Let me get disclosure out of the way first: I'm just beginning iOS programming, furthermore I am a student and this is homework.
The project I am currently doing requires the creation of a Table View with custom cells in it. I've achieved that. However, it also requires putting the Table View into edit mode for deleting stuff (i.e. making the red icon thingies appear). That is something I haven't achieved. Here is the code directly used to change the editing mode. (view is the tv, it's wired to a UIButton)
-(IBAction)toggleEdit:(id)sender
{
if(isEditing)
{
NSLog(#"true");
isEditing = false;
[view setEditing:false];
}
else
{
NSLog(#"false");
isEditing = true;
[view setEditing:true];
}
}
Cell Allocation code:
-(UITableViewCell*)tableView:(UITableView*)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString* cellID = #"Cell";
ShipCell *cell = [tableView dequeueReusableCellWithIdentifier:cellID];
if (!cell)
{
NSArray* views = [[NSBundle mainBundle] loadNibNamed:#"ShipCellView" owner:self options:nil];
cell = [views objectAtIndex:0];
}
cell.nameLabel.text = [dataController getNameAtIndex:indexPath.row];
cell.operatorLabel.text = [dataController getOperatorAtIndex:indexPath.row];
cell.flagImage.image = [dataController getFlagAtIndex:indexPath.row];
return cell;
}
Relevant UIBuilder screenshots:
I've been through my school-appointed iOS5 textbook (building for iOS6), as well as a lot of the school videos, which say my current code will work. (which it does in terms of displaying custom cells, but not for showing the editing icons.)
Full Source (of relevant files) for sake of completion:
http://pastebin.com/upLYXz4i
The controller for the cell nib is boilerplate.
The problem came from me using a pseudo-reserved keyword for one of my outlets; changing it resolved the problem.
To be specific, I named an outlet view, which isn't a great thing to do.
Related
I have a class that defines a custom contact cell called ContactItemCell and a xib file that lays out that cell. When I create the table view it opens up and six of these ContactItemCell classes are created. When I navigate back they aren't deallocated, and when I open the tableview again another 6 are created. Here's the tableview code:
- (UITableViewCell *)tableView:(UITableView *)tableView
cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
Contact* contact = [self contactAtIndexPath:indexPath];
static NSString *cellID = #"ContactItemWithTagsForBothCell";
ContactItemCell *cell = [tableView dequeueReusableCellWithIdentifier:cellID];
if (cell == nil)
{
NSArray *arr = [[NSBundle mainBundle] loadNibNamed:#"ContactItemWithTagsForBothCell" owner:nil options:nil];
if (arr.count <= 0)
{
NSLog(#"couldnt find cell with ID: %#", cellID);
return nil;
}
cell = [arr firstObject];
}
[cell configureCellForContact:contact];
return cell;
}
The fileowner in the xib file is just set to be blank which I'm assuming means NSObject. I've tried looking for a strong reference cycle to see if the class is kept alive by pointers but I haven't seen anything after days of investigation. I'm really at my limit and I'm not sure what else I can do, I've been using instruments too and that's how I've figured out that they're being created 6 at a time but I can't find out what's pointing to them. Why is this happening? Am I doing something wrong with the table view? If I'm not and you think it's a strong reference cycle then how can I find every object that points to this ContactItemCell? Thanks in advance!
If anyone was curious I used the memory debugger and found that there was a strong reference cycle with a pod I was using.
I have an app with some posts placed at an UITableView. Each post have a favorite button and I need to change its image when the user clicks on it. Here are the code:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *identifier = #"identifier";
CustomCell *cell = (CustomCell *)[tableView dequeueReusableCellWithIdentifier:identifier];
if(cell == nil){
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"myNib" owner:self options:nil];
cell = [nib objectAtIndex:0];
}
NSDictionary *post = [posts objectAtIndex:indexPath.row];
[cell.likeButton addTarget:self
action:#selector(clickedOnLike:)
forControlEvents:UIControlEventTouchUpInside];
cell.likeButton.tag = indexPath.row;
And on click handler:
-(IBAction)clickedOnLike:(id)sender
{
int tag = buttonSender.tag;
NSDictionary *post = [posts objectAtIndex:tag];
if( ![self likedAlready:post] ){
//set liked on this view...
//update view
NSLog(#"button: %#",buttonSender);
[sender setImage:[UIImage imageNamed:#"newImage.png"] forState:UIControlStateNormal];
//send like to server...
}
}
At this point, everything is going alright. The problem is, after click a button, update the view and scroll to other cells, the other buttons views I never clicked are updated too. For example, when I click a button at indexPath 1, the ones at 5 and 9 change their images automatically. This is a mistery to me, since I call the action sender directly and update only it. Thanks for help.
The reusable cell do it: dequeueReusableCellWithIdentifier.
U need to deal manually with things like this.
U can invoke manually to your clickedOnLike: method from the CellForRowAtIndexPath:
Try to maintain inside your modal (from your MVC development architecture), and access there from the CellForRowAtIndexPath:
That will solve your problem :)
Good Luck!
In your cellForRowAtIndexPath, set the default image of your button, then change it if its a favorite. The rows tend to get cached so always set your data to what you expect it to be.
As others have said, the problem is because the view is recycled for everyline, and in the recycled copy the button may have had its picture changed to the new one.
you need to keep somewhere in memory the status of the post, and on the cellForRowAtIndexpath set the correct image for the button every time the row is rendered.
Alternatively, if you have a very small number of posts, just eliminate recycling by doing
static NSString *identifier = nil;
I'm newbie in IOS and again i face another issue. How can i prevent data vanish from a table cell when i scroll a tableview.
I'm using the code below to load data on the table...Works fine but the data disappear when table cell go in not visible to the screen.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
list = [self.listas objectAtIndex:[indexPath row]];
static NSString *CellIdentifier = #"drop";
item_drop *cell = (item_drop*) [tabela_listas dequeueReusableCellWithIdentifier:CellIdentifier];
if (cell == nil) {
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"item_drop" owner:self options:nil];
cell = [nib objectAtIndex:0];
}
cell.texto_drop.text = list.nome_lista;
return cell;
}
In android i used a holder to do it. There is anything similiar on IOS?
Since you are using reusable cells of a custom subclass of UITableViewCell, make sure you register the cell identifier in the UITableView, associating it to your custom cell type. i.e:
[yourTableView registerClass:[item_drop class] forCellReuseIdentifier:#"drop"];
You typically do this when you configure subviews in the UIViewController that controls the view your UITableView is a part of, in viewDidLoad.
With that in place, you should never hit the code inside if (cell == nil).
I am using the same code in two of my view controllers (they are implementing the same class what changes is the url they download) and in one occassion the image is displayed correclty while in the other I do see an empty cell.
Here is my code:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
static NSString *simpleTableIdentifier=#"MyCell";
//this is the identifier of the custom cell
MyCell *cell = (MyCell *)[tableView dequeueReusableCellWithIdentifier:simpleTableIdentifier];
tableView.backgroundColor=[UIColor clearColor];
tableView.opaque=NO;
tableView.backgroundView=nil;
if (cell == nil)
{
NSArray *nib = [[NSBundle mainBundle] loadNibNamed:#"MyCell" owner:self options:nil];
cell = [nib objectAtIndex:0];
}
NSLog(#"Image url is:%#",[images_url objectAtIndex:indexPath.row]);
NSURL *url_image=[NSURL URLWithString:[images_url objectAtIndex:indexPath.row]];
cell.myimage.image=[UIImage imageWithData:[NSData dataWithContentsOfURL:url_image]];
return cell;
}
As i told you I have 2 view controllers implementing the same class. In the view did load the url is set depending on the value of a flag. If I open controller A, I see no image, if I open view B i can see the image. Both of the urls are correct as I can check it with the NSLog I have inserted.
What might be the problem?
Unfortunately calling "NSData dataWithContentsOfURL" is a blocking call. Execution of your program will stop until iOS is able to fetch all the data from the server or fails trying. This may often be "fast" if you're on LTE or WiFi; but can potentially take a LONG time.
Meanwhile, you're on the "main thread" in your app - so your app will appear to freeze-up, and the system's watchdog timer may kill your app. If anyone besides you will use this ap, you absolutely need to populate your tableview cell's image with local data that's retrieved immediately or use asynchronous methods.
Just google for "lazy load UIImage". This SO question has some good tips on the subject:
lazy-load-images-in-uitableview
Additionally, you should move these lines to some setup code. You don't need to perform them every time to update a cell:
tableView.backgroundColor=[UIColor clearColor];
tableView.opaque=NO;
tableView.backgroundView=nil;
Best of luck!
Whenever I scroll my tableview it is very laggy. I think it has to do with how I am loading up my cells. I use UINib (5.0+) whenever I can while still providing backwards compatibility. Then I load my custom cell's labels and images with items from a NSDictionary from a NSArray which is loaded from NSUserDefaults in the ViewDidLoad.
Is there any way to improve the efficiency of this cellForRowAtIndexPath?
- (UITableViewCell *)tableView:(UITableView *)aTableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
CustomCell *cell = (CustomCell *)[aTableView dequeueReusableCellWithIdentifier:#"Cell"];
if (cell == nil) {
if ([self labelCellNib]) {
[[self labelCellNib] instantiateWithOwner:self options:nil];
} else {
[[NSBundle mainBundle] loadNibNamed:#"CustomCell" owner:self options:nil];
}
cell = [self CustomTableCell];
[self setCustomTableCell:nil];
}
NSDictionary *dictionary = [myArray objectAtIndex:indexPath.row];
NSData *data = [dictionary objectForKey:#"OCRImage"];
cell.previewPicture.image = [self roundCorneredImage:[UIImage imageWithData:data] radius:60];
cell.titleLabel.text = [dictionary objectForKey:#"Title"];
cell.titleLabel.delegate = self;
cell.dateLabel.text = [dictionary objectForKey:#"Date"];
if (indexPath.row%2) {
cell.backgroundImage.image = firstImage;
}
else {
cell.backgroundImage.image = secondImage;
}
return cell;
}
Edit:
- (UIImage*)roundCorneredImage: (UIImage*)orig radius:(CGFloat) r {
UIGraphicsBeginImageContextWithOptions(orig.size, NO, 0);
[[UIBezierPath bezierPathWithRoundedRect:(CGRect){CGPointZero, orig.size}
cornerRadius:r] addClip];
[orig drawInRect:(CGRect){CGPointZero, orig.size}];
UIImage* result = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return result;
}
Edit2: These are the lines that are causing the lag:
NSData *data = [dictionary objectForKey:#"OCRImage"];
cell.previewPicture.image = [self roundCorneredImage:[UIImage imageWithData:data] radius:60];
As #Till said in a comment, you should launch your app in Instruments (Product -> Profile in Xcode), and select the CPU -> Time Profiler instrument.
Then, scroll around over the place for a few seconds, then hit the Record toolbar icon in instruments to close your app. You will be able to see the scrolling section because CPU usage will probably be pinned at 100% (unless it's slow because of network activity problem).
Click on the timeline after the start of the high CPU activity area, and click the "start inspection range" toolbar button, then click before the end of the high CPU activity area and click the "stop inspection range" toolbar button.
You can now drill down into the call tree view at the bottom of the window to figure out exactly where all your CPU usage is. In my experience it's usually easier to find the problem if you turn off "invert call tree" option on the left.
Performance bugs can be very hard to find, and sometimes a line of code that is obviously slow actually isn't causing any problems at all. The only way to fix performance issues without wasting time is to use Instruments.
Make sure that you've set the reuse identifier for your cell to the same thing that you've specified in your code, i.e. #"Cell". If they don't match, then you won't be reusing cells properly, and probably spending a lot more time creating cells than necessary.
If you are properly recycling cells, then you should take a look at the code after the if (cell == nil) {...} block. You'll be skipping that entire block once the table has created enough cells to fill the screen (and maybe one or two more), so most of the time attributable to this method while scrolling will be due to the following code. It'd be interesting to know what myArray is, and if it's actually an array, what the objectForKey: method does. Nothing else there looks like it should take a long time, but the best way to find out where the cycles are going is to profile your code in Instruments.
Some of my notes after looking at your code:
Is roundCorneredImage:radius: caching the result? If not, executing CG calls for every cell would surely present a bottleneck. Updated: Use instruments to be sure, but it might be faster (memory allowing) to store the processed UIImage in a collection so that you can pull it out again the next time that method is called with the same parameters.
All of your UIImages could be declared elsewhere and then presented in this method. Your current code instantiates a new UIImage for each cell which can also bottleneck your scrolling. Updated: Since Image1.png and Image2.png are basically static, you could declare them in your interface or as a static ivar and then just assign them to the background image rather than instantiating UIImage each time.
It may be faster to subclass UITableViewCell and instantiate that instead of reaching into UINib. Also, you'd then be able to separate your layout/data logic from the delegate method. Here's a gist of what I did in my UITableViewCell subclass. Basically, I store the entity with the cell and the cell knows about it's labels and such. This keeps the cell layout logic out of my data source code.
It looks like you're using an NSDictionary as your data source. If you have a lot of objects in that dictionary, it may be considerable faster to use CoreData and an NSFetchedResultsController. Here's a good post on the matter. Updated: Ok, that shouldn't be an issue.
-
Edit
So if you removed all of this:
NSDictionary *dictionary = [myArray objectForKey:#"OCRImage"];
cell.previewPicture.image = [self roundCorneredImage:[UIImage imageWithData:data] radius:60];
if (indexPath.row%2) {
cell.backgroundImage.image = firstImage;
}
else {
cell.backgroundImage.image = secondImage;
}
and it still lags, let's look at your constructors...what do these lines do?
cell = [self CustomTableCell];
[self setCustomTableCell:nil];
Also, you're not using any transparent images or anything in your table cell are you? Those have been known to cause drawing lag...
-
Edit #2
If you strip down to this, what happens?
CustomCell *cell = (CustomCell *)[aTableView dequeueReusableCellWithIdentifier:#"Cell"];
if (cell == nil) {
if ([self labelCellNib]) {
[[self labelCellNib] instantiateWithOwner:self options:nil];
} else {
[[NSBundle mainBundle] loadNibNamed:#"CustomCell" owner:self options:nil];
}
cell = [self CustomTableCell];
[self setCustomTableCell:nil];
}
cell.titleLabel.text = [dictionary objectForKey:#"Title"];