objective-c - 打印ivar值的通用Objective-C描述方法

Question

在 Objective-C 中，通常使用打印对象 ID 和实例变量名称/值的方法来覆盖 -description。我想制作一个通用的 -description 方法，它通过内省(introspection)来执行此操作，而不是为每个类手动执行此操作。我希望输出类似于:

<ClassName: 0x??????, ivar1: value1, ivar2: value2, ivar3: value3, ...>

按实例变量名排序也很好(所以它们总是以相同的顺序)。最后，如果可以将其放入一个安全覆盖 NSObject 功能的类别中，那将是完美的(但我认为这并不简单，因为 NSObject.m 有一个关于在 -description 中使用 -[NSString stringWithFormat:]。

Answer 1

这是一个很好的问题!因为我还没有找到这样的东西，所以我写了一个小函数来为你做这件事。它使用 method swizzling 替换了 - (NSString *)description 的 NSObject(是的，我就是这么邪恶。MAHAHAHAHAHahahahaha)并按照它们在类(您可以轻松编辑它以按字母顺序显示它们)。

不要!忘记调用 NSObjectSwizzleDescription()!

.h文件:

@interface NSObject (JSObjectAdditions)
@end


void NSObjectSwizzleDescription();

.m文件:

#import <objc/objc.h>
#import "JSObject.h"

@implementation NSObject (JSObjectAdditions)

- (NSString *)verboseDescription
{
    NSMutableString *description = [NSMutableString stringWithFormat:@"<%@: %p>", NSStringFromClass([self class]), self];

    uint32_t ivarCount;
    Ivar *ivars = class_copyIvarList([self class], &ivarCount);

    if(ivars)
    {
        [description appendString:@"\n{"];

        for(uint32_t i=0; i<ivarCount; i++)
        {
            Ivar ivar = ivars[i];
            const char *ivarType = ivar_getTypeEncoding(ivar);
            id ivarObject = object_getIvar(self, ivar);

            [description appendFormat:@"\n   %s: ", ivar_getName(ivar)];

            // Default signed data types
            if(strcmp(ivarType, "c") == 0)
            {
                char character = (char)ivarObject;
                [description appendFormat:@"'%c'", character];
            }
            else if(strcmp(ivarType, "i") == 0 || strcmp(ivarType, "l") == 0) // l is also 32 bit in the 64 bit runtime environment
            {
                int integer = (int)ivarObject;
                [description appendFormat:@"%i", integer];
            }
            else if(strcmp(ivarType, "s") == 0)
            {
                short shortVal = (short)ivarObject;
                [description appendFormat:@"%i", (int)shortVal];
            }
            else if(strcmp(ivarType, "q") == 0)
            {
                long long longVal = (long long)ivarObject;
                [description appendFormat:@"%l", longVal];
            }
            // Default unsigned data types
            else if(strcmp(ivarType, "C") == 0)
            {
                unsigned char chracter = (unsigned char)ivarObject;
                [description appendFormat:@"'%c'", chracter];
            }
            else if(strcmp(ivarType, "I") == 0 || strcmp(ivarType, "L") == 0)
            {
                unsigned int integer = (unsigned int)ivarObject;
                [description appendFormat:@"%u", integer];
            }
            else if(strcmp(ivarType, "S") == 0)
            {
                unsigned short shortVal = (unsigned short)ivarObject;
                [description appendFormat:@"%i", (int)shortVal];
            }
            else if(strcmp(ivarType, "Q") == 0)
            {
                unsigned long long longVal = (unsigned long long)ivarObject;
                [description appendFormat:@"%ll", longVal];
            }
            // Floats'n'stuff
            else if(strcmp(ivarType, "f") == 0)
            {
                float floatVal;
                memcpy(&floatVal, &ivarObject, sizeof(float));

                [description appendFormat:@"%f", floatVal];
            }
            else if(strcmp(ivarType, "d") == 0)
            {
                double doubleVal;
                memcpy(&doubleVal, &ivarObject, sizeof(double));

                [description appendFormat:@"%f", doubleVal];
            }
            // Boolean and pointer
            else if(strcmp(ivarType, "B") == 0)
            {
                BOOL booleanVal = (BOOL)ivarObject;
                [description appendFormat:@"%@", (booleanVal ? @"YES" : @"NO")];
            }
            else if(strcmp(ivarType, "v") == 0)
            {
                void *pointer = (void *)ivarObject;
                [description appendFormat:@"%p", pointer];
            }
            else if(strcmp(ivarType, "*") == 0 || strcmp(ivarType, ":") == 0) // SEL is just a typecast for a cstring
            {
                char *cstring = (char *)ivarObject;
                [description appendFormat:@"\"%s\"", cstring];
            }
            else if(strncmp(ivarType, "@", 1) == 0)
            {
                [description appendFormat:@"%@", ivarObject];
            }
            else if(strcmp(ivarType, "#") == 0)
            {
                Class objcClass = (Class)ivarObject;
                [description appendFormat:@"%s", class_getName(objcClass)];
            }
            else
                [description appendString:@"???"];
        }

        [description appendString:@"\n}"];
        free(ivars);
    }

    return description; 
}

@end


void NSObjectSwizzleDescription()
{
    Method origMethod = class_getInstanceMethod([NSObject class], @selector(description));
    Method newMethod = class_getInstanceMethod([NSObject class], @selector(verboseDescription));

    method_exchangeImplementations(origMethod, newMethod);
}