使用发布者过滤字符串字段中的数字

Question

我正在为用于引入数量的 textField 构建包装器。我正在尝试使用 Combine 构建所有内容。其中一个用例在于，如果文本字段发送的 stringValue 有一个字母，我会过滤字母并将新值重新分配给同一个 var，因此文本字段会过滤这些值。还有一个代码可以将此值更改为 int，以便其他组件可以读取 int 值。这是代码：

class QuantityPickerViewModel: ObservableObject {
    private var subscriptions: Set<AnyCancellable> = Set<AnyCancellable>()
    @Published var stringValue: String = ""
    @Published var value : Int? = nil
    
    init(initialValue: Int?) {
        $stringValue
            .removeDuplicates()
            .print("pre-filter")
            .map {
                [=10=].filter {[=10=].isNumber}
            }
            .print("post-filter")
            .map {
                Int([=10=])
            }
            .assign(to: \.value, on: self)
            .store(in: &subscriptions)

        $value.map {
            [=10=] != nil ? String([=10=]!): ""
        }
        .print("Value")
        .assign(to: \.stringValue, on:self)
        .store(in: &subscriptions)
    
        value = initialValue
    }
}

我使用测试验证行为，我将只对失败的测试进行验证：

class QuantityPickerViewModelTest: AppTestCase {
    var model: QuantityPickerViewModel!
    override func setUpWithError() throws {
        super.setUp()
        model = QuantityPickerViewModel(initialValue: 10)
    }
    
    func test_changeStringValueWithLetters_filtersLettersAndChangesValue() {
        model.stringValue = "30a"
        
        XCTAssertEqual(model.value, 30)
        XCTAssertEqual(model.stringValue, "30") // fails saying stringValue is still "30a"
    }
}

测试的输出是：

Test Case '-[SourdoughMasterTests.QuantityPickerViewModelTest test_changeStringValueWithLetters_filtersLettersAndChangesValue]' started.
pre-filter: receive subscription: (RemoveDuplicates)
post-filter: receive subscription: (Print)
post-filter: request unlimited
pre-filter: request unlimited
pre-filter: receive value: ()
post-filter: receive value: ()
Value: receive subscription: (PublishedSubject)
Value: request unlimited
Value: receive value: ()
Value: receive value: (10)
pre-filter: receive value: (10)
post-filter: receive value: (10)
Value: receive value: (10)
pre-filter: receive value: (30a)
post-filter: receive value: (30)
Value: receive value: (30)
pre-filter: receive value: (30)
post-filter: receive value: (30)
Value: receive value: (30)
/Users/jpellat/workspace/SourdoughMaster/SourdoughMasterTests/QuantityPickerViewModelTest.swift:54: error: -[SourdoughMasterTests.QuantityPickerViewModelTest test_changeStringValueWithLetters_filtersLettersAndChangesValue] : XCTAssertEqual failed: ("30a") is not equal to ("30")

有谁知道为什么没有赋值？谢谢

Answer 1

这不是 Combine 问题本身导致的，但似乎 Published 发布者在属性上实际设置值之前发出。所以，基本上 "30a" 会覆盖 assign.

中设置的任何内容

无论如何，这个循环的管道链似乎有点可疑。我也不认为你真的需要 Combine 这里 - 它可以用两个计算属性和一个公共存储属性:

来解决

@Published 
private var _value: Int? = nil

var value: Int? {
   get { _value }
   set { _value = newValue }
}

var stringValue: String {
   get { _value?.description ?? "" }
   set {
      _value = Int(newValue.filter { "0"..."9" ~= [=10=] })
   }
}

Answer 2

即使我认为 New Dev 的解决方案更好，因此是官方答案，我也会 post 我的 Combine 解决方案以防有人好奇。我基本上通过分离用户输入和用户输出来消除循环。对于界面，它看起来是一样的，但我可以创建一个 userInput -> value -> user output 结构：

class QuantityPickerViewModel: ObservableObject {
    private var subscriptions: Set<AnyCancellable> = Set<AnyCancellable>()
    var stringValue: String {
        get {
            userOutput
        }
        set {
            userInput = newValue
        }
    }
    @Published var value : Int? = nil
    @Published private var userInput: String = ""
    private var userOutput: String = ""
    
    init(initialValue: Int?) {
        $userInput
            .map {
                [=10=].filter {[=10=].isNumber}
            }
            .map {
                Int([=10=])
            }
            .assign(to: \.value, on: self)
            .store(in: &subscriptions)
        
        $value
            .map {
                [=10=] == nil ? "": String([=10=]!)
            }
            .assign(to: \.userOutput, on: self)
            .store(in: &subscriptions)
        
        value = initialValue
    }
}

如果您对规格感到好奇，这里还有一些测试：

class QuantityPickerViewModelTest: XCTestCase {
    var model: QuantityPickerViewModel!
    override func setUpWithError() throws {
        super.setUp()
        model = QuantityPickerViewModel(initialValue: 10)
    }

    func test_initWith10_valueAfterInit_is10() {
        XCTAssertEqual(model.value, 10)
        XCTAssertEqual(model.stringValue, "10")
    }

    func test_initWithNil_valueAfterInit_isNilAndEmptyString() {
        model = QuantityPickerViewModel(initialValue: nil)
        XCTAssertNil(model.value)
        XCTAssertEqual(model.stringValue, "")
    }
    
    func test_changeStringValue_changesValue() {
        model.stringValue = "20"
        
        XCTAssertEqual(model.value, 20)
        XCTAssertEqual(model.stringValue, "20")
    }
    
    func test_changeValue_changesStringValue() {
        model.value = 20
        
        XCTAssertEqual(model.value, 20)
        XCTAssertEqual(model.stringValue, "20")
    }
    
    func test_changeValueToNil_changesStringValueToEmpty() {
        model.value = nil
        
        XCTAssertEqual(model.value, nil)
        XCTAssertEqual(model.stringValue, "")
    }
    
    func test_changeStringValueWithLetters_filtersLettersAndChangesValue() {
        model.stringValue = "30a"
        
        XCTAssertEqual(model.value, 30)
        XCTAssertEqual(model.stringValue, "30")
    }
}

使用发布者过滤字符串字段中的数字

Use publishers to filter numbers in a string field

ios

swift

combine