Objective-C麻烦:EXC_BAD_ACCESS code = 2
我试图编写一个计算器程序,但是当按下与函数expressionEvaluation关联的特定键时,我遇到了这个错误。我的计算器工作正常,但我试图添加使用/存储变量的功能。为此,我使用expressionEvaluation按钮。但是,只要我按下链接到该方法的按钮,整个应用程序崩溃,xcode给我错误EXC_BAD_ACCESS code = 2。我是新来的Objective-C,所以我不知道如何调试这个错误。据我所知,问题是与行Objective-C麻烦:EXC_BAD_ACCESS code = 2
double result = [CalculatorBrain evaluateExpression:self.brain.expression usingVariableValues:testValues];
...在我的视图控制器。我在这条线之前设置了一个断点,但它没有崩溃,但将它设置在这条线上导致了我遇到的崩溃。 我试图在下面切下代码,并且只包含直接链接到expressionEvaluation按钮的东西。感谢您的帮助!
下面是我的大脑方法.H:
// CalculatorBrain.h
#import <Foundation/Foundation.h>
@interface CalculatorBrain : NSObject
- (void) pushOperand:(double)operand;
- (void) setVariableAsOperand:(NSString *)variableName;
- (void) performWaitingOperation;
- (double) performOperation:(NSString *)operation;
@property (readonly) id expression;
+ (double)evaluateExpression: (id)anExpression
usingVariableValues: (NSDictionary *)variables;
+ (NSSet *)variablesInExpression:(id)anExpression;
+ (NSString *)descriptionOfExpression:(id)anExpression;
+ (id)propertyListForExpression:(id)anExpression;
+ (id)expressionForPropertyList:(id)propertyList;
@end
这里的.M:
// CalculatorBrain.m
#import "CalculatorBrain.h"
#define VARIABLE_PREFIX @"^"
@interface CalculatorBrain()
@property (nonatomic) double operand;
@property (nonatomic, strong) NSString *waitingOperation;
@property (nonatomic) double waitingOperand;
@property (nonatomic) double storedOperand;
@property (nonatomic) NSMutableArray *internalExpression;
@end
@implementation CalculatorBrain
@synthesize operand = _operand; //operand in use
@synthesize waitingOperation = _waitingOperation; //waiting to be computed
@synthesize waitingOperand = _waitingOperand; //waiting to be used
@synthesize storedOperand = _storedOperand; //stored in memory
@synthesize internalExpression = _internalExpression; //private expression stored
@synthesize expression = _expression;
- (id) expression {;
return [NSMutableArray arrayWithArray:self.internalExpression];
}
//here I have instance methods that add objects to the array internalExpression
//these work fine as far as I can tell
+ (double) evaluateExpression:(id)anExpression usingVariableValues:(NSDictionary *)variables {
double result = 0;
int count = [anExpression count];
CalculatorBrain *brain;
for (int i = 0; i < count; i++) {
if([[anExpression objectAtIndex:i] isKindOfClass:[NSNumber class]]) {
double operand = [[anExpression objectAtIndex:i] doubleValue];
[brain pushOperand:operand];
}
if([[anExpression objectAtIndex:i] isKindOfClass:[NSString class]]) {
NSString *string = [anExpression objectAtIndex:i];
if([string characterAtIndex:0] == '^') {
NSString* variable = [NSString stringWithFormat:@"%c",[string characterAtIndex:1]];
double valueOfVariable = [[variables objectForKey:variable] doubleValue];
[brain pushOperand:valueOfVariable];
}
else {
NSString* operator = [anExpression objectAtIndex:i];
result = [brain performOperation:operator];
}
}
}
return result;
}
@end
下面是我的看法控制器.H:
// CalcViewController.h
#import <UIKit/UIKit.h>
//view controller for calculator
@interface CalcViewController : UIViewController
@property (weak, nonatomic) IBOutlet UILabel *display; //real-time display
@property (strong, nonatomic) IBOutlet UILabel *miniDisplay; //past display
@property (strong, nonatomic) IBOutlet UILabel *memDisplay; //display stored digits
- (IBAction)digitPressed:(UIButton *)sender; //pressed number
- (IBAction)operandPressed:(UIButton *)sender; //pressed operation
- (IBAction)variablePressed:(UIButton *)sender; //pressed variable
- (IBAction)expressionEvaluation:(UIButton *)sender; //evaluate expression with variables
@end
这里的.m:
// CalcViewController.m
#import "CalcViewController.h"
#import "CalculatorBrain.h"
@interface CalcViewController()
@property (nonatomic, strong) CalculatorBrain *brain;
@property (nonatomic) BOOL userIsInTheMiddleOfTypingANumber;
@end
@implementation CalcViewController
- (CalculatorBrain *) brain {
if (!_brain) _brain = [[CalculatorBrain alloc] init];
return _brain;
}
- (IBAction)expressionEvaluation:(UIButton *)sender {
NSDictionary* testValues = [NSDictionary dictionaryWithObjectsAndKeys:@"x", 2, @"y", 3, @"z", 4, nil];
double result = [CalculatorBrain evaluateExpression:self.brain.expression usingVariableValues:testValues];
NSString *resultString = [NSString stringWithFormat:@"%g", result];
self.display.text = resultString;
}
@end
编辑:就像一个侧面说明,我没有得到任何错误,只有一个警告:不完整的实现。这是因为我还没有完成一对夫妻班的方法,但我不认为这会导致车祸。
通过在xCode中添加异常断点,您将获得有关引发异常的代码行的更多信息。
然而,给我例外的那一行是:0x10e5098:movl(%eax),%edx – 2013-02-25 23:34:45
当你查看左边的调用堆栈时,如果你停下来,你应该能够在一个点上找到你自己的代码(它应该是黑色文字而不是灰色)。 – Kirualex 2013-02-25 23:47:03
谢谢!这帮了很多忙。 – 2013-02-26 00:37:27
NSDictionary* testValues = [NSDictionary dictionaryWithObjectsAndKeys:@"x", 2, @"y", 3, @"z", 4, nil];
原来是错误的一行。它应该是:
NSDictionary* testValues = [NSDictionary dictionaryWithObjectsAndKeys:@"x", [NSNumber numberWithInt:2], @"y", [NSNumber numberWithInt:3], @"z", [NSNumber numberWithInt:4], nil];
感谢所有帮助过的人!
打开异常断点: http://developer.apple.com/library/mac/#recipes/xcode_help-breakpoint_navigator/articles/adding_an_exception_breakpoint.html – lottscarson 2013-02-25 23:33:57
@lottscarson我跟着步骤添加一个异常断点,然后试图运行它,但它在同一个地方坠毁,没有提出任何例外。 – 2013-02-25 23:40:20