Question

我是Objective-C编码的Begginer，我需要一些关于NSPredicates的帮助。

我需要过滤（通过id_especie）我从Json文件解析的字典数组，并将数据检索到另一个数组。不幸的是，我得到的是一个空数组;

这是我的字典数组（id_especie表示species_id，id_raca表示breed_id）：

{
    "id_especie" = 1;
    "id_raca" = 1;
    raca = Afghanhound;
},
    {
    "id_especie" = 1;
    "id_raca" = 2;
    raca = "Airedale Terrier";
},
    {
    "id_especie" = 1;
    "id_raca" = 3;
    raca = Akita;
},...,
    {
    "id_especie" = 2;
    "id_raca" = 47;
    raca = "N/I";
},
    {
    "id_especie" = 2;
    "id_raca" = 48;
    raca = Siames;
},
    {
    "id_especie" = 3;
    "id_raca" = 49;
    raca = Periquito;
},
    {
    "id_especie" = 4;
    "id_raca" = 50;
    raca = Cobra;
},
    {
    "id_especie" = 4;
    "id_raca" = 51;
    raca = Lagarto;
},
    {
    "id_especie" = 5;
    "id_raca" = 52;
    raca = "Furao";
},
    {
    "id_especie" = 5;
    "id_raca" = 53;
    raca = Hamster;
},
    {
    "id_especie" = 6;
    "id_raca" = 54;
    raca = Outros;
}

这是我的代码：

·H

@property (nonatomic, strong) NSMutableArray *arrayBreedAndSpecies;
@property (nonatomic, strong) NSArray *filteredArray; //edited

的.m

NSError  *errorLoad = nil;
NSURL    *jsonUrl = [[NSURL alloc]initWithString:@"http://marcosdegni.com.br/petsistema/teste/raca.php"];
NSString *jsonString = [NSString stringWithContentsOfURL:jsonUrl encoding:NSUTF8StringEncoding error:&errorLoad];

if (!errorLoad) {
    NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
    NSArray *jsonArray = [NSJSONSerialization JSONObjectWithData:jsonData options:kNilOptions error:nil];
    self.arrayBreedAndSpecies = [[NSMutableArray alloc] initWithArray:jsonArray];
}

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%@ = %@",@"id_especie", @"2"];
[self.filteredArray setArray: [self.arrayBreedAndSpecies filteredArrayUsingPredicate:predicate]];
NSLog(@"Filter: %@", self.filteredArray);

Answer 1

这里只是一个猜测，因为这里没有一个有效的代码示例：

[self.filteredArray setArray: [self.arrayBreedAndSpecies filteredArrayUsingPredicate:predicate]];

如果self.filteredArray为零，那条线将什么都不做......我敢打赌你的意思是：

self.filteredArray = [self.arrayBreedAndSpecies filteredArrayUsingPredicate:predicate];

Answer 2

好的，我注意到你的NSPredicate代码有一些错误：

1）谓词中的动态密钥路径应为%K而不是%@。

2）要检查数字值是否等于另一个，您需要使用==而不仅仅是=

因此，代码的最后一部分应为：

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%K == %i",@"id_especie", 2];
self.filteredArray = [NSArray arrayWithArray:[self.arrayBreedAndSpecies filteredArrayUsingPredicate:predicate]];
NSLog(@"Filter: %@", self.filteredArray);

我假设id_especie属性是数字值。如果是字符串值，则可以使用谓词：[NSPredicate predicateWithFormat:@"%K MATCHES[cd] %@", @"id_especie", @"2"];

希望这有帮助

NSPredicate用于生成空数组的字典数组

2 个答案: