Question

我有这段代码

SBJsonParser *vol= [[SBJsonParser alloc]init];
if (body) {
    NSArray *feeds = [vol objectWithString:body error:nil];
    NSDictionary *results = [body JSONValue];
    NSArray *subs = [results valueForKey:@"subscriptions"];
    NSArray *list;
    NSMutableArray *sub;

    for (NSDictionary *iscrizione in subs){
        NSLog([iscrizione objectForKey:@"title"]);
        NSLog([iscrizione objectForKey:@"htmlUrl"]);
        list=[NSArray arrayWithObjects:[iscrizione objectForKey:@"title"], [iscrizione objectForKey:@"htmlUrl"], nil];  
        [sub addObject:list];

    }

但是当我尝试将列表添加到NSMutableArray时，程序崩溃了。为什么？如何插入[iscrizione objectForKey:@"title"]和[iscrizione objectForKey:@"htmlUrl"] 在数据结构中？

编辑**

SBJsonParser *vol= [[SBJsonParser alloc]init];
if (body) {
    NSArray *feeds = [vol objectWithString:body error:nil];
    NSDictionary *results = [body JSONValue];
    NSArray *subs = [results valueForKey:@"subscriptions"];
    NSMutableArray *sub = [[NSMutableArray alloc] initWithCapacity:[subs count]];
    for (NSDictionary *iscrizione in subs){

        [sub addObject:iscrizione];

    }
    NSDictionary *it=[[NSDictionary alloc]initWithDictionary:[sub objectAtIndex:0]];
    NSLog([it objectForKey:@"title"]);

}

这是我的代码。但我无法理解为什么我不能NSLog [it objectForKey：@“title”]。

Answer 1

您没有初始化您的NSMutableArray。

应该是

NSMutableArray *sub = [[NSMutableArray alloc] initWithCapacity:[subs count]];

从技术上讲，你可以简单地分配它 NSMutableArray *sub = [[NSMutableArray array]; 同样，但这可能更有效率，因为您已经知道将有多少数据条目。

只需注意内存管理，你需要在第一种情况下释放它，并在第二种情况下自动释放它。

Answer 2

sub未分配内存。您可以在if条件之外创建一个空数组NSMutableArray *sub = [NSMutableArray array];，或者在代码中保留一个引用。

Answer 3

在使用MutableArray之前，您应该alloc和init。

SBJsonParser *vol= [[SBJsonParser alloc]init];
if (body) {
    NSArray *feeds = [vol objectWithString:body error:nil];
    NSDictionary *results = [body JSONValue];
    NSArray *subs = [results valueForKey:@"subscriptions"];
    NSArray *list;
    NSMutableArray *sub = [[NSMutableArray alloc] initWithCapacity:[subs count]];

    for (NSDictionary *iscrizione in subs){
        NSLog(@"title: %@" ,[iscrizione objectForKey:@"title"]);
        NSLog(@"htmlUrl: %@", [iscrizione objectForKey:@"htmlUrl"]);
        list=[NSArray arrayWithObjects:[iscrizione objectForKey:@"title"], [iscrizione objectForKey:@"htmlUrl"], nil];  
        [sub addObject:list];

    }
    // here you should add code to handle the sub array.

    // Do not forget to release the allocated array
    [sub release], sub =nil;
}

Answer 4

以下将正常工作......

    NSMutableArray *sub = [[NSMutableArray alloc] init];
    for (NSDictionary *iscrizione in subs)
    {
        NSString *title = [NSString stringWithFormat:@"%@", [iscrizione objectForKey:@"title"]];
        NSString *htmlURL = [NSString stringWithFormat:@"%@",[iscrizione objectForKey:@"htmlUrl"]];
        list=[NSArray arrayWithObjects:title, htmlURL, nil];  
        [sub addObject:list mutableCopy];
    }

NSMutable数组错误

4 个答案: