Outputting iVars from description method?
-
10-07-2019 - |
Question
I am pretty sure I am just missing the point here and getting confused. Can anyone tell me how I might write a simple description for an object that will print out the value of its instance variables to the console.
Also: is there anyway to present the information as a block (i.e. if you had 10 iVars its going to be a pain getting them all to return one by one)
@interface CelestialBody : NSObject {
NSString *bodyName;
int bodyMass;
}
- (NSString *)description {
return (@"Name: %@ Mass: %d", bodyName, bodyMass);
}
cheers -gary-
Solution
- (NSString*)description
{
return [NSString stringWithFormat:@"Name: %@\nMass: %d\nFoo: %@",
bodyName, bodyMass, foo];
}
OTHER TIPS
Look at the answer to this question. The code is reproduced below:
unsigned int varCount;
Ivar *vars = class_copyIvarList([MyClass class], &varCount);
for (int i = 0; i < varCount; i++) {
Ivar var = vars[i];
const char* name = ivar_getName(var);
const char* typeEncoding = ivar_getTypeEncoding(var);
// do what you wish with the name and type here
}
free(vars);
As Jason wrote you should use stringWithFormat: to format strings with printf like syntax.
-(NSString*)description;
{
return [NSString stringWithFormat:@"Name: %@ Mass: %d", bodyName, bodyMass];
}
To avoid writing this over and over again for many classes you could add a category on NSObject that allows you to inspect instance variables easily. This will be bad performance, but works for debugging purposes.
@implementation NSObject (IvarDictionary)
-(NSDictionary*)dictionaryWithIvars;
{
NSMutableDictionary* dict = [NSMutableDictionary dictionary];
unsigned int ivarCount;
Ivar* ivars = class_copyIvarList([self class], &ivarCount);
for (int i = 0; i < ivarCount; i++) {
NSString* name = [NSString stringWithCString:ivar_getName(ivars[i])
encoding:NSASCIIStringEncoding];
id value = [self valueForKey:name];
if (value == nil) {
value = [NSNull null];
}
[dict setObject:value forKey:name];
}
free(vars);
return [[dict copy] autorelease];
}
@end
With this in place implementing description is also a piece of cake:
-(NSString*)description;
{
return [[self dictionaryWithIvars] description];
}
Do not add this description
as a category on NSObject, or you might end up with infinite recursions.
That's not a bad idea what you had there, it's almost achievable too.
// choose a short name for the macro
#define _f(x,...) [NSString stringWithFormat:x,__VA_ARGS__]
...
- (NSString *) description
{
return _f(@"Name: %@ Mass: %d", bodyName, bodyMass);
}