計算器：按下“Enter”按鈕后，運行時應用程序崩潰

Question

我寫了一個計算器程序編譯得很好，但是當我點擊“Enter”按鈕時崩潰了。

這是崩潰日志：

2012-03-05 14:35:46.561 Calculator[35699:f803] -[CalculatorViewController enterPressed:]: unrecognized selector sent to instance 0x6a590f0
2012-03-05 14:35:46.657 Calculator[35699:f803] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[CalculatorViewController enterPressed:]: unrecognized selector sent to instance 0x6a590f0'
*** First throw call stack:
(0x13bb052 0x154cd0a 0x13bcced 0x1321f00 0x1321ce2 0x13bcec9 0x155c2 0x1555a 0xbab76 0xbb03f 0xba2fe 0x3aa30 0x3ac56 0x21384 0x14aa9 0x12a5fa9 0x138f1c5 0x12f4022 0x12f290a 0x12f1db4 0x12f1ccb 0x12a4879 0x12a493e 0x12a9b 0x20fd 0x2065)
terminate called throwing an exception(lldb) 

視圖控制器的實現：

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

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

@implementation CalculatorViewController
@synthesize display = _display;
@synthesize userIsInTheMiddleOfEnteringANumber = _userIsInTheMiddleOfEnteringANumber;
@synthesize brain = _brain;

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

- (IBAction)digitPressed:(UIButton *)sender 
{
    NSString *digit = [sender currentTitle];
    if (self.userIsInTheMiddleOfEnteringANumber) {
        self.display.text = [self.display.text stringByAppendingString:digit];
    } else {
        self.display.text = digit;
        self.userIsInTheMiddleOfEnteringANumber = YES;
    }

}

- (IBAction)enterPressed 
{
    [self.brain pushOperand:[self.display.text doubleValue]];
    self.userIsInTheMiddleOfEnteringANumber = NO;
}

- (IBAction)operationPressed:(UIButton *)sender 
{
    if(self.userIsInTheMiddleOfEnteringANumber) {
        [self enterPressed];
    }
    NSString *operation = sender.currentTitle;
    double result = [self.brain performOperation:operation];
    self.display.text = [NSString stringWithFormat:@"%g",result];
}

@end

Answer 1

答案在於錯誤消息-[CalculatorViewController enterPressed:] ，它表示發送到視圖控制器的選擇器應該采用參數。 但是，您已經定義enterPressed沒有任何參數的enterPressed 。 enterPressed方法看起來應該像operationPressed: ie：

- (IBAction) enterPressed:(UIButton *)sender