NSMutable 数组错误

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。但我不明白为什么我不能 NSLog [it objectForKey:@"title"]。

Answer 1

您没有初始化 NSMutableArray。

应该是

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

从技术上讲，您可以简单地分配它
NSMutableArray *sub = [[NSMutableArray 数组];
也是如此，但这可能会更有效，因为您已经知道会有多少数据条目。

只要注意内存管理，在第一种情况下需要释放它，在第二种情况下它会自动释放。

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]; 或在代码中维护引用。

Answer 3

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];
    }

Answer 4

在使用 MutableArray 之前，您应该alloc并init它。

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;
}