NSMutable 数组 - “不是 Objective-C 对象"错误 [英] NSMutable array - "Not an objective-C object" error
问题描述
我不完全确定为什么它在注释行返回错误不是目标 C 对象".任何帮助将不胜感激.
I am not totally sure why it is that it is returning the error "not an objective-C object" at the commented line. Any help would be appreciated.
此外,我对 Objective-C 非常陌生,我确实意识到这很可能是一个非常愚蠢的错误.但是,任何建议都会有所帮助.
Additionally, I am very new to objective-C, and I do realize there is a high possibility this is a very silly mistake. However any advice will help.
#import "CalculatorBrain.h"
@interface CalculatorBrain()
@property (nonatomic, strong) NSMutableArray *operandStack;
@end
@implementation CalculatorBrain
@synthesize operandStack = _operandStack;
- (NSMutableArray *)operandStack
{
if(!_operandStack){
_operandStack = [[NSMutableArray alloc] init];
}// end if
return _operandStack;
}//end operandStack
- (void)pushOperand:(double)operand
{
NSNumber *operandObject = [NSNumber numberWithDouble:operand];
[self.operandStack addObject:operandObject];
}//end pushOperand
- (double)popOperand
{
NSNumber *operandObject = [self.operandStack lastObject];//error "Not an objective-c object"
if(operandObject) [self.operandStack removeLastObject];
return [operandObject doubleValue];
}//end popOperand
- (double)performOperation:(NSString *)operation
{
double result = 0;
if([operation isEqualToString:@"+"]){
result = [self popOperand] + [self popOperand];
} else if([operation isEqualToString:@"-"]){
double subtrahend = [self popOperand];
result = [self popOperand] - subtrahend;
} else if([operation isEqualToString:@"*"]){
result = [self popOperand] * [self popOperand];
} else if([operation isEqualToString:@"/"]){
double divisor = [self popOperand];
if(divisor) result = [self popOperand] / divisor;
}//end if
[self pushOperand:result];
return result;
}//performOperation
@end
推荐答案
我认为这可能是由于函数 popOperand 中的操作顺序不正确造成的.看我的内联评论,最后一行 return [operandObject doubleValue] 访问了一个已经发布的对象.多次运行此代码后,可能会导致内存问题,反过来,您可能会在注释行看到错误.
I think this might be caused by the the incorrect operation order in the function popOperand. See my comments inline, the last line return [operandObject doubleValue] accessed a already released object. After running this code several time, it might cause memory problem and in turn, you might see the error at your comment line.
- (double)popOperand
{
NSNumber *operandObject = [self.operandStack lastObject];
if(operandObject) [self.operandStack removeLastObject];
// When you remove the lastObject(operandObject) from the Array, the operandObject retainCount is zero.
// Here, the operandObject is deallocated and should not be used.
// But you call it after it was released.
return [operandObject doubleValue];
}//end popOperand
这可能没问题,当您只调用一次或多次 popOperand 时.但这会导致内存错误.我想每次调用 popOperand 时都不会发生错误.这是我的解决方案.
This might be OK, when you only call popOperand once or several times. But this will result memory error. I guess the error doesn't occur every time when the popOperand is called. Here is my solution.
- (double)popOperand
{
double result = 0.0;
NSNumber *operandObject = [self.operandStack lastObject];
if(operandObject)
{
result = [operandObject doubleValue];
[self.operandStack removeLastObject];
}
return result;
}
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