OK, maybe I'm not seeing clear anymore and hope you can help.
I'm trying to select an Object from a NSMutableArray using:
if([car.seat isEqualToString:#"fancyOne"]){
fancyThings = [[NSMUtableArray]init];
[fancyThings addObjects: car];
}
Now I forgot to tell you I'm new at this Objective-C, so maybe I'm thinking the wrong way.
What I'm basically trying to do is to get an Object from one array by selecting a value of it's components.
This is the way to do it, I am however keep having trouble with my if-statement.
If I leave out the IF-statement it does fill my other NSMutableArray with the exact same object (thisCar) but if I put in the IF-statement it doesn't pick up that the string is the same in thisCar.seat.
I next example it puts everything in the normalThings but there are some aCar.seats which contain the string FANCYONE. I checked the XML file on spaces and that sort of things but everything is in order as far as I can see.
Shall I build it using NSScanner instead of IsEqualToString?
- (void)viewDidLoad {
appDelegate = (XMLAppDelegate *)[[UIApplication sharedApplication] delegate];
appDelegate.fancyThings = [[NSMutableArray alloc]init];
for (CARS *aCar in appDelegate.someCars) {
if ([aCar.seats isEqualToString:#"FANCYONE"]){
[appDelegate.fancyThings addObject:aCar];
}
else {
[appDelegate.normalThings addObject:aCar];
}
}
self.title = #"Cars";
super viewDidLoad];
}
EDIT:
My BAD!! The code supplied was in fact in order!
There was a mistake in my XMLParser, which added blank lines to the strings, so I couldn't get an equal string!
Hopefully this will give you some guidance:
//init new array
NSMutableArray *fancyThings = [[NSMutableArray alloc] init];
//walk your array
for (SomeCarObject *thisCar in arrayOfCars) {
//is thisCar a qualifying object
if ([thisCar.seat isEqualToString:#"fancyOne"]) {
//yes, add thisCar object
[fancyThings addObject:thisCar];
}
}
You'll want to create that NSMutableArray outside of the for loop (assuming you're iterating through a collection). Then you can add to that NSMutableArray like you did.
Hope this helps!
BTW, you should edit your question with the comment you made to elaborate on it..
It's depends from volume of objects, which u deal with. If there is 1000 objects or less, this method looks good. But if there is more objects, u have risk to freeze u application and have a big memory leaks.
Also if u will need concurrency code later, u have to keep in u mind some
other solutions.
U can using not just a string objects in u array, u can try to fill u array after application startup in objects, which response if string is same or not. Or using nsdictionary with appropriate keys.
Please read my post multithread search design
Related
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 have dozens of NSStrimgs that when the app loads I want to all be set to the same set. All of them. How can I do this without typing out every single one? Is there a shortcut method?
Thanks.
Also the problem is that Josh isn't specific enough about how he's using his dozens of strings... I think this would be better:
NSMutableArray *stringsArray = [NSMutableArray arrayWithCapacity:1];
NSString *tempStr = #"My unique string"; // Thanks Sven!
// Say you want a dozen strings
for (int i = 0; i < 12; i ++) {
[stringsArray addObject:tempStr];
}
// Now you can use them by accessing the array
[self doSomethingWithString:[stringsArray objectAtIndex:8]];
Instead of having dozens of strings that have the same value, could you make a single static global string and reference that? If you need to change it to separate values later, use instance variables that are initialized to the global string.
This sounds like your model is not very good at all. Since you want to initialize all of your strings to the same value they are obviously related and probably should be modeled as an array like iPhoneDevProf described. That makes other things a lot easier too, you can move other code that is repeated for every string into a loop.
If the value is known when you are compiling the code AND it is not going to change after subsequent application sessions then you can use a simple #define.
#define MY_DEFAULT_STRING #"THE DEFAULT STRING"
Now all you have to do is the following.
{
NSString *myString1 = MY_DEFAULT_STRING;
NSString *myString2 = MY_DEFAULT_STRING;
....
NSString *myStringN = MY_DEFAULT_STRING;
}
If all the strings are in the same code file, just put the define at the top. If the strings are in separate code files, then it could be put into your precompiled header. Having a constants file is usually better.
Using constant extern NSString would probably be more correct, but this is simple and easy to do.
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!