字典中查找空值的捷径技术? [英] short cut technique for finding null value from Dictionary?

问题描述

我在nsmutabledictornary中有100个键和值，我想检查任何值是否为null.您有任何简短的功能或技巧吗?

I have 100 key and value in nsmutabledictornary and i want to check that any value have null or not. Do you have any short function or technique?

我不想使用多个行代码，例如检查每个键和值.您的回答将不胜感激.

I don't want to multiple line code like check every key and value. Your answer would be appreciated.

推荐答案

此代码将为您提供一组具有(非)空值的键.您无法在字典中存储实际的nil值，因此假定为[NSNull null].谓词对于任何其他条件都是微不足道的.

This code will give you the set of keys which have (non)null values. You can't store actual nil values in a dictionary, so [NSNull null] is assumed. The predicate is trivially alterable to any other condition.

NSDictionary *d = @{ @"a" : @"1", @"b" : [NSNull null] };

NSSet *nullKeys = [d keysOfEntriesPassingTest:^BOOL(NSString *key, id obj, BOOL *stop) {
    return [d[key] isKindOfClass:[NSNull class]];
}];

NSSet *nonnullKeys = [d keysOfEntriesPassingTest:^BOOL(NSString *key, id obj, BOOL *stop) {
    return [d[key] isKindOfClass:[NSNull class]] == NO;
}];

如果需要，您可以从此处使用键生成相应的字典.

From here, you can use the keys to generate a corresponding dictionary, if needed.

NSMutableDictionary *nonNullDict = [NSMutableDictionary dictionary];
[d enumerateKeysAndObjectsUsingBlock:^(NSString *key, id obj, BOOL *stop) {
    if ([nonnullKeys contains:key]) {
        nonNullDict[key] = obj;
    }
}];

如果您不需要单独的键列表，而只需要过滤后的字典，请跳过第一步，然后将第二部分修改如下:

If you don't need a separate list of keys, and just need the filtered dictionary, skip the first step and modify the second part to read as follows:

NSMutableDictionary *nonNullDict = [NSMutableDictionary dictionary];
[d enumerateKeysAndObjectsUsingBlock:^(NSString *key, id obj, BOOL *stop) {
    if ([obj isKindOfClass:[NSNull null]] == NO) {
        nonNullDict[key] = obj;
    }
}];

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