RootViewController - tableView:cellForRowAtIndexPath - Load image from assetsLibrary - iphone

Question

StackOverflow friends and colleague programmers,
My RootViewController (a flowerTableView on a view) should display cell's with title, subtitle and an image thumbnail (loaded from the camera roll). A very basic table I guess.
All content is stored in 'Core Data' but the images are stored as imagePaths to the camera roll. Example: flower.imagePath = assets-library://asset/asset.JPG?id=1000000002&ext
Using the code at the bottom everything should run smoothly but it doesn't . When starting the App the title's and subtitle's are shown, but the images are not. When I press a cell, which display's the detail view, and pop back again to the main view the image for this specific cell is shown.
When I press 'Show All', a button on a toolbar which executes the following code
NSFetchRequest *fetchRequest = [[self fetchedResultsController] fetchRequest];
[fetchRequest setPredicate:nil];
NSError *error = nil;
if (![[self fetchedResultsController] performFetch:&error]) {
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
[self.flowerTableView reloadData];
and reloads the table, all the beautiful flowers are now shown.
Why didn't the flowers be displayed the first time? Is this a caching problem?
When debugging this code the string: 'This debug string was logged after this function was done' was logged after loading the table on starting the app, not after pressing 'Show All'
This means that all images are loaded from the camera roll successfully but attached to the cell after the cell was displayed and therefore not shown.
The same line is printed as intended when pressing 'Show All'
Hope someone can tell me what's going on here and even better, what to change in my code to make this work. I'm stuck at the moment...
Thank for helping me out!
Edwin
:::THE CODE:::
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath (NSIndexPath *)indexPath
{
Flower *flower = [fetchedResultsController_ objectAtIndexPath:indexPath];
static NSString *CellIdentifier = #"Cell";
UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease];
}
// Configure the cell...
// Display the image if one is defined
if (flower.imagePath && ![flower.imagePath isEqualToString:#""])
{
// Should hold image after executing the resultBlock
__block UIImage *image = nil;
ALAssetsLibraryAssetForURLResultBlock resultBlock = ^(ALAsset *asset)
{
NSLog(#"This debug string was logged after this function was done");
image = [[UIImage imageWithCGImage:[asset thumbnail]] retain];
};
ALAssetsLibraryAccessFailureBlock failureBlock = ^(NSError *error)
{
NSLog(#"Unresolved error: %#, %#", error, [error localizedDescription]);
};
[assetsLibrary_ assetForURL:[NSURL URLWithString:flower.imagePath]
resultBlock:resultBlock
failureBlock:failureBlock];
[cell.imageView setImage:image];
}
return cell;
}

Answer 1

-[ALAssetsLibrary assetForURL:resultBlock:failureBlock] runs asynchronously. That means that the call returns immediately in your tableView:cellForRowAtIndexPath: method. The cell is displayed in the table view before the actual loading of the asset has taken place.
What you need to do is set the image for the cell in the result block. Something like this:
if (flower.imagePath && ![flower.imagePath isEqualToString:#""])
{
ALAssetsLibraryAssetForURLResultBlock resultBlock = ^(ALAsset *asset)
{
NSLog(#"This debug string was logged after this function was done");
[cell.imageView setImage:[UIImage imageWithCGImage:[asset thumbnail]]];
//this line is needed to display the image when it is loaded asynchronously, otherwise image will not be shown as stated in comments
[cell setNeedsLayout];
};
ALAssetsLibraryAccessFailureBlock failureBlock = ^(NSError *error)
{
NSLog(#"Unresolved error: %#, %#", error, [error localizedDescription]);
};
[assetsLibrary_ assetForURL:[NSURL URLWithString:flower.imagePath]
resultBlock:resultBlock
failureBlock:failureBlock];
}

Answer 2

Fellow Overflowist let me propose the following solution:
rather than creating your cells in - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath (NSIndexPath *)indexPath
create an NSMutableArray populated with UITableViewCells (the same ones you create in the cellForRowAtIndexPath method) that you want to display in the table
and simply return the relevant UITableViewCell (which will be an object in the NSMutableArray) in the cellForRowAtIndexPath method.
This way the cellForRowAtIndexPath method will show cells which have already been loaded and are ready to be shown.