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!
