Creating a property from a CGFloat array - iOS
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22-06-2021 - |
Question
Trying to create a property, so I can set CGfloat array values on an instance of a class. Having a hard time figuring out how to do it. The CGFloat needs to have "size" [2] variable and numeric components like below:
CGFloat locations[2] = {1.0, 0.0};
Here is how it looks in the class itself (this works), before I created the property in an attempt to set these values from an instance (this creates a gradient BTW via drawRect in a UIView sunclass):
CGContextRef context = UIGraphicsGetCurrentContext();
CGColorSpaceRef myColorspace=CGColorSpaceCreateDeviceRGB();
CGFloat locations[2] = {1.0, 0.0};
CGFloat components[8] = { 1.0, 0.0, 0.0, 1.0, 0.5, 0.25, 1.0, 1.0 };
CGGradientRef myGradient = CGGradientCreateWithColorComponents(myColorspace, components,locations, num_locations);
CGContextDrawLinearGradient (context, myGradient, myStartPoint, myEndPoint, 0);
I tried creating a property like below in the .h
@property (nonatomic, assign) CGFloat locations;
and in the .m
@synthesize locations;
But I cant figure out how to properly set the values for the [size] and the components from the instance. Also I get errors when I set up the property: ERROR: "Passing 'CGFloat' (aka 'float') to parameter of incompatible type 'const CGFloat *' (aka 'const float *'); take the address with &"
you can get the project here is you feel like taking a look tinyurl.com/cmgy482 Any help much appreciated.
Solution 2
From another answer found here: "C arrays are not one of the supported data types for properties". I think that was my issue. The solution I used, is to make the property an NSMutableArray and to convert the values to a CGFloat.
.h
@property (nonatomic, retain) NSMutableArray *locations;
.m
CGFloat locationsFloat[[locations count]];
for (int i = 0; i < [locations count]; i++) {
NSNumber *number = [locations objectAtIndex:i];
locationsFloat[i] = [number floatValue];
}
viewController
- (void)viewDidLoad
{
NSMutableArray *arrayPoints = [[NSMutableArray alloc]init];
[arrayPoints addObject:[NSNumber numberWithFloat:1.0]];
[arrayPoints addObject:[NSNumber numberWithFloat:0.0]];
[myInstance setLocations:arrayPoints];
...
OTHER TIPS
Ideally you would be able to just declare your property like this:
@property (nonatomic) CGFloat locations[2];
Alas, clang does not allow you to create a property with an array type.
One alternative is to use a pointer type instead. You probably want to write a comment to explain how many elements it points to:
#define kMyClassLocationCount 2
// This is an array of kMyClassLocationCount elements. The setter copies
// the new elements into existing storage.
@property (nonatomic) CGFloat *locations;
To implement it, you need to create the instance variable and define the getter and setter:
@implementation MyClass {
CGFloat _locations[kMyClassLocationCount];
}
- (CGFloat *)locations {
return _locations;
}
- (void)setLocations:(CGFloat *)locations {
memcpy(_locations, locations, kMyClassLocationCount * sizeof *_locations);
}
Note that you don't need @synthesize
, because you have explicitly defined everything that @synthesize
might generate.
When you use an instance of the class, you can read an individual location like this:
CGFloat location1 = myInstance.locations[1];
and you can set an individual location like this:
myInstance.locations[0] = 0.5;
and you can set all of the locations at once like this:
CGFloat newLocations[2] = { 7, 11 };
myInstance.locations = newLocations;
i think you had better code like this:
NSArray * locations = [[NSArray alloc ] initWithObjects:[NSNumber numberWithFloat:1.0f],[NSNumber numberWithFloat:0.0f],nil];