noobie question.. What is the best way to check if the index of an NSArray or NSMutableArray exists. I search everywhere to no avail!!
This is what I have tried:
if (sections = [arr objectAtIndex:4])
{
/*.....*/
}
or
sections = [arr objectAtIndex:4]
if (sections == nil)
{
/*.....*/
}
but both throws an "out of bounds" error not allowing me to continue
(do not reply with a try catch because thats not a solution for me)
Thanks in advance
if (array.count > 4) {
sections = [array objectAtIndex:4];
}
If you have an integer index (e.g. i), you can generally prevent this error by checking the arrays bounds like this
int indexForObjectInArray = 4;
NSArray yourArray = ...
if (indexForObjectInArray < [yourArray count])
{
id objectOfArray = [yourArray objectAtIndex:indexForObjectInArray];
}
Keep in mind NSArray is in sequential order from 0 to N-1 items
Your are trying to access item which has exceeded limit and a array is nil then compiler would throw out of bound error.
EDIT : #sch's answer above shows how can we check if NSArray has required ordered item present in it or not.
You can use the MIN operator to fail silently like this [array objectAtIndex:MIN(i, array.count-1)], to either get next object in the array or the last. Can be useful when you for example want to concatenate strings:
NSArray *array = #[#"Some", #"random", #"array", #"of", #"strings", #"."];
NSString *concatenatedString = #"";
for (NSUInteger i=0; i<10; i++) { //this would normally lead to crash
NSString *nextString = [[array objectAtIndex:MIN(i, array.count-1)]stringByAppendingString:#" "];
concatenatedString = [concatenatedString stringByAppendingString:nextString];
}
NSLog(#"%#", concatenatedString);
Result: "Some random array of strings . . . . . "
Related
This is what I'm trying to do. Get 7 random, non-repeating numbers each time my viewDidLoad starts. I got it to create the randoms, but I've been trying to clear the NSMutableSet when it loads to get a fresh set and I'm having trouble. The NSLog is clearly showing nothing is in the NSMutableSet, but it always comes up with the same numbers in the same order?
// Create set
NSMutableSet *mySet = [NSMutableSet setWithCapacity:6];
// Clear set
NSMutableSet *mutableSet = [NSMutableSet setWithSet:mySet];
[mutableSet removeAllObjects];
mySet = mutableSet;
NSLog(#"mutableSet: %#", mutableSet); // Shows nothing
NSLog(#"mySet: %#", mySet); // Shows nothing
// Assign random numbers to the set
while([mySet count]<=6){
int Randnum = arc4random() % 7+1;
[mySet addObject:[NSNumber numberWithInt:Randnum]];
}
NSLog(#"mySet1: %#", mySet); // Always shows 5,1,6,2,7,3,4 ???
An NS(Mutable)Set is an unordered collection, it does not preserve the order of the elements as they were inserted. So your output only shows that the set contains the
numbers from 1 to 7.
You have different options to get your expected output.
Use an NSMutableOrderedSet instead.
Use a set to keep track of the numbers that already occurred, but store the
numbers also in an array:
NSMutableArray *numbers = [NSMutableArray array];
NSMutableSet *mySet = [NSMutableSet set];
while ([numbers count] < 6) {
NSNumber *randNum = #(arc4random_uniform(7) + 1);
if (![mySet containsObject:randNum]) {
[numbers addObject:randNum];
[mySet addObject:randNum];
}
}
NSLog(#"numbers: %#", numbers);
For a small set (like 7 numbers in your case), you could simply use an array only:
NSMutableArray *numbers = [NSMutableArray array];
while ([numbers count] < 6) {
NSNumber *randNum = #(arc4random_uniform(7) + 1);
if (![numbers containsObject:randNum]) {
[numbers addObject:randNum];
}
}
NSLog(#"numbers: %#", numbers);
I have an NSTableView and need to add values. I was thinking of doing it with a NSArrayController, but near my table there are four buttons: Move to top, Move up, Move down, Move to bottom. I must be able to reorder the entries in the table with these buttons.
The only thing I can think of is to use an array of dictionaries, where the first entry of the dictionary is the value displayed and the second entry of the dictionary is a double that is used to sort the array. If I move a value up or down, I take the sort value of the entry before and after the destination sum them, and then I divide by two.
I am not sure that the solution I was thinking of is appropriate. What would be the best approach to this scenario?
------EDIT-----
Working on it, and now I am having difficulties writing the updated "order" value into the arraycontroller. Beside that i am having trouble in actually sorting the table with the "order" column once that the value has been updated. Here is my code:
-(IBAction)singleMoveKeywordUp:(id)sender
{
NSInteger selectedRow = [singleKeywordTable selectedRow];
double firstnum;
double secondnum;
double newnum;
NSMutableDictionary *kwmutabledict = [[NSMutableDictionary alloc] init];
if (selectedRow < 2)
{
firstnum = 0;
kwmutabledict = [keywordscontroller.arrangedObjects objectAtIndex:0];
secondnum = [[kwmutabledict valueForKey:#"order"] doubleValue];
}
else
{
kwmutabledict = [keywordscontroller.arrangedObjects objectAtIndex:selectedRow-2];
firstnum = [[kwmutabledict valueForKey:#"order"] doubleValue];
kwmutabledict = [keywordscontroller.arrangedObjects objectAtIndex:selectedRow-1];
secondnum = [[kwmutabledict valueForKey:#"order"] doubleValue];
}
NSMutableDictionary *newkwmutabledict = [[NSMutableDictionary alloc] init];
newnum = (firstnum + secondnum)/2;
[newkwmutabledict setObject:[NSString stringWithFormat:#"%#",[kwmutabledict valueForKey:#"keyword"]] forKey: #"keyword"];
[newkwmutabledict setObject:[NSString stringWithFormat:#"%f",newnum] forKey: #"order"];
[keywordscontroller.arrangedObjects replaceObjectAtIndex:selectedRow withObject:newkwmutabledict] ; //<--------
NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:#"order" ascending:YES];
[singleKeywordTable setSortDescriptors:[NSArray arrayWithObject:sort]];
}
This is failing at the row marked with an Arrow with the error message -[_NSControllerArrayProxy replaceObjectAtIndex:withObject:]: unrecognized selector sent to instance 0x100450520
I can't figure out whats wrong.
keywordscontroller.arrangedObjects returns (NSArray *) which is NOT mutable, and NSArray does not contain selector "replaceObjectAtIndex:withObject:". Hence the exception/error "unrecognized selector".
I'm trying to create a basic quiz app where the questions will not repeat. I've looked at several examples and believe I should be storing the questions in an array and then removing one from the array each time its used. I've tried the following code.
- (void)viewDidLoad
{
//The array of questions
NSMutableArray *questionArray = [[NSMutableArray alloc] initWithObjects:
[NSMutableArray arrayWithObjects:#"First Question",#"Answer A", nil],
[NSMutableArray arrayWithObjects:#"Second Quesiton",#"AnswerA",#"AnswerB", nil],
nil];
//remove used question from array
for (int i = questionArray.count; i>=0; --i) {
_questions = [questionArray objectAtIndex:arc4random() % questionArray.count];
[questionArray exchangeObjectAtIndex:i withObjectAtIndex:_questions];
}
//use array object
self.lblQuestion.text = [_questions objectAtIndex:0];
[self.btnA setTitle:[_questions objectAtIndex:1] forState:UIControlStateNormal];
[super viewDidLoad];
}
I'm getting the following warning:
Incompatible pointer to integer conversion sending NSMutableArray*_strong to parameter of type 'NSUInteger'
I take it this means I shouldn't be using another array to store the random question as I can't use this to remove the question from the array. However I don't know how else to do this?
Am I completely misunderstanding how I should go about this?
Since your goal here is to get non-repeating questions...
I believe that instead of removing the question you have already used, you should SHUFFLE your array at the beginning and then loop through the array one index at a time using a simple counter.
I hope you can find this piece of code helpful -- give it a shot:
-(NSMutableArray *)shuffleArray:(NSMutableArray *)anArray
NSUInteger count = [anArray count];
for (NSUInteger i = 0; i < count; ++i)
{
int nElements = count - i;
int n = (arc4random() % nElements) + i;
[anArray exchangeObjectAtIndex:i withObjectAtIndex:n];
}
return anArray;
}
-(void)viewDidLoad
{
//The array of questions
NSMutableArray *questionArray = [[NSMutableArray alloc] initWithObjects:
[NSMutableArray arrayWithObjects:#"First Question",#"Answer A", nil],
[NSMutableArray arrayWithObjects:#"Second Quesiton",#"AnswerA",#"AnswerB", nil],
nil];
//Shuffle the question array -- Now all indexes are shuffled and Random
questionArray = [self shuffleArray:questionArray];
//Every time you want to move to the next question, all you have to do is connect a button to the nextIndex action and let it do all the work!
//Use the nextIndex method to initialise -- we call it manually the first time so things would get going and something is displayed -- you can remove the line below if you want it to initialise on first button click! Your call the shots sir!
[self nextIndex];
[super viewDidLoad];
}
//Edit -- This method shows how to change question array index using a method
int currentIndex = 0;
-(IBAction)nextIndex
{
if ( currentIndex == [questionArray count] )
{
currentIndex = 0; //Resets the var when getting to the final Index
//The above line will result in a question loop -- meaning if you arrive at the last question, the next question will be the first! Pacman mode!
//If you want to stop at the last question just change the above line to return; and you're all set!
}
//Set _questions object to the current Index Array element
_questions = [questionArray objectAtIndex:currentIndex];
//Increment currentIndex for next use
currentIndex++;
//use the array object to set your objects' values
self.lblQuestion.text = [_questions objectAtIndex:0];
[self.btnA setTitle:[_questions objectAtIndex:1] forState:UIControlStateNormal];
}
You will end up having totally different questions that are shuffled every time.
I hope you find this helpful.
I have an NSArray and a lot of the values have the same values (i know this isn't the best way to do an array). How can i search for a string within the array and have it return me an array of indexes. For example if i wanted to search the array for "DJ Ez", how can i have it so it returns all the indexes where the index is equal to that string? So far i have tried this:
do {
isTheObjectThere = [array containsObject: #"DJ Ez"];
if(isTheObjectThere == true){
indexOfTheObject = [array indexOfObject: #"DJ Ez"];
[arrayOfIndexes addObject:[NSNumber numberWithInt:indexOfTheObject]];
[array removeObjectAtIndex:indexOfTheObject];
NSLog(#"%#", [indexesForAll objectAtIndex:intCtrl]);
hasFinished = false;
}else{
hasFinished = true;
}
intCtrl++;
} while (hasFinished == false);
However this doesn't work as when it deletes the item it messes up all the indexes for the next search. What do i do?
How about something like this:
NSIndexSet *indexes = [array indexesOfObjectsPassingTest:^BOOL(NSString *obj, NSUInteger idx, BOOL *stop) {
return [obj isEqualToString:#"DJ Ez"];
}];
That should return all of the matching indexes as an NSIndexSet, which allows you do check if specific indexes matched, or you can get the count and loop through the matching indexes however you wish.
I'm trying to compare two strings
NSString strOne = #"Cat, Dog, Cow";
NSString strTwo = #"Cow";
How do I determine if strOne contains strTwo
Try using rangeOfString:
NSRange result = [strOne rangeOfString:strTwo];
From the documentation:
Returns an NSRange structure giving the location and length in the receiver of the first occurrence of aString. Returns {NSNotFound, 0} if aString is not found or is empty (#"").
For anyone needing the code to check is a string exists within a string, here's my code thanks to fbrereto. This example checks to see if any string contained in an array of strings (stringArray) can be found within a string (myString):
int count = [stringArray count];
for (NSUInteger x = 0; x < count; ++x) {
NSRange range = [self.myString rangeOfString:[stringArray objectAtIndex:x]];
if (range.length > 0) {
// A match has been found
NSLog(#"string match: %#",[stringArray objectAtIndex:x]);
}
}
I believe this is the correct syntax for checking if the range exists (correcting response from Kendall):
range.location != NSNotFound
Gradually straying off topic, but I always explode my strings, which would mean just exploding it using your search string as a key and you can use the array count to see how many instances you have.
Just incase anyone is coming from a code language that uses "explode" to blow a string up into an array like me, I found writing my own explode function tremendously helpful, those not using "explode" are missing out:
- (NSMutableArray *) explodeString : (NSString *)myString key:(NSString*) myKey
{
NSMutableArray *myArray = [[NSMutableArray alloc] init];
NSRange nextBreak = [myString rangeOfString:myKey];
while(nextBreak.location != NSNotFound)
{
[myArray addObject: [myString substringToIndex:nextBreak.location]];
myString = [myString substringFromIndex:nextBreak.location + nextBreak.length];
nextBreak = [myString rangeOfString:myKey];
}
if(myString.length > 0)
[myArray addObject:myString];
return myArray;
}
works like this:
[self explodeString: #"John Smith|Age: 37|Account Balance: $75.00" key:#"|"];
which will return this array:
[#"John Smith", #"Age: 37", #"Account Balance: $75.00"];
This lets you quickly pull out a specific value in a tight space, Like if you have a client and you want to know how much money he has:
[[self explodeString: clientData key: pipe] objectAtIndex: 1];
or if you wanted specifically the dollar amount as a float:
[[[self explodeString: [[self explodeString: clientData key: pipe] objectAtIndex: 1] key: #": "] objectAtIndex: 2] floatValue];
anyway I find arrays way easier to work with and more flexible, so this is very helpful to me. Additionally with a little effort you could make an "explodable string" data type for your private library that lets you treat it like a string or return an index value based on the key
ExplodableString *myExplodableString;
myExplodableString.string = #"This is an explodable|string";
NSString *secondValue = [myExplodableString useKey: #"|" toGetValue: index];