iOS开发中如遇到频繁的Http请求，如何取消之前已经发送的Http请求?

iOS开发中如遇到频繁的Http请求，如何取消之前已经发送的Http请求?

以上面的代码段为例，他是这么操作的

主要精髓在于

第一点：不要initialize a newAFHTTPSessionManager object everytime 一定要把manager用成全局的

第二点：把请求返回的task对象丢进数组，下次触发的时候把遍历数组，把之前的所有任务[task cancel]

1. //somewhereinyourclass,let'ssayinViewDidLoadyoushouldinittheAFHTTPSessionManagerobject
2. -(void)viewDidLoad{
3. [superviewDidLoad];
4.  
5. ///createtheAFHTTPSessionManagerobject,we'regonnauseitineveryrequest
6. self.manager=[[AFHTTPSessionManageralloc]init];
7. self.manager.responseSerializer=[AFJSONResponseSerializerserializer];
8.  
9. ///createanarraythatisgoingtoholdtherequeststaskwe'vesenttotheserver.sowecangetbacktothemlater
10. self.arrayOfTasks=[NSMutableArraynew];
11. ///discussion:
12. ///anarrayholdsmultipleobjects.ifyoujustwanttoholdareftothelatesttaskobject
13. ///thencreateapropertyofNSURLSessionDataTaskinsteadofNSMutableArray,andletitpointtothelatestNSURLSessionDataTaskobjectyoucreate
14.  
15. }
16.  
17.  
18.  
19. -(BOOL)textField:(UITextField*)textFieldshouldChangeCharactersInRange:(NSRange)rangereplacementString:(NSString*)string;{
20. ///yourcodegoeshere
21. ///.....
22. ///.....
23. ///.....
24. ///.....
25. ///tillwereach
26. if(stringLength>=3){
27. ///cancelallprevioustasks
28. [self.arrayOfTasksenumerateObjectsUsingBlock:^(NSURLSessionDataTask*taskObj,NSUIntegeridx,BOOLBOOL*stop){
29. [taskObjcancel];///whensendingcanceltothetaskfailure:blockisgoingtobecalled
30. }];
31.  
32. ///emptythearraOfTasks
33. [self.arrayOfTasksremoveAllObjects];
34.  
35. ///initnewtask
36. NSURLSessionDataTask*task=[self.managerGET:urlStringparameters:nilsuccess:^(NSURLSessionDataTask*task,idresponseObject){
37. ///yourcode
38. }failure:^(NSURLSessionDataTask*task,NSError*error){
39. ///yourcode
40. }];
41.  
42. ///addthetasktoourarrayOfTasks
43. [self.arrayOfTasksaddObject:task];
44. }
45. returnYES;
46. }