objective-c - Objective C 计算器编程变量

Question

好吧，我一直在研究他们在线免费发布的斯坦福 iOS 开发类(class)。我一直在研究如何制作一个可编程变量。到目前为止，它一直运行良好，除了我认为以下代码行将变量编程为 @"x="而不是之前输入的数字。

View Controller :

#import "ViewController.h"
#import "CalculatorBrain.h"

@interface ViewController()
@property (nonatomic) BOOL userIsInTheMiddleOfEnteringANumber;
@property (nonatomic) BOOL userPressedSomethingElse;
@property (nonatomic, strong) CalculatorBrain *brain;
@end

@implementation ViewController
@synthesize display;
@synthesize inputHistory;
@synthesize userPressedSomethingElse;
@synthesize userIsInTheMiddleOfEnteringANumber;
@synthesize brain = _brain;

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

NSString *xValue = @"0";

- (IBAction)enterPressed 
// A specific action if enter is pressed
{
    [self.brain pushOperand:[self.display.text doubleValue]];
    self.userIsInTheMiddleOfEnteringANumber = NO;
    if (self.userPressedSomethingElse) 
    {
        self.inputHistory.text = [self.inputHistory.text stringByAppendingString:@" "];
    }
    self.userPressedSomethingElse = NO;
}

- (IBAction)variableChanged:(id)sender 
{
    if (self.userIsInTheMiddleOfEnteringANumber) 
    {
        [self enterPressed];
    }
    NSString *operation = [sender currentTitle];
    xValue = [self.brain programVariable:operation];
    self.inputHistory.text = [self.inputHistory.text stringByAppendingString:@"X="];
    self.inputHistory.text = [self.inputHistory.text stringByAppendingString:xValue];
}

计算器大脑(.m 之一):

#import "CalculatorBrain.h"

@interface CalculatorBrain()
@property (nonatomic,strong) NSMutableArray *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];
    if (operandObject) [self.operandStack removeLastObject];
    return [operandObject doubleValue];
}

- (NSString *) programVariable: (NSString *) operation
{
    double result = [self popOperand];
    NSString *resultString = [NSString stringWithFormat:@"%.2d",result];
    return resultString;
}

.h 计算器大脑:

#import <Foundation/Foundation.h>

@interface CalculatorBrain : NSObject

- (void) pushOperand: (double) operand;
- (double) performOperation: (NSString *) operation;
- (NSString *) programVariable: (NSString *) operation;

@end

按下的按钮显示“x=”，由于我添加了一些跟踪语句，我发现它被设置为 xValue。但是，我不知道如何解决...有什么想法吗？

Answer 1

在您的 variableChanged: 方法中，您可能需要 if (!self.userIsInTheMiddleOfEnteringANumber) 开头。注意逻辑否定，我从你的变量名的意义上推导出需要。我看不出该变量是如何设置的，所以我相信您已在应用程序的其他地方正确设置了它。

此外，将变量 xValue 更改为 ViewController 上的实例变量。它目前是一个全局静态变量。如果您创建了多个 ViewController 对象，就会遇到问题。