I need to compare a key object from a div to a string. I access the key object in a for loop:
for (id key in _photosDic) {
...
}
In the loop, I want to compare the key with a string. Do I have to convert the key to a string?
id type can be anything so the first step would be to check if it is actually a NSString or not.
for that you can use this:
if ([idObject isKindOfClass:[NSString class]])
{
//Now do a simple casting
NSString *myString = (NSString *)idObject;
//Now compare the strings
NSComparisonResult result = [myOtherString compare:myString];
}
Related
I have NSArray of NSDictionaries I need to extract 2 values or remove the values I don't need from the dictionary in the example below I need to remove id and NumberValue. any of you knows how can I do that?
Array: (
{
customerUS= {
DisplayName = "level";
InternalName = "Number 2";
NumberValue = 1;
id = xwrf
},
customerCAN= {
DisplayName = "PurchaseAmount";
InternalName = "Number 1";
NumberValue = 3500;
id = adf;
};
}
)
I'll really appreciate your help.
First thing, You can not remove/insert/update value in (immutable) NSDictionary/NSArray you need to convert NSDictionary/NSArray to (mutable) NSMutableDictionary/NSMutableArray.
such like
NSArray *myArr = ....;
NSMutableArray *newMutableArr = [myArr mutableCopy];
Then you can change in newMutableArr.
Such like
for(int i = 0 ; i < newMutableArr.count ; i ++)
{
[[newMutableArr objectAtIndex:i] removeObjectForKey:#"id"];
[[newMutableArr objectAtIndex:i] removeObjectForKey:#"NumberValue"];
}
EDITED:
Without Use of for loop and removeObjectForKey, if you have array of dictionary and both are mutable then you can also delete a key and its object from all elements of the array like this:
[newMutableArr makeObjectsPerformSelector:#selector(removeObjectForKey:) withObject:#"id"];
[newMutableArr makeObjectsPerformSelector:#selector(removeObjectForKey:) withObject:#"NumberValue"];
I would advice you to read Apple documents.
For modifying any Collection object after it is created, you need the mutable version.
For NSDictionary we have NSMutableDictionary. Read here.
We have a method for removing objects:
- (void)removeObjectForKey:(id)aKey
There are other methods as well. You can easily refer them in the above mentioned documentation.
Find out removeObjectForKey for deleting record from NSMutabledictionary.
removeObjectForKey pass the key value whatever you have like
all this are your key
DisplayName,
InternalName,
NumberValue,
id
do like this
removeObjectForKey:#"id";
First of all you have to convert the array to mutable array and then you can remove the key-value pairs from dictionary.
NSMutableArray *mutableArray = [yourArray mutableCopy];for(int i=0;i<mutableArray.count;i++){ NSMutableDictionary *outerDictionary = [mutableArray objectAtIndex:i]; for(NSString *key in outerDictionary.allKeys){ NSMutableDictionary *innerDictionary = [outerDictionary objectForKey:key]; [innerDictionary removeObjectForKey:#"id"]; [innerDictionary removeObjectForKey:#"NumberValue"]; }
}
I've got an method that takes NSDictionary arg. This NSDictionary has some predefined keys it'll take. All the obj's should be strings. But only certain string objs are valid for each key.
So my approach was to typedef NSString for each valid string per key. I'm hoping not to extend the NSString class.
I've typedef'd some NSString's...
typedef NSString MyStringType
Then I define a few...
MyStringType * const ValidString = #"aValidString";
Here's what I'd like to do in my sample method..
- (void)setAttrbiutes:(NSDictionary *)attributes {
NSArray *keys = [attributes allKeys];
for (NSString *key in keys) {
if ([key isEqualToString:#"ValidKey"]) {
id obj = [attributes objectForKey:key];
//Here's where I'd like to check..
if (**obj is MyStringType**) {
}
}
}
}
I'm open to other ideas if there's a better approach to solve the obj type problem of an NSDictionary.
Doesn't work like that; typedefs are a compile time alias that don't survive being passed through a dictionary.
In any case, using typedefs for something like this would be unwieldy.
I suggest you create a property list -- either as a file in your project or in code -- that contains the specifications of your various keys and valid values, then write a little validator that, passed a string and value, can validate the string-value pair for validity.
This also gives you the flexibility to extend your validator in the future. For example, you might have a #"Duration" key that can only be in the range of 1 to 20.
Instead of setting up a typedef for you special values, one possible option would be to create an NSSet of the special values. Then in your code you can verify that the object in the dictionary is in your set.
What about a combination of category on NSString + associated object?
Something along the lines (untested!!):
#interface NSString (BBumSpecial)
- (NSString *) setSpecial: (BOOL) special ;
- (BOOL) special ;
#end
and:
#implementation NSString (BBumSpecial)
static void * key ;
- (NSString *) setSpecial: (BOOL) special {
objc_setAssociatedObject(self, &key, special ? #YES : #NO, OBJC_ASSOCIATION_ASSIGN) ;
return self ;
}
- (BOOL) special {
id obj = objc_getAssociatedObject(self, &key) ;
return obj && [obj boolValue] ;
}
#end
Which you could then use as:
NSString * mySpecialString = [#"I'm Special" setSpecial:YES] ;
?
I got a NSMutableArray object with int values
and I can get a certain value via :
int *v0=[[[arrayObj objectAtIndex:0] intValue];
there is no problem.
But
I got a NSMutableArray object with NSString values
and I cannot get a certain value via :
NSString *v0=[[[arrayObj objectAtIndex:0] stringValue];
//raises error
I want to learn and understand exactly what stringValue for... and why this error occurs ?
NSString *v0=[arrayObj objectAtIndex:0];
works as expected.I asusme its some kind of pointer with null terminated so it can leech value.
Im not sure this line is also unicode/encoded string safe code.
in conclusion:
want to know the purpose of stringValue with some lines o code snippets
I got a NSMutableArray object with int values
That's not possible, Cocoa arrays always contain objects. You probably have an array of NSNumber objects that wrap the integers, like:
NSArray *arrayOfNumbers = #[#1, #2, #3];
NSNumber objects have an intValue method, so this works:
int value = [arrayOfNumbers[0] intValue];
On the other hand when you have an array of strings ...
NSArray *arrayOfStrings = #[#"1", #"2", #"3"];
... you want to access individual elements directly, without converting the string object to something else:
NSString *element = arrayOfStrings[0];
NSString objects do not understand the stringValue method:
[arrayOfStrings[0] stringValue]; // crash: does not recognize selector
Back at the beginning, our NSNumber objects from the first array do understand stringValue. You can use it to convert the number to a string:
NSString *intString = [arrayOfNumbers[0] stringValue];
To make the confusion perfect, NSString also understand the intValue message:
int value = [arrayOfStrings[0] intValue];
Here intValue means to try to convert the string to a plain C int value.
The error you will be getting (but failing to post with your question) will be Unknown selector sent to instance and this is because NSString doesn't have a stringValue method.
The approach you suggest is correct:
NSString *v0 = [arrayObj objectAtIndex:0];
EDIT (prompted by #Answerbot's answer):
The reason you are confused is that [NSString intValue] is used to convert the string value to an integer, as long as the string represents an integer (i.e. #"123"). However you don't need this for string as the object is already a string. It's therefore not provided.
I hope i can explain this clearly.
I have a NSMutableArray * myMut.
I have user input in the form of an NSString * anyoldString.
I have user input of some numeric values stored in the variable someNumber;
As users input their string and values, I want to update myMut, and name the fields anyoldString
like this: myMut.anyoldString=someNumber;
depending on the user's input, the name will be different of course
i'm new to objective c.
in Matlab, I would do this:
myMut.(anyoldString)=someNumer.
I know that's too easy for objective c! but any fast way to do this??
You'll probably want to do something like so:
NSMutableDictionary *myMutableDictionary; // A mutable **dictionary**, not an array!
NSInteger someNumber; // filled by the number
NSString *key; // filled by anyOldString
[myMutableDictionary setObject:[NSNumber numberWithInteger:someNumber] forKey:key];
NSArray and friends aren't associative; but indexed. What you want is NSDictionary and friends; your friendly neighborhood key-value mapping!
Edit: For funsies; getting someNumber back out, given anyOldString:
NSMutableDictionary *myMutableDictionary; // The same dictionary as above
NSInteger someNumber; // out number
NSString *key; // filled by anyOldString
NSNumber *storedNumber = [myMutableDictionary objectForKey:key];
if (storedNumber) {
someNumber = [storedNumber integerValue];
} else {
someNumber = APPLICATION_APPROPRIATE_DEFAULT_VALUE;
}
How do i check the key in dictionary is same as the string in method parameter?
i.e in below code , dictobj is NSMutableDictionary's object , and for each key in dictobj i need to compare with string. How to achieve this ? Should i typecase key to NSString??
-(void)CheckKeyWithString:(NSString *)string
{
//foreach key in NSMutableDictionary
for(id key in dictobj)
{
//Check if key is equal to string
if(key == string)// this is wrong since key is of type id and string is of NSString,Control doesn't come into this line
{
//do some operation
}
}
}
When you use the == operator, you are comparing pointer values. This will only work when the objects you are comparing are exactly the same object, at the same memory address. For example, this code will return These objects are different because although the strings are the same, they are stored at different locations in memory:
NSString* foo = #"Foo";
NSString* bar = [NSString stringWithFormat:#"%#",foo];
if(foo == bar)
NSLog(#"These objects are the same");
else
NSLog(#"These objects are different");
When you compare strings, you usually want to compare the textual content of the strings rather than their pointers, so you should the -isEqualToString: method of NSString. This code will return These strings are the same because it compares the value of the string objects rather than their pointer values:
NSString* foo = #"Foo";
NSString* bar = [NSString stringWithFormat:#"%#",foo];
if([foo isEqualToString:bar])
NSLog(#"These strings are the same");
else
NSLog(#"These string are different");
To compare arbitrary Objective-C objects you should use the more general isEqual: method of NSObject. -isEqualToString: is an optimized version of -isEqual: that you should use when you know both objects are NSString objects.
- (void)CheckKeyWithString:(NSString *)string
{
//foreach key in NSMutableDictionary
for(id key in dictobj)
{
//Check if key is equal to string
if([key isEqual:string])
{
//do some operation
}
}
}