Question

我有一些obj-c代码，我打算在插件中发送不支持的消息。但是，我似乎无法忽略消息。我想“ - （id）forward：（SEL）选择器：（marg_list）arglist;”会解决它，但它没有。如何在没有收到警告和终止呼叫的情况下完全运行此应用程序？

#import <stdio.h>
#import <objc/Object.h>

//------- @interface section -------

@interface Fraction: Object
{
    int  numerator;
    int  denominator;
}

-(void)   print;
-(void)   setNumerator: (int) n;
-(void)   setDenominator: (int) d;
-(id)     forward: (SEL) selector: (marg_list) arglist;

@end

//------- @implementation section -------


@implementation Fraction;
-(void) print
{
    printf (" %i/%i ", numerator, denominator);
}

-(void) setNumerator: (int) n
{
    numerator = n;
}

-(void) setDenominator: (int) d
{
    denominator = d;
}

-(id) forward: (SEL) selector: (marg_list) arglist
{
    return nil;
}

@end

//------- program section -------


int main (int argc, char *argv[])
{
    Fraction  *myFraction;

    // Create an instance of a Fraction

    myFraction = [Fraction alloc];
    myFraction = [myFraction init];

    // Set fraction to 1/3

    [myFraction setNumerator: 1];
    [myFraction setDenominator: 3];

    // Display the fraction using the print method

    printf ("The value of myFraction is:");
    [myFraction print];
    printf ("\n");
    [myFraction someMsg: 99];
    [myFraction free];
    printf("end");  
    return 0;
}

Answer 1

最好在调用者中执行此操作，而不是将其插入插件中。而不是：

[myFraction someMsg: 99];

您应该检查myFraction是否响应someMsg选择器：

if ([myFraction respondsToSelector:@selector(someMsg:)]) {
    [myFraction someMsg: 99];
}

-respondsToSelector:方法在NSObject Protocol Reference中定义，请注意您的MyFraction对象需要从NSObject继承，而不是Object（或者是你自己的NSObject协议。当然，这无论如何都是最佳实践 - 通常不鼓励直接继承Object类。

忽略目标C中的消息

1 个答案: