i use xcode 9
NSMutableArray *Upcase_Keys = #[#"1",#"2",#"3",#"4,"#"5",#"6",#"7",#"8",#"9",#"0"];
NSString *str = [Upcase_Keys objectAtIndex:0];
str = #"test";
[Upcase_Keys replaceObjectAtIndex:0 withObject:str];
Gets specific data for NSMutableArray
It transforms the value and overwrites the existing index.
However, this code causes a crash.
What did I do wrong?
NSMutableArray replaceObjectAtIndex Crash
So there should be an error in console. Console will help you 99% of the cases when there is a crash, read it!
It should be something like -[NSArrayI replaceObjectAtIndex:withObject:] unrecognized selector sent to instance. That's the important part of your error. NSArrayI meaning NSImmutableArray (NSArray in other words), which is not a NSMutableArray which points out that the issue is about the creation of Upcase_Keys.
Why then? Because #[#"1",#"2",#"3",#"4,"#"5",#"6",#"7",#"8",#"9",#"0"]; that's a short hand syntax for NSArray, not NSMutableArray. So even if it's declared as a NSMutableArray, the object is in fact a NSArray.
In fact, if you'd listen to XCode, it should give you this warning:
Incompatible pointer types initializing 'NSMutableArray *' with an
expression of type 'NSArray *'
Which concords with everything said before.` Sometimes XCode may be wrong, but try to listen to it.
There are a few possibilities call:
NSMutableArray *Upcase_Keys = [NSMutableArray arrayWithArray:#[#"1",#"2",#"3",#"4,"#"5",#"6",#"7",#"8",#"9",#"0"]];
NSMutableArray *Upcase_Keys = [[NSMutableArray alloc] initWithArray:#[#"1",#"2",#"3",#"4,"#"5",#"6",#"7",#"8",#"9",#"0"]];
NSMutableArray *Upcase_Keys = [#[#"1",#"2",#"3",#"4,"#"5",#"6",#"7",#"8",#"9",#"0"] mutableCopy];
And finally, a recommendation use camelcase:
Avoid naming your var with an uppercase. Use a lower case for the first letter. I'd say that after the _ is less problematic, but we tend in iOS to write instead.
Upcase_Keys => upcase_Keys => upcaseKeys
You have defined as immutable object, The syntax will assign NSArray reference not NSMutableArray. You can't update the NSArray.
Try like this,
NSMutableArray *Upcase_Keys = [NSMutableArray arrayWithArray:#[#"1",#"2",#"3",#"4,"#"5",#"6",#"7",#"8",#"9",#"0"]];
Related
I want to remove objects from NSmutableArray can one tell me the Best way to remove from NSMutableArray
.h
#property(nonatomic,retain)NSMutableArray *arr_property;
.m
_arr_property=[[NSMutableArray alloc]init];
MTPop *lplv = [[MTPop alloc] initWithTitle:SelectProperty(APP_SHARE.language)
options:[_arr_property valueForKeyPath:#"property_list.property_type_name"]
handler:^(NSInteger anIndex) {
txt_Property.text=[[_arr_property valueForKeyPath:#"property_list.property_type_name"] objectAtIndex:anIndex];
NSLog(#"index number %ld",(long)anIndex);
remove object--->>>
NSLog(#"index number %#",[_arr_property valueForKey:#"property_list"]);
[[_arr_property valueForKeyPath:#"property_list.property_type_name"] removeObjectAtIndex:anIndex]; ////hear the app is crashing
app is crashing error iam getting is
2015-06-09 13:21:31.104 Estater[2170:62264] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFArray removeObjectAtIndex:]: mutating method sent to immutable object'
Think about your code:
_arr_property=[[NSMutableArray alloc]init];
You now have an empty NSMutableArray. It has no elements.
[... removeObjectAtIndex:0];
What did we just say? The array has no elements. It has no element 0 - to have an element 0 it would need to have one element at least, but it doesn't. There is nothing to remove.
[_arr_property valueForKeyPath:#"property_list.property_type_name"]
That part is the weirdest, but let's carry on. When called on an array, valueForKeyPath: results in an NSArray - not an NSMutableArray. So this gives you an empty NSArray. But you cannot say removeObjectAtIndex: to an NSArray, even if it empty - it is not mutable. That's the crash you are experiencing.
The real error is that you are calling removeObject on an element of your NSMutableArray:
[-->[_arr_property valueForKeyPath:#"property_list.property_type_name"]<-- removeObjectAtIndex:0];
The array looks empty, but if filled with something, to remove the first element you should do instead:
[_arr_property removeObjectAtIndex:0];
Firstly, you cannot work with NSMutableArray for key value coding it does not support. You must better use NSMutableDictionary for it.
As dictionaries store objects based on a key, whereas arrays store objects based on an index.
You can use NSMutableDictionary like this:
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
[dict setObject:something forKey:#"Some Key"];
// ... and later ...
id something = [dict objectForKey:#"Some Key"];
Secondly, valueForKeyPath: returns a value not array and valueForKey: returns array of value for the key and also that array is not mutable.
Edit:
Thirdly, after researching more on valueForKeyPath:, found its use in collection operation and syntax for using is. So, do it by changing
[_arr_property valueForKeyPath:#"property_list.property_type_name"]
To
[_arr_property valueForKeyPath:#"#property_list.property_type_name"]
Write an empty NSMutableArray to disk, then read it back, it becomes an immutable object.
But, if the NSMutableArray is not empty, it won't. How to explain that?
here are the codes:
NSMutableArray *testItems1 = [NSMutableArray array];
NSMutableDictionary *testList1 = [NSMutableDictionary dictionaryWithObjectsAndKeys:testItems1, #"list_items", #"list1", #"list_name", nil];
NSMutableArray *testItems2 = [NSMutableArray arrayWithObjects:#"item11", #"item22", nil];
NSMutableDictionary *testList2 = [NSMutableDictionary dictionaryWithObjectsAndKeys:testItems2, #"list_items", #"list2", #"list_name", nil];
NSMutableArray *testLists = [NSMutableArray arrayWithObjects:testList1, testList2, nil];
[testLists writeToFile:#"/tmp/testLists" atomically:YES];
NSMutableArray *testReadLists = [NSMutableArray array];
[testReadLists setArray:[NSArray arrayWithContentsOfFile:#"/tmp/testLists"]];
NSMutableDictionary *testReadList = [testReadLists objectAtIndex:0];
NSMutableArray *testReadItems = [testReadList objectForKey:#"list_items"];
[testReadItems addObject:#"item3"]; // Crashes here: "*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFArray insertObject:atIndex:]: mutating method sent to immutable object'"
These two lines of code:
NSMutableArray *testReadLists = [NSMutableArray array];
[testReadLists setArray:[NSArray arrayWithContentsOfFile:#"/tmp/testLists"]];
give you a mutable array of immutable objects. You can add and remove objects from testReadLists but everything you get from this array (originally loaded from the plist) will be immutable.
Update - I was about to post info about the solution but the answer by Vivek describes what I was going to say.
Haven't tested this myself, but you probably want to first read the plist into an NSData, and then get the actual array by doing +[NSPropertyListSerialization propertyListWithData:options:format:error:], specifying NSPropertyListMutableContainers in the options argument (apple doc here)
Note this should give you a full hierarchy of mutable containers (an NSMutableArray containing NSMutableDictionaries, and so on). If all you want is an NSMutableArray at one particular level in the hierarchy, then the other posted solution/comments would probably be a more appropriate solution.
Objects read straight from property lists are always immutable. You might create a mutable object from them, but the objects themselves are immutable. These lines are the problem:
NSMutableDictionary *testReadList = [testReadLists objectAtIndex:0];
NSMutableArray *testReadItems = [testReadList objectForKey:#"list_items"];
testReadList is the first object in the mutable array testReadLists, but that object itself is still immutable despite the fact that the declared type of testReadList is NSMutable*. Likewise, the object you get back from the objectForKey: call is an instance of NSArray even though you're assigning it to testReadItems, which is declared as NSMutableArray*. You can avoid the problem by simply making a mutable copy before you add new items:
NSMutableArray *testReadItems = [[testReadList objectForKey:#"list_items"] mutableCopy];
Specifically:
self.words = (NSMutableArray*)[self.text componentsSeparatedByString:#" "];
works fine so long as there are separators. I see that the method returns the original string wrapped in an NSArray if there isn't, though. This single element NSArray stubbornly refuses to be cast as an NSMutableArray.
But, when I do:
self.words = [NSMutableArray arrayWithArray:self.words];
It works just fine.
Is there something I'm missing here? Is it bad practice to cast from NSArray to NSMutableArray?
You are confused.
This code:
self.words = (NSMutableArray*)[self.text componentsSeparatedByString:#" "];
...is wrong, and is setting you up for a crash later on. Casting just tells the compiler "trust me, I know what I'm doing." It does not change the type of the underlying object. The method componentsSeparatedByString returns an NSArray, not a mutable array. If you then try to mutate the resulting array, you will crash with an unrecognized selector message. With the cast, the compiler trusts you that your object will really be a mutable array at runtime, but it will not be.
This would crash:
self.words = (NSMutableArray*)[self.text componentsSeparatedByString:#" "];
[self.words addObject: #"new"];
However, this code:
self.words = [[self.text componentsSeparatedByString:#" "] mutableCopy];
[self.words addObject: #"new"];
...does the right thing. It doesn't cast a pointer, it is a method call to a method that takes an NSArray as input and returns a mutable array with the same contents. Thus the second line will work because the first line takes the immutable array it gets back from componentsSeparatedByString and uses it to create a mutable array.
It is bad practice to cast from NSArray to NSMutableArray. It may works if you are lucky because the array are constructed using NSMutableArray, but you can't rely on it.
If you want NSMutableArray from NSArray, use mutableCopy
self.words = [[self.text componentsSeparatedByString:#" "] mutableCopy];
Is it bad practice to cast from NSArray to NSMutableArray?
Yes. Bordering on nonsensical, really.
Typecasting does not change the object in any way at all, it just tells the compiler that it should regard the object as if it were an instance of the new type. At run time though, the object stays exactly the same. You may cast an NSArray to an NSMutableArray but it doesn't make the object transform into an NSMutableArray. It's still the same object of the same type.
Your misconception seems to be about the nature of casting. Casting doesn't change the object, it just tells the compiler to pretend that it's an object of that type. If the object really isn't an NSMutableArray, casting is not expected to make it become one.
NSString* string1 = #"this thing";
NSString* string2 = #"this";
NSMutableArray* array1;
NSMutableArray* array2;
array1 = (NSMutableArray*)[string1 componentsSeparatedByString:#" "];
array2 = (NSMutableArray*)[string2 componentsSeparatedByString:#" "];
[array1 addObject:string1]; //(A)
[array2 addObject:string1]; //(B)
This will break at (B) the last line with :
-[__NSArrayI addObject:]: unrecognized selector sent to instance 0x1702257a0
But will not break at (A)1
An object that is publicly declared as immutable may have been privately created as mutable. In this case, if you cast from the immutable public type to the private mutable type, everything will work fine. Where the object was not created as mutable, such a cast will not get you what you want.
In the case of componentsSerparatedByString, this suggests that the method implementation creates a mutable array only if it needs to - i.e. if it has to add more than one object to the array. If it only finds one object, you get an NSArray, if it finds more than one, you get an NSMutableArray. This is an implementation detail that is deliberately hidden from you as the user.
The interface tells you to expect an NSArray in all cases, and in all cases this will work.
You should not rely on such details to get you what you want. Stick to the public API, that's what it is for.
1 rather, as Bryan Chen points out, it may not break now but could well do so in the future
When you do that:
self.words = (NSMutableArray*)[self.text componentsSeparatedByString:#" "];
the array still remains immutable and if you send it a message from NSMutableArray class it will crash. The trick (NSMutableArray*) is only good to make the compiler happy.
In the second case:
self.words = [NSMutableArray arrayWithArray:self.words];
you do not CAST, you CREATE a new array object.
And of course you don't need to cast the arrays this way. NSMutableArray object IS already NSArray just like any object of a derived class is an object of a base class at the same time
Use second variant in all cases because it is right solution and more clearly for users who will support your code:
NSArray *array = [self.text componentsSeparatedByString:#" "];
self.words = [NSMutableArray arrayWithArray:array];
Never do this one:
self.words = [NSMutableArray arrayWithArray:self.words];
It will totally confuse all devs =)
In the first case, the componentsSeparatedByString: method is specifically returning an NSArray, which can't just be cast to the mutable type. If you wanted that to be mutable, you would have to do this:
self.words = [[self.text componentsSeparatedByString:#" "] mutableCopy];
The second one is calling the arrayWithArray: method on the NSMutableArray class, meaning it is making an instance of NSMutableArray. That's why it works. You can cast an NSMutableArray to an NSArray, but not the other way around, because an NSMutableArray is a subclass of NSArray.
Casting does nothing with an object. example:
NSString *mouse = (id)#[#"mouse"];
it will compile, but variable mouse is not NSString. it is NSArray. you can check it simply by writing
po mouse
in console.
The only way to create mutable copy of an object is to call 'mutableCopy' method on it:
NSArray *array = #[#"a"];
NSMutableArray *mutableCopy = [array mutableCopy];
I see a new kind of alloc&init NSMutableArray way in one project. It's like this A
NSMutableArray *array = [#[] mutableCopy]; and this works well, and i want to try whether its possible to use BNSMutableArray *array = [NSMutableArray mutableCopy]; it build succeeded, but got this error when used: +[NSMutableArray addObject:]: unrecognized selector sent to class 0x38bedc2c
Now i want to know how does A work? and why B is wrong? A is better than normal alloc&init?
Any help will be appreciated.
mutableCopy is an instance method declared in NSObject class. It is called on any instance to create a mutable copy of it.
In first case #[] will create an autoreleased NSArray instance on which calling mutableCopy will create NSMutableArray instance.
In second case calling mutableCopy on the class is incorrect because it is not meant to be called that way. This will get compiled but will cause exception at runtime.
Hope that helps!
In the first case, you're first initializing an empty NSArray instance; think of #[] as equivalent to [[NSArray alloc] init]. Therefore you're sending mutableCopy to a correct instance, so it works fine.
In the second case, you're sending the message to a class (as opposed to an instance of it), which doesn't make much sense, because the addObject message can only be sent to an instance, not the class itself.
#[] means an NSArray with no object. It returns an NSArray, and then its mutableCopy is copied to array.
+[NSMutableArray addObject:] is invalid as addObject is an instance method and you are trying to use it as class method.
Even NSMutableArray *array = [NSMutableArray mutableCopy]; is incorrect!!! As nothing is created, it is not been allocated and inited. If you log the array, it will only print the string NSMutableArray. Also you can't use array to addObject and other operations.
You should use NSMutableArray *array = [NSMutableArray array];
The first one is lazy typing.
You should avoid it.
It creates an empty NSArray from the array literal syntax and the creates a mutable copy.
That's saving a little typing by creating an unnecessary array.
You should just use
[NSMutableArray new]
Or
[[NSMutableArray alloc] init]
Or if possible because you know the initial capacity in advance
[[NSMutableArray alloc] initWithCapacity:someNSUIntegerValue]
Anything else above is laziness.
Only use mutableCopy when you are actually copying some content.
I have declared an NSMutableArray *arrAllRecordsM and am trying to add NSMutableDictionary *dicRecordM to it using addObject. The dicRecordM gets added to arrAllRecordsM but on doing [dicRecordM removeAllObjects] it sets to nil in arrAllRecordsM. Below is the code, please help me fix it.
self.arrAllRecordsM = [NSMutableArray array];
self.dicRecordM = [NSMutableDictionary dictionary];
// Some Method
[self.dicRecordM setObject:#"Test" forKey:#"ADDRESS"];
[self.arrAllRecordsM addObject:self.dicRecordM];
// Value: Test
NSLog(#"Value: %#", [[self.arrAllRecordsM objectAtIndex:0] valueForKey:#"ADDRESS"]);
[self.dicRecordM removeAllObjects];
// Value: null
NSLog(#"Value: %#", [[self.arrAllRecordsM objectAtIndex:0] valueForKey:#"ADDRESS"]);
Adding an object to an NSMutableArray just stores a pointer (or "strong reference")
to the object into the array. Therefore
[self.arrAllRecordsM objectAtIndex:0]
and
self.dicRecordM
are two pointers to the same object. If your remove all key/value pairs from self.dicRecordM then [self.arrAllRecordsM objectAtIndex:0] still points to the same
(now empty) dictionary. That is the reason why
[[self.arrAllRecordsM objectAtIndex:0] valueForKey:#"ADDRESS"]
returns nil.
If you want an independent copy of the dictionary in the array, use
[self.arrAllRecordsM addObject:[self.dicRecordM copy]];
copy can be used on many classes, such as NSDictionary, NSArray and NSString
and their mutable variants, to get a "functionally independent object". Formally, it is available for all classes conforming to the NSCopying protocol.
This is expected behavior.
You removed all the objects from the dictionary by calling removeAllObjects, then tried to retrieve an object from it and rightfully getting nil, since it doesn't exist in the dictionay anymore (you removed it).
What's maybe unclear to you is that NSArray doesn't copy the element you add to it, instead it just holds a strong reference.
So both dicRecordM and arrAllRecordsM are holding a reference to the same object, hence any modification to it (in this case removeAllObjects) will affect the same dictionary.
Incidentally, you shouldn't use valueForKey: for accessing the dictionary's entries. Use objectForKey: or the shorter subscripted syntax. For instance
self.arrAllRecordsM[0][#"ADDRESS"]
You can read this answer Difference between objectForKey and valueForKey? as a reference, but the main problem is that valueForKey: can behave very differently from objectForKey: in case the key contains special KVC characters, such as # or ..