如何在阵列中放置Firebase数据的节点

Question

在我的应用程序的第一页上，我使用的是UIViewPicker，它允许用户选择他们想要选择的国家。 而不是我通过数组将国家/地区名称硬编码到UIPicker中（如下所示）：

var country = ["USA", "CANADA"]

我认为最好将应用程序连接到我的Firebase数据库，在该数据库中可以获取所有国家/地区，然后将其附加到数组中，并从中读取UIPicker。

这样，如果我想添加更多的国家/地区，则无需发布新版本的应用程序。 我只需在数据库中添加另一个国家，应用程序就会自动更新它。 但是我不确定如何做到这一点。 当我打印数据库快照时，我得到了整个数据库，但是我只是想将美国和加拿大放入一个阵列中。

所以这是我的firebase数据库的结构：

countries
  Canada
     states
        Alberta
        British Columbia
  USA
     states
        Alabama
        Arkansas

这是我当前的代码：

import UIKit
import FirebaseDatabase

class ViewController: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource {

    @IBOutlet weak var countryPicker: UIPickerView!

    //let country = ["USA", "Canada"] I am no longer using this hardcoded array

    var countrySelected = String()
    var action = 0 

    override func viewDidLoad() {
        super.viewDidLoad()

        //this is where I reach out to the database
        let database = Database.database().reference()
        database.child("countries").observeSingleEvent(of: .value) { (Snapshot) in
            print(Snapshot)
        }

        //add code here that takes the snapshot and appends the the array below
        var country = string()

        countrySelected = country[0]
        countryPicker.selectRow(action, inComponent: 0, animated: false)
        //print(countrySelected)
    }

    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }

    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return country.count
    }

    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return country[row]
    }

    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        countrySelected = country[row]
        action = country.firstIndex(of: countrySelected)!
        //print(countrySelected)
    }
}

如果有人可以帮助解释，那就太好了！

Answer 1

为了使事情变得容易，我们可以创建一些结构来代表国家和州。

struct Country {
    struct State {
        let country: String
        let name: String
    }

    let name: String
    let states: [State]

    static var ref: DatabaseReference {
        return Database.database().reference(withPath: "countries")
    }

    static func from(key: String, value: Any?) -> Country? {
        guard
            let value = value as? [String:[String]],
            let states = value["states"] else { return nil }

        return Country(name: key, states: states.map {
            State(country: key, name: $0)
        })
    }

    static func countries(from snapshot: DataSnapshot) -> [Country]? {
        return snapshot.snapshots.compactMap {
            Country.from(key: $0.key, value: $0.value)
        }
    }
}

对DataSnapshot的扩展使我们可以方便地访问快照的子级。

extension DataSnapshot {
    var snapshots: [DataSnapshot] {
        return children.allObjects as? [DataSnapshot] ?? []
    }
}

接下来，我们创建一些属性来处理国家/地区–一个存储它们的数组以及一些计算出的属性以返回所选国家和州。

class CountryStatePickerViewController: UIViewController {

    // MARK: Outlets

    @IBOutlet weak var pickerView: UIPickerView! {
        didSet {
            loadCountries()
        }
    }

    // MARK: Properties

    private var countries = [Country]() {
        didSet {
            pickerView.reloadAllComponents()
        }
    }

    var selectedCountry: Country? {
        return country(at: pickerView.selectedRow(inComponent: 0))
    }

    var selectedState: Country.State? {
        return selectedCountry.flatMap {
            state(at: pickerView.selectedRow(inComponent: 1), in: $0)
        }
    }
}

我们还需要一些方法来安全地访问特定索引下的国家和州，以及一种首先加载国家/地区的方法。

extension DataSnapshot {
    var snapshots: [DataSnapshot] {
        return children.allObjects as? [DataSnapshot] ?? []
    }
}

extension CountryStatePickerViewController {

    private func loadCountries() {
        Country.ref.observeSingleEvent(of: .value, with: { [weak self] in
            self?.countries = Country.countries(from: $0) ?? []
        })
    }

    private func country(at index: Int) -> Country? {
        return countries.indices.contains(index) ? countries[index] : nil
    }

    private func state(at index: Int, in country: Country) -> Country.State? {
        return country.states.indices.contains(index) ? country.states[index] : nil
    }
}

最后，在我们的UIPickerView协议一致性中，countries数组填充了数据源。 我们可以使用两个组件来代表国家及其相应的州。

extension CountryStatePickerViewController: UIPickerViewDataSource, UIPickerViewDelegate {

    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 2
    }

    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        switch component {
        case 0:
            return countries.count
        case 1:
            return selectedCountry?.states.count ?? 0
        default:
            return 0
        }
    }

    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        switch component {
        case 0:
            return country(at: row)?.name
        case 1:
            return selectedCountry.flatMap { state(at: row, in: $0)?.name }
        default:
            return nil
        }
    }

    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {

        if component == 0 { pickerView.reloadComponent(1) }

        selectedState.flatMap { print($0.name, $0.country) }
    }
}

Answer 2

var countries : [Any] = []

override func viewDidLoad() {
    super.viewDidLoad()
    database.child("countries").observeSingleEvent(of: .value) { (snapshot) in
        if snapshot.exists() {
            if let dict : [String : AnyObject] = snapshot.value as? [String : AnyObject] {
                let array : [Any] = (dict as AnyObject).allValues
                self.countries = array
                // reload countryPicker data 

            } 
        } 
        else {
            // not exist in db 
        }
    }
}