This is my code:
NSString *newString = #"new value";
[breakdownCollection objectAtIndex:i] = newString;
breakdownCollection is an NSArray of multiple strings. I need to access a given string contained in the array via index number, and change the string's content to that of the new string. Note that I cannot simply replace the string with the new one, I am only trying to replace its contents.
When I try to do this, however, I get an "lvalue required as left operand of assignment" error.
Any help with this issue would be very much appreciated!
The error you get is because you wrote the assignement instruction incorrectly. That is, you cannot assign newString to [breakdownCollection objectAtIndex:i].
Also, you won't be able to do it this way. Instead, in order to modify string object content, use NSMutableString, which provides methods to do so (NSString are immutable objects).
So, for example you should try :
[[breakdownCollection objectAtIndex:i] setString:newString];
assuming you put NSMutableString into breakdownCollection.
PS : in order to change the object at the index i, you have to use NSMutableArray instead of NSArray, and then call :
[breakdownCollection replaceObjectAtIndex:i withObject:newString];
Good luck !
NSMutableString class reference
NSMutableArray class reference
Use an NSMutableArray instead and then you can use the method -replaceObjectAtIndex: withObject:
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.
If I have this code, why doesn't the textview's text update? As far as I knew a * meant a pointer, and I haven't done a copy.
NSString *searchText = myTextView.text;
searchText = [searchText stringByReplacingOccurrencesOfString:#" " withString:#";"];
So why isn't myTextView's text changed as if I did:
myTextView.text = [searchText stringByReplacingOccurrencesOfString:#" " withString:#";"];
And how would I write the code, so that the first code example works as I intend?
The method stringByReplacing... Doesn't change the string, it returns a new string object (autoreleased, according to the naming conventions). So after the 2nd line of code, searchText points to a totally differen NSString object.
Besides, NSString objects cannot be changed, for that there's NSMutableString
If you expect to modify myTextView.text, you have to write it like your second example, and assign a new value to the property you're trying to modify. Assigning a new value to some other variable or property won't do the job - "spooky action at a distance" may work when we eventually have quantum computing, but we're not there yet. :-)
To expand a bit: Yes, searchText is a pointer. But so is myTextView.text, and when you do "searchText = myTextView.text", you're not creating any sort of lasting relationship between the two - all you're doing is making searchText point to the same target as myTextView.text. Changing either one of them after that point will have no effect on the other. So, when you assign the result of stringByReplacing... to searchText, you're making it and only it point to a different target.
Your second example invokes the setter of the "text" property.
Your first example takes the pointer of the string, and then changes the pointer within the same scope. Hence, "text" is not changed.
BTW: Depending on how your property is defined, the setter you use will either copy, retain or assign the value you give the setter. So if you use the following:
#property(copy) NSString* text;
Then yes, the setter will copy the value you give it when you invoke:
myTextArea.text = //some string
I have the following code that populates an array (this is within a loop):
NSString *code = [NSString stringWithFormat:#"%# - (%#) %#",[tempDic objectForKey:#"state"],[tempDic objectForKey:#"city"],[tempDic objectForKey:#"name"]];
[tempArrayOfAirports removeObjectIdenticalTo:code]; // checks for a previous object, then removes if found
[tempArrayOfAirports addObject:code]; //adds the object
Previously, code had simply been:
NSString *code = [tempDic objectForKey:#"city"];
[tempArrayOfAirports removeObjectIdenticalTo:code];
[tempArrayOfAirports addObject:code];
Which worked fine, but for some reason, changing "code" is keeping it from finding other identical strings. My result is a huge array with many, many repeated objects.
Since you're creating a new string in your new code, you probably want to use removeObject: instead of removeObjectIdenticalTo:. The removeObjectIdenticalTo: method uses object addresses to test for "identicalness," whereas removeObject: tests for equality using isEqual:. If you only care about the contents of the strings, use removeObject:.
In your old code, you probably inserted the same object into both tempDic and tempArrayOfAirports so the address check worked. This is not the case in your new code, in which you create a new string (at a new address) with stringWithFormat:.
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.