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我正在开发一个可编程计算器，对于我的生活，我无法理解我做错了什么。

以下是代码的相关部分。（代码未完成，所以我知道周围有额外的东西。）

计算器视图控制器.m

#import "CalculatorViewController.h"
#import "CalculatorBrain.h"

@interface CalculatorViewController ()
@property (nonatomic) BOOL userIsEnteringNumber;
@property (nonatomic) BOOL numberIsNegative;
@property (nonatomic,strong) CalculatorBrain *brain;
@property (nonatomic) NSArray *arrayOfDictionaries;
@property (nonatomic) NSDictionary *dictionary;
@end

@implementation CalculatorViewController
@synthesize display = _display;
@synthesize history = _history;
@synthesize userIsEnteringNumber = _userIsEnteringNumber;
@synthesize numberIsNegative;
@synthesize brain = _brain;
@synthesize arrayOfDictionaries;
@synthesize dictionary;

-(CalculatorBrain *)brain
{
if (!_brain) _brain = [[CalculatorBrain alloc] init];
return _brain;
}

/*snip code for some other methods*/

- (IBAction)variablePressed:(UIButton *)sender 
{
NSString *var = sender.currentTitle; 
NSDictionary *dict = [self.dictionary initWithObjectsAndKeys:[NSNumber numberWithDouble:3],@"x",[NSNumber numberWithDouble:4.1],@"y",[NSNumber numberWithDouble:-6],@"z",[NSNumber numberWithDouble:8.7263],@"foo",nil];
[self.brain convertVariable:var usingDictionary:dict];
self.display.text = [NSString stringWithFormat:@"%@",var];
self.history.text = [self.history.text stringByAppendingString:sender.currentTitle];
[self.brain pushOperand:[dict objectForKey:var] withDictionary:dict];
}

@end

这是 CalculatorBrain.m。

#import "CalculatorBrain.h"

@interface CalculatorBrain ()
@property (nonatomic, strong) NSMutableArray *operandStack;
@end

@implementation CalculatorBrain
@synthesize operandStack = _operandStack;


-(void)pushOperand:(id)operand withDictionary:(NSDictionary *)dictionary
{
NSNumber *operandAsObject;
if (![operand isKindOfClass:[NSString class]])
{
    operandAsObject = operand;
}
else 
{
    operandAsObject = [dictionary objectForKey:operand];
}
[self.operandStack addObject:operandAsObject];
}

-(double)popOperand
{
NSNumber *operandAsObject = [self.operandStack lastObject];
if (operandAsObject) [self.operandStack removeLastObject];
return [operandAsObject doubleValue];
}

-(double)convertVariable:(NSString *)variable usingDictionary:dictionary
{
double convertedNumber = [[dictionary objectForKey:variable] doubleValue];
return convertedNumber;
}

@end

我无法理解的是CalculatorViewController.m方法- (IBAction)variablePressed:(UIButton *)sender。此行使程序崩溃：

NSDictionary *dict = [self.dictionary initWithObjectsAndKeys:[list of objects and keys]];

但如果我成功了

NSDictionary *dict = [[NSDictionary alloc] initWithObjectsAndKeys:[list of objects and keys]];

然后一切正常。但如果我尝试做

NSDictionary *dict = [[self.dictionary alloc] initWithObjectsAndKeys:[list of objects and keys]];

在我看来这是正确的做法，然后 XCode 不会让我这样做，所以我显然不理解某些东西。

有什么想法吗？

4

1 回答 1

3

+alloc为对象分配内存。-init...方法初始化对象。

[self.dictionary initWithObjectsAndKeys:...调用-dictionary将返回该属性中设置的字典或 nil 然后尝试调用init...它。如果字典存在，那么您将尝试多次初始化一个无效的对象。如果该属性尚未设置，则 getter 将返回 nil 并且向 nil 发送init...消息将什么也不做。无论哪种方式，这都不是您想要做的。

[[self.dictionary alloc] init...也是无效的，因为编译器会警告您。现在你尝试从中获取一个对象-dictionary，然后调用+alloc它的类方法。

这里似乎存在一些关于如何创建对象以及属性访问器做什么的基本混淆。除了建议查看对象创建和点语法之外，我不确定如何解决这个问题。

于 2012-08-01T01:43:15.690 回答