Convert dispatch_data_t to NSString after a read operation - ios

Question

In my small iOS app I have a CSV file that represents an histogram. The content of file is:
label0,value0
...
labelN,valueN
In my ViewController I read the file async with Grand Central Dispatch this way:
//create the channel with which read the CSV file
dispatch_io_t ch = dispatch_io_create_with_path(DISPATCH_IO_STREAM, [[[NSBundle mainBundle] pathForResource:#"histogram1" ofType:#"csv"] UTF8String], O_RDONLY, 0, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(int error) {
if(!error){
NSLog(#"Channel created!");
}
});
//read the whole file
dispatch_io_read(ch, 0, SIZE_MAX, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^(bool done, dispatch_data_t dataRead, int error) {
if(!error && done){
NSString *ma = ; //???
NSLog(#"%#", ma);
}
});
I'd like to convert the dataRead (of type dispatch_data_t) to NSString to extract the values that represent the bars of the histogram.

Answer 1

There are a number of ways to do this, but the function you're looking for is dispatch_data_apply. Assuming the string you're reading is UTF8, this should work:
#interface NSString (FromDispatchData)
+ (instancetype)stringFromDispatchData: (dispatch_data_t)data;
#end
#implementation NSString (FromDispatchData)
+ (instancetype)stringFromDispatchData: (dispatch_data_t)data
{
if (!data)
return nil;
NSMutableString* str = [NSMutableString string];
dispatch_data_apply(data, ^bool(dispatch_data_t region, size_t offset, const void *buffer, size_t size) {
[str appendString: [[NSString alloc] initWithBytes:buffer length:size encoding: NSUTF8StringEncoding]];
return true;
});
return [[self class] stringWithString: str];
}
#end