iOS ARC 的内存管理问题

Question

我创建了一个名为“ConnectionManager”的 class，它将处理所有网络请求并从服务器获取数据，然后调用完成处理程序。

ConnectionManager.h

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
#import "UIAlertView+CustomAlertView.h"
#import <Crashlytics/Crashlytics.h>


@interface ConnectionManager : NSObject<NSURLSessionDataDelegate>

@property (weak, nonatomic) NSMutableData *receivedData;
@property (weak, nonatomic) NSURL *url;
@property (weak, nonatomic) NSURLRequest *uploadRequest;
@property (nonatomic, copy) void (^onCompletion)(NSData *data);
@property BOOL log;

-(void)downloadDataFromURL:(NSURL *)url withCompletionHandler:(void (^)(NSData *data))completionHandler;
-(void)uploadDataWithRequest:(NSURLRequest*)request withCompletionHandler:(void (^)(NSData *data))completionHandler;

@end

ConnectionManager.m

#import "ConnectionManager.h"


@implementation ConnectionManager

-(void)uploadDataWithRequest:(NSURLRequest*)request withCompletionHandler:(void (^)(NSData *data))completionHandler{
    // Instantiate a session configuration object.
    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];

    // Configure Session Configuration
    [configuration setAllowsCellularAccess:YES];

    // Instantiate a session object.
    NSURLSession *session=[NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];

    // Assign request for later call
    self.uploadRequest = request;

    // Create an upload task object to perform the data uploading.
    NSURLSessionUploadTask *task = [session uploadTaskWithRequest:self.uploadRequest fromData:nil];

    // Assign completion handler
    self.onCompletion = completionHandler;

    // Inititate data
    self.receivedData = [[NSMutableData alloc] init];

    // Resume the task.
    [task resume];

}

-(void)downloadDataFromURL:(NSURL *)url withCompletionHandler:(void (^)(NSData *data))completionHandler{
    // Instantiate a session configuration object.
    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];

    // Configure Session Configuration
    [configuration setAllowsCellularAccess:YES];

    // Instantiate a session object.
    NSURLSession *session=[NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];

    // Assign url for later call
    self.url = url;

    // Create a data task object to perform the data downloading.
    NSURLSessionDataTask *task = [session dataTaskWithURL:self.url];

    // Assign completion handler
    self.onCompletion = completionHandler;

    // Inititate data
    self.receivedData = [[NSMutableData alloc] init];

    // Resume the task.
    [task resume];
}

-(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data {
    [self.receivedData appendData:data];
}

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
    if (error) {
        if (error.code == -1003 || error.code == -1009) {
            [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"Unable to connect to the server. Please check your internet connection and try again!" delegate:nil cancelButtonTitle:@"cancel" otherButtonTitles:@"retry",nil];
                [alert showWithCompletion:^(UIAlertView *alertView, NSInteger buttonIndex) {
                    if (buttonIndex==1) {
                        // Retry
                        if (self.url) {
                            NSURLSessionDataTask *retryTask = [session dataTaskWithURL:self.url];
                            [retryTask resume];
                        }else{
                            NSURLSessionUploadTask *task = [session uploadTaskWithRequest:self.uploadRequest fromData:nil];
                            [task resume];
                        }
                    }else{
                        self.onCompletion(nil);
                    }
                }];
            }];
        }else{
            [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"An unkown error occured! Please try again later, thanks for your patience." delegate:nil cancelButtonTitle:@"cancel" otherButtonTitles:@"retry",nil];
                [alert show];
                CLS_LOG(@"Error details: %@",error);
                self.onCompletion(nil);

            }];
        }
    }
    else {
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            self.onCompletion(self.receivedData);
        }];
    }
}

@end

这是我用来调用它的一段代码：

-(void)loadDataFromServer{
    NSString *URLString = [NSString stringWithFormat:@"%@get_people_number?access_token=%@", global.baseURL, global.accessToken];
    URLString = [URLString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    NSURL *url = [NSURL URLWithString:URLString];

    ConnectionManager *connectionManager = [[ConnectionManager alloc] init];
    [connectionManager downloadDataFromURL:url withCompletionHandler:^(NSData *data) {
        if (data != nil) {
            // Convert the returned data into an array.
            NSError *error;
            NSDictionary *number = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
            if (error != nil) {
                CLS_LOG(@"Error: %@, Response:%@",error,[[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding]);
            }
            else{
                [_mapView updateUIWithData:[number objectForKey:@"number"]];
            }
        }
    }];
}

我在使用 Instruments 时发现，即使在从服务器获取数据并调用完成处理程序之后，所有 ConnectionManager 类型的对象都是持久的。

我试图将完成处理程序属性从复制更改为强，但我得到了相同的结果。将其更改为 weak 会导致崩溃并且永远不会被调用。

请有人指导我正确的方法。

Answer 1

经过大量研究，我发现 URL Session 对象仍然存在。

基于Apple Documentation Life Cycle of URL Session有两种情况：

使用系统提供的委托（通过不设置委托），这里系统将负责使 NSURLSession 对象无效。
使用自定义委托。当您不再需要会话时，通过调用 invalidateAndCancel（以取消未完成的任务）或 finishTasksAndInvalidate（以允许未完成的任务在使对象失效之前完成）来使其无效。

为了修复上面的代码，我只更改了委托方法 "didCompleteWithError"，如下所示：

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
if (error) {
    if (error.code == -1003 || error.code == -1009) {
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"Unable to connect to the server. Please check your internet connection and try again!" delegate:nil cancelButtonTitle:@"cancel" otherButtonTitles:@"retry",nil];
            [alert showWithCompletion:^(UIAlertView *alertView, NSInteger buttonIndex) {
                if (buttonIndex==1) {
                    // Retry
                    if (self.url) {
                        NSURLSessionDataTask *retryTask = [session dataTaskWithURL:self.url];
                        [retryTask resume];
                    }else{
                        NSURLSessionUploadTask *task = [session uploadTaskWithRequest:self.uploadRequest fromData:nil];
                        [task resume];
                    }
                }else{
                    [session finishTasksAndInvalidate];
                    self.onCompletion(nil);
                }
            }];
        }];
    }else{
        [[NSOperationQueue mainQueue] addOperationWithBlock:^{
            UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@"An unkown error occured! Please try again later, thanks for your patience." delegate:nil cancelButtonTitle:@"cancel" otherButtonTitles:@"retry",nil];
            [alert show];
            [session finishTasksAndInvalidate];
            self.onCompletion(nil);
        }];
    }
}
else {
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
        [session finishTasksAndInvalidate];
        self.onCompletion(self.receivedData);
    }];
}

}

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