ALAssetLibrary and iOS 5.0 - iphone

Question

I have coded simple method to fetch data from assets library which is working fine on iOS4.3 but makes delay in fetching images in iOS5. What should i do to fasten fetching process on iOS 5.
-(void)setImages
{
int count =0;
int photoNumber = [[templateDictionary objectForKey:#"ElementsOnPage"] intValue];
for (int i=currentCount; count<photoNumber; i++) {
[self data:count+1 count:i];
count++;
}
}
-(void)data:(int)photoNumber count:(int)currentCount
{
NSURL *url;
UIImageView *firstImageView = [[UIImageView alloc]init];
CGFloat x,y,wid,h;
float ang;
if (currentCount>=[ImageURLArray count]) {
[firstImageView release];
return;
}
else
{
url = [NSURL URLWithString:[ImageURLArray objectAtIndex:currentCount]];
switch (photoNumber) {
case 1:
{
x = [[templateDictionary objectForKey:#"FirstElement_X"]floatValue];
y=[[templateDictionary objectForKey:#"FirstElement_Y"]floatValue];
wid = [[templateDictionary objectForKey:#"FirstElement_Width"]floatValue];
h=[[templateDictionary objectForKey:#"FirstElement_Height"]floatValue];
ang =[[templateDictionary objectForKey:#"FirstElement_Angle"]floatValue];
firstImageView.tag = 1+10;
//FirstImage
}
break;
case 2:
{
x = [[templateDictionary objectForKey:#"SecondElement_X"]floatValue];
y=[[templateDictionary objectForKey:#"SecondElement_Y"]floatValue];
wid = [[templateDictionary objectForKey:#"SecondElement_Width"]floatValue];
h=[[templateDictionary objectForKey:#"SecondElement_Height"]floatValue];
ang =[[templateDictionary objectForKey:#"SecondElement_Angle"]floatValue];
firstImageView.tag=2+10;
//SecondImage
}
break;
case 3:
{
x = [[templateDictionary objectForKey:#"ThirdElement_X"]floatValue];
y=[[templateDictionary objectForKey:#"ThirdElement_Y"]floatValue];
wid = [[templateDictionary objectForKey:#"ThirdElement_Width"]floatValue];
h=[[templateDictionary objectForKey:#"ThirdElement_Height"]floatValue];
ang =[[templateDictionary objectForKey:#"ThirdElement_Angle"]floatValue];
firstImageView.tag = 3+10;
//ThirdImage
}
break;
default:
break;
}
[firstImageView setFrame:CGRectMake(x, y, wid, h)];
dispatch_async(dispatch_get_main_queue(), ^
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
// Enumerate just the photos and videos group by using ALAssetsGroupSavedPhotos.
[library assetForURL:url
resultBlock:^(ALAsset* asset)
{
UIImage* img = [UIImage imageWithCGImage:[asset.defaultRepresentation fullResolutionImage]];
[firstImageView setImage:img];
}
failureBlock:^(NSError* error)
{
NSLog(#"error requesting asset");
}
];
[library release];
// Group enumerator Block
[pool release];
});
if ([[contentType objectAtIndex:currentCount]isEqualToString:#"1"]) {
UIButton *videoImage = [[UIButton alloc]initWithFrame:CGRectMake((firstImageView.frame.size.width/2)-25,(firstImageView.frame.size.height/2)-25,50,50)];
videoImage.transform = CGAffineTransformMakeRotation(ang*(3.14/180));
[videoImage setBackgroundImage:[UIImage imageNamed:#"videothumb.png"] forState:UIControlStateNormal];
[videoImage addTarget:self action:#selector(PlayMusicOnClickofButton:) forControlEvents:UIControlEventTouchUpInside];
[firstImageView addSubview:videoImage];
videoImage.tag = currentCount+1000;
[videoImage release];
}
}
firstImageView.transform = CGAffineTransformMakeRotation(ang*(3.14/180));
firstImageView.userInteractionEnabled = YES;
[coverImageView addSubview:firstImageView];
[coverImageView setImage:[UIImage imageNamed:innerBackground]];
[firstImageView release];
}

Answer 1

I already reported a bug to Apple (following a request of an Apple employee in the dev forums) on the performance degradation of assetForUrl in iOS5.
Background: The assetLibrary was refactored and it is now based on CoreData, on each assetForUrl call, the SDK actually opens a new SQLite connection (BAH...), causing a significant performance hit.
Temp solution: In my app I need to load 200 pics using assetForUrl. in IOS4 it took 100ms, in iOS5 around 5+ seconds. I found out that enumerating the entire library (around 1500 pics) and caching it in a URL-->ASSET dictionary, takes around 3 seconds. I'm using this technique for now. Watch out for stale assets if you hold on to them and changes to the library occur.