Obj-C Code needed to show progress of an image downloading using NSURLSession

ImageDownloaderCommonBlocks.h

//
//  ImageDownloaderCommonBlocks.h
//  AsyncImageDownloader
//
//  Created by Paul Wood on 9/23/19.
//  Copyright © 2019 Paul Wood. All rights reserved.
//

#ifndef ImageDownloaderCommonBlocks_h
#define ImageDownloaderCommonBlocks_h

typedef void (^ImageCallback)(UIImage * _Nonnull);
typedef void (^ProgressBlock)(NSNumber * _Nonnull);
typedef void (^ImageWithErrorCallback)(NSError * _Nullable, UIImage * _Nullable);

#endif /* ImageDownloaderCommonBlocks_h */

ProgressiveSingleImageDownloader.h

//
//  ProgressiveSingleImageDownloader.h
//  AsyncImageDownloader
//
//  Created by Paul Wood on 9/23/19.
//  Copyright © 2019 Paul Wood. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
#import "ImageDownloaderCommonBlocks.h"

NS_ASSUME_NONNULL_BEGIN

@interface ProgressiveSingleImageDownloader : NSObject<NSURLSessionDownloadDelegate>

- (void)downloadBy_NSURLSession:(NSString *)urlString
         progress:(ProgressBlock)progressHandler withErrorCallback:(ImageWithErrorCallback) callback;

@end

NS_ASSUME_NONNULL_END

ProgressiveSingleImageDownloader.m

//
//  ProgressiveSingleImageDownloader.m
//  AsyncImageDownloader
//
//  Created by Paul Wood on 9/23/19.
//  Copyright © 2019 Paul Wood. All rights reserved.
//

#import "ProgressiveSingleImageDownloader.h"

NSString *TASK_PROGRESS_CONTEXT = @"SingleImageDownloaderTaskProgressChanged";

@interface ProgressiveSingleImageDownloader ()
@property (nonatomic, retain) NSURLSessionDownloadTask* progressiveTask;
@property (nonatomic, retain) NSURLSession* progressiveSession;
@property (nonatomic, copy, nullable) void (^progressBlock)(NSNumber * _Nonnull);
@property (nonatomic, copy, nullable) void (^completionBlock)(NSError * _Nullable, UIImage * _Nullable);
@end

@implementation ProgressiveSingleImageDownloader

- (void)downloadBy_NSURLSession:(NSString *)urlString
                       progress:(ProgressBlock)progressHandler
              withErrorCallback:(ImageWithErrorCallback) callback {
  self.progressBlock = progressHandler;
  self.completionBlock = callback;
  NSURLSessionConfiguration *configuration = NSURLSession.sharedSession.configuration.copy;
  self.progressiveSession = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
  NSURL *url = [NSURL URLWithString:urlString];
  NSURLRequest* request = [[NSURLRequest alloc] initWithURL:url];
  self.progressiveTask = [self.progressiveSession downloadTaskWithRequest:request];
  [self.progressiveTask resume];
}

- (void)URLSession:(NSURLSession *)session
      downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location {

  __block UIImage *img = [UIImage imageWithData: [NSData dataWithContentsOfURL:location]];
  dispatch_async(dispatch_get_main_queue(), ^{
    __weak typeof (self) weakSelf = self;
    weakSelf.completionBlock(nil, img);
  });
}

- (void)URLSession:(NSURLSession *)session
      downloadTask:(NSURLSessionDownloadTask *)downloadTask
                                           didWriteData:(int64_t)bytesWritten
                                      totalBytesWritten:(int64_t)totalBytesWritten
                              totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite {
  double progress = (double)totalBytesWritten / (double)totalBytesExpectedToWrite;
  NSNumber* progressNum = [NSNumber numberWithDouble:progress];
  dispatch_async(dispatch_get_main_queue(), ^{
    self.progressBlock(progressNum);
  });
}

@end

ViewController.m

//
//  ViewController.m
//  AsyncImageDownloader
//
//  Created by Paul Wood on 9/23/19.
//  Copyright © 2019 Paul Wood. All rights reserved.
//

#import "ViewController.h"
#import "SingleImageDownloader.h"
#import "ProgressiveSingleImageDownloader.h"

@interface ViewController ()
@property (nonatomic, retain) NSString* urlString;
@property (nonatomic, retain) SingleImageDownloader* imageDownloader;
@property (nonatomic, retain) ProgressiveSingleImageDownloader* progressiveDownloader;
@end

@implementation ViewController

- (void)viewDidLoad {
  [super viewDidLoad];
  //Setup
  self.imageName.text = @"Downloading Image";
  self.imageDownloader = [SingleImageDownloader new];
  self.progressiveDownloader = [ProgressiveSingleImageDownloader new];
  self.urlString = @"https://i.redd.it/4c4slwzhni901.png";
  [self.progressView setProgress:0.0 animated:NO];

  [self.progressiveDownloader downloadBy_NSURLSession:self.urlString
                                       progress:^(NSNumber * _Nonnull progress) {
    __weak typeof (self) weakSelf = self;
    [weakSelf.progressView setHidden:NO];
    [weakSelf.progressView setProgress:progress.floatValue animated:YES];
    weakSelf.imageName.text = [NSString stringWithFormat:@"Downloading Image %@", progress];
  }
                              withErrorCallback:^(NSError * _Nullable err, UIImage * _Nullable img) {
    __weak typeof (self) weakSelf = self;
    if ( err == nil && img != nil) {
      weakSelf.imageView.image = img;
      [weakSelf.progressView setHidden:YES];
      weakSelf.imageName.text = @"Downloaded Image";
    } else if ( err != nil ) {
      //handle error
      weakSelf.imageName.text = @"Image Download Failed";
    }
  }];
}

@end