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Form validation with LiveData
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| // https://oozou.com/blog/modern-android-form-validations-with-data-binding-147 | |
| typealias Predicate<T> = (value: T?) -> Boolean | |
| class LiveDataValidator<T>(private val liveData: LiveData<T>){ | |
| private val validationRules = mutableListOf<Predicate<T>>() | |
| private val errorMessages = mutableListOf<String>() | |
| var error = MutableLiveData<Message?>() | |
| fun addRule(errorMsg: String, predicate: Predicate<T>) { | |
| validationRules.add(predicate) | |
| errorMessages.add(errorMsg) | |
| } | |
| private fun emitErrorMessage(messageRes: String?) { | |
| error.value = messageRes | |
| } | |
| fun isValid(): Boolean { | |
| for(i in 0 until validationRules.size){ | |
| if(validationRules[i](liveData.value) ){ | |
| emitErrorMessage(errorMessages[i]) | |
| return false | |
| } | |
| } | |
| emitErrorMessage(null) | |
| return true | |
| } | |
| } |
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| class LiveDataValidatorResolver(private val validators: List<LiveDataValidator<*>>){ | |
| fun isValid() : Boolean = validators.all { it.isValid() } | |
| } |
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| val password = MutableLiveData<String>() | |
| val passwordValidator = LiveDataValidator<String>(password).apply{ | |
| addRule("password is required") { it.isNullOrBlank() } | |
| addRule("password length must be 7") { it?.length != 7 } | |
| } | |
| val isFormValid = MediatorLiveData<Boolean>().apply { | |
| value = false | |
| addSource(username) { value = validateForm() } | |
| } | |
| private fun validateForm() : Boolean { | |
| val validators = listOf(passwordValidator) | |
| val validatorResolver = LiveDataValidatorResolver(validators) | |
| return validatorResolver.isValid() | |
| } |
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