I am developing a game for iPhone in which I have 2 arrays.
One with the objects "living" in the game, and when these objects "die" they are placed in another array to be removed from the first one in the end of the first loop.
This is necessary because if the object dies in the loop and it is removed immediately from the first array, the index is lost and sometimes gives an invalid address access.
Then I have an NSMutableArray that contains objects to be removed from the living objects array.
In the array with objects to remove, I am constantly adding and removing items. Sometimes when I use objectAtIndex with the array with items to remove, it is retuning me other object.
For example in the first moment _enemiesToRemove has 2 objects:
([0]-> 0x0a8b5120, [1]->0x18f3a090)
for(int i = [_enemiesToRemove count] - 1; i >= 0 ; i--){
fish = [_enemiesToRemove objectAtIndex:i];
[self removeEnemy:fish];
}
and then
int i = [_enemiesToRemove count] - 1
gives i=1 but when it is doing
[_enemiesToRemove objectAtIndex:i]
it is returning me other object with address 0xbfffcd58 and it should be [1]->0x18f3a090
What is happening here, somebody knows? It is not happening always. It happens randomly.
Related
I have two different arrays and I want to check firstArray objects and accordingly insert objects in second array.If my firstArray contains particular object then at that index, I am trying insert value in secondArray.
Currently, I am inserting values like :
[secondArray replaceObjectAtIndex:0 withObject:transIdArray];
[secondArray replaceObjectAtIndex:1 withObject:fullCaseArray];
[secondArray replaceObjectAtIndex:2 withObject:caseTitleArray];
[secondArray replaceObjectAtIndex:3 withObject:filingDateArray];
My problem is, If in firstArray transIdArray is at 2 index then my these two arrays data getting mismatched.Please suggest me better way to check add insert values in arrays. Thanks.
NSArray elements are naturally packed together, not sparse, like C arrays can be. To accomplish what you want, the secondArray needs to carry placeholders that are considered non-objects semantically by your app. [NSNull null], an instance of NSNull (not to be confused with nil) is a common choice.
You could initialize one or both arrays like this:
for (NSInteger i=0, i<SOME_KNOW_MAX_LENGTH; ++i) {
[secondArray addObject:[NSNull null]];
}
Then an instance of NSNull in the second array means 'there's nothing at this index in this array corresponding to firstArray'. And you can check if that condition holds for a given index like this:
id secondArrayElement = secondArray[index];
if ([secondArrayElement isMemberOfClass:[NSNull class]]) { // ...
As an aside - often, when I find myself needing to coordinate parallel arrays, it usually means I have some undone representational work, and what I really need is a single array with a more thoughtful object, or the containing object must be more thoughtfully designed.
I am newly to iphone. I am working on an application where we need to calculate the value from an array of objects.
I have created a NSObject class "Catalogue", which includes catalogue_Value and catalogue_quantity. Now, suppose if we have two catalogue object in my array, then i need to calculate the total value.
here is my code :
int initialTotalPoints = 9999;
int totalUsedPoints = 0;
for (int i = 0; i<[arrayCheckout count];i++)
{
Catalogue *catalog = [[Catalogue alloc] init];
catalog = [arrayCheckout objectAtIndex:i];
NSLog(#"checkout voucher %d is = %d*%d", i, catalog.catalogue_Value,catalog.catalogue_quantity);
totalUsedPoints = catalog.catalogue_Value * catalog.catalogue_quantity;
}
initialTotalPoints = initialTotalPoints-totalUsedPoints;
The problem is due to the for loop, always it is taking "totalUsedPoints" of my last array object. But in actually, i need to add "catalog.catalogue_Value,catalog.catalogue_quantity" in my "totalUsedPoints" as per my total array objects. Please help me to solve this problem. Thanks!
If you just want to sum up quantity*value per catalog
int totalPoints = 0;
for (int i = 0; i<[arrayCheckout count];i++) {
Catalogue *catalog = [arrayCheckout objectAtIndex:i];
totalPoints += catalog.catalogue_Value * catalog.catalogue_quantity;
}
// totalPoints is now the sum of each arrays catalogue_Value*catalogue_quantity
You could check out Blockskit, a nice package to make array iterations easier
There is nothing specific to objective c here. Every loop you are overwriting totalUsedPoints with a new value. You then do nothing with it, and it gets overwritten again. At the end of the loop it will only contain the last value assigned to it.
I think what you are looking for is:
totalUsedPoints += catalog.catalogue_Value * catalog.catalogue_quantity;
+= is equal to:
totalUsedPoints = totalUsedPoints + catalog.catalogue_Value * catalog.catalogue_quantity;
meaning it will be assigned with the previous value, plus the new value
This is computer science 101 stuff, not unique to Objective-C. Others have already posted info on what you were doing wrong and how to fix it. I wanted to point out another flaw in your code. Take a look at these 2 lines:
Catalogue *catalog = [[Catalogue alloc] init];
catalog = [arrayCheckout objectAtIndex:i];
In the first line you create a new, empty Catalogue object and save a pointer to it in the variable catalog. In the very next line you fetch an object from your arrayCheckout object and save a pointer to it in your catalog variable. You end up discarding the object you created one line before.
This is like building a brand new car, putting it in front of your house, then junking it and fetching an existing car from a numbered parking space in a parking lot.
In ARC the empty Catalogue object you create in the first object will get deallocated on the very next line, so you aren't leaking memory, but it's pointless and wasteful to create an object that you immediately discard. (Memory allocation is one of the slowest tasks in an OS like iOS. It has to make a kernel call)
If your program was using manual reference counting then you would have leaked the Catalogue object. It would never get deallocated. Those two lines should read like this:
Catalogue *catalog;
catalog = [arrayCheckout objectAtIndex:i];
Or even as 1 line:
Catalogue *catalog = [arrayCheckout objectAtIndex:i];
I am developing an iPad application and for this application I have one function as below :-
-(void)testcurrentest:(NSMutableDictionary *)keydictionary{
NSArray *allKeys = [keydictionary allKeys];
if ([allKeys count] > 0) {
for(int i = 0;i< allKeys.count;i++){
[_currenies removeAllObjects];
NSString *product = [NSString stringWithFormat:#"%#", [keydictionary objectForKey:allKeys[i]]];
int kl = [productPriceSeasonCode intValue];
for(int i =0;i<kl;i++){
[_currenies addObject:#"0"];
}
NSLog(#"................%#",_currenies);
[_currencydictionary1 setObject:_currenies forKey:allKeys[i]];
NSLog(#"full dictionary...%#",_currencydictionary1);
}
}
}
Here, NSLog print the currencies array based on the kl integer values but when I'm trying to set the NSMutableDictionary the currencies but mutable array always show the latest array values.
You are using the same array for all values, they should be unique objects if you don't want change of one value to affect the other values. Initialise _currenies on every loop step or use its deep copy when preparing a new object.
A bit of code:
[_currenies removeAllObjects]; // < The same array you've added to dict on previous loop steps
Creating a new array at each loop step would create a unique object for all key-value pair:
_currenies = [NSMutableArray array]; // < Note it is not retained, apply memory management depending on your project configuration
Your code is a garbled mess. As others have pointed out, you are using the same loop index, i, in 2 nested loops, making it very hard to tell your intent. Don't do that, ever. It's horrible programming style.
You are also creating a string "product" that you never use, and fetching the same integer value of productPriceSeasonCode on every pass through the outer loop. I suspect you meant to fetch a value that varies with each entry in your keydictionary.
Then, you have an array, _currenies, which you empty on each pass through your outer loop. You then add a number of "0" strings to it, set a key/value pair in your _currencydictionary1 dictionary to the contents of that array, and then repeat. Since you re-use your _currenies array each time, every key/value pair you create in your _currencydictionary1 dictionary points to the exact same array, which you keep changing. At the last iteration of your outer loop, all the entries in your _currencydictionary1 will point to your _currenies array, which will contain the last set of contents you put there.
Create a new array for each pass through your outer array, and add that newly created array to your _currencydictionary1. You want a unique array in each key/value pair of your _currencydictionary1.
In short, NSMutableDictionary is working just fine. It's your code that isn't working properly.
Not an answer but comments don't have formatting.
The question should provide more information on the input and desired output.
First simplify your code and it should be easier to find the error:
-(void)testcurrentest:(NSMutableDictionary *)keydictionary{
NSArray *allKeys = [keydictionary allKeys];
for(NSString *key in allKeys) {
[_currenies removeAllObjects];
int kl = [productPriceSeasonCode intValue];
for(int i =0; i<kl; i++){
[_currenies addObject:#"0"];
}
NSLog(#"................%#",_currenies);
_currencydictionary1[key] = _currenies;
NSLog(#"full dictionary...%#",_currencydictionary1);
}
}
Note: product was never used.
This question already has answers here:
Getting a random object from NSArray without duplication
(3 answers)
Closed 7 years ago.
I have an array of random properties I would like to assign to equipment within the game I'm developing.
The code that I use below is returning an NSArray. I'm interested if there's way to get item indices from that array without getting duplicate values. The obvious solution is to create a mutable array with the returned array, do random, remove item that was returned and loop until the number of items is received.
But is there a different way of getting X random items from NSArray without getting duplicates?
//get possible enchantments
NSPredicate *p = [NSPredicate predicateWithFormat:#"type = %i AND grade >= %i", kEnchantmentArmor,armor.grade];
NSArray* possibleEnchantments = [[EquipmentGenerator allEnchantmentDictionary] objectForKey:#"enchantments"];
//get only applicable enchantments
NSArray *validEnchantments = [possibleEnchantments filteredArrayUsingPredicate:p];
NSMutableArray* mutableArray = [NSMutableArray arrayWithArray:validEnchantments];
NSDictionary* enchantment = nil;
if(mutableArray.count>0)
{
//got enchantments, assign number and intensity based on grade
for (int i = 0; i<3;i++)
{
enchantment = mutableArray[arc4random()%mutableArray.count];
[mutableArray removeObject:enchantment];
//create enchantment from dictionary and assign to item.
}
}
You can shuffle the array using one of the following techniques:
What's the Best Way to Shuffle an NSMutableArray?
Non repeating random numbers
Then, take the first X elements from the array.
Many years ago, I was working on card game and I realized that shuffling the deck was an inefficient way to get random cards. What I would do in your shoes is pick a random element, and then replace it with the element at the end of the array, like so:
#interface NSMutableArray (pickAndShrink)
- (id) pullElementFromIndex:(int) index // pass in your random value here
{
id pickedItem = [self elementAtIndex:index];
[self replaceObjectAtIndex:index withObject:[self lastObject]];
[self removeLastObject];
return pickedItem;
}
#end
The array will shrink by one every time you pull an element this way.
You could use a random number generator to pick a starting index, and then pick the subsequent indices based on some kind of math function. You would still need to loop depending on how many properties you want.
Eg:
-(NSMutableArray*)getRandomPropertiesFromArray:(NSArray*)myArray
{
int lengthOfMyArray = myArray.count;
int startingIndex = arc4random()%lengthOfMyArray;
NSMutableArray *finalArray = [[NSMutableArray alloc]init]autorelease];
for(int i=0; i<numberOfPropertiesRequired; i++)
{
int index = [self computeIndex:i usingStartingIndex:startingIndex origninalArray:myArray];
[finalArray addObject:[myArray objectAtIndex:index]];
}
return finalArray;
}
-(int)computeIndex:(int)index usingStartingIndex:(int)startingIndex
{
//You write your custom function here. This is just an example.
//You will have to write some code to make use you don't pick an Index greater than the length of your array.
int computedIndex = startingIndex + index*2;
return startingIndex;
}
EDIT: Even your computeIndex function could use randomness in picking the subsequent indices. Since you have a startingIndex, and another index, you could use that to offset your function so that you never pick a duplicate.
EDIT: If your array is very large, and the subset you need to pick is small, then rather than shuffle the entire array (maybe more expensive), you could use this method to pick the number of items you need. But if your array is small, or if the number of items you need to pick are almost the size of the array, then the godel9's solution is better.
You can use a mutable array and then remove them as the are selected, use something like random()%array.count to get a random index. If you don't want to modify the array then copy it with [array mutableCopy].
I cant find this any where, I may be searching the wrong terms or words but I just need to know how to check if an array is a certain length:
if ([scores objectAtIndex:3]){
//code
}
This comes up with an error and crashes if the array isnt this long yet, but surly this should just check if there is an index, and if not move on??
How to I check this without the app crashing??
count method of NSArray returns the number of objects in the array. If [myArray count] returns n then valid indexes are 0 to n - 1. There is no automatic move on if the index is not valid. Before trying to access an index you need to make sure that the index is valid.
if ([scores count] >= 4) {
id obj = [scores objectAtIndex:3];
}