How to parse string that contains objects as a string to list of objects

I had a list of objects and saved them as a String in shared preferences. Now I need to extract that saved string and convert it back to the list of objects. So how to convert this kind of string

[DataClass(label=testLabel, testData=someData), DataClass(label=testLabel, testData=someData)]

To val result = listOf<DataClass>()

So as result I will be able to get data from dataclass.label and dataclass.testData

CodePudding user response：

I would recommend to go with @BenP's and @cactustictacs suggestions in the comments below your question.

val str = "[DataClass(label=testLabel, testData=someData), DataClass(label=testLabel, testData=someData)]"

data class DataClass(
  val label: String,
  val testData: String
)

val result = str
  .removeSurrounding("[DataClass(label=", ")]")
  .split(", testData=", "), DataClass(label=")
  .chunked(2)
  .map { DataClass(it[0], it[1]) }

result.forEach(::println)

CodePudding user response：

As all other comments and answer recommend you to use a serialization library instead of manually converting string to the object, because it would be more idiomatic, less error-prone, and easier to maintain.

You can use Kotlin-Serialization for this. To enable it, perform these three steps

Add kotlin-serialization plugin to dependencies of your project-level build.gradle

dependencies {
    //..
    classpath "org.jetbrains.kotlin:kotlin-serialization:$kotlin_version"
    //..
}

Apply plugin in your module-level build.gradle

apply plugin: "kotlinx-serialization"

Add Json encoder dependency to module's build.gradle

dependencies {
    implementation "org.jetbrains.kotlinx:kotlinx-serialization-json:2.0.1"
}

To serialize your data class annotate it with @Serializable

@Serializable
data class DataClass{
    val label: String,
    val testData: String
}

Now to convert list of DataClass to String just use encodeToString method of Json class.

val dataClassList = listOf(DataClass("dfd", "fdf"), DataClass("dfd", "fdf"), DataClass("dfd", "fdf"))
val jsonString = Json.encodeToString(dataClassList)

Save jsonString to shared preferences

To convert it back to the list of DataClass use decodeFromString of Json class.

val decodedDataClassList = Json.decodeFromString<List<DataClass>>(jsonString)

CodePudding user response：

I would recommend you to use Gson, instead of calling toString() as already mention, there's no fromString() method.

private fun DataClassToJson(data: Data): String {
    val gson = GsonBuilder().create()
    return gson.toJson(data)
}

// save the string to preferences and retrieve it

private fun jsonToDataClass(data: String): Data {
    val dataType = object : TypeToken<Data>() {}.type
    // convert string back to object
    return Gson().fromJson(data, dataType)
}