Concurrent / Asynchronous NSOperation

//
//  GetLocationCommand.m
//  Buzzrd
//
//  Created by Brian Mancini on 6/29/14.
//  Copyright (c) 2014 Buzzrd. All rights reserved.
//

#import "GetLocationCommand.h"

@interface GetLocationCommand()

@property (strong, nonatomic) NSTimer *timeoutTimer;
@property (strong, nonatomic) NSThread *mainThread;

@end

@implementation GetLocationCommand {
    bool executing;
    bool finished;
}

- (id)init
{
    self = [super init];
    if(self) {
        self.completionNotificationName = @"getLocationComplete";
        executing = false;
        finished  = false;
    }
    return self;
}


// iOS8 support for asynchronous NSOperations
- (bool) isAsynchronous {
    return true;
}


// iOS7 support for asynchronous NSOperations
- (bool) isConcurrent {
    return true;
}


// Override for isExecuting, required by async NSOperations
- (bool) isExecuting {
    return executing;
}


// Overrivde for isFinished, required by async NSOperations
- (bool) isFinished {
    return finished;
}


// Required by async NSOperations
// This will perform KVO for isExecuting property and call main
- (void) start {
    NSLog(@"%p:GetLocationCommand:start", self);
    
    [self willChangeValueForKey:@"isExecuting"];
    [NSThread detachNewThreadSelector:@selector(main) toTarget:self withObject:nil];
    executing = true;
    [self didChangeValueForKey:@"isExecuting"];
}


// Main NSOperation code
- (void) main {
    NSLog(@"%p:GetLocationCommand:main", self);
    
    // add event handlers
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(locationUpdated:) name:BZLocationManagerUpdated object:nil];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(locationErrored:) name:BZLocationManagerErrored object:nil];
    
    // start the location request
    [[BZLocationManager instance] requestLocation];
    
    // add timeout mechanism
    dispatch_async(dispatch_get_main_queue(), ^{
        self.timeoutTimer = [NSTimer scheduledTimerWithTimeInterval:15.0 target:self selector:@selector(timeout) userInfo:nil repeats:false];
    });
}


// Fires on deallocation
- (void)dealloc {
    NSLog(@"%p:GetLocationCommand:dealloc", self);
}


// Fires when after the elapsed timeout period
- (void)timeout {
    NSLog(@"%p:GetLocationCommand:timeout", self);
    
    CLLocation *lastLocation = [[BZLocationManager instance] requestLastLocation];
    
    if(lastLocation) {
        NSLog(@"  -> Sending last location: (%f, %f)", lastLocation.coordinate.longitude, lastLocation.coordinate.latitude);
        [self sendSuccess:lastLocation];
    } else {
        NSLog(@"  -> Sending error");
        [self  sendError:[[NSError alloc] init]];
    }
    
    [self shutdownCommand];
}


// Event handler for BZLocationManager errors
- (void)locationErrored:(NSNotification *)notification {
    NSLog(@"%p:GetLocationCommand:locationErrored", self);
        
    NSError *error = notification.userInfo[BZLocationManagerErroredErrorInfoKey];
    [self sendError:error];
    [self shutdownCommand];
}


// Event handler for BZLocationManager updates
- (void)locationUpdated:(NSNotification *)notification {
    NSLog(@"%p:GetLocationCommand:locationUpdated", self);
    
    CLLocation *location = notification.userInfo[BZLocationManagerUpdatedLocationInfoKey];
    [self sendSuccess:location];
    [self shutdownCommand];
}


// Triggers an error for the NSOperation
- (void)sendError:(NSError*)error {
    self.status = kFailure;
    self.results = error;
    [self sendCompletionFailureNotification];
}


// Triggers a succses for the NSOperation
- (void)sendSuccess:(CLLocation *)location {
    self.status = kSuccess;
    self.results = location;
    [self sendCompletionNotification];
}


// Shuts down the NSOperation
- (void)shutdownCommand {
    NSLog(@"%p:GetLocationCommand:shutdownCommand", self);
    
    // Clear out observers
    [[NSNotificationCenter defaultCenter] removeObserver:self];

    // Invalidate the timeout
    [self invalidateTimeout];
    
    // Execute KVO for isExecuting and isFinished properties
    [self willChangeValueForKey:@"isFinished"];
    [self willChangeValueForKey:@"isExecuting"];
    
    executing = false;
    finished = true;
    
    [self didChangeValueForKey:@"isExecuting"];
    [self didChangeValueForKey:@"isFinished"];
}

// Invalidates the timer used for timeout handling
- (void)invalidateTimeout {
    NSLog(@"%p:GetLocationCommand:invalidateTimeout", self);
    
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.timeoutTimer invalidate];
    });
}

@end

NSOperation Class Reference

Concurrency Programming Guide Example