In my viewDidLoad, I have self.todaySession = (id)[fetchedResultsController objectAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]]; which works fine when it finds this object. But when it doesn't, it crashes the app. Is there a logic statemnt I can do to fix this?
There are a few ways of doing this depending on the context.
You can use the count of fetchedObjects or sections from the NSFetchedResultsController. Make sure you call performFetch: beforehand.
[fetchedResultsController performFetch:self];
// Option 1
BOOL someResultsReturned = ([[fetchedResultsController fetchedObjects] count] > 0);
// Option 2
BOOL someResultsReturned = ([[fetchedResultsController sections] count] > 0);
if (someResultsReturned) {
self.todaySession = (id)[fetchedResultsController objectAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0]];
} else {
// Handle no results here
}
More Information
Read more about NSFetchedResultsController here.
Related
TL:DR version: I used NSZombieEnabled to find source of EXC_BAD_ACCESS error and saw a library has 1 more release than retains. Can I assume that this library is causing the crash or can that release be associated with a retain from another library?
I am having some problems in my app with a UITableViewCell subclass instance getting messages after its retain count reaches 0. I ran the app with NSZombies and am currently trying to pair the retain/release calls to find where exactly is the error originating from. I noticed that there are only 2 retains and 3 releases with "Responsible Library" set to QuartzCore. Does it mean that that extra release call is the one that causes my app to crash? Or is it possible that a release has associated retain in another library?
Additional info:
My section headers are tappable, when one is selected, the row for this section is inserted into table view and any previously visible row is deleted. In other words, there can be only 1 section at a time that has 1 row, all other sections must have 0 rows.
The release/retain calls from QuartzCore that I paired are:
CALayer layoutSublayers (retains)
CA::Layer::layout_if_needed(CA::Transaction*) (releases)
The release without a pair is:
CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*)
The exact line where I get the crash is the endUpdates line in:
- (void)sectionHeaderView:(SectionHeaderView *)sectionHeaderView sectionOpened:(NSInteger)sectionOpened {
SectionInfo *sectionInfo = [self.sectionInfoArray objectAtIndex:sectionOpened];
sectionInfo.open = YES;
NSMutableArray *indexPathsToInsert = [[NSMutableArray alloc] init];
[indexPathsToInsert addObject:[NSIndexPath indexPathForRow:0 inSection:sectionOpened]];
/*
Create an array containing the index paths of the rows to delete: These correspond to the rows for each quotation in the previously-open section, if there was one.
*/
NSMutableArray *indexPathsToDelete = [[NSMutableArray alloc] init];
NSInteger previousOpenSectionIndex = self.openSectionIndex;
if (previousOpenSectionIndex != NSNotFound) {
SectionInfo *previousOpenSection = [self.sectionInfoArray objectAtIndex:previousOpenSectionIndex];
previousOpenSection.open = NO;
previousOpenSection.category.model = nil;
[previousOpenSection.headerView toggleOpenWithUserAction:NO];
[indexPathsToDelete addObject:[NSIndexPath indexPathForRow:0 inSection:previousOpenSectionIndex]];
}
// Style the animation so that there's a smooth flow in either direction.
UITableViewRowAnimation insertAnimation;
UITableViewRowAnimation deleteAnimation;
if (previousOpenSectionIndex == NSNotFound || sectionOpened < previousOpenSectionIndex) {
insertAnimation = UITableViewRowAnimationTop;
deleteAnimation = UITableViewRowAnimationBottom;
}
else {
insertAnimation = UITableViewRowAnimationBottom;
deleteAnimation = UITableViewRowAnimationTop;
}
NSIndexPath *indexToDelete = [indexPathsToDelete firstObject], *indexToInsert = [indexPathsToInsert firstObject];
if (indexToDelete == nil) {
NSLog(#"no row to delete");
}
else {
NSLog(#"deleting row %d section %d", [indexToDelete row], [indexToDelete section]);
}
NSLog(#"inserting row %d section %d", [indexToInsert row], [indexToInsert section]);
// Apply the updates.
[self.tableView beginUpdates];
[self.tableView insertRowsAtIndexPaths:indexPathsToInsert withRowAnimation:insertAnimation];
[self.tableView deleteRowsAtIndexPaths:indexPathsToDelete withRowAnimation:deleteAnimation];
[self.tableView endUpdates]; // this is the crash.
self.openSectionIndex = sectionOpened;
[self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:sectionOpened] atScrollPosition:UITableViewScrollPositionNone animated:YES];
}
The error happens on iOS7.
You can get a EXC_BAD_ACCESS at the endUpdates line if the index paths in the arrays are invalid (e.g. a section number of -1). You should NSLog your indexPathsToInsert and indexPathsToDelete and make sure they have valid values in them.
I have already found a fix to this problem. It seems that one of the subviews of the table cell was calling becomeFirstResponder after an asynchronous request has ended. Of course if the cell was freed already by that moment, the crash happened. I just assumed at first that the problem is because of unbalance in retains and releases but looks like that wasn't it.
And to answer the question in title: When running with NSZombieEnabled Instruments app already pair some retain/releases when it can assume they are connected. On one of the runs of my app, Instruments joined paired that release coming from QuartzCore with a retain coming from UIKit. Even though I can't be 100% sure that it's right, I assume that "Responsible library" tags being identical is not obligatory.
TL:DR - I'm pretty sure that retain can be paired with release coming from another library.
I created a UITableView that contains custom section header views. Now, I want it to display a bit more data on the uppermost current visible section. I plan to use the event scrollViewDidEndDecelerating to update the section headers. Currently, the problem is that I cannot set the section header height for a specific section number.
I did try using heightForHeaderInSection beforehand, but the app just crashes with the following output:
'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array'
I was using the code:
- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section
{
if (tableView == self.tableView)
{
NSArray *visibleCells = [self.tableView visibleCells];
NSMutableArray *visibleSections = [[NSMutableArray alloc] init];
for (NSInteger index = 0; index < [visibleCells count]; index++)
{
UITableViewCell *currentCell = [visibleCells objectAtIndex:index];
NSIndexPath *currentPath = (NSIndexPath *)[self.tableView indexPathForCell:currentCell];
if (![visibleSections containsObject:[NSNumber numberWithInt:currentPath.section]])
{
[visibleSections addObject:[NSNumber numberWithInt:currentPath.section]];
NSLog([NSString stringWithFormat:#"%ld", (long)[visibleSections count]]);
[visibleSections sortedArrayUsingDescriptors:[NSArray arrayWithObject:[[NSSortDescriptor alloc] initWithKey:nil ascending:YES]]];
}
}
if (visibleSections == nil)
{
return 42.0;
}
else if ([[visibleSections objectAtIndex:0] integerValue] == section)
{
return 58.0;
}
else
{
return 42.0;
}
}
}
I couldn't quite work out what went wrong in my heightForHeaderInSection method, but I knew it had something to do with the NSMutableArray, visibleSections.
Any hints or answers as to how I can go about changing the height for a specific section header view outside of heightForHeaderInSection and/or how I can fix my code above would be really helpful.
Edit:
Just to make the solution to my crashing problem a bit clearer, if (visibleSections == nil) should not be used in place of if ([visibleSections count] < 1) or if ([visibleSections count] == 0).
I think you could also do it like this, if you want the first section header to be taller when the table first appears (topSection is an NSInteger property):
-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
self.topSection = ((NSIndexPath *)[self.tableView indexPathsForVisibleRows][0]).section;
[self.tableView reloadSections:[NSIndexSet indexSetWithIndex:self.topSection] withRowAnimation:NO];
}
- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section {
if (self.topSection == section)
{
return 58.0;
}
else
{
return 42.0;
}
}
OK so it turns out this is a harder problem than it first seems. The best I have come up with so far is
Don't treat the header that is for the top section any different and populate them all with the extra data.
You can show and hide different parts by being clever with positioning the "additional" items so that they will be outside of the parent view's bounds when it is smaller and making the parent view clipToBounds.
Failing that you can make a custom UIView subclass and do some manipulation in layoutSubviews
The end implementation I was settling on was this
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
NSArray *indexPaths = [self.tableView indexPathsForVisibleRows];
self.topSection = [indexPaths count] ? [indexPaths[0] section] : -1;
if (indexPaths.count > 1) {
self.topSection = [indexPaths[1] section];
}
[self.tableView beginUpdates];
[self.tableView endUpdates];
}
- (CGFloat)tableView:(UITableView *)tableView heightForHeaderInSection:(NSInteger)section;
{
if (section <= self.topSection) {
return 60;
} else {
return 20;
}
}
It's by no means perfect but it looked semi reasonable and could be tweaked.
Things to note:
You may need to assess if there is too much work going on in scrollViewDidScroll: but it didn't appear to cause any lag for me (I've not really tested properly)
I set the top section using the second indexPath if available as it looked slightly more pleasing/less clunky
I use section <= self.topSection because the header's before are all of screen so there is no point in reducing the size of them which causes really clunky animation.
So after trying this you may need to dig deeper or want to rethink your design a little
You cannot directly refer to the arrays first object by calling objectAtIndex:0, you gotta stay defensive so change this:
else if ([[visibleSections objectAtIndex:0] integerValue] == section)
{
return 58.0;
}
To
else if([visibleSections count]>0)
{
if ([[visibleSections objectAtIndex:0] integerValue] == section)
{
return 58.0;
}
}
Try changing this line:
NSMutableArray *visibleSections = [[NSMutableArray alloc] init]
to:
NSMutableArray *visibleSections = [NSMutableArray array];
Which initializes the array.
This code causes the app to crash! I'm looping through a dictionary and everything logs out fine. It works when i write -1 in the for loop but not otherwise,
-(void)updateProjectTimes {
for(int i = 0; i < [projectsTable numberOfRowsInSection:0]-1; i++) {
NSString *currentValue = [[[projects objectForKey:#"activeProjects"] objectAtIndex:i] objectForKey:#"timepassed"];
NSString *finishValue = [[[projects objectForKey:#"activeProjects"] objectAtIndex:i] objectForKey:#"timeleft"];
if([currentValue intValue] < [finishValue intValue]) {
[[[projects objectForKey:#"activeProjects"] objectAtIndex:i] setObject:[NSString stringWithFormat:#"%d", ([currentValue intValue] + 1)] forKey:#"timepassed"];
} else {
[(NSMutableArray *)[projects objectForKey:#"activeProjects"] removeObjectAtIndex:i];
if([[projects objectForKey:#"activeProjects"] count] == 0) {
[projectTimer invalidate];
projectTimer = nil;
}
}
//[projectsTable reloadData]; works if i put it here!
}
[projectsTable reloadData]; //<- But not here!! :(
}
I assume you are wokring with tableView. Apparently you are modifing the data source of your tableView. When you remove an object from the data source, you have to adjust your tableView as well. Meaning either call reloadData, or call [tableView deleteRowsAtIndexPaths:(NSArray *)indexPaths withRowAnimation:(UITableViewRowAnimation)animation].
The reason your app doesn't crash if you put -1, could be -- perhaps -- because there is only on item that matches the [currentValue intValue] < [finishValue intValue] condition, so that if you go through [projectsTable numberOfRowsInSection:0]-1, after removing that object, numberOfRowsInSection matches the count of projectsTable.
But it is good only for one cycle. When the next cycle happens, in the if...loop, you app crashes again, unless you include the [projectsTable reloadData] in the same if...loop.
While the reloadData method works just fine, but if you are simply removing a row, or adding a row to your table by adding or removing objects, its better to use deleteRowsAtIndexPaths or insertRowsAtIndexPaths methods. There will be less overhead and work for your app, and would make it smoother and faster.
The bottom line, to make your code work, right after [(NSMutableArray *)[projects objectForKey:#"activeProjects"] removeObjectAtIndex:i]; remove the corresponding object from your tableView by calling deleteRowsAtIndexPaths.
Alternatively, you can also use beginUpdates and endUpdates. For a complete reference, refer to http://developer.apple.com/library/ios/#documentation/uikit/reference/UITableView_Class/Reference/Reference.html
Hope it helps.
Sorry for the long title. In essence, I want to accomplish the same thing that the Calendar app does for Event details.
The first cell shows the title and date of the event. The second shows an alert, if there is one, otherwise Notes, if there are any, or nothing else if none of these fields is present.
The way I am doing it now is a really long if condition in cellForRowAtIndexPath:
if(indexPath.row == 0) {
TitleCell *titlecell = [[TitleCell alloc] init];
// config cell to do title here, always
return titlecell;
} else if (indexPath.row == 1 && foo) {
FooCell *foocell = [[FooCell alloc] init];
// config cell to show foo, if it exists
return foocell;
} else if (indexPath.row == 1 && bar) {
BarCell *barcell = [[BarCell alloc] init];
// foo doesn't exist, but bar, so show bar in cell 1
return barcell;
} // etc etc
That's really ugly, and since I create the cells in the if and return, the static analyzer tell me that each one of those is a potential leak. There is no else, since I need to cover all scenarios anyway, and that also gives a warning about the method potentially not returning anything.
Is there a better way that makes this cleaner and doesn't give me warnings?
Thanks!
Christoph
The warning are because you are leaking memory, you have to autorelease the cell: TitleCell *titlecell = [[[TitleCell alloc] init] autorelease];. Also there is a chance of not having a return statement because you don't have else in your if block.
Here is another way of doing it:
// Call this beforehand
- (void)loadTable {
// Since we are not using objects, we need to use a non-retaining array
// A better way of doing this would be with delegates or NSInvocations
array = (NSMutableArray*)CFArrayCreateMutable(NULL, 0, NULL);
[array addObject:(id)#selector(buildTitleCell)];
if (foo)
[array addObject:(id)#selector(buildFooCell)];
if (bar)
[array addObject:(id)#selector(buildBarCell)];
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
if (indexPath.row < array.count) {
SEL selector = (SEL)[array objectAtIndex:indexPath.row];
return [self performSelector:selector];
}
return nil;
}
- (UITableViewCell*)buildTitleCell {
TitleCell *titlecell = [[[TitleCell alloc] init] autorelease];
// config cell to do title here, always
return titlecell;
}
...
EDIT: fixed as per #Christoph's comment
Clang is right when it says that you're leaking memory - The UITableView retains the UITableViewCells that you give it, so you should be autoreleasing them in cellForRowAtIndexPath.
Instead of using if statments, I think you should be using a switch.
I'm new to iPhone dev and programming in general, having recently completed Stephen Kochan's Programming in Objective-C 2.0, and parts of Erica Sadun's iPhone Cookbook. Just reading answered questions on this site has helped me a lot, so I owe a big thanks to all its users. Now I'm working on my first iPhone app, and am making good progress, save for one thing that's got me stumped.
I'm having some trouble with a UITableView. Basically, I have a table that needs to have a maximum of 6 rows per section, with no minimum (except if the row of a 1-row section is deleted, in which case the section goes along with it). The table can also be reordered by the user. When the user drags a row into a section that already has the maximum 6 allotted rows, I want the bottom row of that section to sort-of 'budge' down to become the top row of the next section.
As for implementing this, my first thought was to call a method in tableView:moveRowAtIndexPath:toIndexPath: that would go through the sections in a loop, making sure that none of them had 7+ rows, adjusting the array as needed, and then using a [myTable beginUpdates] block to delete and insert the required rows. This is what all that looks like (note: my array structure is: Array (Table) > Arrays (Sections) > Dictionaries (Items)):
-(void) tableView: (UITableView *) tableView moveRowAtIndexPath: (NSIndexPath *) from toIndexPath: (NSIndexPath *) to
{
// Get the dictionary object for the icon.
NSMutableDictionary *theIcon = [[[TABLE_ARRAY_MACRO objectAtIndex: from.section] objectAtIndex: from.row] mutableCopy];
// Now remove it from the old position, and insert it in the new one.
[[TABLE_ARRAY_MACRO objectAtIndex: from.section] removeObjectAtIndex: from.row];
[[TABLE_ARRAY_MACRO objectAtIndex: to.section] insertObject: theIcon atIndex: to.row];
if ( [[TABLE_ARRAY_MACRO objectAtIndex: to.section] count] > 6 )
[self budgeRowsAtSection: to.section];
// Now we're done with the dictionary.
[theIcon release];
if ( PM_DEBUG_MODE )
NSLog(#"Pet moved!");
}
-(void) budgeRowsAtSection: (NSUInteger) section
{
if ( PM_DEBUG_MODE )
NSLog(#"Budging rows...");
// Set up an array to hold the index paths of the cells to move.
NSMutableArray *budgeFrom = [[NSMutableArray alloc] init];
NSMutableArray *budgeTo = [[NSMutableArray alloc] init];
// Start at the current section, and enumerate down to the nearest page with < 6 items.
int i = section;
while ( i < [TABLE_ARRAY_MACRO count] ) {
if ( PM_DEBUG_MODE )
NSLog(#"Attempting to budge rows in section %i!", i);
if ( [[TABLE_ARRAY_MACRO objectAtIndex: i] count] > 6 ) {
// Grab the last object, and move it to the beginning of the next array.
NSMutableDictionary *lastIcon = [[[PET_ICON_DATA objectAtIndex: i] lastObject] mutableCopy];
[[TABLE_ARRAY_MACRO objectAtIndex: i] removeLastObject];
[[TABLE_ARRAY_MACRO objectAtIndex: (i + 1)] insertObject: lastIcon atIndex: 0];
// Create an index path, and reflect the changes in the table.
[budgeFrom addObject: [NSIndexPath indexPathForRow: 6 inSection: i]];
[budgeTo addObject: [NSIndexPath indexPathForRow: 0 inSection: (i + 1)]];
// Now we're done with the icon.
[lastIcon release];
}
if ( PM_DEBUG_MODE )
NSLog(#"Rows budged for section %i!", i);
++i;
}
if ( PM_DEBUG_MODE )
NSLog(#"From cells: %#\nTo cells: %#", budgeFrom, budgeTo);
if ( PM_DEBUG_MODE )
NSLog(#"Data budged! Updating table...");
[editTable beginUpdates];
[editTable deleteRowsAtIndexPaths: budgeFrom withRowAnimation: UITableViewRowAnimationBottom];
[editTable insertRowsAtIndexPaths: budgeTo withRowAnimation: UITableViewRowAnimationTop];
[editTable endUpdates];
[budgeFrom release];
[budgeTo release];
if ( PM_DEBUG_MODE )
NSLog(#"Row budge done!");
}
The problem is when I run this, it invariably throws an exception; it gives me either Invalid update: number of rows in section after update must be equal to number of rows before update, + or - the number inserted or deleted (etc.), or Attempted to create two animations for cell, depending upon which tweak I'm trying. As for what those tweaks are, I've also tried using reloadSections:withRowAnimation:, and of course a simple [editTable reloadData]. I've tried placing the call to this method in the relevant TableView delegate/data source methods, including targetIndexPathForMoveFromRowAtIndexPath:toProposedIndexPath:, and the somewhat mysterious willMoveToRowAtIndexPath:fromIndexPath: method that is mentioned in the Apple guide on TableViews, but is non-existent elsewhere.
I've searched all over the Google, this site, and Apple's docs for any inkling of a solution, but to no avail.
So, to put my question simply, what is the best way to go about this? Is there some obvious thing that I'm overlooking? Or is my implementation concept just fundamentally flawed from the get-go?
Thanks in advance for the help! Any insight would be much appreciated.
-- Drew R. Hood
UPDATE: Following Jordan's advice from his comment on his answer, I've verified that the actual edits to the data source are going through correctly. I now consistently get the error Attempt to create two animations for cell when the table edit block executes (that timing verified by common sense and breakpoints). So I'm doing something wrong in my edit block. The current code for that is exactly as shown above. Ideas?
[editTable beginUpdates]; [editTable
deleteRowsAtIndexPaths: budgeFrom
withRowAnimation:
UITableViewRowAnimationBottom];
[editTable insertRowsAtIndexPaths:
budgeTo withRowAnimation:
UITableViewRowAnimationTop];
[editTable endUpdates];
I believe you need to update the DataSource before you actually delete the Row in whatever section you're deleting it from. So in this code, before you do the delete, delete the row from Table_Array_Macro (which I think is where your data is).
So, I've finally solved the problem and thought I'd post what I did here for the sake of posterity. It's quite simple, really: I just moved the actual insertion and deletion of rows in the table off to a separate method, which I then invoked after a delay. It had been clear from the start, and Jordan helped me to confirm, that the problem was occurring when performing the updates on the table itself, rather than in the process of actually changing data. So here's the code that did the trick:
-(void) performBudges
{
if ( PM_DEBUG_MODE )
NSLog(#"Performing budge animations...");
[editTable beginUpdates];
[editTable deleteRowsAtIndexPaths: budgeFrom withRowAnimation: UITableViewRowAnimationRight];
[editTable insertRowsAtIndexPaths: budgeTo withRowAnimation: UITableViewRowAnimationRight];
[editTable endUpdates];
[editTable performSelector: #selector(reloadData) withObject: nil afterDelay: 0.5];
[reloadedSections release];
[budgeFrom release];
[budgeTo release];
if ( PM_DEBUG_MODE )
NSLog(#"Budges completed!");
}
And all I have to do to perform this is add this snippet into my moveRowAtIndexPath: method:
if ( [[PET_ICON_DATA objectAtIndex: to.section] count] > 6 ) {
[self budgeRowsAtSection: to.section];
[self performSelector: #selector(performBudges) withObject: nil afterDelay: 1.0];
}
So I hope this helps anyone who may have this problem in the future. Thanks to Jordan and all who viewed this question. :)