I'm trying to use a HKAnchoredObjectQuery on iOS.
To do so I have to provide an anchor to the query which in this case is a NSUInteger. I want to save this integer for queries in the future in the NSUserDefaults and just simply want to use
if(anchor != nil) {
// do stuff
}
But the complier tells me that I'm not allowed to do this because I'm comparing a integer to a pointer and I understand why I'm not able to do this but I don't know how to do it.
The error code is this
Comparison between pointer and integer ('NSUInteger' (aka 'unsigned long') and 'void *')
Does anyone know how I'm able to determine if my anchor has a value or not?
NSUInteger is a primitive type, not an object type. NSNumber is an object type. For an NSNumber object, you can check whether it is nil or not. An NSUInteger is never nil because it is an integer, not a pointer.
Many functions that return NSUInteger as a result for a search return the constant NSNotFound if the search failed. NSNotFound is defined as a very large integer (2^31 - 1 for 32 bit, 2^63 - 1) for 64 bit).
NSUInteger is not an object and cannot be compared to nil. In over-simplistic terms, an object is a pointer to a memory location that may contain an value or be nil. NSUInteger is just a value. It may be 0, or some other value that you don't expect, but it will have a value.
An NSUInteger cannot be nil because it is not an object. The default value on creation would be zero. To save in NSUserDefaults, you could store it as an NSNumber, which could be checked for nil later.
To store it in NSUserDefaults:
NSNumber *aNumber = #(anchor);
[[NSUserDefaults standardUserDefaults] setObject:aNumber forKey:aKey];
To get the anchor back from NSUserDefaults:
NSNumber *aNumber = [[NSUserDefaults standardUserDefaults] objectForKey:aKey];
if (aNumber != nil) {
NSUInteger anchor = [aNumber integerValue];
}
NSUInteger or simply int are basically primitive data types and they should be compared with the integer values with in the range of the corresponding data types. nil is used with referenced objects.
In your case, as anchor is NSUInteger so you should use integer value for comparison in place of nil as-
if(anchor != 0) {
// do stuff
}
Related
I have this code
if ([args valueForKey:#"showSetupScreen"]) {
BOOL showSetupScreen = [args valueForKey:#"showSetupScreen"];
NSLog(showSetupScreen ? #"YES" : #"NO");
// meetingConfig.showSetupScreen = showSetupScreen;
}
Where args is NSMutableDictionary.
args value in my dictionary is NO but when I set to BOOL showSetupScreen = [args valueForKey:#"showSetupScreen"]; it changes into YES
Can someone help me in comprehending why this could be happening.
Attached Screenshot for your reference
A NSDictionary (or NSMutableDictionary) cannot directly contain a primitive C type, such as BOOL. Primitive numeric types (including Boolean) in NSDictionary are wrapped in NSNumber objects. See Numbers Are Represented by Instances of the NSNumber Class and Most Collections Are Objects.
Thus, use NSNumber method boolValue to extract the Boolean from the NSNumber, e.g.,
BOOL showSetupScreen = [[args valueForKey:#"showSetupScreen"] boolValue];
Or, more simply:
BOOL showSetupScreen = [args[#"showSetupScreen"] boolValue];
E.g., examples with primitive C types, including BOOL, NSInteger, and double:
NSDictionary *args = #{
#"foo": #NO,
#"bar": #YES,
#"baz": #42,
#"qux": #3.14
};
BOOL foo = [args[#"foo"] boolValue]; // NO/false
BOOL bar = [args[#"bar"] boolValue]; // YES/true
NSInteger baz = [args[#"baz"] integerValue]; // 42
double qux = [args[#"qux"] doubleValue]; // 3.14
For what it's worth, if you expand the values contained within args, that will show you the internal types for those values, and you will see that that the value associated with showSetupScreen (or foo in my example), is not a BOOL, but rather a pointer to a __NSCFBoolean/NSNumber:
[args valueForKey:#"showSetupScreen"] statement returns pointer (address in memory) and it has two options: some address (non zero value) and NULL (zero). For C programming language true is any non zero value (any address in memory in our case). And for this reason you get true in if operator and in showSetupScreen variable. But it only tells you that there is some object in the dictionary for the specified key, but not the value of this key (the value wrapped in this object). To get this value (BOOL in our case), you must call the boolValue.
I have a JSON dictionary that contains what I will call an integer (in mathematics) i.e. 1.
I would like to save this number to a core data attribute that is an NSInteger. The following code is issuing warning:
Incompatible Pointer to Integer Conversion initializing NSInteger with an expression of type 'id'
NSInteger insertID = jsonResults[#"insert_id"];
I have tried various combinations of int, NSNumber, etc. to no avail. Can anyone suggest right way to do this?
NSDictionary can't store NSInteger. It is storing NSNumber. So you need to unwrap the NSNumber:
NSInteger insertID = [jsonResults[#"insert_id"] integerValue];
in core data you should save numeric value as Number Type.
For eaxample,
To save:
insert_id = #(100)//say 100 is your insert_id value
To read:
NSInteger insertID = [jsonResults[#"insert_id"] intValue];
I had a NSDictionary contains 2 key/value pairs:
NSDictionary *dic = #{#"tag":#2, //NSNumber
#"string":#"someString"}; //NSString
NSLog(#"%i",(int)[dic objectForKey:#"tag"]); //print out 34
NSLog(#"%i",[dic objectForKey:#"tag"] intValue]); //print out 2
Why does "converting id value to int with (int)"get me the wrong result but not the other way? are they in different levels of conversion?
Why does "converting id value to int with (int)"get me the wrong result but not the other way? are they in different levels of conversion?
id is a pointer type. id pointers point to Objective-C objects in memory. By casting id to (int), you are merely reinterpreting (some of) the pointer's bit pattern as an int, which is quite meaningless. You have to call the proper conversion methods of NSString and NSNumber if you want to reliably get the primitive values out of the Objective-C object.
If you ever seemingly get the "correct" value of 2 in the case of pointer-casting with NSNumber, that may be because the Objective-C runtime makes use of an optimization technique called tagged pointers, whereby small objects are not really created and allocated, but their semantics (the number's bits which the NSNumber object stores) is stuffed into the unused bits of the pointer.
#2 is not an int but a NSNumber you can't cast an NSNumber into an int. You have to use intValue method to get the correct result.
The method objectForKey: returns a pointer to the NSNumber object #2, not the value stored in the object itself. So you're typecasting the pointer, not the value 2. In the last line you don't typecast the object but you access a property called intValue which returns the value of the object expressed as an int.
NSDictionary contains Object with Key value pairs,but you passed int(#2) into object
NSDictionary *dic = #{#"tag":#2, //NSNumber
#"string":#"someString"};
so Change int to NSNumber like
NSDictionary *dic = #{#"tag":[NSNumber numberWithInt:2];,#"string":#"someString"};
and you can get it..
int number = [[dict objectForKey:#"tag"] intValue];
I have a simple object which has one NSNumber which is used to store some flags.
I have a conienience getter method which in fact does:
[self.flags integerValue] & SomeConstantFlag
for a property#property (readonly, nonatomic, assign) BOOL someConstantFlag
and this works fine when accesing the underlying bool value like
model.someConstantFlag
but when I try to
id value = [model valueForKey:#"someConstantFlag"];
Then it returns a bad boolean representation e.g. NSNumber with value 2, 4 etc.
Why is this happening when the declaration of the property is BOOL? Is there a "Pretty" way to overcome this issue?
Wrapping on the other hand works ok:
BOOL someBool = 42;
NSNumber* numberVal = #(someBool);
//The underlying is an __NSCFBoolean with the proper 0/1 val!
valueForKey always returns an Objective-C object, even if the property has scalar type.
From the documentation (emphasis mine):
The default implementations of valueForKey: and setValue:forKey:
provide support for automatic object wrapping of the non-object data
types, both scalars and structs.
Once valueForKey: has determined the specific accessor method or
instance variable that is used to supply the value for the specified
key, it examines the return type or the data type. If the value to be
returned is not an object, an NSNumber or NSValue object is created
for that value and returned in its place.
The return value of your method is BOOL, which is defined as
typedef signed char BOOL;
on OS X and on the 32-bit iOS platform. So what valueForKey returns is a NSNumber
containing the result of
signed char val = [self.flags integerValue] & SomeConstantFlag;
and that can be in the range -128 .. 127.
To ensure that you get only YES or NO (aka 1 or 0) write your custom getter as:
-(BOOL)someConstantFlag
{
return ([self.flags integerValue] & SomeConstantFlag) != 0;
}
Remark: On the 64-bit iOS platform (but not on 64-bit OS X), BOOL is defined as the C99 _Bool, which is a "proper" boolean type and can take only the value 0 or 1.
NSNumber *value = #([model objectForKey:#"someConstantFlag"]);
BOOL boolVal = [value boolValue];
I think you should consider the following problems. Firstly, integerValue returns NSInteger which means if you support 64Bit architecture it will return int_64 not int_32, what is more in your code here
[self.flags integerValue] & SomeConstantFlag
this does the following if flags is 00010 and somConstantFlags is 00001 the & of those will do something you probably does not expect because you will get value of 00000 which equals 0 or if they are 00011 and 00110 you will get 00010 which equals 2. So that is why when you call valueForKey you get 2 or 4 or something else depending on your flags :)
What is more in objective-C everything different then 0 is YES.
Try reconsidering your bit logic :). See The following example
enum
{
kWhite = 0,
kBlue = 1 << 0,
kRed = 1 << 1,
kYellow = 1 << 2,
kBrown = 1 << 3,
};
typedef char ColorType;
and in your setter check the following
ColorType pinkColor = kWhite | kRed;
if (pinkColor & (kWhite | kBlue | kRed | kYellow)) {
// any of the flags has been set
}
The flags kWhite, kBlue, kRed and kYellow have been set.
However, kBrown has not been set.
I want to have an Entity property in Core Data be a 64-bit integer. Since the model is going to run on iOS, and as far as I know these devices are not 64-bit, I figured that NSNumber was the way to go (core data gives you the option of objects or scalar properties for primitive types).
I'm assuming that NSNumber will internally take care of keeping track of a suitable representation for 64 bits.
Now, I need to subtract 1 from this "64 bit" property in my entity at some point (in case you didn't guess, the 64 bit property is the max_id parameter in the Twitter API), but to do so, I first need to unbox the number inside the NSNumber property.
So should i get the intValue? longValue? unsignedIntValue? unsignedLongValue? long long? which one?
Since you already know the type (64 bit integer), you don't need to check for it.
To get a 64 bit integer out of a NSNumber, do one of the following:
NSInteger myInteger = [myNSNumber integerValue];
int64_t myInteger = [myNSNumber integerValue];
In order to just add one to it, you can use something like this:
myNSNumber = [NSNumber numberWithInteger:[myNSNumber integerValue]+1]];
Note that iOS does have 64 bit data types like int64_t and NSInteger.
EDIT:
If the only reason that you are using NSNumber is to store the 64 bit integer, you can just declare the property like this in your model subclass and skip the unboxing/boxing altogether:
#property (nonatomic) int64_t myIntValue;
Note that core data does this by default if you select the Use scalar properties for primitive data types option of the Create NSManagedObject Subclass feature.
Try putting this in a NSNumber category:
-(int64_t) int64value
{
if (sizeof(short) == 8)
return [self shortValue];
if (sizeof(int) == 8)
return [self intValue];
if (sizeof(long) == 8)
return [self longValue];
if (sizeof(long long) == 8)
return [self longLongValue];
return -1; // or throw an exception
}
To get the C type contained in NSNumber use objCType
Example
NSNumber *myFloat = [NSNumber numberWithFloat:5.5f];
NSLog(#"%s", [myFloat objCType]);
Will print "f" as it contains a value of type float.
Also, check out #encode() which will return a C type character.
Example
NSNumber *myFloat = [NSNumber numberWithFloat:5.5f];
if (strcmp(myFloat) == #encode(float)) {
NSLog(#"This is a float");
}
Also
NSNumber *myFloat = [NSNumber numberWithFloat:5.5f];
CFNumberType numberType = CFNumberGetType((CFNumberRef)myFloat);