名單

Question

是否有一種方式來獲得某種類屬性的陣列？例如，如果我有像這樣的接口

@interface MyClass : NSObject 
    @property (strong,nonatomic) UILabel *firstLabel; 
    @property (strong,nonatomic) UILabel *secondLabel;   
@end 

我可以在不知道名稱的情況下獲得對這些標籤的引用嗎？

@implementation MyClass 
    -(NSArray*)getListOfAllLabels 
    { 
      ????? 
    }   
@end 

我知道我可以[NSArray arrayWithObjects:firstLabel,secondLabel,nil]輕鬆地做到這一點，但我想以某種類枚舉要做得像for (UILabel* oneLabel in ???[self objects]???)

Answer 1

所以更準確地說，你想動態，運行時observaion性質的，如果我沒有得到它。做這樣的事情（實現自我這種方法，您希望類反思）：

#import <objc/runtime.h> 

- (NSArray *)allPropertyNames 
{ 
    unsigned count; 
    objc_property_t *properties = class_copyPropertyList([self class], &count); 

    NSMutableArray *rv = [NSMutableArray array]; 

    unsigned i; 
    for (i = 0; i < count; i++) 
    { 
     objc_property_t property = properties[i]; 
     NSString *name = [NSString stringWithUTF8String:property_getName(property)]; 
     [rv addObject:name]; 
    } 

    free(properties); 

    return rv; 
} 

- (void *)pointerOfIvarForPropertyNamed:(NSString *)name 
{ 
    objc_property_t property = class_getProperty([self class], [name UTF8String]); 

    const char *attr = property_getAttributes(property); 
    const char *ivarName = strchr(attr, 'V') + 1; 

    Ivar ivar = object_getInstanceVariable(self, ivarName, NULL); 

    return (char *)self + ivar_getOffset(ivar); 
} 

使用方法如下：

SomeType myProperty; 
NSArray *properties = [self allPropertyNames]; 
NSString *firstPropertyName = [properties objectAtIndex:0]; 
void *propertyIvarAddress = [self getPointerOfIvarForPropertyNamed:firstPropertyName]; 
myProperty = *(SomeType *)propertyIvarAddress; 

// Simpler alternative using KVC: 
myProperty = [self valueForKey:firstPropertyName]; 

希望這有助於。

Answer 2

看看這個link。它是在目標C運行時的客觀C包裝。

您可以使用如下代碼如下

uint count; 
objc_property_t* properties = class_copyPropertyList(self.class, &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); 

Answer 3

必須包括運行時頭

#import<objc/runtime.h> 
uint propertiesCount; 
objc_property_t *classPropertiesArray = class_copyPropertyList([self class], &propertiesCount); 
free(classPropertiesArray); 

Answer 4

使用NSObject中的attributeKeys方法。

for (NSString *key in [self attributeKeys]) { 

     id attribute = [self valueForKey:key]; 

     if([attribute isKindOfClass:[UILabel class]]) 
     { 
     //put attribute to your array 
     } 
    } 

Answer 5

serhats的解決方案是大不幸的是它並不適用於iOS的工作（如你所提到的）（這個問題被標記爲iOS）。一種解決方法是獲取對象的NSDictionary中表示，然後正常訪問作爲鍵值對。我會建議類別NSObject的：

頁眉文件：

@interface NSObject (NSDictionaryRepresentation) 

/** 
Returns an NSDictionary containing the properties of an object that are not nil. 
*/ 
- (NSDictionary *)dictionaryRepresentation; 

@end 

的實現文件：

#import "NSObject+NSDictionaryRepresentation.h" 
#import <objc/runtime.h> 

@implementation NSObject (NSDictionaryRepresentation) 

- (NSDictionary *)dictionaryRepresentation { 
    unsigned int count = 0; 
    // Get a list of all properties in the class. 
    objc_property_t *properties = class_copyPropertyList([self class], &count); 

    NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] initWithCapacity:count]; 

    for (int i = 0; i < count; i++) { 
     NSString *key = [NSString stringWithUTF8String:property_getName(properties[i])]; 
     NSString *value = [self valueForKey:key]; 

     // Only add to the NSDictionary if it's not nil. 
     if (value) 
      [dictionary setObject:value forKey:key]; 
    } 

    free(properties); 

    return dictionary; 
} 

@end 

從這篇文章借用：http://hesh.am/2013/01/transform-properties-of-an-nsobject-into-an-nsdictionary/

這樣你可以做提到serhats類似的東西：

for (NSString *key in objectDic.allKeys) { 
    if([objectDic[key] isKindOfClass:[UILabel class]]) 
    { 
     //put attribute to your array 
    } 
} 

Answer 6

答案通過@ user529758不會與ARC工作，它不會顯示任何祖先類的屬性。

要解決此問題，您需要遍歷類層次結構，並使用兼容ARC的[NSObject valueForKey:]來獲取屬性值。

Person.h：

#import <Foundation/Foundation.h> 

extern NSMutableArray *propertyNamesOfClass(Class klass); 

@interface Person : NSObject 

@property (nonatomic) NSString *name; 

@end 

人。L：

#import "Person.h" 
#import <objc/runtime.h> 

NSMutableArray *propertyNamesOfClass(Class klass) { 
    unsigned int count; 
    objc_property_t *properties = class_copyPropertyList(klass, &count); 

    NSMutableArray *rv = [NSMutableArray array]; 

    for (unsigned int i = 0; i < count; i++) 
    { 
     objc_property_t property = properties[i]; 
     NSString *name = [NSString stringWithUTF8String:property_getName(property)]; 
     [rv addObject:name]; 
    } 

    free(properties); 

    return rv; 
} 

@implementation Person 

- (NSMutableArray *)allPropertyNames { 
    NSMutableArray *classes = [NSMutableArray array]; 
    Class currentClass = [self class]; 
    while (currentClass != nil && currentClass != [NSObject class]) { 
     [classes addObject:currentClass]; 
     currentClass = class_getSuperclass(currentClass); 
    } 

    NSMutableArray *names = [NSMutableArray array]; 
    [classes enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(Class currentClass, NSUInteger idx, BOOL *stop) { 
     [names addObjectsFromArray:propertyNamesOfClass(currentClass)]; 
    }]; 

    return names; 
} 

- (NSString*)description { 
    NSMutableArray *keys = [self allPropertyNames]; 
    NSMutableDictionary *properties = [NSMutableDictionary dictionaryWithCapacity:keys.count]; 
    [keys enumerateObjectsUsingBlock:^(NSString *key, NSUInteger idx, BOOL *stop) { 
     properties[key] = [self valueForKey:key]; 
    }]; 

    NSString *className = NSStringFromClass([self class]); 
    return [NSString stringWithFormat:@"%@ : %@", className, properties]; 
} 

Student.h：

#import "Person.h" 

@interface Student : Person 

@property (nonatomic) NSString *studentID; 

@end 

Student.m：

#import "Student.h" 

@implementation Student 

@end 

的main.m：

#import <Foundation/Foundation.h> 
#import "Student.h" 

int main(int argc, const char * argv[]) { 
    @autoreleasepool { 
     // insert code here... 
     Student *student = [[Student alloc] init]; 
     student.name = @"John Doe"; 
     student.studentID = @"123456789"; 
     NSLog(@"student - %@", student); 
    } 
    return 0; 
}