The issue I am having is that I'm using an image height stored in a Parse class column with a type of Number. I'm then taking that height number and using it to set the UITableview row height. The problem is that when I try to use the number column value, it returns an error saying the types don't match. I'm doing this in Objective C. How can I use the Number value for the row height? I'm pretty sure I need to convert the Number value to a CGFloat but I'm not sure.
NSNumber has already provided options for you to do it.
I suggestion you read on the documentation found here.
excerpt from Apple doc:
NSNumber is a subclass of NSValue that offers a value as any C scalar (numeric) type. It defines a set of methods specifically for setting and accessing the value as a signed or unsigned char, short int, int, long int, long long int, float, or double or as a BOOL.
to answer your question.
you can use the floatValue to get a CGFloat from an NSNumber
example:
CGFloat myFloat = [number floatValue];
Related
I am writing a framework in Objective-C, and the goal is it should be a joy to use in Swift as well.
One of my properties is a nullable NSNumber. Is there any way to bridge this to an optional Int when the API is used in Swift?
As per the documentation:
Swift automatically bridges certain native number types, such as Int
and Float, to NSNumber.
It also allows you to pass a value of type Int, for example, to an
argument expecting an NSNumber. Note that because NSNumber can contain
a variety of different types, you cannot pass it to something
expecting an Int value.
All of the following types are automatically bridged to NSNumber:
Int
UInt
Float
Double
Bool
So you can safely use these scalar types in swift and cast them to NSNumber in objc, but not the other way around. NSNumber may represent a float value, and you will see an error if you cast it to Int in swift.
What is the highest int that NSNumber allows? I've seen the answer elsewhere on these forums hence why I'm deeply confused here.
int miles = 35000;
vehicle.mileage = [NSNumber numberWithInt:miles];
NSLog(#"int value = %d", miles);
NSLog(#"mileage = %#", vehicle.mileage);
The output is:
int value = 35000
mileage = -30536
I must be missing some terrible easy here, but can someone explain to me why this is not working correctly?
UPDATE:
After looking further, vehicle.mileage is getting set correctly to 35000 but when I display this via NSLog(#"%#", vehicle.mileage) it is outputting it incorrectly. I have yet to find the "magic" value when this stops working because as of now, it works for values up to ~30,000.
NSNumber is just a wrapper so it goes in overflow when the wrapped primitive type goes in overflow.
So if you use numberWithInt the maximum number allowed is INT_MAX (defined in limits.h), if you use a numberWithFloat the maximum number allowed is FLOAT_MAX, and so on.
So in this case you aren't going in overflow, I doubt that INT_MAX would be so low.
Overview
NSNumber is a subclass of NSValue that offers a value as any C scalar
(numeric) type. It defines a set of methods specifically for setting
and accessing the value as a signed or unsigned char, short int, int,
long int, long long int, float, or double or as a BOOL. (Note that
number objects do not necessarily preserve the type they are created
with.) It also defines a compare: method to determine the ordering of
two NSNumber objects.
So NSNumber is as big as what it wraps. For your unexpected result you can check comment bellow your qestion from #sjs.
+numberWithInt: interprets the value as signed int. Mileage would never be negative, so I suggest using [NSNumber numberWithUnsignedInt:]
The limit NSNumber integer can have is known as INT_MAXbut 35, 000 is nowhere close to that. The problem must be with vehicle object or the mileage property in the vehicle, either of them may be nil
So, go ahead and log with this conditional statement:
if (!vehicle) {
NSLog(#"Vehicle is nil");
}
else if (!vehicle.mileage) {
NSLog(#"Vehicle's mileage is nil");
}
Tell me your result
I have a float value, that I would like to show it in format string and if it corresponds to an int, showing the integer, if not, showing it with one decimal.
Like this :
3.1
3
2.9
2.8
For now I'm stuck, in the concept, I'd do something like that :
float myFloat = 3.1
float mySecondFloat = 3
[NSString stringWithFormat:#"%g %g", myFloat, mySecondFloat];
My question is:
1/ the type format "%g" works in most cases but sometimes i have result shown like "0.600001" while in reality there should be 0.6 because all I do is 0.7 - 0.1.
Is there a kind of type cast for float at 1 decimal or maybe a bitwise operation to get rid of the final imprecision, or other way to make it works in 100% of cases ?
Thanks for your answers.
If your need absolute precision when working with decimal numbers, you may consider using the NSDecimalNumber class.
Number and Value Programming Topics: Using Decimal Numbers
Otherwise, the %.1g format specifier will be OK.
You have to use this code:
float myFloat = 3.1
float mySecondFloat = 3
[NSString stringWithFormat:#"%.1f %.1f", myFloat, mySecondFloat];
EDIT:
If I really want to print the integer value of a float, i would do it this way (ugly code)
int intValue = myFloatNumber/1;
NSString *string;
if(myFloatNumber == intValue)
{
string = [NSString stringWithFormat:#"%.0f", myFloatValue];
}
else
{
string = [NSString stringWithFormat:#"%.1f", myFloatValue];
}
Doing an integer division by 1, you automatically cast your float to an int.
Once you have the NSString *string you can concat it to your string.
Seeing others answers, it seems that there is no standard C formatter to achieve this.
I went following Nicolas answer (NSDecimalNumber), hence the solve flag. It worked fine indeed, but, in my (very simple) case it might be overkill. Giving it a second thought, if I had to do it again, I think that I would go using only NSNumberFormatter on a NSNumber (using numberWithFloat: method)
If it can help someone..
I'm trying to get a double value from a dictionary. How can I accomplish this in objective-c?
Dave's response to your previous question holds true for this, as well. To store a double value in an NSDictionary, you will need to box it in an NSNumber.
To set a double value in the dictionary, you'd use code like the following:
[someDict setObject:[NSNumber numberWithDouble:yourDouble] forKey:#"yourDouble"];
and read it back using the following:
double isTrue = [[someDict objectForKey:#"yourDouble"] doubleValue];
Brad Larson's response is exactly right. To elaborate on this a little more, you have to explicitly "wrap up" non-object number types (e.g., int, unsigned int, double, float, BOOL, etc.) into NSNumber when working with anything that expects an object.
On the other hand, however, some mechanisms in Objective-C, like Key-Value Coding (KVC), will automatically do this wrapping for you.
For example, if you have a #property of type int called intProperty, and you call NSObject (NSKeyValueCoding)'s valueForKey: method like [ someObject valueForKey:#"intProperty" ], the return result will be an NSNumber *, NOT an int.
Frankly, I don't care for having to switch between dealing with object and non-object types (especially structs and enums!) in Objective-C. I'd rather everything be treated as an object, but maybe that's just me. :)
I'm still learning, and I'm just stuck. I want the user to enter any number and in result, my program will do this equation:
x = 5*y
(y is the number the user adds, x is outcome)
How would I do this? I'm not sure if I'm suppose to add in an int or NSString. Which should I use, and should I enter anything in the header files?
I'm not sure if I'm suppose to add in an int or NSString.
Well, one of these is a numeric type and the other is a text type. How do you multiply text? (Aside from repeating it.)
You need a numeric type.
I would caution against int, since it can only hold integers. The user wouldn't be able to enter “0.5” and get 2.5; when you converted the “0.5” to an int, the fractional part would get lopped off, leaving only the integral part, which is 0. Then you'd multiply 5 by 0, and the result you return to the user would be 0.
Use double. That's a floating-point type; as such, it can hold fractional values.
… should I enter anything in the header files?
Yes, but what you enter depends on whether you want to use Bindings or not (assuming that you really are talking about Cocoa and not Cocoa Touch).
Without Bindings, declare an outlet to the text field you're going to retrieve the multiplier from, and another to the text field you're going to put the product into. Send the input text field a doubleValue message to get the multiplier, and send the output text field a setDoubleValue: message with the product.
With Bindings, declare two instance variables holding double values—again, one for the multiplier and one for the product—along with properties exposing the instance variables, then synthesize the properties, and, finally, bind the text fields' value bindings to those properties.
If you're retrieving the NSString from a UI, then it's pretty simple to do:
NSString * answer = [NSString stringWithFormat:#"%d", [userInputString integerValue]*5];
This can be done without any objective C. That is, since Objective-C is a superset of C, the problem can be solved in pure C.
#include <stdio.h>
int main(void)
{
int i;
fscanf(stdin, "%d", &i);
printf("%d\n", i * 5);
}
In the above the fscanf takes care of converting the character(s) read on the standard input to a number and storing it in i.
However, if you had characters from some other source in a char* and needed to convert them to an int, you could create an NSString* with the – initWithCString:encoding: and then use its intValue method, but in this particular problem that simply isn't needed.