如何过滤视图中显示的数据？

Question

下面的我的 XCODE Swift VIEW 代码显示了我的数据中所有 Flavor Groups 和 Descriptors 的列表。我想做的是过滤数据以显示所有风味组和描述符，除非 isSeltzer 为假。

我尝试在我的视图模型中使用类似的东西，然后在我的视图中使用过滤后的数组进行迭代，但我无法让它工作：

let flavorsNoSeltzers = flavors.filter({ return $0.isSeltzer != false })

这是我的本地 JSON 数据示例：

    [
    {
        "id": "562811",
        "flavorGroup": "APRICOT",
        "name": "NATURAL AND ARTIFICIAL APRICOT FLAVOR",
        "isBeer": true,
        "isSeltzer": false,
        "isArtificial": true,
        "descriptors": ["FRUITY"],
        "keywords": ["juicy", "skunky", "peach", "floral", "slight green (sierra nevada pale ale)"]
    },
    {
        "id": "U39252",
        "flavorGroup": "BANANA",
        "name": "NATURAL BANANA FLAVORING",
        "isBeer": true,
        "isSeltzer": true,
        "isArtificial": false,
        "descriptors": [""],
        "keywords": ["missing"]
    },
    {
        "id": "681686",
        "flavorGroup": "WHITE CHOCOLATE",
        "name": "NATURAL WHITE CHOCOLATE FLAVOR WONF",
        "isBeer": true,
        "isSeltzer": true,
        "isArtificial": false,
        "descriptors": ["LACTONIC", "COCOA", "CREAMY"],
        "keywords": ["nutty", "milk chocolate", "french vanilla", "custard", "cakey"]
    }
]

这是我的模型的一个例子：

struct Flavor: Codable, Identifiable {
    enum CodingKeys: CodingKey {
        case id
        case flavorGroup
        case name
        case isBeer
        case isSeltzer
        case isArtificial
        case descriptors
        case keywords
    }
    let id, flavorGroup, name: String
    let isBeer, isSeltzer, isArtificial: Bool
    let descriptors, keywords: [String]
}

这是我的视图模型的示例：

class ReadData: ObservableObject  {
    @Published var flavors = [Flavor]()  
    init(){
        loadData()
    }
    func loadData()  {
        guard let url = Bundle.main.url(forResource: "flavors", withExtension: "json")
            else {
                print("Json file not found")
                return
            }
        let data = try? Data(contentsOf: url)
        let flavors = try? JSONDecoder().decode([Flavor].self, from: data!)
        self.flavors = flavors!
    }
}

这是我的 VIEW 示例：

struct myView: View {
    @ObservedObject var flavorData = ReadData()
    var body: some View{
        List(flavorData.flavors){ flavor in
            VStack(alignment: .leading) {
                Text(flavor.flavorGroup)
                ForEach(flavor.descriptors, id: \.self) { descriptor in
                    if descriptor.isEmpty {
                        // do nothing
                    } else {
                        Text("- \(descriptor)")
                    }
                }
            }
        }
    }
}

Answer 1

一个简化的工作示例，过滤Flavor 对象列表并返回一个仅包含Flavor 对象的新列表，其中isSeltzer 是true。

import Foundation

struct Flavor {
    let id: String
    let isSeltzer: Bool
}

let flavors = [Flavor(id: "First", isSeltzer: false), Flavor(id: "Second", isSeltzer: true), Flavor(id: "Third", isSeltzer: false)]
let flavorsSeltzersTrue = flavors.filter({ $0.isSeltzer })

print(flavorsSeltzersTrue) // Prints the flavors with isSeltzer == true

如果你想要相反的（即isSeltzer 是false），你可以简单地将闭包中的$0.isSeltzer 更改为!$0.isSeltzer。另外，check out the documentation 在 filter(_:) 方法上。

如果这不能解决您的问题，那么您的代码还有其他问题。

编辑：

在您的代码中，您可能希望像这样添加这行代码：

class ReadData: ObservableObject  {
    @Published var flavors = [Flavor]()  
    init(){
        loadData()
    }
    func loadData()  {
        guard let url = Bundle.main.url(forResource: "flavors", withExtension: "json")
            else {
                print("Json file not found")
                return
            }
        let data = try? Data(contentsOf: url)
        let flavors = try? JSONDecoder().decode([Flavor].self, from: data!)
        self.flavors = flavors.filter({ $0.isSeltzer }) // I've added it here.
    }
}

请注意，强制展开 (flavors!) 是不好的做法，当 flavors 为 nil 时可能会导致崩溃。