Loading images in background to optimize the loading in ios

Question

I am trying to optimize the load in my application, in fact, I have a lot of images that loaded in my application, and I spend a lot of time waiting for a view controller to ope

Answer 1

Use IDAsyncImageView.h

 //////////////////////////////////////
    IDAsyncImageView.h
 /////////////////////////////////////

        @interface IDAsyncImageView : NSObject

        @property (nonatomic, strong) NSCache *cache;    

        + (instancetype)instance;

        - (void)loadImageView:(UIImageView*)imageView withURLString:(NSString *)urlString;

        @end

    //////////////////////////////////////
    IDAsyncImageView.m
    /////////////////////////////////////

        #import "IDAsyncImageView.h"



            @implementation IDAsyncImageView

                + (instancetype)instance
                {
                    static IDAsyncImageView *_instance = nil;
                    static dispatch_once_t onceToken;
                    dispatch_once(&onceToken, ^{
                        _instance = [[self alloc] init];
                });
                return _instance;
            }

        - (instancetype)init
        {
            self = [super init];
            if (self) {
                self.cache =  [[NSCache alloc] init];
            }

            return self;
        }

        - (void)loadImageView:(UIImageView*)imageView withURLString:(NSString *)urlString
        {
            UIActivityIndicatorView* activityView;
            activityView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
            activityView.hidesWhenStopped = YES;
            activityView.center = CGPointMake(imageView.bounds.size.width / 2.0f, imageView.bounds.size.height / 2.0f);
            activityView.autoresizingMask = UIViewAutoresizingFlexibleLeftMargin | UIViewAutoresizingFlexibleTopMargin | UIViewAutoresizingFlexibleRightMargin | UIViewAutoresizingFlexibleBottomMargin;
            [imageView addSubview:activityView];
            [activityView startAnimating];

            UIImage* imageLoad = [self.cache objectForKey:urlString];
            if (nil != imageLoad) {
                imageView.image = imageLoad;
                [activityView removeFromSuperview];
            }
            else {

            // Block variable to be assigned in block.
            __block NSData *imageData;

            // Dispatch a background thread for download
            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
                imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:urlString]];
                UIImage* imageLoad = [[UIImage alloc] initWithData:imageData];

                // Update UI on main thread
                dispatch_async(dispatch_get_main_queue(), ^(void) {
                    [self.cache setObject:imageLoad forKey:urlString];
                    imageView.image = imageLoad;
                    [activityView removeFromSuperview];
                });
            });
            }
        }

    //////////////////////////////////////
    ViewController.m
    //////////////////////////////////////

        - (void)viewDidLoad {
        [super viewDidLoad];
        [[IDAsyncImageView instance] loadImageView:myImageView withURLString:aUrl];
        }