I am making a program where I need to loop through an array with a list of letters. I want the letters to be shown on their specific label. I have therefore created an outlet of each (about 38) and given them the name "alif01", "alif02", etc.
for (int i = 0; i < [arabicLetters count]; i++) {
int num = i;
NSString *letterString = [arabicLetters objectAtIndex:i];
NSLog(#"alif0%d is %#", num, letterString);
alif0**[i]**.text = arabicLetters[i];
}
is it possible to use the index [i] instead of writing it all manually?
You should not have 38 IBOutlet properties for this. You should have an array (possibly an IBOutletCollection) so that you can loop over the array / index into the array.
While technically you can create a key name and use KVC valueForKey: (appending strings / string format), the array approach is a much better solution.
Indeed, as you already have a loop, you would be better served by creating the labels in the loop directly, then you know you have the correct number. This is particularly beneficial later, when you change the contents of arabicLetters (though that sounds like it isn't a concern in this particular case).
Try with below code:
for (int i = 0; i < [arabicLetters count]; i++) {
NSString *letterString = [arabicLetters objectAtIndex:i];
NSString *propertyName = [NSString stringWithFormat:#"alif0%d.text",i];
[self setValue:letterString forKeyPath:propertyName];
}
Related
for(int i=0;i<[serviceNamesFilterArray count];i++){
NSLog(#"state : %#", [serviceNamesFilterArray objectAtIndex:i]);
NSString *str = [serviceNamesFilterArray objectAtIndex:i];
if (tag_id == [serviceNamesFilterArray indexOfObject:str] ) {
// filterButtonArray = serviceNamesFilterArray;
[filterButtonArray addObject:str];
NSLog(#"%#",filterButtonArray);
}
}
I want to access index of serviceNamesFilterArray. How can i access index's of my array so that i can compare it with integer tag_id?
Even Objective-C provides smarter filter APIs than a loop.
index will contain the index of the object in the array matching tag_id
NSInteger index = [self.serviceNamesFilterArray indexOfObjectPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop) {
return (NSString *)obj.integerValue == tag_id;
}];
you can compare i value with your tag_id as follows:
for(int i=0;i<[serviceNamesFilterArray count];i++) {
NSLog(#"state : %#", [serviceNamesFilterArray objectAtIndex:i]);
NSString *str = [serviceNamesFilterArray objectAtIndex:i];
if (tag_id == i) {
//perform your logic here
}
}
you can use the enumerateObjectsUsingBlock method, like
[serviceNamesFilterArray enumerateObjectsUsingBlock:^(id _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
// ...
}];
Preamble: you are using [array objectAtIndex:index] in your code, while this was the way to index historically in modern Objective-C you simply write array[index]. If you are learning Obj-C from a book/website you might want to look for a newer text.
It is unclear what you are asking let’s see what we can figure out.
You start with a loop:
for(int i=0;i<[serviceNamesFilterArray count];i++)
Here i is going to be used as an index into the array serviceNamesFilterArray. Inside the loop you then access the object at index i (updating your code as above):
NSString *str = serviceNamesFilterArray[i];
and having obtained the object at index i you ask what is the index of that object:
[serviceNamesFilterArray indexOfObject:str]
There are two possible answer here:
i – this is the most obvious answer and will be the result if there are no duplicates in serviceNamesFilterArray. It will be the answer as you just obtained str from index i of the array.
j where j < i – this will be the answer if the array contains duplicates and the same string is found at indices j and i. This result happens because indexOfObject: returns the first index at which the object occurs with the array.
The most likely result seems to be (1) in your case (guessing you do not have duplicate “service names”). In this case your conditional is equivalent to:
if (tag_id == i) {
[filterButtonArray addObject:str];
}
However if this is your intention then the loop is completely unnecessary as your code is equivalent to:
NSString *str = serviceNamesFilterArray[tag_id];
[filterButtonArray addObject:str];
If the serviceNamesFilterArray does contain duplicates then your code as written may add the string at index tag_id multiple times to filterButtonArray or it may add it no times – we'll leave figuring out why as an exercise, and we doubt this is your intention anyway.
At the time of writing #vadian has made a different guess as to your aim. Their solution finds the index, if any, where the string value if interpreted as an integer is equal to the value of tag_id (an integer). If that is your aim then #vadian’s solution provides it.
Of course both our and #vadian’s guesses might be wrong at to what your aim is. If so you can edit the question to explain, or delete it and ask a new one instead – given this question has at the time of writing 3 answers already deletion in this case might be better to reduce future confusion when people read the (revised) question and (outdated) answers.
HTH
Maybe you just need to judge whether the tag_id is less than count of serviceNamesFilterArray, then you can get the value by tag_id directlly.
if (tag_id < [serviceNamesFilterArray count]){
NSString *str = [serviceNamesFilterArray objectAtIndex:tag_id];
// other logic here
}
This is a pretty simple concept, but I'm not getting the results I'm wanting. I have an NSMutableArray that is populated with NSArrays, I want to loop through that NSMutableArray and remove certain NSArrays based on a key-value pair. My results have many of the NSArrays that I should be removing and I think it has something to do with the count of the NSMutableArray and the int I declare in the For Loop.
Here is my code: (restArray is the NSMutableArray)
for (int i=0; i<restArray.count; i++) {
NSArray *array = restArray[i];
if ([[array valueForKey:#"restaurant_status"] isEqualToString:#"0"]) {
[restArray removeObjectAtIndex:i];
}
}
Does someone know what I am doing wrong here?
It is not recommended to modify an array on what are you currently iterating.
Lets create a tmp array, and reverse your logic.
NSMutableArray * tmpArray = [NSMutableArray array];
for (int i=0; i<restArray.count; i++) {
NSArray *array = restArray[i];
if (![[array valueForKey:#"restaurant_status"] isEqualToString:#"0"] {
[tmpArray addObject:array];
}
}
So at the end of the iteration, you should end up with tmpArray having the arrays you needed.
Use NSPredicate:
NSArray *testArray = #[#{#"restaurant_status" : #"1"}, #{#"restaurant_status" : #"0"}];
NSArray *result = [testArray filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:#"(restaurant_status == %#)", #"1"]];
When you remove an element all the elements past it shift down by one, e.g. If you remove the element at index 3 then the element previously at index 4 moves to index 3.
Every iteration you increase the index by one.
Combine the above two and you see that when you remove an element your code skips examining the following element.
The simple solution is to reverse the order of the iteration:
for (int i = restArray.count - 1; i >= 0; i--)
and then your algorithm will work.
Addendum
You can safely ignore this addendum if your arrays contain < 2^32 elements and you use Clang or GCC (and most other C compilers).
It has been raised in the comments that this answer has a problem if the array has 0 elements in it. Well yes & no...
First note that the code in the question is technically incorrect: count returns an NSUInteger which on a 64-bit machine is a 64-bit unsigned integer, the loop variable i is declared as an int which is 32-bit signed. If the array has more than 2^31-1 elements in it then the loop is incorrect.
Most people don't worry too much about this for some reason ;-) But let's fix it:
for (NSInteger i = restArray.count - 1; i >= 0; i--)
Back to the problem with an empty array: in this case count returns unsigned 0, C standard arithmetic conversions convert the literal 1 to unsigned, the subtraction is done using modular arithmetic, and the result is unsigned 2^64-1.
Now that unsigned value is stored into the signed i. In C converting from signed to unsigned of the same type is defined to be a simple bit-copy. However converting from unsigned to signed is only defined if the value is within range, and implementation defined otherwise.
Now 2^64-1 is greater than the maximum signed integer, 2^32-1, so the result is implementation defined. In practice most compilers, including Clang and GCC, choose to use bit-copy, and the result is signed -1. With this the above code works fine, both the NSInteger and the int (if you've less than 2^32-1 elements in your array) versions.
What the comments raise is how to avoid this implementation-defined behaviour. If this concerns you the following will handle the empty array case correctly with ease:
for (NSUInteger i = restArray.count; i > 0; )
{
i--; // decrement the index
// loop body as before
}
If the array is empty the loop test, i > 0, will fail immediately. If the array is non-empty i, being initialised to the count, will start as one greater than the maximum index and the decrement in the loop will adjust it - effectively in the loop test i contains the number of elements left to process and in the loop body after the decrement contains the index of the next element to process.
Isn't C fun (and mathematically incorrect by definition)!
I am trying to return the lowest number in an array.
Parameter: arrayOfNumbers - An array of NSNumbers.
Return: The lowest number in the array as an NSInteger.
The code I have thus far doesn't give me any errors, but does not pass the unit tests. What am I doing wrong?
- (NSInteger) lowestNumberInArray:(NSArray *)arrayOfNumbers {
NSNumber* smallest = [arrayOfNumbers valueForKeyPath:#"#min.self"];
for (NSInteger i = 0; i < arrayOfNumbers.count; i++) {
if (arrayOfNumbers[i] < smallest) {
smallest = arrayOfNumbers[i];
}
}
NSInteger smallestValue = [smallest integerValue];
return smallestValue;
}
This is the unit test:
- (void) testThatLowestNumberIsReturned {
NSInteger lowestNumber = [self.handler lowestNumberInArray:#[#3, #8, #-4, #0]];
XCTAssertEqual(lowestNumber, -4, #"Lowest number should be -4.");
lowestNumber = [self.handler lowestNumberInArray:#[#83, #124, #422, #953, #1004, #9532, #-1000]];
XCTAssertEqual(lowestNumber, -1000, #"Lowest number should be -1000.");
}
This method
NSNumber* smallest = [arrayOfNumbers valueForKeyPath:#"#min.self"];
will already determine the smallest number in the array, so the loop inside the method is superfluous (on top of being plain wrong, as #vikingosegundo notices).
you are comparing objects with c types, resulting im pointer addresses being compared with an int.
Beside the fact your smallest is already the smallest, as you used the KVC collection operator #min.self (see Glorfindel answer), the following code shows you correct comparison
if (arrayOfNumbers[i] < smallest)
should be
if ([arrayOfNumbers[i] compare:smallest] == NSOrderingAscending)
or
if ([arrayOfNumbers[i] integerValue] < [smallest integerValue])
This question already has answers here:
Objective C Equivalent of PHP's "Variable Variables" [duplicate]
(2 answers)
Closed 8 years ago.
For my iOS app, I created a class named Tile which is a subclass of UIImageView.
The tiles are displayed in a kind of an array of 6 rows and 5 column.
I previously created 30 instances of my Tile class. These instances are all named this way: RiCj where i is the row number and j is the column number.
I would like to create a for loop where I would apply a specific treatment to each of my tiles (basically, I want to display the tiles where displayTile is an instance method of the class Tile).
I would love to do something like (I know the code below is incorrect):
for (int i = 1; i <= numberOfRows ; j++) {
for (int j = 1; j <= numberOfColumns ; j++) {
[self.RiCj displayTile];
}
}
I don't know how to do a call to my tiles based on their dynamic string title.
Yes, technically, it is possible - you may use Key-Value Coding like this:
for (int i = 1; i <= numberOfRows; i++) {
for (int j = 1; j <= numberOfColumns; j++) {
NSString* tileName = [NSString stringWithFormat:#"R%dC%d", i, j];
[[self valueForKey:tileName] displayTile];
}
}
But you should not. It won't be a clean solution. Array is a more natural choice here.
Yes, you can actually access a property of a class dynamically by creating a string naming the property then using KVC like so:
NSString *propertyName = [NSString stringWithFormat:#"R%dC%d", i, j];
tile = [self valueForKey:propertyName];
But should you? No, not in this case. It's a horrible hack when the perfectly nice alternative of making an array (or array of arrays) is available.
Here's what array of array creation and access might look like (by using handy Objective C literals for arrays):
NSArray *tiles = #[
#[ tile0C0, tile0C1, tile0C2 ],
#[ tile1C0, tile1C1, tile1C2 ],
#[ tile2C0, tile2C1, tile2C2 ],
];
for (int i = 0; i < numberOfRows ; j++) {
for (int j = 0; j < numberOfColumns ; j++) {
tile = tiles[j][i];
// do stuff with tile
}
}
If I understand correctly, you're trying to access the instances by their variable names dynamically. You can't do that, as your variable name is designed for you, the programmer, and is not available at runtime.
What you can do, however, is to keep a list of your created instances in an array somewhere, and simply iterate over that array when you need to access them.
Alternatively, if you created the 30 tiles as 30 different properties, you could use some dynamic code to get them. At that point, however, I would strongly recommend to use the array technique.
I have an NSArray filled with only NSStrings
I understand that to iterate over a NSArray of n elements, all I have to do is use for (NSString *element in arrayOfElements). However, I was wondering if there is specific function that will perform a comparison between every string element in the array with each other. For example, if I have the array:
[#"apple", #"banana", #"peach", #"kiwi"],
how would I do the comparison so apple is compared to banana, peach and then kiwi; and then banana is against peach and wiki, and finally peach is against kiwi?
Try using nested for loops, ex:
for (int i = 0 ; i < array.count ; i ++) {
for (int j = i + 1 ; j < array.count ; j ++) {
// compare array[i] to array [j]
}
}
Edit: And although wottle's suggestion would work, I'd recommend mine in this case, since it won't waste iterations going over the same comparisons multiple times. What I've done in this algorithm by setting j = i + 1 is compare each element in the array only to the ones after it.
Given "the array will not have any duplicates, and every NSString will be unique" this sounds like a great case for using NSSet classes instead of NSArray. NSMutableSet provides:
minusSet:
Removes each object in another given set from the receiving
set, if present.
and
intersectSet:
Removes from the receiving set each object that isn’t a
member of another given set.
I'm not sure which operation you're looking for but it sounds like one of those should cover your exact use case.
What you're trying to do is a bit beyond what custom comparators were meant to do. Typically when you have a list and you want to run a custom comparator, you're doing it to sort the list. You seem to want to do some specific action when certain items in the list compare to others, and for that, I think a loop within a loop is your best bet. It won't be very good performance, so hopefully you are not expecting a large array:
-(void) compareArrayToSelf
{
NSArray *array=#[#"apple", #"bananna", #"peach", #"kiwi"];
for( NSString *value1 in array)
{
for( NSString *value2 in array)
{
if( ![value1 isEqualToString:value2] && [self compareArrayValue:value1 toOtherValue:value2])
{
//Do something with either value1 or value2
}
}
}
}