Here is part of a class definition in an iOS program using reference counting (ARC):
#interface CapViewController : UIViewController
{
NSString *bottomBn;
NSString *topBn;
}
#property (nonatomic, strong) NSString *bottomBn;
#property (nonatomic, strong) NSString *topBn;
#end
In the implementation I synthesize them:
#implementation CapViewController
#synthesize bottomBn;
#synthesize topBn;
The problem is when I try to assign values. If I step through the following lines in a class method (first time each instance variable is being used):
bottomBn = [NSString stringWithString:#"bottomBn"];
topBn = [NSString stringWithString:#"topBn"];
After the first line has executed, the value of topBn becomes #"bottomBn" and bottomBn is nil
The second line has no impact.
If I change the order the instance variables are defined in the class, i.e.:
NSString *topBn;
NSString *bottomBn;
then the first assignment has no effect and the second assignment results in "topBn" being assigned to bottomBn.
Using local variables it works as expected:
NSString *localbottomBn = [NSString stringWithString:#"defaultbottombutton"];
NSString *localtopBn = [NSString stringWithString:#"defaulttopbutton"];
This seems bizarre behavior to me. I'd appreciate any help.
You are not setting the autoreleased strings, you should set the strings as:
self.bottomBn = [NSString stringWithString:#"bottomBn"];
self.topBn = [NSString stringWithString:#"topBn"];
I have same problems with other types and objects (even CGFloat and CGPoint). I think the problem is in debugger. Try to print you strings instead of look variables via debugger. For me NSLog function print what I expected.
I have no ideas why debugger have this unpredictable behavior (may be it's a bug), but now I prefere "NSLog debugging". It is sad.
Related
I tried initializing the array :
In .h file
#property (nonatomic, retain) NSArray *accounts;
In .m file :
#synthesize accounts;
- (void)viewDidLoad
{
[super viewDidLoad];
NSArray *arrList = [acAccountStore accountsWithAccountType:accountType];
// This returns array
self.accounts = [NSArray arrayWithArray:arrList]; // I tried debug after
// this and it gives me data in debugger.
// Note array List have 3 data in it.
}
Now On button click i call a method:
- (IBAction) ButtonClicked :(id) sender {
NSLog(#" data : %#",[self.accounts objectAtIndex:0]); // Breaks at this point.
// When i tried with debug it gives me (no Objective-C description available)
}
Is the initialization of array correct Or If the code is not right please let me know.
Main concern is when i do debug in viewDidLoad, the self.accounts show me proper values. But after doing the click event its empty and throws EXEC_BAD_ACCESS error.
Thanks for help in advance
hm looks fine. A couple of questions then:
Where are you calling the self.accounts = [NSArray arrayWithArray:arrList];
I assume that the array is being setup before your button is being pressed?
There's no real reason that arc should be clearing out the variable. Have you set a strong reference to it or a weak one? If you're using self. on a variable, you should have :
#property (nonatomic, strong) NSArray *accounts;
or similar to that in the .h file and then
#synthesize accounts;
in the .m file.
If you've got weak instead of strong then ARC may possibly clear the memory but it still shouldn't.
Update:
Create a property for your account store as well. I had this exact issue recently and this fixed it.
#property (nonatomic, strong) ACAccountStore *accountStore;
Original Answer
Because you're using ARC, you need to change your property declaration from
#property (nonatomic, retain) NSArray *accounts;
to:
#property (nonatomic, strong) NSArray *accounts;
With the latest LLVM compiler, you don't need to synthesize properties either. So you can remove #synthesize accounts.
You should always use defensive coding as well, so in your - buttonClicked: method, you should do:
- (IBAction)buttonClicked:(id)sender {
if (self.accounts) {
NSLog(#"data: %#", [self.accounts objectAtIndex:0]);
}
}
This makes sure that the pointer to the array is valid.
You can also check to make sure an item in an array exists before trying to read it by doing:
- (IBAction)buttonClicked:(id)sender {
if (self.accounts.count > 0)
NSLog(#"data: %#", [self.accounts objectAtIndex:0]);
}
}
I want to store a list of data records in a NSMutableArray for use in a UITableView. In other languages I would have used a simple 'type' structure to define the record structure but I understand the way to do this in Obj-C is to define a new class. I've done this as follows :
#interface CustSuppListItem : NSObject
#property (nonatomic, copy, readwrite) NSString *acCode;
#property (nonatomic, copy, readwrite) NSString *acCompany;
#property (nonatomic, copy, readwrite) NSString *acContact;
#property (nonatomic, assign, readwrite) double osBalBase;
#property (nonatomic, assign, readwrite) unsigned int acAccStatus;
#end
#implementation CustSuppListItem
#synthesize acCode, acCompany, acContact, osBalBase, acAccStatus;
#end
In the viewDidLoad of my UITableViewController I instantiate the array :
tableListDataArray = [[NSMutableArray alloc] init];
Once I have retrieved my data, I add it to the array as follows :
CustSuppListItem *custSuppItem = [[CustSuppListItem alloc] init];
[custSuppItem setAcCode:[jsonCustSuppRecord getStringForKey:#"acCode"]];
[custSuppItem setAcCompany:[jsonCustSuppRecord getStringForKey:#"acCompany"]];
[custSuppItem setAcContact:[jsonCustSuppRecord getStringForKey:#"acContact"]];
[custSuppItem setOsBalBase:[jsonCustSuppRecord getDoubleForKey:#"osBalBase"]];
[custSuppItem setAcAccStatus:[jsonCustSuppRecord getIntForKey:#"acAccStatus"]];
[tableListDataArray addObject:custSuppItem];
[custSuppItem release];
In my table cellForRowAtIndexPath method, I retrieve the data for the current cell as follows:
CustSuppListItem *listDataRecord = [tableListDataArray objectAtIndex:indexPath.row];
[cell.lblCompanyName setText:listDataRecord.acCompany]; // EXC_BAD_ACCESS here
[cell.lblAcCodeContact setText:[NSString stringWithFormat:#"%#, %#",
listDataRecord.acCode, listDataRecord.acContact]];
[cell.lblBalance setText:[Utils fmtNumber:listDataRecord.osBalBase withDecPlaces:2]];
[cell.lblStatus setText:[Utils exchAccStatusDesc:listDataRecord.acAccStatus]];
return cell;
In the dealloc method for the view controller I release the NSMutableArray :
[tableListDataArray release];
I'm very new to Obj-C so it would be great if somebody could confirm everything I've done so far makes sense and is in order. I am getting an intermittent EXC_BAD_ACCESS error when trying to read the acCompany property (see comment next to line) so something must not be right.
Any help appreciated,
Jonathan
All your code looks reasonable and correct to me at first glance.
A few things that I would look at are:
Confirm that cell definitely has a property lblCompanyName. If you're trying to assign to a property that doesn't exist then you will get this type of error. Have you defined a custom cell object type?
Confirm that it is always the acCompany property that is causing the EXC_BAD_ACCESS, and not just any property on the object. One way to do this would be to change the ordering of the lines in the cellForRowAtIndexPath method.
Confirm that the listDataRecord that's causing the crash is getting populated correctly in the first place. In other words, confirm that your jsonCustSuppRecord is always valid. What does jsonCustSuppRecord getStringForKey: return if the key doesn't exist in the jsonCustSuppRecord?
Set a breakpoint at this line: [tableListDataArray addObject:custSuppItem]; and examine the contents of the custSuppItem each time (this is an extension of point 3. above)
I'm getting an expected identifier error when I try to compile my code.
careerURL is setup like this in .h file:
#property (nonatomic, copy) NSString *careerURL;
And synthesized like this in .m file:
#synthesize careerURL;
I really do not understand what is the issue here. The exact code works in another viewcontroller.
You should either use dot . syntax,
NSString *wtf = self.careerURL;
Or Objective-C message syntax,
NSString *wtf = [self careerURL];
Not both at the same time.
You should write:
NSString *wtf = self.careerURL;
When you are writing [object method] it is expected that you want to call method method from object object. If you want just access some value (that is defined as #property) you can type:
[self nameOfValue];
or
self.nameOfValue;
I'm a beginner to XCode.
Below is my code. I want to add an object to a mutablearray. From the debugger window I can see there is one object added to the array "words". I can also see the property "flag" of that object is "NO". The problem is another property "str" is shown as "out of scope".
Can anyone help me with this issue? Thanks a loooooot! Stucked on this one for the whole afternoon.
NSMutableArray * words=[[NSMutableArray alloc] initWithCapacity:numberOfWords];
Word *w=[[Word alloc] init];
[w setStr:#"abc" flag:NO];
[words addObject: w];
[w release];
--
#interface Word : NSObject{
NSString *str;
BOOL flag;
}
-(void) setStr: (NSString *) s flag:(BOOL) b
{
self.str=s;
flag=b;
}
Do you have a property declaration for your string? Are you retaining the string you are setting?
Still AFAIK 'out of scope' does not necessarily mean it was not set or that nothing has been set. Try an NSLog of the value or something. You might find that there is nothing wrong.
Have a look at this question that talks about scope in GDB:
Objective-C: instance variables out of scope in debugger
Your problem is that the string #"abc" is a temporary object who's scope only exists during the [w setStr:#"abc" flag:NO] method call. You should be able to resolve this problem by making str a #property of Word:
#interface Word : NSObject{
NSString *str;
BOOL flag;
}
#property (retain) NSString* str;
#end
And in your implementation file
#implementation Word
#synthesize str;
-(void) setStr: (NSString *) s flag:(BOOL) b
{
self.str=s;
flag=b;
}
#end
I have a doubt about initializing string with synthesize keyword.
In my Event.h class I have
#interface Event : NSObject {
NSString *title;
}
#property (nonatomic, retain) NSString *title;
and in Event.h I have
#synthesize title;
However when I want to set the title from my main class and I display the content in the console, I get null:
[self.currentEvent.title stringByAppendingString:#"hello"];
NSLog(#"%#", self.currentEvent.title); //this is null
Is because I don't properly initialize the title variable in Event? Isn't synthesize initializing it for me?
[self.currentEvent.title stringByAppendingString:#"hello"];
You call stringByAppendingString: on a null object (since it was never initialized), so it doesn't do anything. Plus, even if it were to return something, you're not storing the return value anywhere.
if(self.currentEvent.title==nil){
self.currentEvent.title = #"hello";
}
else{
self.currentEvent.title = [self.currentEvent.title stringByAppendingString:#"hello"];
}
#synthesize creates the setter and getter methods for you, but does not initialize
Fastest way to get up to speed with this stuff is to watch "Developing Apps for iOS" by Paul Hegarty / Stanford University, available free on iTunes.
You are not storing the result of your call into a variable. I also suggest using this method since it's a little bit cleaner because you do not need to have an if statement.
[self setTitle:[NSString stringWithFormat:#"hello %#", [self title]]];