Question

我想更新字段中的密钥'distance'的值不是Mutable，我有一个由json读取的字典数组，我需要更新app中的所有距离值，请你提供给我一个示例代码，我该怎么做？

这是我创建这个数组的地方：

NSData *responseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&err];
    self.seachResult =[NSJSONSerialization JSONObjectWithData:responseData options:nil error:nil];

以下是样本信息：

2013-07-20 00:04:41.753 MyApp[61075:16a03] sorted array of dictionaries: (
    {
    cid = 2;
    distance = 0;
    image = "http://images.png";
    latitude = "48.245565";
    longitude = "16.342333";
    manual = "";
    movie = "http://jplayer.org/video/m4v/Big_Buck_Bunny_Trailer.m4v";
    pcode = 023942435228;
    pid = 1;
    pname = "example product";
    price = "12.00";
    qrcode = "";
    rid = 1;
    rname = "Example Retailer Name";
    sale = 0;
    "sale_percent" = 0;
    "sale_price" = "0.00";
    text = "here is text about sample product number 1...\nasdasdasda\nsdfsdfsd\nSdfsdf
},
    {
    cid = 1;
    distance = 0;
    image = "";
    latitude = "";
    longitude = "";
    manual = "";
    movie = "";
    pcode = 1;
    pid = 3;
    pname = "test product";
    price = "46.00";
    qrcode = "";
    rid = 2;
    rname = "";
    sale = 0;
    "sale_percent" = 0;
    "sale_price" = "35.00";
    text = "some text here...

},
    {
    cid = 2;
    distance = 0;
    image = "httpestImage";
    latitude = "48.245565";
    longitude = "16.342333";
    manual = "";
    movie = "";
    pcode = 1;
    pid = 2;
    pname = "sample product 2";
    price = "126.00";
    qrcode = "";
    rid = 1;
    rname = "Example Retailer Name";
    sale = 1;
    "sale_percent" = 20;
    "sale_price" = "99.99";
    text = "here is text about sample product number 2...\nblah blah blah\nasdasdasd\nASdasdas\nASdasdasd";
}
)

for test我试过这个，但即使我不能更新这样一个简单字典的值：

NSMutableDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
                      @"value1", @"key1", @"value2", @"key2", nil];
[dict setValue:@"test" forKey:@"key2"];

错误：

2013-07-20 00：46：08.086 NSdictionaryTest [61130：11303] *由于未捕获的异常'NSUnknownKeyException'而终止应用程序，原因：'[＆lt; __ NSDictionaryI 0x7556390＆gt; setValue：forUndefinedKey：]：此类不是密钥值2的密钥值编码。 * 第一次抛出调用堆栈：（0x1c90012 0x10cde7e 0x1d18fb1 0xb79e41 0xafb5f8 0xafb0e7 0x2200 0xf31c7 0xf3232 0x423d5 0x4276f 0x42905 0x4b917 0xf96c 0x1094b 0x21cb5 0x22beb 0x14698 0x1bebdf9 0x1bebad0 0x1c05bf5 0x1c05962 0x1c36bb6 0x1c35f44 0x1c35e1b 0x1017a 0x11ffc 0x1e5d 0x1d85） libc ++ abi.dylib：terminate调用抛出异常

Answer 1

如果要修改JSONObjectWithData返回的字典，请使用NSJSONReadingMutableContainers选项。这会导致该方法返回可变容器类。例如：

self.seachResult =[NSJSONSerialization JSONObjectWithData:responseData options:NSJSONReadingMutableContainers error:nil];

Answer 2

您是否需要使用不可变字典？

您可以使用NSMutableDictionary

我猜self.seachResult是你的NSDictionary，你可以简单地将它声明为NSMutableDictionary。

用以下内容初始化：

self.seachResult = [NSMutableDictionary dictionaryWithCapacity:10];
[self.seachResult addEntriesFromDictionary: NSJSONSerialization JSONObjectWithData:responseData options:nil error:nil]]; 
[self.seachResult setObject:YOUR_UPDATED_VALUE_HERE forKey:@"distance"];

另外你也可以创建一个新的NSMutableDictionary，并用非可变的条目填充它，如下所示：

NSMutableDictionary *mutableSearchResults = [NSMutableDictionary dictionaryWithCapacity:[self.seachResult count]];
[mutableSearchResults addEntriesFromDictionary: self.seachResult];
[self.seachResult setObject:YOUR_UPDATED_VALUE_HERE forKey:@"distance"];

如果你想再次返回一个不可变的，你可以这样做：

[mutableSearchResults copy];

我希望它有所帮助。请注意我刚刚在SO编辑器中输入了代码，所以我可能拼错了一些。

Answer 3

NSDictionary是不可变的（创建后无法更改）。请看一下NSMutableDictionary。 BTW - 从NSDictionary创建NSMutableDictionary很容易。

更新字典中键的值

3 个答案: