Objective-C 内省/反思

Question

是否有内置方法、函数、API、普遍接受的方式等来转储 Objective-C 中实例化对象的内容，特别是在 Apple 的 Cocoa/Cocoa-Touch 环境中？

我希望能够做类似的事情

MyType *the_thing = [[MyType alloc] init];
NSString *the_dump = [the_thing dump]; //pseudo code
NSLog("Dumped Contents: %@", the_dump);

并显示对象的实例变量名称和值，以及可在运行时调用的任何方法。最好是易于阅读的格式。

对于熟悉 PHP 的开发人员，我基本上是在寻找反射函数（var_dump()、get_class_methods()）和 OO 反射 API 的等效项。

Answer 1

更新：任何想要做这类事情的人都可能想查看Mike Ash's ObjC wrapper for the Objective-C runtime。

这或多或少是你的做法：

#import <objc/runtime.h>

. . . 

-(void)dumpInfo
{
    Class clazz = [self class];
    u_int count;

    Ivar* ivars = class_copyIvarList(clazz, &count);
    NSMutableArray* ivarArray = [NSMutableArray arrayWithCapacity:count];
    for (int i = 0; i < count ; i++)
    {
        const char* ivarName = ivar_getName(ivars[i]);
        [ivarArray addObject:[NSString  stringWithCString:ivarName encoding:NSUTF8StringEncoding]];
    }
    free(ivars);

    objc_property_t* properties = class_copyPropertyList(clazz, &count);
    NSMutableArray* propertyArray = [NSMutableArray arrayWithCapacity:count];
    for (int i = 0; i < count ; i++)
    {
        const char* propertyName = property_getName(properties[i]);
        [propertyArray addObject:[NSString  stringWithCString:propertyName encoding:NSUTF8StringEncoding]];
    }
    free(properties);

    Method* methods = class_copyMethodList(clazz, &count);
    NSMutableArray* methodArray = [NSMutableArray arrayWithCapacity:count];
    for (int i = 0; i < count ; i++)
    {
        SEL selector = method_getName(methods[i]);
        const char* methodName = sel_getName(selector);
        [methodArray addObject:[NSString  stringWithCString:methodName encoding:NSUTF8StringEncoding]];
    }
    free(methods);

    NSDictionary* classDump = [NSDictionary dictionaryWithObjectsAndKeys:
                               ivarArray, @"ivars",
                               propertyArray, @"properties",
                               methodArray, @"methods",
                               nil];

    NSLog(@"%@", classDump);
}

从那里，很容易得到实例属性的实际值，但是你必须检查它们是原始类型还是对象，所以我懒得放了。你也可以选择扫描继承链来获取对象上定义的所有属性。然后是在类别上定义的方法，等等……但几乎所有东西都是现成的。

以下是 UILabel 的上述代码转储的摘录：

{
    ivars =     (
        "_size",
        "_text",
        "_color",
        "_highlightedColor",
        "_shadowColor",
        "_font",
        "_shadowOffset",
        "_minFontSize",
        "_actualFontSize",
        "_numberOfLines",
        "_lastLineBaseline",
        "_lineSpacing",
        "_textLabelFlags"
    );
    methods =     (
        rawSize,
        "setRawSize:",
        "drawContentsInRect:",
        "textRectForBounds:",
        "textSizeForWidth:",
        . . .
    );
    properties =     (
        text,
        font,
        textColor,
        shadowColor,
        shadowOffset,
        textAlignment,
        lineBreakMode,
        highlightedTextColor,
        highlighted,
        enabled,
        numberOfLines,
        adjustsFontSizeToFitWidth,
        minimumFontSize,
        baselineAdjustment,
        "_lastLineBaseline",
        lineSpacing,
        userInteractionEnabled
    );
}

Answer 2

缺少description 方法（如Java 中的.toString()），我还没有听说过内置的，但创建一个不会太难。 The Objective-C Runtime Reference 有很多函数可以用来获取对象的实例变量、方法、属性等信息。

Answer 3

这是我目前用于在最终公开发布的库中自动打印类变量的方法 - 它通过将实例类中的所有属性一直转储到继承树上来工作。感谢 KVC，您无需关心属性是否是原始类型（对于大多数类型）。

// Finds all properties of an object, and prints each one out as part of a string describing the class.
+ (NSString *) autoDescribe:(id)instance classType:(Class)classType
{
    NSUInteger count;
    objc_property_t *propList = class_copyPropertyList(classType, &count);
    NSMutableString *propPrint = [NSMutableString string];

    for ( int i = 0; i < count; i++ )
    {
        objc_property_t property = propList[i];

        const char *propName = property_getName(property);
        NSString *propNameString =[NSString stringWithCString:propName encoding:NSASCIIStringEncoding];

        if(propName) 
        {
            id value = [instance valueForKey:propNameString];
            [propPrint appendString:[NSString stringWithFormat:@"%@=%@ ; ", propNameString, value]];
        }
    }
    free(propList);


    // Now see if we need to map any superclasses as well.
    Class superClass = class_getSuperclass( classType );
    if ( superClass != nil && ! [superClass isEqual:[NSObject class]] )
    {
        NSString *superString = [self autoDescribe:instance classType:superClass];
        [propPrint appendString:superString];
    }

    return propPrint;
}

+ (NSString *) autoDescribe:(id)instance
{
    NSString *headerString = [NSString stringWithFormat:@"%@:%p:: ",[instance class], instance];
    return [headerString stringByAppendingString:[self autoDescribe:instance classType:[instance class]]];
}

Answer 4

我对 Kendall 的打印属性值的代码进行了一些调整，这对我来说非常方便。我将它定义为实例方法而不是类方法，因为这就是超类递归调用它的方式。我还为不符合 KVO 的属性添加了异常处理，并在输出中添加了换行符以使其更易于阅读（和区分）：

-(NSString *) autoDescribe:(id)instance classType:(Class)classType
{
    NSUInteger count;
    objc_property_t *propList = class_copyPropertyList(classType, &count);
    NSMutableString *propPrint = [NSMutableString string];

    for ( int i = 0; i < count; i++ )
    {
        objc_property_t property = propList[i];

        const char *propName = property_getName(property);
        NSString *propNameString =[NSString stringWithCString:propName encoding:NSASCIIStringEncoding];

        if(propName) 
        {
         @try {
            id value = [instance valueForKey:propNameString];
            [propPrint appendString:[NSString stringWithFormat:@"%@=%@\n", propNameString, value]];
         }
         @catch (NSException *exception) {
            [propPrint appendString:[NSString stringWithFormat:@"Can't get value for property %@ through KVO\n", propNameString]];
         }
        }
    }
    free(propList);


    // Now see if we need to map any superclasses as well.
    Class superClass = class_getSuperclass( classType );
    if ( superClass != nil && ! [superClass isEqual:[NSObject class]] )
    {
        NSString *superString = [self autoDescribe:instance classType:superClass];
        [propPrint appendString:superString];
    }

    return propPrint;
}

Answer 5

老实说，适合这项工作的工具是 Xcode 的调试器。它以视觉方式轻松访问所有这些信息。花时间学习如何使用它，它是一个非常强大的工具。

更多信息：

Using the Debugger

Outdated Xcode Debugging Guide - Apple 存档

About Debugging with Xcode - Apple 存档

About LLDB and Debugging - Apple 存档

Debugging with GDB - Apple 存档

SpriteKit Debugging Guide - Apple 存档

Debugging Programming Topics for Core Foundation - Apple 存档

Answer 6

我用这个做了cocoapod，https://github.com/neoneye/autodescribe

我修改了 Christopher Pickslay 的代码，并将其设为 NSObject 上的一个类别，并为其添加了一个单元测试。使用方法如下：

@interface TestPerson : NSObject

@property (nonatomic, strong) NSString *firstName;
@property (nonatomic, strong) NSString *lastName;
@property (nonatomic, strong) NSNumber *age;

@end

@implementation TestPerson

// empty

@end

@implementation NSObject_AutoDescribeTests

-(void)test0 {
    TestPerson *person = [TestPerson new];
    person.firstName = @"John";
    person.lastName = @"Doe";
    person.age = [NSNumber numberWithFloat:33.33];
    NSString *actual = [person autoDescribe];
    NSString *expected = @"firstName=John\nlastName=Doe\nage=33.33";
    STAssertEqualObjects(actual, expected, nil);
}

@end

Answer 7

我之前对自省和反思感到困惑，所以请在下面获取一些信息。

自省是对象检查它是哪种类型、它符合的协议或它可以响应的选择器的能力。 objc api如isKindOfClass/isMemberOfClass/conformsToProtocol/respondsToSelector等。

Refection 能力比 Introspection 更进一步，它不仅可以获取对象信息，还可以操作对象元数据、属性和函数。比如object_setClass可以修改对象类型。