iphone - 使用allKeys时应用崩溃，是因为只有一个对象吗？

Question

我不明白为什么 xcode 继续抛出这个错误

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-    
[__NSCFString allKeys]: unrecognized selector sent to instance 0x9367330'

每当我使用此代码时

NSDictionary *nextArray = [_classDictionary 
valueForKeyPath:@"response.page_records.page_record"];
for (NSDictionary *roster2 in nextArray) {
NSArray *keys = [roster2 allKeys];
if ([keys containsObject:@"title"]){
    [pageName addObject:[roster2 objectForKey:@"title"]];
}
if ([keys containsObject:@"id"]) {
[pageID addObject:[roster2 objectForKey:@"id"]];
}
}

在尝试调试后，我发现只有当键只有一个对象时才会引发异常。例如，当“nextArray”是这样的:

 (
 {
    "class_id" = 0001;
    "id" = 1234;
    "title" = "First Page";
},
{
     "class_id" = 0002;
     "id" = 12345;
     "title" = Assignments;
 }
 )

代码无异常运行，但是当代码很简单时

      {
         "class_id" = 0001;
         "id" = 1234;
         "title" = "First Page";
     }

抛出异常。为什么会发生这种情况？即使只有一个对象，键仍然包含对象标题。任何其他想法为什么会引发此异常？跟括号有关系吗？ (总猜测)有没有更好的方法来调试真正发生的事情？

编辑:这是_userDictionary。拥有 objectforKey:@"title"的有序数组并避免上述错误的最佳方法是什么？

response =     {
    "status" = ok;
    "page_records" =         {
        "page" = 1;
        "page_count" = 1;
        "records_per_page" = 50;
        "total_record_count" = 2;
        "page_record" =             (
                            {
                "class_id" = 0001;
                "id" = 1234;
                "title" = "Test page";
            },
                            {
                "class_id" = 0002;
                "id" = 12345;
                "title" = "testing page 2";
            }
        );
    };
};
}

Answer 1

在您的第一个示例中，您正在遍历字典数组，因此，NSArray *keys = [roster2 allKeys];正在调用一个数组。但是，在您的第二个示例中，您只有一本字典。它不是字典数组。所以你的循环for (NSDictionary *roster2 in nextArray)正在遍历字典的键，它们只是字符串，而不是数组。因此，错误。

首先，您的命名令人困惑。一个 NSDictionary命名为 nextArray ?试试这个:

id *response = [_classDictionary valueForKeyPath:@"response.page_records.page_record"];  
NSMutableArray *records;  

if ([response isKindOfClass: [NSDictionary class]]) {
    records = [[NSMutableArray alloc] init];
    [records addObject: response];
}
else {
    records = [NSMutableArray arrayWithArray: response];
}

for (NSDictionary *roster2 in records) {
    NSArray *keys = [roster2 allKeys];
    if ([keys containsObject:@"title"]){
        [pageName addObject:[roster2 objectForKey:@"title"]];
    }
    if ([keys containsObject:@"id"]) {
        [pageID addObject:[roster2 objectForKey:@"id"]];
    }
}