Parameter type must not include a type variable or wildcard

Question

in my android app I use Retrofit 2:

public enum OperationType {
    @SerializedName("payment")
    PAYMENT,
    @SerializedName("payout")
    PAYOUT,
    @SerializedName("transfer")
    TRANSFER
}




fun getOperationsList(typeList: List<OperationType>, callback: Callback<List<Operation>>) {
        val call = myRestClient.getOperationsList(typeList)
        executeRequest(call, callback)
}


@GET("/operations")
fun getOperationsList(@Query("type") typeList: List<OperationType>): Call<List<Operation>>

but I get runtime error in this line:

val call = myRestClient.getOperationsList(typeList)

error:

Shutting down VM
 FATAL EXCEPTION: main
 Process: md.qsystems.android.tango.debug, PID: 22714
 java.lang.IllegalArgumentException: Parameter type must not include a type variable or wildcard: java.util.List<? extends OperationType> (parameter #1)
     for method TangoRestClient.getOperationsList
    at retrofit2.Utils.methodError(Utils.java:52)
    at retrofit2.Utils.methodError(Utils.java:42)
    at retrofit2.Utils.parameterError(Utils.java:61)
    at retrofit2.RequestFactory$Builder.validateResolvableType(RequestFactory.java:764)
    at retrofit2.RequestFactory$Builder.parseParameterAnnotation(RequestFactory.java:401)
    at retrofit2.RequestFactory$Builder.parseParameter(RequestFactory.java:306)
    at retrofit2.RequestFactory$Builder.build(RequestFactory.java:193)
    at retrofit2.RequestFactory.parseAnnotations(RequestFactory.java:67)
    at retrofit2.ServiceMethod.parseAnnotations(ServiceMethod.java:26)
    at retrofit2.Retrofit.loadServiceMethod(Retrofit.java:170)
    at retrofit2.Retrofit$1.invoke(Retrofit.java:149)
    at java.lang.reflect.Proxy.invoke(Proxy.java:393)
    at $Proxy1.getOperationsList(Unknown Source)
    at mTransportService.getOperationsList(TransportService.kt:160)

Masaccio

Answer 1

You can add @JvmSuppressWildcards either inside the angle brackets before the String type, or before the List. Both should work and remove the wildcard.

Workaround taken from this issue.

Phytoplankton

IDE was showing Unresolved reference error until I added s at the end, so use @JvmSuppressWildcards – Nonpartisan

Answer 2

If you have several Lists in a request probably you should add several @JvmSuppressWildcardss.

@GET("/get-teams")
suspend fun teams(
    @Query("statuses") statuses: List<@JvmSuppressWildcards TeamStatus>? = null,
    @Query("types") types: List<@JvmSuppressWildcards TeamType>? = null,
    @Query("name") name: String? = null,
): List<Team>

Or replace complex types with simple. For instance, TeamStatus is a enum:

enum class TeamStatus {
    ENABLED,
    DISABLED,
}

Then replace the method:

@GET("/get-teams")
suspend fun teams(
    @Query("statuses") statuses: List<String>? = null,
    @Query("types") types: List<String>? = null,
    @Query("name") name: String? = null,
): List<Team>

and convert data:

teams(
    statuses = statuses.map { it.name },
    types = types.map { it.name },
)

Laudianism