我正在參加Stanford's iPhone application development的講座,第一項任務是構建RPN計算器。將項添加到NSMutableArray不起作用
我有一個問題,可能是我錯過了一些簡單的事情。
有一個模型類,稱爲CalculatorBrain:
.H
#import <Foundation/Foundation.h>
@interface CalculatorBrain : NSObject
- (void)pushOperand:(double)operand;
- (double)performOperation:(NSString *)operation;
@property (nonatomic, strong) NSMutableArray *operandStack;
@end
.M
#import "CalculatorBrain.h"
@interface CalculatorBrain()
@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];
}
@end
還有的控制器類,CalculatorViewController: .H
#import <UIKit/UIKit.h>
@interface CalculatorViewController : UIViewController
@property (weak, nonatomic) IBOutlet UILabel *display;
@end
.m
#import "CalculatorViewController.h"
#import "CalculatorBrain.h"
@interface CalculatorViewController()
@property (nonatomic) BOOL userIsInTheMiddleOfEnteringANumber;
@property (nonatomic, strong) CalculatorBrain *brain;
@end
@implementation CalculatorViewController
- (IBAction)digitPressed:(UIButton *)sender {
NSString *digit = [sender currentTitle];
NSString *currentDisplayText = self.display.text;
if (self.userIsInTheMiddleOfEnteringANumber) {
self.display.text = [currentDisplayText stringByAppendingString:digit];
}
else {
self.display.text = digit;
self.userIsInTheMiddleOfEnteringANumber = YES;
}
}
- (IBAction)enterPressed {
[self.brain pushOperand:[self.display.text doubleValue]];
NSLog(@"count: %lu", (unsigned long) [self.brain.operandStack count]);
NSLog(@"index 0: %@", [self.brain.operandStack objectAtIndex:0]);
self.userIsInTheMiddleOfEnteringANumber = NO;
}
@end
問題出在enterPressed方法中。正如你所看到的,我把2個NSLog行看看數字是否被壓入數組,但它們不是。這兩行返回我0和null。 我知道我不需要再使用@synthesize(在CalculatorBrain類中),但是我嘗試過使用和不使用它,而且項目也沒有被添加。
任何人都可以幫助我嗎?
謝謝。
懶惰創作的NSMutableArray在吸氣劑是相當不規範。最好在初始化器中創建它,這也可以完全消除自定義getter/setter。 – bbum