将嵌套Plist转换为NSDictionaries和数组时出现问题

Question

给定此P-List字典：

​

​

我怎么才能到第三站。键-“晚餐”-它本身也是一个字典，并正确地解析它的值？

或者，我是不是应该从一开始就改变P列表的结构，这样我就可以更容易地获得所有东西？

下面是我得到的结果，首先从我的“MenuDictionary”中获取所有的键，并将它们存储在一个数组中：

// Load the Property-List file into the Dictionary:
MenuDictionary = [[NSDictionary alloc] initWithContentsOfFile:menuPath];

// Get all the Keys from the Dictionary, put 'em into a 'mealTimesArray':
mealTimesArray = [[MenuDictionary allKeys] sortedArrayUsingSelector:@selector(compare:)];

// For each meal-type KEY, grab all the Values (dishes) in it and store them in a 'mealDishesArray':
for (NSString *mealTime in mealTimesArray) {
    NSArray *mealDishesArray = [MenuDictionary valueForKey:mealTime];

    // Now I can iterate through the 'mealDishesArray' to access each dish at
    // a time, so I can print them out or do whatever else:
    for (NSString *dish in mealDishesArray) {
        NSLog(@"Iterating through 'mealDishesArray' now...");
        NSLog(@"Current 'dish' is: %@", dish);

当我找到“晚餐”键时，问题就出现了:它是一个字典，包含2个键和2个数组值。那么如何将其内容加载到Dictionary对象中呢？更具体地说，我应该使用什么'init‘方法将“晚餐”内容加载到我的新Dictionary对象中？

我试过了--不管用：

// I put this inside the first fast-enum loop:

if ([mealTime isEqualToString: @"Dinner"]) {
   // init new Dictionary object (declared previously):
   dinnerDictionary = [[NSDictionary alloc] initWith ???];

我想初始化它与“晚餐”键的内容，但它显然不是一个P-List文件，所以我不能使用

   initWithContentsOfFile: pathName

我不明白哪个init方法能让我同时访问“晚餐”的键和值。因为尽管“晚餐”被构造为一个字典，但它目前位于一个数组中，该数组并不将其视为字典(我认为……)

显然，我对此有点不清楚。

或者，我是否应该一开始就以不同的方式构造我的P列表，这样我就可以获得这个嵌套的晚餐字典？

有什么想法吗？

Answer 1

我认为plist结构是有意义的，并且基于类有条件地处理内容也是完全可以的。我会在一个合理的预期范围内对plist中的内容做出反应，所以...

// for each meal...
for (NSString *mealTime in mealTimesArray) {
    // we're not sure what kind of meal we have
    id mealInfo = [MenuDictionary valueForKey:mealTime];

    if ([id isKindOfClass:[NSArray self]]) {
        // it's an array? cast as an array and deal with the array
        NSArray *mealDishesArray = (NSArray *)mealInfo;
        [self handleMealArray:mealDishesArray];
    } else if ([id isKindOfClass:[NSDictionary self]]) {
        // it's a dictionary?  that's cool, too. cast as a dictionary and deal with it
        NSDictionary *mealDictionary = (NSDictionary *)mealInfo;
        [self handleMealDictionary:mealDictionary];
    }
}

// you've worked out to handle the array
- (void)handleMealArray:(NSArray *)mealDishesArray {
    for (NSString *dish in mealDishesArray) {
        NSLog(@"Iterating through 'mealDishesArray' now...");
        NSLog(@"Current 'dish' is: %@", dish);
    }
}

// handle the dictionary like a dictionary, realizing that it contains
// arrays, which you've already worked out how to handle
- (void)handleMealDictionary:(NSDictionary *)mealDictionary {
    for (NSString *dishType in [mealDictionary allKeys]) {
        NSArray *mealDishesArray = [mealDictionary valueForKey:dishType];
        [self handleMealArray:mealDishesArray];
    }
}

Answer 2

“问题”出在这一行：

NSArray *mealDishesArray = [MenuDictionary valueForKey:mealTime];

当mealTime为'Dinner‘时，您为mealDishesArray赋值的值是一个NSDictionary。假设你有一个数组，然后你就可以使用：

for (NSString *dish in mealDishesArray)

迭代数组中的元素，这不会给你带来你所期望的“晚餐”。您可以考虑添加如下内容：

NSAssert ([mailDishesArray isKindOfClass: [NSArray class]], @"Expecting an array");

在你分配给mealDishesArray之后。

解决方案是什么？你的PLIST在“早餐”、“午餐”和“晚餐”之间有着完全不同的结构。为什么“晚餐”是NSDictionary，其他的是NSArray？使它们都属于同一类型。如果它们不能，那么您必须根据以下条件对您的代码进行条件化：

if ([mealTime isEqualToString: @"Dinner"]) {
   NSDictionary *dinnerDictionary = (NSDictionary *) [MenuDictionary valueForKey:mealTime];
   /* ... */ }

您不需要分配任何内容，也不需要从文件中读取任何内容；您已经有了一个用于“晚餐”数据的字典。