Run Code at Deallocation of Any Object
I was reading this article by Jeff Kelley and trying to do the same. However the code was written before ARC was adopted and now fails to compile.
http://blog.slaunchaman.com/2011/04/11/fun-with-the-objective-c-runtime-run-code-at-deallocation-of-any-object/
The main problem is in this part of the printout, some casting errors and then blocked release messages. I found it to be a very interesting example but I can't seem to get it to work.
The problems are:
0. Autosynthesized property 'block' will use synthesized instance variable '_block', not existing instance variable 'block' on the @implementation JKBlockExecutor
1. Cast of block pointer type 'voidBlock' (aka 'void (^)(void)') to C pointer type 'const void *' requires a bridged cast and Cast of C pointer type 'void *' to block pointer type 'typeof (aBlock)' (aka 'void (^__strong)(void)') requires a bridged cast" on the block = Block_copy(aBlock); line
2. Cast of block pointer type 'voidBlock' (aka 'void (^)(void)') to C pointer type 'const void *' requires a bridged cast on Block_release(block);
typedef void (^voidBlock)(void);
@interface JKBlockExecutor : NSObject {
voidBlock block;
}
@property (nonatomic, readwrite, copy) voidBlock block;
- (id)initWithBlock:(voidBlock)block;
@end
@implementation JKBlockExecutor
@synthesize block;
- (id)initWithBlock:(voidBlock)aBlock
{
self = [super init];
if (self) {
block = Block_copy(aBlock);
}
return self;
}
- (void)dealloc
{
if (block != nil) {
block();
Block_release(block);
}
[super dealloc];
}
@end
This is where he creates a category on NSObject.
const void *runAtDeallocBlockKey = &runAtDeallocBlockKey;
@interface NSObject (JK_RunAtDealloc)
- (void)runAtDealloc:(voidBlock)block;
@end
@implementation NSObject (JK_RunAtDealloc)
- (void)runAtDealloc:(voidBlock)block
{
if (block) {
JKBlockExecutor *executor = [[JKBlockExecutor alloc] initWithBlock:block];
objc_setAssociatedObject(self,
runAtDeallocBlockKey,
executor,
OBJC_ASSOCIATION_RETAIN);
[executor release];
}
}
@end
This is how you execute the example.
NSObject *foo = [[NSObject alloc] init];
[foo runAtDealloc:^{
NSLog(@"Deallocating foo!");
}];
[foo release];
Or another way to get other information.
NSObject *foo = [[NSObject alloc] init];
__block id objectRef = foo;
[foo runAtDealloc:^{
NSLog(@"Deallocating foo at address %p!", objectRef);
}];
[foo release];
Can this code be fixed somehow? I took out all the release messages to no avail.
Code below builds and works (or at least seems so), and prints "Deallocating foo!" when I expect it to print it. Part 1:
typedef void (^voidBlock)(void);
@interface JKBlockExecutor : NSObject {
voidBlock block;
}
@property (nonatomic, readwrite, copy) voidBlock block;
- (id)initWithBlock:(voidBlock)block;
@end
@implementation JKBlockExecutor
@synthesize block = block;
- (id)initWithBlock:(voidBlock)aBlock
{
self = [super init];
if (self) {
block = [aBlock copy];
}
return self;
}
- (void)dealloc
{
if (block != nil) {
block();
block = nil;
}
}
@end
Part 2:
const void *runAtDeallocBlockKey = &runAtDeallocBlockKey;
@interface NSObject (JK_RunAtDealloc)
- (void)runAtDealloc:(voidBlock)block;
@end
@implementation NSObject (JK_RunAtDealloc)
- (void)runAtDealloc:(voidBlock)block
{
if (block) {
JKBlockExecutor *executor = [[JKBlockExecutor alloc] initWithBlock:block];
objc_setAssociatedObject(self,
runAtDeallocBlockKey,
executor,
OBJC_ASSOCIATION_RETAIN);
}
}
@end
Testing if it works:
@autoreleasepool {
NSObject *foo = [[NSObject alloc] init];
[foo runAtDealloc:^{
NSLog(@"Deallocating foo!");
}];
}
EDIT
Changed Block_release(block); to block = nil;
If you want to know more about the code below ,please go to Fun With the Objective-C Runtime: Run Code at Deallocation of Any Object
Part 1：create one class: the object We Want To Be Released When That Happens--- this class is like an event：when the target obj dealloc,it happens。use block to execute the event 。
// .m file
// http://weibo.com/luohanchenyilong/
// https://github.com/ChenYilong
// the object We Want To Be Released When That Happens--- this class is like an event：when the target obj dealloc,it happens。use block to execute the event 。
typedef void (^voidBlock)(void);
@interface CYLBlockExecutor : NSObject
- (id)initWithBlock:(voidBlock)block;
@end
// .m file
// http://weibo.com/luohanchenyilong/
// https://github.com/ChenYilong
// the object We Want To Be Released When That Happens--- this class is like an event：when the target obj dealloc,it happens。use block to execute the event 。
#import "CYLBlockExecutor.h"
@interface CYLBlockExecutor() {
voidBlock _block;
}
@implementation CYLBlockExecutor
- (id)initWithBlock:(voidBlock)aBlock
{
self = [super init];
if (self) {
_block = [aBlock copy];
}
return self;
}
- (void)dealloc
{
_block ? _block() : nil;
}
@end
Part 2：core code：use runtime to realize cyl_runAtDealloc method
// CYLNSObject+RunAtDealloc.h file
// http://weibo.com/luohanchenyilong/
// https://github.com/ChenYilong
// use runtime to realize cyl_runAtDealloc method
#import "CYLBlockExecutor.h"
const void *runAtDeallocBlockKey = &runAtDeallocBlockKey;
@interface NSObject (CYLRunAtDealloc)
- (void)cyl_runAtDealloc:(voidBlock)block;
@end
// CYLNSObject+RunAtDealloc.m file
// http://weibo.com/luohanchenyilong/
// https://github.com/ChenYilong
// use runtime to realize cyl_runAtDealloc method
#import "CYLNSObject+RunAtDealloc.h"
#import "CYLBlockExecutor.h"
@implementation NSObject (CYLRunAtDealloc)
- (void)cyl_runAtDealloc:(voidBlock)block
{
if (block) {
CYLBlockExecutor *executor = [[CYLBlockExecutor alloc] initWithBlock:block];
objc_setAssociatedObject(self,
runAtDeallocBlockKey,
executor,
OBJC_ASSOCIATION_RETAIN);
}
}
@end
How to use :
#import "CYLNSObject+RunAtDealloc.h"
then
NSObject *foo = [[NSObject alloc] init];
[foo cyl_runAtDealloc:^{
NSLog(@"Deallocating foo!");
}];
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