Mobile Kotlin fields

This is a Kotlin MultiPlatform library that add form fields abstraction to implement any input forms with validations.

Table of Contents

• Features
• Requirements
• Installation
• Usage
• Samples
• Set Up Locally
• Contributing
• License

Features

• Input field abstraction;
• Validation based on reactive approach (on LiveData from moko-mvvm or Flow from kotlinx.coroutines).

Requirements

• Gradle version 6.8+
• Android API 16+
• iOS version 11.0+

Installation

root build.gradle

allprojects {
    repositories {
      mavenCentral()
    }
}

project build.gradle

dependencies {
    commonMainApi("dev.icerock.moko:fields-core:0.12.0")

    // integration with reactive flows
    commonMainApi("dev.icerock.moko:fields-livedata:0.12.0")
    commonMainApi("dev.icerock.moko:fields-flow:0.12.0")
 
    androidMainApi("dev.icerock.moko:fields-material:0.12.0")
}

Flow additions

to work correctly on the iOS side, you need to export the mvvm-flow and mvvm-core dependencies to the iOS framework.

Usage

Live Data

Create FormField to text input with empty validation:

val textField = FormField<String, StringDesc>("", { inputLiveData ->
    inputLiveData.map { text ->
        if (text.isBlank()) "should be not blank!".desc()
        else null
    }
})

Use liveBlock to simplify validation create.

val textField = FormField<String, StringDesc>("", liveBlock { text ->
    if (text.isBlank()) "should be not blank!".desc()
    else null
})

Use LiveData in validation lambda to merge with other fields.

val passwordField = FormField<String, StringDesc>("", { inputLiveData ->
    inputLiveData.map { text ->
        if (text.isBlank()) "should be not blank!".desc()
        else null
    }
})
val passwordConfirmField = FormField<String, StringDesc>("", { inputLiveData ->
    passwordField.data.mergeWith(inputLiveData) { password, passwordConfirm ->
        if (passwordConfirm.isBlank()) "should be not blank!".desc()
        else if(passwordConfirm != password) "passwords not same".desc()
        else null
    }
})

Call validate to perform validations and show error to user by field.error LiveData.

class LoginViewModel(
    override val eventsDispatcher: EventsDispatcher<EventsListener>
) : ViewModel(), EventsDispatcherOwner<LoginViewModel.EventsListener> {
    val emailField = FormField<String, StringDesc>("", liveBlock { email ->
        if (email.isBlank()) MR.strings.cant_be_blank.desc()
        else null
    })
    val passwordField = FormField<String, StringDesc>("", liveBlock { password ->
        if (password.isBlank()) MR.strings.cant_be_blank.desc()
        else null
    })

    private val fields = listOf(emailField, passwordField)

    fun onLoginPressed() {
        if (!fields.validate()) return

        val email = emailField.value()
        val password = passwordField.value()
        val message = "$email:$password"

        eventsDispatcher.dispatchEvent { showMessage(message.desc()) }
    }

    interface EventsListener {
        fun showMessage(message: StringDesc)
    }
}

Bind FormField to UI by data and error LiveDatas.

<com.google.android.material.textfield.TextInputLayout
    app:error="@{viewModel.emailField.error.ld}">

    <EditText
        android:text="@={viewModel.emailField.data.ld}" />
</com.google.android.material.textfield.TextInputLayout>

emailField.bindTextTwoWay(liveData: viewModel.emailField.data)
emailField.bindError(liveData: viewModel.emailField.error)

Flow

Create FormField to text input with empty validation:

val emailField: FormField<String, StringDesc> = FormField(
    scope = viewModelScope,
    initialValue = "",
    validationTransform = { email ->
        ValidationResult.of(email) {
            notBlank(MR.strings.cant_be_blank.desc())
            matchRegex(MR.strings.wrong_format.desc(), EMAIL_REGEX)
        }
    }
)

FormField to work with coroutines, CoroutineScope is required.

Call validate to perform validations and show error to user by field.error StateFlow.

class LoginViewModel : ViewModel() {
    private val _actions: Channel<Action> = Channel(Channel.BUFFERED)
    val actions: CFlow<Action> get() = _actions.receiveAsFlow().cFlow()

    val emailField: FormField<String, StringDesc> = FormField(
        scope = viewModelScope,
        initialValue = "",
        validation = flowBlock { email ->
            ValidationResult.of(email) {
                notBlank(MR.strings.cant_be_blank.desc())
                matchRegex(MR.strings.wrong_format.desc(), EMAIL_REGEX)
            }
        }
    )

    @Suppress("MagicNumber")
    val passwordField: FormField<String, StringDesc> = FormField(
        scope = viewModelScope,
        initialValue = "",
        validation = fieldValidation {
            notBlank(MR.strings.cant_be_blank.desc())
            minLength(MR.strings.must_contain_more_char.desc(), 4)
        }
    )

    private val fields = listOf(emailField, passwordField)

    fun onLoginPressed() {
        if (!fields.validate()) return

        val email = emailField.value()
        val password = passwordField.value()
        val message = "$email:$password"

        _actions.trySend(Action.ShowMessage(message.desc()))
    }

    sealed interface Action {
        data class ShowMessage(val message: StringDesc) : Action
    }

    companion object {
        @Suppress("MaxLineLength")
        private val EMAIL_REGEX =
            Regex("[a-zA-Z0-9\\+\\.\\_\\%\\-\\+]{1,256}\\@[a-zA-Z0-9][a-zA-Z0-9\\-]{0,64}(\\.[a-zA-Z0-9][a-zA-Z0-9\\-]{0,25})+")
    }
}

Bind FormField to UI by data and error StateFlows:

val email: String by viewModel.emailField.data.collectAsState()

TextField(
    placeholder = @Composable { 
        Text("Email") 
    }, 
    value = email, 
    onValueChange = { viewModel.emailField.data.value = it }
)

For ease of use in working with SwiftUI, you can use this CocoaPods dependency.

struct LoginScreen: View {
    @StateObject var viewModel: LoginViewModel = LoginViewModel()
    
    var body: some View {
        LoginScreenBody(
             email: viewModel.binding(\.emailField.data),
             emailError: viewModel.state(\.emailField.error)
        )
    }
}

struct LoginScreenBody: View {
    @Binding var email: String
    let emailError: StringDesc?
    
    var body: some View {
        VStack {
            TextField("email", text: viewModel.binding(\.passwordField.data))
            if let emailError = emailError {
                Text(emailError.localized())
            }
        }
    }
}

Validations packet

There is a useful ValidationResult class for building validation monads for a form fields. Two formats for creating validation are implemented:

• Chain/monad validation:

ValidationResult.of(emailFieldValue)
    .notBlank(blankErrorStringDesc)
    .matchRegex(wrongEmailErrorStringDesc, EMAIL_REGEX)
    .validate()

For this variant, do not forget to call function validate at the end!

• DSL validation:

ValidationResult.of(emailFieldValue) {
    notBlank(blankErrorStringDesc)
    matchRegex(wrongEmailErrorStringDesc, EMAIL_REGEX)
}

To create a new function for validation monad, you need to create an extension function of class ValidationResult using builder nextValidation. For example, this is how the ready-made function for checking String values for blankness looks like:

fun ValidationResult<String>.notBlank(errorText: StringDesc) = nextValidation { value ->
    if (value.isNotBlank()) {
        ValidationResult.success(value)
    } else {
        ValidationResult.failure(errorText)
    }
}

All the ready-made validation functions of the library can be found in the source codes in the files AnyValidations.kt for Any class and StringValidations.kt for String class.

To simplify of adding validation to the FormField object (without mapping of a LiveData objects) you can use the builder-function fieldValidation:

val passwordField = FormField<String, StringDesc>(
    initialValue = "",
    validation = fieldValidation {
        notBlank(MR.strings.cant_be_blank.desc())
        minLength(MR.strings.must_contain_more_char.desc(), 4)
    }
)

Samples

More examples can be found in the sample directory or sample-declarative-ui directory.

Set Up Locally

• In fields-core directory contains the core - validations logic and the interface for interacting with fields;
• In fields-flow directory contains implementation of the FormField interface using kotlinx.coroutines;
• In fields-livedata directory contains implementation of the FormField interface using moko-mvvm LiveDatas
• In sample directory contains samples use fields-livedata on Android, iOS & mpp-library connected to apps
• In sample-declarative-ui directory contains samples use fields-flow on Android with Compose,on iOS with SwiftUI and shared module connected to apps

Contributing

All development (both new features and bug fixes) is performed in develop branch. This way master sources always contain sources of the most recently released version. Please send PRs with bug fixes to develop branch. Fixes to documentation in markdown files are an exception to this rule. They are updated directly in master.

The develop branch is pushed to master during release.

More detailed guide for contributers see in contributing guide.

License

Copyright 2019 IceRock MAG Inc

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.