方法swizzling和isa swizzling是同一回事吗？

Question

方法swizzling和isa swizzling是同一回事吗？如果没有，那么什么是isa swizzling？

Answer 1

方法摆动

方法swizzling 在运行时中交换类的两种方法。这将影响修改后的类的每个实例，这些实例过去或将要创建。

示例:让我们假设您已经为NSString编写了一个类别：

@interface NSString (Swizzling)
@end
@implementation NSString (Swizzling)
- (NSString *)swizzled_uppercaseString {
    //when the method is swizzled, the original method will be called 
    //with swizzled_uppercaseString (so this will not create a stack overflow).
    NSString *result = [self swizzled_uppercaseString];
    // our custom code
    result = [result stringByAppendingString:@" (swizzled)"];
    return result;
}
@end

然后，您可以将uppercaseString-method的实现与swizzled_uppercaseString-method交换，以便在调用swizzled_uppercaseString方法时执行swizzled_uppercaseString方法的实现。(在调用uppercaseString时，将执行swizzled_uppercaseString的原始实现)：

#import <objc/runtime.h>

NSString *sample = @"abc";

// original method is called:
NSLog([sample uppercaseString]); 

//Obtaining original and swizzled method:
original = class_getInstanceMethod([NSString class], @selector(uppercaseString));
swizzled = class_getInstanceMethod([NSString class], @selector(swizzled_uppercaseString));

//Exchange implementations here:
method_exchangeImplementations(original, swizzled);

// swizzled method is called:
NSLog([sample uppercaseString]); //prints "ABC (swizzled)"

​

​

伊萨斯威兹林

ISA swizzling修改单个对象上的属性，ISA (‘是’)属性，它描述对象的类，因此您可以在运行时将给定单个对象的类型与另一个类型交换。。

示例:让我们假设您有这个类结构：

@interface Sample : NSObject
@property (nonatomic) NSString *sampleStringToLoad;
@end
@implementation Sample
@synthesize sampleStringToLoad;
@end

@interface SampleWithStringLoader :NSObject
@property (nonatomic) NSString *sampleStringToLoad;
-(void)loadString;
@end
@implementation SampleWithStringLoader
@synthesize sampleStringToLoad;
-(void)loadString {
self.sampleStringToLoad = @"abc";
}
@end

然后可以将类设置为SampleWithStringLoader，这样sampleStringToLoad-method就可用了：

#import <objc/runtime.h>

Sample *sample = [Sample new];
// switch isa to new class:
object_setClass(sample, [SampleWithStringLoader class]);

// invoke method that is only in SampleWithStringLoader: 
[sample performSelector:@selector(loadString)]; 

// switch isa back to original class:
object_setClass(sample,[Sample class]); 

// Prints 'abc':
NSLog(sample.sampleStringToLoad);