CODEWITHSUNDEEP
iphoneiosobjective-ccocoa-touch
R.Lambert
R.Lambert

Reputation: 1170

Faster way to load Images in Collection View

I have a little flow problem with my UICollectionView. I want to display PDF's thumbnails just like in Apple's iBook app, when I scroll my collection view I can see it's not really smooth. Here is the way I use to load my pictures :

- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:    (NSIndexPath *)indexPath
{
     GridCell *cell = [cv dequeueReusableCellWithReuseIdentifier:@"gridCell" forIndexPath:indexPath];

    ...

    // Set Thumbnail
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        if ([Tools checkIfLocalFileExist:cell.pdfDoc])
        {
            UIImage *thumbnail = [Tools generateThumbnailForFile:((PDFDocument *)[self.pdfList objectAtIndex:indexPath.row]).title];

            dispatch_async( dispatch_get_main_queue(), ^{
                [cell.imageView setImage:thumbnail];
            });
        }
    });

    ...

    return cell;
}

Method to get thumbnail :

+ (UIImage *)generateThumbnailForFile:(NSString *) fileName
{
    // ----- Check if thumbnail already exist
    NSString* documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];

    NSString* thumbnailAddress = [documentsPath stringByAppendingPathComponent:[[fileName stringByDeletingPathExtension] stringByAppendingString:@".png"]];
    BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:thumbnailAddress];

    if (fileExists)
        return [UIImage imageWithContentsOfFile:thumbnailAddress];

    // ----- Generate Thumbnail
    NSString* filePath = [documentsPath stringByAppendingPathComponent:fileName];

    CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:filePath];
    CGPDFDocumentRef documentRef = CGPDFDocumentCreateWithURL(url);
    CGPDFPageRef pageRef = CGPDFDocumentGetPage(documentRef, 1);
    CGRect pageRect = CGPDFPageGetBoxRect(pageRef, kCGPDFCropBox);

    UIGraphicsBeginImageContext(pageRect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(context, CGRectGetMinX(pageRect),CGRectGetMaxY(pageRect));
    CGContextScaleCTM(context, 1, -1);
    CGContextTranslateCTM(context, -(pageRect.origin.x), -(pageRect.origin.y));
    CGContextDrawPDFPage(context, pageRef);

    // ----- Save Image
    UIImage *finalImage = UIGraphicsGetImageFromCurrentImageContext();
    NSData *imageData = [NSData dataWithData:UIImagePNGRepresentation(finalImage)];
    [imageData writeToFile:thumbnailAddress atomically:YES];
    UIGraphicsEndImageContext();

    return finalImage;    
}

Do you have any suggestion ?

Upvotes: 3

Views: 1163

Answers (1)

savner
savner

Reputation: 840

Take a look at https://github.com/rs/SDWebImage. The library works great for async image loading particularly the method setImageWithURL:placeholderImage:

You can call that method and set a place holder with a loading image or blank png and once the image you are trying to retrieve is loaded it will fill in the place holder. This should speed up your app quite a bit.

Upvotes: 3

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