[英]Don't know how to access property from class method in Xcode
我想从类方法popOperandOffStack:
访问属性storedValue
,但出现错误。 我读到您不能访问storedValue
因为它是一个类方法或类似的方法。 谁能告诉我如何访问storedValue
或如何使storedValue
全局化,以便可以在popOperandOffStack:
使用它?
这是我的标题:
#import <Foundation/Foundation.h>
@interface CalculatorBrain : NSObject
- (void)pushOperand:(double)operand; // - = instance method
- (double)performOperation: (NSString *)operation;
@property (nonatomic,readonly) id program;
+ (double)runProgram:(id)program; // + = class method
+ (NSString *)descriptionOfProgram:(id)program;
@end
这是我的m文件:
#import "CalculatorBrain.h"
@interface CalculatorBrain()
@property (nonatomic,strong) NSMutableArray *programStack;
@property (nonatomic) double storedValue;
@end
@implementation CalculatorBrain
@synthesize programStack = _programStack;
@synthesize storedValue = _storedValue;
- (NSMutableArray *)programStack
{
if (_programStack == nil)
_programStack = [[NSMutableArray alloc] init];
return _programStack;
}
- (void)setOperandStack:(NSMutableArray *)programStack
{
_programStack = programStack;
}
- (void)pushOperand:(double)operand
{
[self.programStack addObject:[NSNumber numberWithDouble:operand]];
}
- (double)performOperation: (NSString *)operation
{
[self.programStack addObject:operation];
return [[self class] runProgram:self.program];
}
- (id)program
{
return [self.programStack copy];
}
+ (NSString *)descriptionOfProgram:(id)program
{
return @"Implement this in Assignment 2";
}
+ (double) popOperandOffStack:(NSMutableArray *)stack
{
double result = 0;
id topOfStack = [stack lastObject];
if (topOfStack)
[stack removeLastObject];
if ([topOfStack isKindOfClass:[NSNumber class]])
{
result = [topOfStack doubleValue];
}
else if ([topOfStack isKindOfClass:[NSString class]])
{
NSString *operation = topOfStack;
if ([operation isEqualToString:@"+"]){
result = [self popOperandOffStack:stack] + [self popOperandOffStack:stack];
} else if ([operation isEqualToString:@"-"]){
result = -[self popOperandOffStack:stack] + [self popOperandOffStack:stack];
} else if ([operation isEqualToString:@"*"]){
result = [self popOperandOffStack:stack] * [self popOperandOffStack:stack];
} else if ([operation isEqualToString:@"/"]){
double divide = [self popOperandOffStack:stack];
if(divide){
result = [self popOperandOffStack:stack] / divide;
} else {
result = 0;
}
} else if ([operation isEqualToString:@"1/x"]){
result = 1 / [self popOperandOffStack:stack];
} else if ([operation isEqualToString:@"sqrt"]){
double sqrtNumber = [self popOperandOffStack:stack];
if (sqrtNumber > 0){
result = sqrt(sqrtNumber);
} else {
result = 0;
}
} else if ([operation isEqualToString:@"sin"]){
result = sin( [self popOperandOffStack:stack]);
} else if ([operation isEqualToString:@"cos"]){
result = cos( [self popOperandOffStack:stack]);
} else if ([operation isEqualToString:@"MS"]){
self.storedValue = [self popOperandOffStack:stack];
} else if ([operation isEqualToString:@"MR"]){
result = self.storedValue; //error here
} else if ([operation isEqualToString:@"MC"]){
result = [self popOperandOffStack:stack];
self.storedValue = 0; //error here
} else if ([operation isEqualToString:@"M+"]){
result = [self popOperandOffStack:stack];
self.storedValue = self.storedValue + result; //error here
} else if ([operation isEqualToString:@"M-"]){
result = [self popOperandOffStack:stack];
self.storedValue = self.storedValue - result; //error here
} else if ([operation isEqualToString:@"C"]){
result = 0;
while ( [self popOperandOffStack:stack] )
{
//clear operands until returns NO
}
} else if ([operation isEqualToString:@"CE"]){
result = 0;
self.storedValue = 0; //error here
while ( [self popOperandOffStack:stack] )
{
//clear operands until returns NO
}
}
if (![operation isEqualToString:@"MS"] && ![operation isEqualToString:@"CE"])
{
return result;
} else {
return self.storedValue;
}
}
return result;
}
+ (double)runProgram:(id)program
{
NSMutableArray *stack;
if ([program isKindOfClass:[NSArray class]]) {
stack = [program mutableCopy];
}
return [self popOperandOffStack:stack];
}
@end
我不能使用self.storedValue
。 除了将+
(静态方法)更改为-
(实例方法)(我不允许这样做)之外,我还应该做什么?
您不能从类方法内部使用实例getter / setter方法,因为您没有作为CalculatorBrain实例的对象。 (我没有使用过该课程,但希望它能解释类和对象之间的区别。)
即使从创建面向对象程序的角度来看这不是一个好主意,您也可以使用静态变量来保存您的double。 查看C语言参考中的短语“ external static”以查看示例。
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