ios - 使用带有异步 UrlConnections 的 NSUserDefaults 的意外行为

Question

我有以下用于异步 UrlConnections 的代码。如果请求失败，我将 a 添加 NSString到NSMutableArray保存在NSUserDefaults. 第一次正确添加，但第二次抛出错误：

'NSInternalInconsistencyException'，原因：'-[__NSCFArray insertObject:atIndex:]：发送到不可变对象的变异方法

代码是：

[NSURLConnection sendAsynchronousRequest:theRequest queue:mainQueue completionHandler:^(NSURLResponse *response, NSData *responseData, NSError *error) {
        NSHTTPURLResponse *urlResponse = (NSHTTPURLResponse *)response;
        if (!error) {
           //something
        }
        else {

            NSMutableArray *unprocessedSubscription=[[NSUserDefaults standardUserDefaults]objectForKey:@"unprocessedSubscription"];
            if(unprocessedSubscription==nil)
                unprocessedSubscription=[[NSMutableArray alloc]init];
            NSString * subscriptionToAdd=@"something";
            [unprocessedSubscription addObject:subscriptionToAdd];
            [[NSUserDefaults standardUserDefaults]setObject:unprocessedSubscription forKey:@"unprocessedSubscription"];
            [[NSUserDefaults standardUserDefaults]synchronize];
        }
    }];

Answer 1

将返回的 NSArray 复制到 NSMutableArray

NSArray *unprocessedSubscription=[[NSUserDefaults standardUserDefaults]objectForKey:@"unprocessedSubscription"];

NSMutableArray *mutableArray = [NSMutableArray arrayWithArray:unprocessedSubscription]

Answer 2

基本上返回的值是不可变的，你可以做的是每次创建一个可变数组，如果NSUserDefaults.

NSMutableArray *unprocessedSubscription=[[NSMutableArray alloc]init];
NSArray * storedValues = [NSUserDefaults standardUserDefaults]objectForKey:@"unprocessedSubscription"];
if(storedValues != nil){
[unprocessedSubscription addObjectsFromArray:storedValues];
}
 NSString * subscriptionToAdd=@"something";
 [unprocessedSubscription addObject:subscriptionToAdd];
 [[NSUserDefaults standardUserDefaults]setObject:unprocessedSubscription forKey:@"unprocessedSubscription"];
 [[NSUserDefaults standardUserDefaults]synchronize];

Answer 3

你可以更换你的

NSMutableArray *unprocessedSubscription=[[NSUserDefaults standardUserDefaults]objectForKey:@"unprocessedSubscription"];

至

NSMutableArray *unprocessedSubscription=[[[NSUserDefaults standardUserDefaults]objectForKey:@"unprocessedSubscription"] mutableCopy];