Ive got the following code:
Trying to debug it for a while. Can't figure it out.
[self.vManager vendorsNearLocation:userLocation block:^(NSArray *vendors, NSError *error)
{
self.vManager.vendors_array = [NSArray arrayWithArray:vendors];
NSLog(#"Vendors array was %d long", [self.vManager.vendors_array count]);
if(vendors && [vendors count])
{
for (id v in vendors)
{
Vendor *aVendor = [[Vendor alloc] initWithAttributes:v];
[self.mapView addAnnotation:aVendor];
[self.vManager.vendor_dict setObject:aVendor
forKey:[aVendor name]];
I was hoping to set the values of the dictionary in that loop. But dictionary is always empty. No errors or warnings, nothing gets set Yet the array has values and my map shows all the vendors. By the way the vManager is a Singleton and Dictionary is being initialized in the viewDidLoad method of the caller
Is there something that Im doing thats obviously wrong?
I think you need to initialize the dictionary in the SINGLETON class itself. I tried the same thing yesterday and it worked.
Just make a function and initialize the dictionary there and call that function before making use of that dictionary.
It will surely work.
Related
I have an Array comprised of further sub-Arrays
I want to display a summary of the contents of the sub-arrays into a TableView with the count of occurrences of each entry. I have determined that the best and easiest way is through a NSMutableDictionary as an intermediate step.
I declare the dictionary in my implementation
#implementation ReviewViewController
{
NSMutableDictionary *dict;
}
and down in my methods I initialise and use it like so:
dict = [NSMutableDictionary new];
[dict setObject:[Observation entryCount] forKey:[observedItem species]];
The swapping of key and object is deliberate as its the count I want. I'm using the fact that values are retained, but keys are overwritten, so if i swap them round i get the curation for free.
It works!, but every time the method is invoked, the Dictionary is clobbered by the re-initalization so I only get the last thing entered. Anywhere else and it falls out of scope.
if I pass it as an arguement in the method name instead, I get the message "Local declaration of 'dict' hides instance variable ". The code is already an irreducable set of parts, so
so, where is the correct place for the instantiation?
I'd love to make my contribution here as a meaningful thanks, but before I can do that I'm going to look silly with such questions.
You would usually initialise it in your init method. For a view controller this is usually the following:
- (id)initWithNibName:(NSString*)nibName bundle:(NSBundle*)bundle {
if ((self = [super initWithNibName:nibName bundle:bundle])) {
dict = [NSMutableDictionary new];
}
return self;
}
I don't understand what you mean by "Anywhere else and it falls out of scope.". It's an instance variable. It is therefore in scope in any method in the class.
By the way, I would name your instance variables with an underscore prefix, e.g. _dict. This is common convention and it helps you to remember when using it that it's an instance variable.
I am having two arrays, Namely
NMutableArray* first;
NMutableArray* second;
Now I am copying first object to the second array like
for (int i=0;i<first.count; i++)
{
[second addObject:[first objectAtIndex:i];
}
This is ok. I don't know how to access the value of the First Array. I tried like this ,
[second addObject:[[first objectAtIndex:i]name]];
I want to get the name value which is in the first object of first array. I tried using the above line, it is showing some warning. Please help me
Assuming you started with an array like this:
NSArray *array1 = #[#{#name : #"Fred"},
#{#name : #"Bill"}];
You could create a second array that contains the value of a given property of each element of the first array as follows:
NSArray *array2 = [array1 valueForKey:#"name"];
If you then logged the second array...
NSLog(#"%#", array2);
...the resulting output would be
2012-04-18 16:26:11.226 ExampleRunner[23320:707] (
Fred,
Bill
)
EDIT
Note that this will work regardless of whether the objects in the first array are instances of NSDictionary as shown in the example above, or instances of a class or classes that have a name property or instance variable (or an _name instance variable, for that matter). For more information on how and why this works, see the documentation for the NSKeyValueCoding informal protocol:
http://developer.apple.com/library/ios/#DOCUMENTATION/Cocoa/Reference/Foundation/Protocols/NSKeyValueCoding_Protocol/Reference/Reference.html
The brackets are currently in the wrong place:
[second addObject:[[first objectAtIndex:i] name]];
Updated Answer:
Again, I think you should split stuff out into easy to parse lines of code:
for (id theObject in first)
{
// without an actual type, I still think the compiler might
// throw a warning on this next line of code;
// but maybe RJR III is correct and it won't warn.
// I didn't check.
NSString * nameOfObject = [theObject name];
if(nameOfObject)
{
[second addObject:nameOfObject];
}
}
Notice that I do some error checking in here as well (i.e. making sure the name is not nil).
Original Answer:
You're getting a warning because the compiler doesn't know what kind of custom object is being fetched from your call to "[first objectAtIndex: i]". In other words, it doesn't know what kind of object you're trying to get the "name" of.
Cast it to the right type and you'll get rid of the warning.
Or even better, split that one line of multiple things happening at once into two or three lines of code and make your code more readable in the process.
I'm attempting to create an NSArray with a grouping of string literals, however I get the compile error "Initializer element is not constant".
NSArray *currencies = [NSArray arrayWithObjects:#"Dollar", #"Euro", #"Pound", nil];
Could someone point out what I'm doing wrong, and possibly explain the error message?
New syntax for creating an array with string literals:
NSArray *currencies = #[#"Dollar", #"Euro", #"Pound"];
To fix your complication error the code must be in a method. If you want to use it statically then create a class method that follows the singleton pattern.
This isn't a problem with the NSArray creation itself (you would get the same error if you wrote [NSArray array] instead), but with where you've written it. I'm guessing this is a global or file-static NSArray. In C, that kind of variable has to have a constant initializer — meaning not a function call (or, by extension, a method call). The solution is to put the actual creation and assignment of the array into a method that will be called before you need the array, such as initialize.
It sounds like Chuck has spotted the problem. One thing you want to be aware of though in coding your solution is that you'll want to avoid storing an autoreleased instance of NSArray in a static variable. Also, a common pattern for these situations is to write a class method that creates and returns the value stored in the static variable, like so:
+ (NSArray *)currencies
{
static NSArray *_currencies;
// This will only be true the first time the method is called...
//
if (_currencies == nil)
{
_currencies = [[NSArray alloc] initWithObjects:#"Dollar", #"Euro", #"Pound", nil];
}
return _currencies;
}
Although this is old, please notice that Apple committed a new patch to the llvm project adding support for new Objective-C literal syntax for NSArray, NSDictionary and NSNumber.
See here and here
I'm a newbie in objective-c, but I think that the correct code is:
NSArray *currencies = [[NSArray alloc] initWithObjects:#"Dollar", #"Euro", #"Pound", nil];
I am not sure tho.
There's nothing wrong with that code. Are you sure the error is being produced at that line?
I have use below syntax for for set the object.
[dict setObject:eventArray forKey:categoryName];
Now i am trying to get below syntax but i got nothing.
NSMutableArray *tempArrayValue=[[NSMutableArray alloc]init];
tempArrayValue =[tempDict valueForKey:categoryValue];
What is the problem i cant understand can u help me?
you have given key as categoryName not categoryValue, and while retrieving you are using categoryValue.
NSMutableArray *tempArrayValue=[[NSMutableArray alloc]init]; tempArrayValue =[tempDict valueForKey:categoryName];
If you're setting the value like this:
[dict setObject:eventArray forKey:categoryName];
Then you should be fetching it back again like this:
NSMutableArray* eventArray = [dict valueForKey:categoryName];
assuming that eventArray is of type NSMutableArray.
What you are doing has at least two different problems.
This line is a memory leak, since you allocate an object and then throw it away, so delete it:
NSMutableArray *tempArrayValue=[[NSMutableArray alloc]init];
This second line may return a nil object, if there is no object stored for the key categoryValue. (You are using an object called categoryName above, as the key to store the value):
tempArrayValue =[tempDict valueForKey:categoryValue];
You haven't posted enough code to be able to tell why it's not working otherwise.
I need to check specific positions in an NSArray to see if they have already been initialized, but I am having trouble. I tried to do the following, but it causes my application to crash!
if ((NSMutableArray *)[arrAllBlocks objectAtIndex:iLine] == nil)
{
[arrAllBlocks insertObject:[[NSMutableArray alloc] init] atIndex:iLine];
}
NSMutableArray *columArray = (NSMutableArray *)[arrAllBlocks
objectAtIndex:iLine];
[columArray insertObject:newBlock atIndex:iColumn];
What is the best to do this? I already tried some methods like isValid, and things like that!
You have a few options here:
Option 1: Pre-fill the array with instances of NSNull, and then use the code given by Dave DeLong in his answer.
Option 2: (Similar to #1) pre-fill the array with instances of NSMutableArray, and then have no extra code at all. (If you're going to pre-fill, you may as well do this).
Option 3: Do not pre-fill the array, but insert items dynamically as required. This will be almost identical to a pre-fill if the first iLine is near the maximum:
while([arrAllBlocks count] <= iLine)
{
[arrAllBlocks addObject:[NSMutableArray arrayWithCapacity:0]];
}
NSMutableArray *columArray = (NSMutableArray *)[arrAllBlocks
objectAtIndex:iLine];
[columArray insertObject:newBlock atIndex:iColumn];
Option 4: Use a dictionary to maintain the list of NSMutableArrays:
NSString *key = [NSString stringWithFormat:#"%d", iLine];
NSMutableArray *columnArray = [dictAllBlocks objectForKey:key];
if (columnArray == nil)
{
columnArray = [NSMutableArray arrayWithCapacity:0];
[dictAllBlocks setObject:columnArray forKey:key];
}
[columArray insertObject:newBlock atIndex:iColumn];
How to choose:
If the maximum value for iLine is not enormous, I would go with option #2. A handful of NSMutableArrays initialized to zero capacity will take up very little memory.
If the maximum value for iLine is enormous, but you expect it to be accessed sparsely (i.e., only a few values of iLine will ever be accessed), then you should go with Option #4. This will save you from having to fill an NSMutableArray with objects that never get used. The overhead of converting the string-value key for the dictionary will be less than the overhead for creating all of those blanks.
If you're not sure, try out each option and profile them: measure your memory usage and the time required to execute. If neither of these options work, you may have to explore more complex solutions, but only do that if it turns out to be necessary.
A note of caution:
The original code that you posted has a memory leak in the following line:
[arrAllBlocks insertObject:[[NSMutableArray alloc] init] atIndex:iLine];
The NSMutableArray objects that you initialize here are never released. When you call [[NSMutableArray init] alloc], a brand new object is created (with a reference count of one). The insertObject method then adds that new object to arrAllBlocks, and retains it (increasing its retain count to 2). Later, when you release arrAllBlocks, the new array will be sent a release message, but that will only reduce its retain count to one again. At that point, it will stick around in RAM until your program exits.
The best thing to do here is to use [NSMutableArray arrayWithCapacity:0] instead (as I have done in my examples). This returns a new NSMutableArray, just the same as your code did, but this instance has already been autoreleased. That way, arrAllBlocks can take ownership of the new object and you can be sure that it will be released when appropriate.
You can't. NSArray (and its subclass NSMutableArray) do not allow you to insert nil into the array. That's clearly outlined in the documentation.
If, for some reason, you need to have "empty" values in an array, then you should insert [NSNull null] instead and test for that. From the docs: "The NSNull class defines a singleton object used to represent null values in collection objects (which don’t allow nil values)."
UPDATE:
This means you could change your code very simply to this:
if ([[arrAllBlocks objectAtIndex:iLine] isEqual:[NSNull null]]) {
[(NSMutableArray *)arrAllBlocks insertObject:[NSMutableArray array] atIndex:iLine];
}
NSMutableArray *columnArray = (NSMutableArray *)[arrAllBlocks objectAtIndex:iLine];
[columnArray insertObject:newBlock atIndex:iColumn];
To check for NSNull you can simply compare against the pointer, since it's a Singleton:
if ([NSNull null] == [arrAllBlocks objectAtIndex:iLine]) {
[arrAllBlocks insertObject:[NSMutableArray array] atIndex:iLine];
}
NSMutableArray *columnArray = [arrAllBlocks objectAtIndex:iLine];
[columnArray insertObject:newBlock atIndex:iColumn];
I also removed the unsightly casts. Casting is rarely necessary in Objective-C. It usually just adds noise, and can hide real bugs. Since you're experiencing crashes, it's worth removing the casts from this code and listen to what the compiler has to tell you about it.
Telling the compiler to ignore warnings for a piece of code does not make the underlying problem with it go away!