ios - NSMutableArray 索引 1 超出范围 [0 .. 0]

Question

我搞砸了 JSON 和 NSMutablearray。我当然是初学者。

我从在线教程中获取并修改了这段代码:

[This is the .m file]
- (void) downloadItems {

    // Download the json file
    NSURL *jsonFileUrl = [NSURL URLWithString:@"http://example.com/service.php"];

    // Create the request
    NSURLRequest *urlRequest = [[NSURLRequest alloc] initWithURL:jsonFileUrl];

    // Create the NSURLConnection
    [NSURLConnection connectionWithRequest:urlRequest delegate:self];

}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    // Initialize the data object
    datiScaricati = [[NSMutableData alloc] init];

}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    // Append the newly downloaded data
    [datiScaricati appendData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {

    // Create an array to store the locations
    NSMutableArray *frasiMemorizzate = [[NSMutableArray alloc] init];

    // Parse the JSON that came in
    NSError *error;
    NSArray *jsonArray = [NSJSONSerialization JSONObjectWithData:datiScaricati options:NSJSONReadingAllowFragments error:&error];


    // Loop through Json objects, create question objects and add them to our questions array
    for (int i = 0; i < jsonArray.count; i++)
    {
        NSDictionary *jsonElement = jsonArray[i];

        // Create a new location object and set its props to JsonElement properties
        Frase *nuovaFrase = [[Frase alloc] init];
        nuovaFrase.fraseDelDatabase = jsonElement[@"Frase"];

        NSLog(@"Phrase read from database: %@", nuovaFrase.fraseDelDatabase);

        // Add this question to the locations array
        [frasiMemorizzate addObject:nuovaFrase.fraseDelDatabase];

        NSLog(@"Phrases stored in the array: %@", frasiMemorizzate);


        prova = [frasiMemorizzate objectAtIndex:0];

        NSLog(@"Phrases at index 0: %@",prova);

    }


}

NSLog 给出了这个:

2014-06-15 11:05:28.705 ProvaMySql[13805:60b] Phrase read from database: Frase uno, Prova!
2014-06-15 11:05:28.706 ProvaMySql[13805:60b] Phrases stored in the array: (
    "Frase uno, Prova!"
)
2014-06-15 11:05:28.706 ProvaMySql[13805:60b] Phrases at index 0: Frase uno, Prova!
2014-06-15 11:05:28.707 ProvaMySql[13805:60b] Phrase read from database: Frase due, Prova!
2014-06-15 11:05:28.707 ProvaMySql[13805:60b] Phrases stored in the array: (
    "Frase uno, Prova!",
    "Frase due, Prova!"
)
2014-06-15 11:05:28.708 ProvaMySql[13805:60b] Phrases at index 0: Frase uno, Prova!
2014-06-15 11:05:28.708 ProvaMySql[13805:60b] Phrase read from database: Frase tre, Prova!!
2014-06-15 11:05:28.709 ProvaMySql[13805:60b] Phrases stored in the array: (
    "Frase uno, Prova!",
    "Frase due, Prova!",
    "Frase tre, Prova!!"
)
2014-06-15 11:05:28.709 ProvaMySql[13805:60b] Phrases at index 0: Frase uno, Prova!

所以，我认为我正在从数据库中一个接一个地获取数据(“frase uno”，然后是“frase due”，然后是“frase tre”)。而且我还看到数组正在填充(短语存储在数组中:)

当我打电话的时候

prova = [frasiMemorizzate objectAtIndex:0];

        NSLog(@"Phrases at index 0: %@",prova);

我得到:“Frase uno”，这是我应该期望的，但是如果我使用“objectAtIndex:1”，我会遇到错误:index 1 beyond bounds [0 .. 0]，但我希望有第二个短语:“Frase Due”。

我想知道为什么以及获取我需要的数据的正确方法，也许，当你回答我的问题时，我怎样才能知道有多少项目存储在一个可变数组中，而不是调用 unallocated索引位置!

感谢您的耐心等待!

Answer 1

由于当只有一个对象时尝试访问数组中的第二个索引，因此会引发错误。

做这个小小的改变，它就会起作用:

    prova = [frasiMemorizzate objectAtIndex:i];

    NSLog(@"Phrases at index %d: %@", i, prova);