Using NSKeyedArchiver throw Exception:[NSConcreteValue length]: unrecognized selector sent to instance - ios

Question

I tried to use NSKeyedArchiver and NSKeyedUnarchiver.The code throw exception: "[NSConcreteValue length]: unrecognized selector sent to instance".
#interface DBTLine() <NSCoding>
#end
#implementation DBTLine
-(void)encodeWithCoder:(NSCoder *)aCoder {
[aCoder encodeCGPoint:self.begin forKey:#"begin"];
[aCoder encodeCGPoint:self.end forKey:#"end"];
[aCoder encodeObject:self.color forKey:#"color"];
}
- (instancetype)initWithCoder:(NSCoder *)coder
{
self = [super init];
if (self) {
//Throw Exception Here.
_begin = [coder decodeCGPointForKey:#"begin"];
_end = [coder decodeCGPointForKey:#"end"];
_color = [coder decodeObjectForKey:#"color"];
}
return self;
}
#end
#interface DBTDrawView()
#property (nonatomic)NSMutableArray *finishedLines;
#end
#implementation DBTDrawView
-(instancetype)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if(self){
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSData* dataFinishedLines = [defaults objectForKey:#"finishedLines"];
NSMutableArray *defaultLines = [NSKeyedUnarchiver unarchiveObjectWithData:dataFinishedLines];
if (defaultLines) {
self.finishedLines = defaultLines;
}
}
return self;
}
-(void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
//some code,"self.finishedLines" add line
NSData *dataFinishedLines = [NSKeyedArchiver archivedDataWithRootObject:self.finishedLines];
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
[defaults setObject:dataFinishedLines forKey:#"finishedLines"];
[self setNeedsDisplay];
}
#end
I searched the Internet for a long time,and I've tried multiple variations of my code.Finally,It works.Here is my changed code:
-(void)encodeWithCoder:(NSCoder *)aCoder {
NSValue *begin = [NSValue valueWithCGPoint:self.begin];
NSValue *end = [NSValue valueWithCGPoint:self.end];
[aCoder encodeObject:begin forKey:#"begin"];
[aCoder encodeObject:end forKey:#"end"];
[aCoder encodeObject:self.color forKey:#"color"];
}
- (instancetype)initWithCoder:(NSCoder *)coder
{
self = [super init];
if (self) {
NSValue *begin = [coder decodeObjectForKey:#"begin"];
NSValue *end = [coder decodeObjectForKey:#"end"];
_begin = [begin CGPointValue];
_end = [end CGPointValue];
_color = [coder decodeObjectForKey:#"color"];
}
return self;
}
But the problem is:
It seems the problem appeared in the process of using "-
encodeCGPoint:forKey: - decodeCGPointForKey:".Was there anything
wrong with what I did?
What is "[NSConcreteValue length]"?I can't find it in the document.
Thanks in advance.