Photo Viewer iPad & iPhone

Question

I've long been trying to make an image viewer, but really I do not what does not work. Here's a picture like you should get!

This is UIScrollView. The UIImage add to UIScrollView. When user scroll - image must download to UIImageView. I think we need download image in a separate thread. For this I am using - NSOperationqueue and NSInvocationOperation.

This is my code.

In delegate:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    MyThumbnailsBook * myThumbnailsBook = [[MyThumbnailsBook alloc] initWithFrame:CGRectMake(0, 20, 768, 1004)];
    [myThumbnailsBook createThumbnails];
    [myThumbnailsBook setContentSize:CGSizeMake(768, 1004 * 10)];
    [myThumbnailsBook setBackgroundColor:[UIColor blackColor]];
    [self.window addSubview:myThumbnailsBook];
    [self.window makeKeyAndVisible];
    return YES;
}

In class inherit UIScrollView MyThumbnailsBook.m

#define COUNT 100

#import "MyThumbnailsBook.h"
#import "MyImageDownload.h"

@implementation MyThumbnailsBook


#pragma mark -
#pragma mark Initialization & Create Thumbnails

- (id)initWithFrame:(CGRect)frame{

    if((self = [super initWithFrame:frame])){

        self.delegate = self;

    }

    return self;
}

- (void)createThumbnails{

    float point_x = 20;
    float point_y = 20;

    for(NSInteger i = 0; i < COUNT; i++){

        if(i%3==0 && i != 0){
            point_x = 20;
            point_y += 220;
        }

        //  Create new image view.
        NSURL * url = [[NSURL alloc] initWithString:@"http://storage.casinotv.com/videos/SOYCL/pages/P68.jpg"];        
        MyImageDownload * imageDownload = [[MyImageDownload alloc] initWithImageURL:url];
        [imageDownload setFrame:CGRectMake(point_x, point_y, 200, 200)];
        [self addSubview:imageDownload];
        [imageDownload release];
        [url release];

        point_x += 220;

    }


}

#pragma mark -
#pragma mark Scroll View Protocol

- (void)scrollViewDidScroll:(UIScrollView *)scrollView{


}


- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate{

    // If scroll view no decelerating.

    if(!decelerate){
        [self asyncImageDownload];
    }

}


- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{ 

    [self asyncImageDownload];

}


#pragma mark -
#pragma mark Download Image

//  If scroll stopped - download image to thumbnails.

- (void)asyncImageDownload{


}


@end

In class inherit UIScrollView MyImageDownload.m

#import "MyImageDownload.h"


@implementation MyImageDownload

//  This is init method. When class init - we add new operation for download image.

- (id)initWithImageURL:(NSURL*)url{

    if((self == [super init])){

        [self setBackgroundColor:[UIColor yellowColor]];        

        NSArray * params = [NSArray arrayWithObjects:url, nil];
        queue = [[NSOperationQueue alloc] init];
        [queue setMaxConcurrentOperationCount:1]; 
        NSInvocationOperation* operation = [[NSInvocationOperation alloc] initWithTarget:self selector:@selector(asyncDownload:) object:params];           
        [queue addOperation:operation];        
        [params release];             

    }

    return self;
}


//  Download image to data and after to self (UIImageView).

- (void)asyncDownload:(NSArray *)params{


    NSData * data = [NSData dataWithContentsOfURL:[params objectAtIndex:0]]; //  Get image data with url.

    if(data) [self setImage:[UIImage imageWithData:data]];

    [data release]; 

}

@end

In this example, the images are not loaded and I do not understand why? I have always used these classes in which the images were loaded from the internet, but I also had problems with memory and I do not know too how to solve it. For example, when to scroll images I get exception - Received memory warning. Level=1 & 2 and after app crash. And I have no idea what to do. I understand what you need as a separate download of images over time and to remove non visible objects but I have found I need the algorithm.

For example - when i go to scrollDidScroll method i get all object when i not see them and remove image:

NSArray *views = [self subviews];
    for (UIImageView *v in views) {
        if(v.frame.origin.y >= self.contentOffset.y && v.frame.origin.y <= self.contentOffset.y + self.frame.size.height){

            //  If image of imageview is equal nil - call new operation
            if(v.image == nil){             
                [self requestImageForIndexPath:[NSNumber numberWithInt:v.tag]];                               
            }
            else
            {
                v.image = nil;
            }

        }
    }

• self - this is class inherit UIScrollView.

I was confused and ask for help in resolving this issue. TNX all!

Answer 1

The Three20 library includes this functionality in the form of TTPhotoViewController .