Preface
As we all know, when a network request is sent out, if you ignore it, the following situations may occur:
Entering a certain page and doing some operation (exiting the page, switching to a certain tab, etc.) causes the previous request to become useless request. At this time, it is possible that although the page has been destroyed, the network request is still flying outside. If you leave it alone, then this request is wasteful of traffic and performance. Especially when the network is relatively poor, a timeout useless request is even more unpleasant. At this time, our best way is to cancel these useless requests.
The traditional cancel method is like this:
1. You need to hold the request object in the class
@property (strong/weak, nonatomic) XXRequest *xxrequest1;
The specific use of strong or weak attributes depends on your network layer design. Some network layer requests are completely temporary variables. If they are directly destroyed after the method is released, strong is needed. Some designs have self-held characteristics. If they will not be destroyed before the request is completed, you can use weak.
2. At the place where the request is initiated, assign a request
xxrequest1 = xxx; self.xxrequest1 = xxrequest1; [xxrequest1 start];
3. Where it needs to be destroyed, it is usually in this class dealloc
[self.xxrequest1 cancel];
You can see that in order to cancel a request, our request objects are everywhere. If there are a few more requests, it will be even more disgusting to process. .
Is there any way to save us your worries and effort?
Target:
We hope to control part of the request, and automatically cancel the request we sent at the time of page destruction, manager release, etc., without us manually writing the code everywhere above.
plan:
Listen to the dealloc method call of the class. When the dealloc is executed, execute the cancel method of the request.
Soon, we found the problem:
The dealloc method of hook class is not allowed under ARC, so hook is not possible. Is there any other way to know that a class is deallocated?
In fact, we can use some workarounds to get it. We know that the attributes of associated binding can be automatically released during dealloc according to the settings during binding, so we can use this to listen to dealloc calls:
- Build an intermediate class A. When destroying the execution of dealloc, the cancel method of the request is executed by the way.
- Through associated binding, bind the destroyed class to any execution class B
- In this way, when the execution class B is destroyed and the internal associated attribute is destroyed, we can get the corresponding execution time.
The core code is given below:
Create a class for cancel requests:
@interface YRWeakRequest : NSObject @property (weak, nonatomic) id request; @end @implementation YRWeakRequest @end
2. Build a class that records all requests for a certain class
@interface YRDeallocRequests : NSObject
@property (strong, nonatomic) NSMutableArray<YRWeakRequest*> *weakRequests;
@property (strong, nonatomic) NSLock *lock;
@end
@implementation YRDeallocRequests
- (instancetype)init{
if (self = [super init]) {
_weakRequests = [NSMutableArray arrayWithCapacity:20];
_lock = [[NSLock alloc]init];
}
return self;
}
- (void)addRequest:(YRWeakRequest*)request{
if (!request||!) {
return;
}
[_lock lock];
[ addObject:request];
[_lock unlock];
}
- (void)clearDeallocRequest{
[_lock lock];
NSInteger count = ;
for (NSInteger i=count-1; i>0; i--) {
YRWeakRequest *weakRequest = [i];
if (!) {
[ removeObject:weakRequest];
}
}
[_lock unlock];
}
- (void)dealloc{
for (YRWeakRequest *weakRequest in _weakRequests) {
[ cancel];
}
}
@end
3. Bind the intermediate class to any class
@implementation NSObject (YRRequest)
- (YRDeallocRequests *)deallocRequests{
YRDeallocRequests *requests = objc_getAssociatedObject(self, _cmd);
if (!requests) {
requests = [[YRDeallocRequests alloc]init];
objc_setAssociatedObject(self, _cmd, requests, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
return requests;
}
- (void)autoCancelRequestOnDealloc:(id)request{
[[self deallocRequests] clearDeallocRequest];
YRWeakRequest *weakRequest = [[YRWeakRequest alloc] init];
= request;
[[self deallocRequests] addRequest:weakRequest];
}
@end
4. Exposed header files
@interface NSObject (YRRequest) /*! * @brief add request to auto cancel when obj dealloc * @note will call request's cancel method , so the request must have cancel method.. */ - (void)autoCancelRequestOnDealloc:(id)request; @end
How to use
How about it? It depends on whether the header file is very simple, and the way to use it is very simple.
For example, we need to automatically cancel the network request when released in a certain VC:
//The place where the request is initiated:xxrequest1 = xxx; [xxrequest1 start]; [self autoCancelRequestOnDealloc:xxrequest1];
Well, from now on, I will no longer worry about requests flying around when such a class is destroyed.
other:
1. In my implementation class, the default call is the cancel method, so theoretically, all requests with cancel method can be called directly using this method (such as AFNetworking, NSURLSessionTask, etc.)
2. Some people will say that I use my own network layer to requests that I encapsulate. If I do not call cancel, the objects that I encapsulate will also be destroyed. What I want to remind me is that it is possible that the objects that you encapsulate are destroyed, but the lower layer, whether it is connected to AF, system, or other request libraries, must have self-held properties. If I don’t say that, the risk is that the request at the bottom layer before the data is returned will be destroyed, and no one will design it like this.
3. In the example, I am bound to self, which can actually be bound to any object, such as the internal properties of a certain class, etc., so that I can further control the cancel timing of the request according to business needs.
Attach the github address, welcome to correct:/YueRuo/NSObject_AutoCancelRequest （Local download）
Summarize
The above is the entire content of this article. I hope that the content of this article has certain reference value for everyone's study or work. If you have any questions, you can leave a message to communicate. Thank you for your support.