Automatically refresh image using parse - ios

Question

I am showing an several images using an UIScrollView. however I would want it to refresh automatically.
I want to refresh it every time I show the view controller.
Using my code I have to push the refresh button every time which is just nonsense.
Here is the code : How can i do this ?
- (IBAction)refresh:(id)sender
{
NSLog(#"Showing Refresh HUD");
refreshHUD = [[MBProgressHUD alloc] initWithView:self.view];
[self.view addSubview:refreshHUD];
// Register for HUD callbacks so we can remove it from the window at the right time
refreshHUD.delegate = self;
// Show the HUD while the provided method executes in a new thread
[refreshHUD show:YES];
PFQuery *query = [PFQuery queryWithClassName:#"TPhoto"];
PFUser *user = [PFUser currentUser];
[query whereKey:#"user" equalTo:user];
[query orderByAscending:#"createdAt"];
[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
if (!error) {
// The find succeeded.
if (refreshHUD) {
[refreshHUD hide:YES];
refreshHUD = [[MBProgressHUD alloc] initWithView:self.view];
[self.view addSubview:refreshHUD];
// The sample image is based on the work by http://www.pixelpressicons.com, http://creativecommons.org/licenses/by/2.5/ca/
// Make the customViews 37 by 37 pixels for best results (those are the bounds of the build-in progress indicators)
refreshHUD.customView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"37x-Checkmark.png"]];
// Set custom view mode
refreshHUD.mode = MBProgressHUDModeCustomView;
refreshHUD.delegate = self;
}
NSLog(#"Successfully retrieved %d photos.", objects.count);
// Retrieve existing objectIDs
NSMutableArray *oldCompareObjectIDArray = [NSMutableArray array];
for (UIView *view in [photoScrollView subviews]) {
if ([view isKindOfClass:[UIButton class]]) {
UIButton *eachButton = (UIButton *)view;
[oldCompareObjectIDArray addObject:[eachButton titleForState:UIControlStateReserved]];
}
}
NSMutableArray *oldCompareObjectIDArray2 = [NSMutableArray arrayWithArray:oldCompareObjectIDArray];
// If there are photos, we start extracting the data
// Save a list of object IDs while extracting this data
NSMutableArray *newObjectIDArray = [NSMutableArray array];
if (objects.count > 0) {
for (PFObject *eachObject in objects) {
[newObjectIDArray addObject:[eachObject objectId]];
}
}
// Compare the old and new object IDs
NSMutableArray *newCompareObjectIDArray = [NSMutableArray arrayWithArray:newObjectIDArray];
NSMutableArray *newCompareObjectIDArray2 = [NSMutableArray arrayWithArray:newObjectIDArray];
if (oldCompareObjectIDArray.count > 0) {
// New objects
[newCompareObjectIDArray removeObjectsInArray:oldCompareObjectIDArray];
// Remove old objects if you delete them using the web browser
[oldCompareObjectIDArray removeObjectsInArray:newCompareObjectIDArray2];
if (oldCompareObjectIDArray.count > 0) {
// Check the position in the objectIDArray and remove
NSMutableArray *listOfToRemove = [[NSMutableArray alloc] init];
for (NSString *objectID in oldCompareObjectIDArray){
int i = 0;
for (NSString *oldObjectID in oldCompareObjectIDArray2){
if ([objectID isEqualToString:oldObjectID]) {
// Make list of all that you want to remove and remove at the end
[listOfToRemove addObject:[NSNumber numberWithInt:i]];
}
i++;
}
}
// Remove from the back
NSSortDescriptor *highestToLowest = [NSSortDescriptor sortDescriptorWithKey:#"self" ascending:NO];
[listOfToRemove sortUsingDescriptors:[NSArray arrayWithObject:highestToLowest]];
for (NSNumber *index in listOfToRemove){
[allImages removeObjectAtIndex:[index intValue]];
}
}
}
// Add new objects
for (NSString *objectID in newCompareObjectIDArray){
for (PFObject *eachObject in objects){
if ([[eachObject objectId] isEqualToString:objectID]) {
NSMutableArray *selectedPhotoArray = [[NSMutableArray alloc] init];
[selectedPhotoArray addObject:eachObject];
if (selectedPhotoArray.count > 0) {
[allImages addObjectsFromArray:selectedPhotoArray];
}
}
}
}
// Remove and add from objects before this
[self setUpImages:allImages];
} else {
[refreshHUD hide:YES];
// Log details of the failure
NSLog(#"Error: %# %#", error, [error userInfo]);
}
}];
}

Answer 1

Call the refresh method from viewDidAppear in your view controller.
However, if that can happen often, you should consider keeping the images in a local cache and only refresh them if there is something new to show on the server.