Kotlin - Parcelable Type mismatch: Required: String, Found: String?

Question

The compiler is giving me the error Type mismatch: Required: String, Found: String? for the lines parcel.writeString(firstName) and parcel.writeString(lastName) inside the constructor of a Parcelable data class.

Here is my class.

data class Mouse(
val firstName: String,
val lastName: String,
val age: Int ) : Parcelable {
constructor(parcel: Parcel) : this(
    parcel.readString(),
    parcel.readString(),
    parcel.readInt()
)

override fun writeToParcel(parcel: Parcel, flags: Int) {
    parcel.writeString(firstName)
    parcel.writeString(lastName)
    parcel.writeInt(age)
}

override fun describeContents(): Int {
    return 0
}

companion object CREATOR : Parcelable.Creator<Mouse> {
    override fun createFromParcel(parcel: Parcel): Mouse {
        return Mouse(parcel)
    }

    override fun newArray(size: Int): Array<Mouse?> {
        return arrayOfNulls(size)
    }
}}

I don't understand why there is the error and how to correct it.

ardenit · Accepted Answer · 2020-02-09 22:40:23Z

6

Actually, your error is caused by other lines. parcel.readString() returns String?, and you try to pass it to your primary constructor as firstName parameter which has String type. To fix it, you can, for example, pass a default value if returned string is null:

constructor(parcel: Parcel) : this(
    parcel.readString() ?: "",
    parcel.readString() ?: "",
    parcel.readInt()
)

answered Feb 9, 2020 at 22:40

ardenit

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2 Comments

DarkCoffee Over a year ago

Thank you for your answer. I should insert ?:"" even if there are the linesval firstName: String, val lastName: String,?

ardenit Over a year ago

Yes, because parcel.readString() returns a nullable type String?, and firstName has non-nullable type String, so you have to deal with null values.

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