Passing a UIImage from a viewcontroller to another - ios

Question

I want to pass a UIImage from a View Controller to another one, but it doesn't work. I actually get (null) if I log the UIImage Value in the second View Controller.
The Image File comes from parse.com. And it works absolutely fine in the first view controller. But as soon as I pass it to the second view controller, the image won't work there.
Here's the code:
My prepareForSegue in the .m file of the firstViewController (BookListTableViewController)
- (void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifier isEqualToString:#"ShowBookDetailSegue"]) {
NSIndexPath *indexPath = [self.bookListTableView indexPathForSelectedRow];
ParseBookDetailTableViewController *pbdtvc = segue.destinationViewController;
PFObject *tempObject = [totalStrings objectAtIndex:indexPath.row];
PFFile *eventImage = [tempObject objectForKey:#"bookImage"];
if(eventImage != NULL)
{
[eventImage getDataInBackgroundWithBlock:^(NSData *imageData, NSError *error)
{
UIImage *thumbnailImage = [UIImage imageWithData:imageData];
pbdtvc.bookImageDetail = thumbnailImage;
}];
}
my .h file of the secondViewController (ParseBookDetailViewController)
#property (strong, nonatomic) UIImage* bookImageDetail;
#property (strong, nonatomic) IBOutlet UIImageView *bookImageDetailView;
viewDidLoad of my .m file of the secondViewController (ParseBookDetailViewController)
NSLog(#"%#",bookImageDetail);
[bookImageDetailView setImage:bookImageDetail];
As I said: in the original View Controller the Image is correct. I can log it and even set it there to an ImageView. But in the second view controller there is (null).
Glad for help, thanks..
EDIT:
This is the code from my cellForRowAtIndexPath.
PFObject *tempObject = [totalStrings objectAtIndex:indexPath.row];
//cell.textLabel.text = [tempObject objectForKey:#"bookTitle"];
cell.titleTextField.text = [tempObject objectForKey:#"bookTitle"];
cell.bookAutor1Label.text = [tempObject objectForKey:#"bookAutor1"];
cell.isbnLabel.text = [tempObject objectForKey:#"bookISBN"];
cell.statusLabel.text = [tempObject objectForKey:#"bookStatus"];
cell.yearLabel.text = [tempObject objectForKey:#"BookDate"];
if ([cell.statusLabel.text isEqualToString:#"nicht verfügbar"]) {
cell.statusLabel.tintColor = [UIColor redColor];
cell.dotImageIcon.image = [UIImage imageNamed:#"dot_red.png"];
}else if ([cell.statusLabel.text isEqualToString:#"verfügbar"]){
cell.statusLabel.tintColor = [UIColor greenColor];
cell.dotImageIcon.image = [UIImage imageNamed:#"dot_green.png"];
}
PFFile *eventImage = [tempObject objectForKey:#"bookImage"];
if(eventImage != NULL)
{
[eventImage getDataInBackgroundWithBlock:^(NSData *imageData, NSError *error)
{
UIImage *thumbnailImage = [UIImage imageWithData:imageData];
prepareForSegueImage = thumbnailImage;
[cell.bookImageView setImage:thumbnailImage];
}];
}
At the bottom I have set the Image (that works) in a new property (prepareForSegueImage). NOW its loaded.
And now I've tried to pass only the prepareForSegueImage to the new view controller, but it actually doesn't pass the one from the cell, it passes the last one loaded in the whole table view from the first view controller.

Answer 1

I'm guessing:
[eventImage getDataInBackgroundWithBlock:^(NSData *imageData, NSError *error)
{
UIImage *thumbnailImage = [UIImage imageWithData:imageData];
pbdtvc.bookImageDetail = thumbnailImage;
}];
is an asynchronous request happening in the background, that will take some time to return. But your code is expecting it to happen instantly.
Load the image first and call the segue in the completion block,
EDIT
If it works in the first viewController (meaning you have the image) why are you requesting it again? why not simply pass the image you already have?
EDIT 2:
As explained in my comment, your variable is being overwritten each time the cellForRowAtindexPath is called. You could either wrap that code in an if statement, checking for an index or a certain image etc. or you can use the below code to get a specific cell and pull the image form that.
[tblView cellForRowAtIndexPath: [NSIndexPath indexPathForRow:2 inSection:0]];
If you have the image downloaded and have a relatively easy means of getting a reference to it you should not be downloading it again. This could cost the user on a 3G data plan as well as waste resources.

Answer 2

This happens because you are using the getDataInBackgroundWithBlock, which is an asynchronous call. As this happens in a background thread, it is probably not finished when you segue to the other viewcontroller.
You said it works fine in the first controller. I assume this means you have already downloaded the image. Put that in a property instead, and send this property to the next controller.