没有可见的界面错误

我在我的模型的实现文件中有一个错误，我已经注释掉了。 我该怎么做才能解决这个问题？

提前致谢。

#import "CalculatorBrain.h" @interface CalculatorBrain() @property (nonatomic, strong) NSMutableSet *operandStack; @end @implementation CalculatorBrain @synthesize operandStack = _operandStack; - (NSMutableArray *)operandStack { if (!_operandStack) { _operandStack = [[NSMutableArray alloc] init]; } return _operandStack; } -(void)pushOperand:(double)operand { NSNumber *operandObject = [NSNumber numberWithDouble:operand]; [self.operandStack addObject:operandObject]; } - (double)popOperand { NSNumber *operandObject = [self.operandStack lastObject]; // No visible interface for 'NSMutableSet' declares the selector 'lastObject' if(operandObject) [self.operandStack removeLastObject]; // No visible interface for 'NSMutableSet' declares the selector 'removeLastObject' return [operandObject doubleValue]; } - (double)performOperation:(NSString *)operation { double result = 0; if([operation isEqualToString:@"+"]) { result = [self popOperand] + [self popOperand]; } else if ([@"*" isEqualToString:operation]) { result = [self popOperand] * [self popOperand]; } else if ([operation isEqualToString:@"-"]) { double subtrahend = [self popOperand]; result = [self popOperand] - subtrahend; } else if ([operation isEqualToString:@"/"]) { double divisor = [self popOperand]; if (divisor)result = [self popOperand] / divisor; } [self pushOperand:result]; return result; } @end 

Answer 1

您已将operandStack属性声明为NSMutableSet ，但您应该将其声明为NSMutableArray ：

 @property (nonatomic, strong) NSMutableArray *operandStack; 

Answer 2

您正试图获取NSSet的“最后一个对象” – 这是不可能的，因为集合是无序的。 NSMutableSet不存在lastObject方法。

您可能想尝试使用NSMutableArray。