numberWithInt:0] forKey:@"soundEffects"];
	}
	[dict writeToFile:[gameOptions dataFilePath]];
	warning: 'gameOptions' may not respond to '+dataFilePath'
	warning: 'NSMutableDictionary' may not respond to '-writeToFile:'
	NSLog("%d", [dict valueForKey:@"soundEffects"]);
	warning: passing argument 1 of 'NSLog' from incompatible pointer type
}

I then want to be able to check for the value and play sound effects (in a different view) if the switch value is set to ON.

Could I do something like this?

NSMutableDictionary *dict = [[NSMutableDictionary alloc] initWithContentsOfFile:[gameOptions dataFilePath]];

if ([dict valueForKey:@"soundEffects"] == 1) {
	//play sound effect
}

Also I wanted to change the default UISwitch value to OFF when the view loads. This doesn't seem to work!

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (id)initWithOptionsSetup {	
	self.soundEffectsMode.on = NO;
	return self;
}

[mohsadster_iphone]

HI,

Is der anyway to read teh files storein iphone. I heard 3.0 supports reading and saving the music files. Is it not possible to load other files as music files. I like to build a Backup and Recovery system.

Awaiting for your reply,

Thanks,
Mohammed Sadiq.

[pannag]

That is great! Thanks a lot.
Is there a way in which I can access the saved files from the Mac for analysis? For example, I want to write the accelerometer data to the file and later read it in Matlab or something?
Thanks
PS

Originally Posted by jgoemat

You could use the NSMutableDictionary's writeToFile methods instead, I find that handy for simple data. It can basically read/write any type you can use in your plist files (Dictionary, Array, Boolean, Data, Date, Number, String).

I use a static method to return the full path to the data file so I don't have to write it twice:

+ (NSString *)dataFilePath {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(
        NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *docDirectory = [paths objectAtIndex:0];
    return [docDirectory stringByAppendingPathComponent:@"GPS.dat"];
}

Save values:

NSMutableDictionary *dict = [[NSMutableDictionary alloc]  init];
[dict setValue:[NSNumber numberWithFloat:43.3] forKey:@"latitude"];
[dict setValue:[NSNumber numberWithFloat:-85.7] forKey:@"longitude"];
[dict writeToFile:[classname dataFilePath]];

Load and log values:

NSMutableDictionary *dict = [[NSMutableDictionary alloc] 
        initWithContentsOfFile:[classname dataFilePath]];
NSLog("%f, %f", 
        [dict valueForKey:@"latitude"], 
        [dict valueForKey:@"longitude"]);

[DonThunder]

Hey jgoemat.

I tried to understand and use your code.
I have one question left: I get an error with the "classname"
XCode tells me that it's not defined. Did you do that in your headerfile or somewhere I don't see it?

Thanks,
Don

[Sophie11]

I am also trying to read from a file and it's causing me trouble.

I have the line of code 'NSArray *line = [fileContents componentsSeparatedByString:@"\n"];

which breaks up the data from my text file into separate strings and it's receiving the error 'Local declaration of 'txtFile' hides instance variable' for some reason?

Can anyone tell me why?

[dmgdpnk]

Originally Posted by Sophie11

I am also trying to read from a file and it's causing me trouble.

I have the line of code 'NSArray *line = [fileContents componentsSeparatedByString:@"\n"];

which breaks up the data from my text file into separate strings and it's receiving the error 'Local declaration of 'txtFile' hides instance variable' for some reason?

Can anyone tell me why?

Try:

NSArray *line = [[NSArray alloc] initWithArray: [fileContents componentsSeparatedByString:@"\n"]];

And make sure you do:

[line release];

somewhere.

Might be wrong - pretty new to this. Hope that helps.

[baja_yu]

There really is no need to answer and bump threads from 2 years ago.