I am in need of a Cocoa control, either Objective C or Swift (not SwiftUI, I still support as low as 10.13.x), that accepts text in the format of:
minutes:seconds.fraction
And returns it in either milliseconds, or NSTimeInterval. The former is preferred, the latter is acceptable, I can convert it to milliseconds if necessary.
I need the control to be able to validate the inverse transformation of the value, and only store the value in my NSUserDefaults storage if the value is non-zero, and a valid timestamp.
I see a question here about validating inputs, unanswered: How do I validate value of a reverse transform input field in Cocoa?
Can a string simply be fed to an NSTimeInterval for processing? And what about converting NSTimeInterval to a string again? Validation is important, as I don't want the user inputting invalid values and just having them clobber their settings.
Related
I'm using ICorProfilerCallback2 interface to profiler my application. On function enter hook I'm trying to read the value from byte array which is passed as an argument to a function. I've the argument info COR_PRF_FUNCTION_ARGUMENT_INFO from which I can get the starting address of the byte array argument.
If it is a string argument I can use "GetStringLayout" method from ICorProfilerInfo2 interface to get the bufferoffset and stringlengthoffset.
How can I find the offsets for byte array and how to read the values from it?
Where can I find the documents for those?
If you have the ObjectID (or COR_PRF_FUNCTION_ARGUMENT_RANGE) of the argument, you have an easy life (at least for Objects/Arrays, not for Value Types. You have to validate the parameter type using the metadata).
You can use ICorProfilerInfo::GetClassFromObject and ICorProfilerInfo::IsArrayClass to determine if it's an array. If so, IsArrayClass gives you the type of array. Arrays in .Net have a specific layout (I don't think it's in the official docs): It's always 8 bytes for ClassID, 8 bytes for size, and than all the elements, without padding (Note: Objects are stored by ObjectID, just like in other memory regions).
You can also use ICorProfilerInfo2::GetArrayObjectInfo to get the size (need to calculate from dimensions) and the starting address of the objects.
Relevant reads:
https://mattwarren.org/2017/05/08/Arrays-and-the-CLR-a-Very-Special-Relationship/
https://windowsdebugging.wordpress.com/2012/04/24/memorylayoutofarraysx64/
I want to compare a number to another: if the comparison is true the current value must pass but if not it must stop. But I can't do this idea because the output of the compare block is boolean so if it is true, the output is 1 so the current value will not pass as same number. How can I do this idea? Thanks.
One way to accomplish this would be to use a Switch block (under Commonly Used Blocks and Signal Routing) instead of the Relational Operator block.
There is also a Data Type Conversion block if you ever do need to convert a Boolean output to double precision, but I don't think that's what you want in this case.
Float values are getting changed after parsing with JSONKit. The problem occurs after calling objectFromJSONString or mutableObjectFromJSONString.
The JSON response is fine before this method is triggered in JSONKit.m:
static id _NSStringObjectFromJSONString(NSString *jsonString, JKParseOptionFlags parseOptionFlags, NSError **error, BOOL mutableCollection)
Original response:
"value":"1002.65"
Response after calling objectFromJSONString:
"value":"1002.6500000001" or sometimes "value":"1002.649999999 "
Thanks.
This is not an issue.
The value 1002.65 can not be represented exactly using a IEEE 754 floating point number.
Floating-point numbers are converted to their decimal representation using the printf format conversion specifier %.17g.
From the Docs:
The C double primitive type, or IEEE 754 Double 64-bit floating-point,
is used to represent floating-point JSON Number values. JSON that
contains floating-point Number values that can not be represented as a
double (i.e., due to over or underflow) will fail to parse and
optionally return a NSError object. The function strtod() is used to
perform the conversion. Note that the JSON standard does not allow for
infinities or NaN (Not a Number). The conversion and manipulation of
floating-point values is non-trivial. Unfortunately, RFC 4627 is
silent on how such details should be handled. You should not depend on
or expect that when a floating-point value is round tripped that it
will have the same textual representation or even compare equal. This
is true even when JSONKit is used as both the parser and creator of
the JSON, let alone when transferring JSON between different systems
and implementations.
Source: See this thread https://github.com/johnezang/JSONKit/issues/110
Solution: You can specify a precision, while converting float to string for output. NSNumberFormatter will be a better choice or use some printf solutions like in the previous answer.
use float fixed point representation like,
NSLog(#"value = %.2f",floatvalue);
now it will show value = 1002.65
How do you use NSCoding to code (and decode) an array of of ten values of primitive type int? Encode each integer individually (in a for-loop). But what if my array held one million integers? Is there a more satisfying alternative to using a for-loop here?
Edit (after first answer): And decode? (#Justin: I'll then tick your answer.)
If performance is your concern here: CFData/NSData is NSCoding compliant, so just wrap your serialized representation of the array as NSCFData.
edit to detail encoding/decoding:
your array of ints will need to to be converted to a common endian format (depending on the machine's endianness) - e.g. always store it as little or big endian. during encoding, convert it to an array of integers in the specified endianness, which is passed to the NSData object. then pass the NSData representation to the NSCoder instance. at decode, you'll receive an NSData object for the key, you conditionally convert it to the native endianness of the machine when decoding it. one set of byte swapping routines available for OS X and iOS begin with OSSwap*.
alternatively, see -[NSCoder encodeBytes:voidPtr length:numBytes forKey:key]. this routine also requires the client to swap endianness.
So I am trying to do a few things with numbers in Objective C and realize there is a plethora of options, and i am just bewildered as to which type to use for my app.
so here are the types.
NSNumber (which is a class)
NSDecmial (which is a struct)
NSDecimalNumber (which is a class)
float/double (which are primitive types)
so essentially what i need to do is take an NSString, which is representing decimal based hours. (10.4 would be 10 hours and (4/10)*60 minutes) and convert it into:
a string representation D H:M (this needs division, multiplication and basic arithmatic)
a Number type to store for easy calculations latter (will mostly be converting between NSTimeIntervals and doing subtractions)
Oh and i need to be able to do an Absolute value as well on these
It appears that the hard part is actually transitioning between the types.
To me this is a very trivial problem so I"m not sure if its getting late or because objective C numerical types suck, but i could use a hand.
Use primitive types (double, CGFLoat, NSInteger) for typical arithmetic and when you need to store a number as an instance variable that's going to be used primarily for arithmetic in other places. You can use C math functions (abs(), pow(), etc) as needed. NSTimeInterval is a typedef for double, so you can interchange the two.
Use NSNumber when you need to store a number as an object, for example if you're creating an NSArray of numbers. Some parts of Cocoa like Core Data or key value coding deal more with NSNumber than primitive types, so you may find yourself using NSNumber more then usual in those situations. For example, if you write [timeKeepersArray valueForKeyPath:#"sum.seconds"] you'll get back an NSNumber, so you may find it easier just to keep that variable instead of converting it to a primitive.
Since it's a small amount of extra code to convert between NSNumber and primitive types, usually your application will end up favoring one or the other depending on what you're doing with numbers.
Oh, and NSDecmial and NSDecimalNumber? Don't worry too much about them, they only come up when you need really precise decimal operations, such as if you're storing financial data.