Objective c 应用程序因未捕获的异常而终止”；“与班级一起发布”；

我正在学习对象C，我无法理解为什么会出现以下错误：

2013-01-08 21:46:12.984 ObjectiveCDemo[38355:c07] -[Calculator subtractFromTotal:]: unrecognized selector sent to instance 0x7568c90
2013-01-08 21:46:12.985 ObjectiveCDemo[38355:c07] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Calculator subtractFromTotal:]: unrecognized selector sent to instance 0x7568c90'

我正在创建一个简单的应用程序，它具有计算器功能。我使用的代码是：

    calculator = [[Calculator alloc] init];
    double sum = [calculator addToTotal:10];
    double difference = [calculator subtractFromTotal:6];
    double results = [calculator multiplyTimesTotal:3];
    double quotient = [calculator divideFromTotal:4];
    [calculator clear];

    NSLog(@"Sum: %f", sum);
    NSLog(@"Difference: %f", difference);
    NSLog(@"Results: %f", results);
    NSLog(@"Quotient: %f", quotient);

错误发生在双差线上。我可以注释掉那一行和引用它的NSlog行，程序运行正常。计算器类的示例如下：

- (double) addToTotal:(double)value{total += value;
return total;}

- (double) subtractfromTotal:(double)value{total -= value;
return total;}

- (double) multiplyTimesTotal:(double)value{total *= value;
return total;}

- (double) divideFromTotal:(double)value{total /= value;
return total;}

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虽然前面已经提到过这个错误，但我看不出其他任何解决方案是如何应用的

您的方法名称与您调用它的方式不匹配

呼叫代码：

double difference = [calculator subtractFromTotal:6];

实施：

- (double) subtractfromTotal:(double)value

应该是：

- (double) subtractFromTotal:(double)value

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毫无疑问，编译器警告过你这一点。您应该注意编译器警告！他们通常会告诉你一些重要的事情

仔细查看错误日志，您可以看到这一行

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Calculator subtractFromTotal:]: unrecognized selector sent to instance 0x7568c90'

它清楚地告诉您，您正在尝试使用

subtractfromtoal:（double）值发送消息，而您使用
subtractfromtoal:（double）值实现它。请注意错误日志