Make UITableView Smoother - objective-c

Question

I have a UITableView that displays both images and text. Its a social app so I have to retrieve all data from the database, I'm using Parse. Heres the code. I know its long but if you could just skim through it that would be great. I have three different custom cells(nibs) that will be loaded depending on the content. A cell - just a string post, groupPost - also a string post, and a imageCell - for image posts. Im confused on how to make a smoother scroll such as facebooks, or instagrams. How I should load the images, and retrieve the data? Ive looked through posts and seen the recommendation of caching it but not exactly sure how to do that. Thanks for the help
postCell *cell = (postCell *)[tableView dequeueReusableCellWithIdentifier:#"postCell"];
groupPostCell *groupPost = (groupPostCell *) [self.tableView dequeueReusableCellWithIdentifier:#"groupPostCell"];
pictureCell *imageCell = (pictureCell *) [self.tableView dequeueReusableCellWithIdentifier:#"imageCell"];
PFObject *object = [self.friendPosts objectAtIndex:indexPath.row];
if ([object objectForKey:#"Image"] != nil) {
if (imageCell == nil) {
imageCell = [[pictureCell alloc]initWithStyle:UITableViewCellStyleDefault reuseIdentifier:#"imageCell"];
}
PFFile *file = [object objectForKey:#"Image"];
NSData *data = [file getData];
imageCell.imagePost.image = [UIImage imageWithData:data];
imageCell.caption.text = [object objectForKey:#"stringPost"];
PFFile *profileFile = [object objectForKey:#"profileImage"];
NSData *profileData = [profileFile getData];
imageCell.profileImage.image = [UIImage imageWithData:profileData];
[imageCell.name setTitle:[object objectForKey:#"User_Name"] forState:UIControlStateNormal];
[imageCell.eventButton setTitle:[object objectForKey:#"Event"] forState:UIControlStateNormal];
imageCell.name.hidden = false;
imageCell.eventButton.hidden = false;
imageCell.name.tag = indexPath.row;
imageCell.profileImageButton.tag = indexPath.row;
imageCell.eventButton.tag = indexPath.row;
[imageCell.name addTarget:self action:#selector(buttonPressed:) forControlEvents:UIControlEventTouchUpInside];
[imageCell.profileImageButton addTarget:self action:#selector(buttonPressed:) forControlEvents:UIControlEventTouchUpInside];
[imageCell.eventButton addTarget:self action:#selector(eventPage:) forControlEvents:UIControlEventTouchUpInside];
NSArray *likesArray = [object objectForKey:#"likes"];
NSString *likeString = [NSString stringWithFormat:#"%lu Likes", (unsigned long)likesArray.count];
if ([likesArray containsObject:[PFUser currentUser].objectId]) {
imageCell.rateButton.hidden = true;
}
else{
imageCell.rateButton.hidden = false;
}
NSArray *commentArray = [object objectForKey:#"Comments"];
NSString *commentString = [NSString stringWithFormat:#"%lu Comments", (unsigned long)commentArray.count];
[imageCell.likesButton setTitle:likeString forState:UIControlStateNormal];
[imageCell.commentsButton setTitle:commentString forState:UIControlStateNormal];
imageCell.rateButton.tag = indexPath.row;
imageCell.likesButton.tag = indexPath.row;
imageCell.commentsButton.tag = indexPath.row;
imageCell.flagButton.tag = indexPath.row;
[imageCell.rateButton addTarget:self action:#selector(like:) forControlEvents:UIControlEventTouchUpInside];
[imageCell.likesButton addTarget:self action:#selector(likesPage:) forControlEvents:UIControlEventTouchUpInside];
[imageCell.commentsButton addTarget:self action:#selector(imageComment:) forControlEvents:UIControlEventTouchUpInside];
[imageCell.flagButton addTarget:self action:#selector(flagPost:) forControlEvents:UIControlEventTouchUpInside];
[imageCell.timeButton setTitle:[self getDaysBetween:object.createdAt] forState:UIControlStateNormal];
return imageCell;
}
if ([object objectForKey:#"Group"] == nil) {
if (cell == nil) {
cell = [[postCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:#"postCell"];
}
cell.personStringPost.text = [object objectForKey:#"stringPost"];
if ([object objectForKey:#"Event"] == nil) {
[cell.noEventNameButton setTitle:[object objectForKey:#"User_Name"] forState:UIControlStateNormal];
cell.noEventNameButton.tag = indexPath.row;
[cell.noEventNameButton addTarget:self action:#selector(buttonPressed:) forControlEvents: UIControlEventTouchUpInside];
cell.nameLabel.hidden = true;
cell.eventLabel.hidden = true;
cell.noEventNameButton.hidden = false;
}
else{
[cell.nameLabel setTitle:[object objectForKey:#"User_Name"] forState:UIControlStateNormal];
cell.nameLabel.tag = indexPath.row;
[cell.nameLabel addTarget:self action:#selector(buttonPressed:) forControlEvents: UIControlEventTouchUpInside];
cell.noEventNameButton.hidden = true;
cell.nameLabel.hidden = false;
cell.eventLabel.hidden = false;
[cell.eventLabel setTitle:[object objectForKey:#"Event"] forState:UIControlStateNormal];
[cell.eventLabel addTarget:self action:#selector(eventPage:) forControlEvents:UIControlEventTouchUpInside];
}
[cell.timeLabel setTitle:[self getDaysBetween:object.createdAt] forState:UIControlStateNormal];
PFFile *imageFile = [object objectForKey:#"profileImage"];
NSData *data = [imageFile getData];
cell.profileImage.image = [UIImage imageWithData:data];
NSArray *likesArray = [object objectForKey:#"likes"];
NSString *likeString = [NSString stringWithFormat:#"%lu Likes", (unsigned long)likesArray.count];
if ([likesArray containsObject:[PFUser currentUser].objectId]) {
cell.likeButton.hidden = true;
}
else{
cell.likeButton.hidden = false;
}
NSArray *commentArray = [object objectForKey:#"Comments"];
NSString *commentString = [NSString stringWithFormat:#"%lu Comments", (unsigned long)commentArray.count];
[cell.likePage setTitle:likeString forState:UIControlStateNormal];
[cell.commentButton setTitle:commentString forState:UIControlStateNormal];
cell.eventLabel.tag = indexPath.row;
cell.profileImageButton.tag = indexPath.row;
cell.likeButton.tag = indexPath.row;
cell.commentButton.tag = indexPath.row;
cell.likePage.tag = indexPath.row;
cell.flagButton.tag = indexPath.row;
[cell.flagButton addTarget:self action:#selector(flagPost:) forControlEvents:UIControlEventTouchUpInside];
[cell.profileImageButton addTarget:self action:#selector(buttonPressed:) forControlEvents:UIControlEventTouchUpInside];
[cell.likePage addTarget:self action:#selector(likesPage:) forControlEvents:UIControlEventTouchUpInside];
[cell.likeButton addTarget:self action:#selector(like:) forControlEvents:UIControlEventTouchUpInside];
[cell.commentButton addTarget:self action:#selector(commentsPage:) forControlEvents:UIControlEventTouchUpInside];
return cell;
}
if ([object objectForKey:#"Group"] != nil) {
if (groupPost == nil) {
groupPost = [[groupPostCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:#"groupPostCell"];
}
[groupPost.groupNameButton setTitle:[object objectForKey:#"Group"] forState:UIControlStateNormal];
groupPost.groupNameButton.tag = indexPath.row;
[groupPost.groupNameButton addTarget:self action:#selector(groupPage:) forControlEvents:UIControlEventTouchUpInside];
[groupPost.groupNameButton setTitleColor:[self checkType:[object objectForKey:#"Type"]] forState:UIControlStateNormal];
NSArray *likesArray = [object objectForKey:#"likes"];
NSString *likeString = [NSString stringWithFormat:#"%lu Likes", (unsigned long)likesArray.count];
if ([likesArray containsObject:[PFUser currentUser].objectId]) {
groupPost.likeButton.hidden = true;
}
else{
groupPost.likeButton.hidden = false;
}
NSArray *commentArray = [object objectForKey:#"Comments"];
NSString *commentString = [NSString stringWithFormat:#"%lu Comments", (unsigned long)commentArray.count];
[groupPost.likePage setTitle:likeString forState:UIControlStateNormal];
[groupPost.commentsButton setTitle:commentString forState:UIControlStateNormal];
groupPost.likePage.tag = indexPath.row;
groupPost.likeButton.tag = indexPath.row;
groupPost.commentsButton.tag = indexPath.row;
[groupPost.likeButton addTarget:self action:#selector(like:) forControlEvents:UIControlEventTouchUpInside];
[groupPost.likePage addTarget:self action:#selector(likesPage:) forControlEvents:UIControlEventTouchUpInside];
[groupPost.commentsButton addTarget:self action:#selector(commentsPage:) forControlEvents:UIControlEventTouchUpInside];
if ([object objectForKey:#"Event"] == nil) {
groupPost.eventButton.hidden = true;
}
else{
groupPost.eventButton.hidden = false;
[groupPost.eventButton setTitle:[object objectForKey:#"Event"] forState:UIControlStateNormal];
groupPost.eventButton.tag = indexPath.row;
[groupPost.eventButton addTarget:self action:#selector(eventPage:) forControlEvents:UIControlEventTouchUpInside];
}
groupPost.flagButton.tag = indexPath.row;
[groupPost.flagButton addTarget:self action:#selector(flagPost:) forControlEvents:UIControlEventTouchUpInside];
[groupPost.timeButton setTitle:[self getDaysBetween:object.createdAt] forState:UIControlStateNormal];
groupPost.postLabel.text = [object objectForKey:#"stringPost"];
return groupPost;
}

Answer 1

Whenever you're working with data on a server, try to avoid, at all costs, loading that data synchronously. The line that says
NSData *data = [imageFile getData];[imageFile getData];
will make it so that nothing else can execute on the main thread until the data is done downloading. Here's how you should do it:
[imageFile getDataInBackgroundWithBlock:^(NSData *imageData, NSError *error) {
if (!error) {
cell.profileImage.image = [UIImage imageWithData:imageData];
}
}];
That will make it so that all other code executes on the main thread and then when the data finishes downloading THEN it will load in the image. I would suggest putting a placeholder or loading view in the "cell.profileImage" and then when the image loads from Parse, it'll overwrite that placeholder.