Question

我正在学习对象C，我无法弄清楚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'

我正在创建一个执行计算器功能的简单应用。我正在使用的代码是：

    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);

双差异线上发生错误。我可以注释掉该行和引用它的NSlog行，程序运行正常。计算器类的示例是：

- (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;}

虽然之前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

Answer 1

您的方法名称与您调用它的方式不匹配。

致电代码：

double difference = [calculator subtractFromTotal:6];

实现：

- (double) subtractfromTotal:(double)value

应该是：

- (double) subtractFromTotal:(double)value

编译器无疑警告过你。你应该注意编译器警告！他们通常会告诉你一些重要的事情！

Answer 2

仔细查看错误日志，您可以看到此行

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

它清楚地告诉您，当您使用subtractFromTotal:(double)value实施邮件时，尝试使用subtractfromTotal:(double)value发送邮件。注意错误日志。

应用程序因未捕获的异常“类的问题”而终止

2 个答案: