Appending data to a string without losing previous data - ios

Question

I have this is on the top of my program:
#property (strong, nonatomic) NSMutableData *data;
I thought this would allow me to store the value from every time this method runs:
- (void)peripheralManager:(CBPeripheralManager *)peripheral didReceiveWriteRequests:(NSArray *)requests
{
for (CBATTRequest *request in requests) {
NSString *stringValue = [[NSString alloc] initWithData: [request value] encoding:NSUTF8StringEncoding];
// Have we got everything we need?
if ([stringValue isEqualToString:#"EOM"]) {
// We have, so show the data,
[self.textview setText:[[NSString alloc] initWithData:self.data encoding:NSUTF8StringEncoding]];
}
// Otherwise, just add the data on to what we already have
[self.data appendData:[request value]];
}
}
This method waits for a write request to be received and stores the value in a string. I have a core bluetooth central that is sending three blocks of data. This is to get around the data transfer size restriction within bluetooth LE. The problem is I can't get the three values stored. I am trying to not just store the last value but add the new value to the end of a nsstring or nssdata every time the method is called. Any help would be greatly appreciated. I thought the property at the top would allow me to do it but it either only stores the last value or nothing at all. I am not used to the ways of objective c yet. Thanks.
Even this doesn't write anything to self.data:
NSString * result = [[requests valueForKey:#"value"] componentsJoinedByString:#""];
NSData* data = [result dataUsingEncoding:NSUTF8StringEncoding];
[self.data appendData:data];
// Log it
NSLog(#"%#",self.data);

Answer 1

You should use NSMutableArray instead of NSString as a mutable string.
- (void)peripheralManager:(CBPeripheralManager *)peripheral didReceiveWriteRequests:(NSArray *)requests
{
NSMutableString *stringValue = [[NSMutableString alloc] init];
for (CBATTRequest *request in requests) {
[stringValue appendString:[[NSString alloc] initWithData:[request value] encoding:NSUTF8StringEncoding]];
// Have we got everything we need?
if ([stringValue isEqualToString:#"EOM"]) {
// We have, so show the data,
[self.textview setText:[[NSString alloc] initWithData:self.data encoding:NSUTF8StringEncoding]];
}
// Otherwise, just add the data on to what we already have
[self.data appendData:[request value]];
}

Answer 2

Remember kids when dealing with NSMutableData always initialize it!
_data = [[NSMutableData alloc] init];
This fixed the null problem for me.