Access argument data in Kotlin from Flutter's Method channel

Question

I have setup a basic Method channel in flutter and Kotlin.

Following is my sample data:

{    
    "user_dob":"15 November 1997", 
    "user_description":"Hello there, I am a User!", 
    "user_gender":"Male", 
    "user_session":"KKDSH3G9OJKJFIHXLJXUGWIOG9UJKLJ98WHIJ"
}

Following method channel can pass the data to Kotlin side from Flutter:

var result = await platform.invokeMethod('updateProfile', data);

Following code catches the data in Kotlin:

MethodChannel(flutterView, channel).setMethodCallHandler { call, result ->
      if(call.method == "updateProfile"){
        var argData = call.arguments
...

Now,argData contains the data I just sent, and two questions come up:

1. How do I access data from argdata? for.eg.

2. How do I get my user_dob from this argData?

Following code is my current solution.

val userDOB : String = call.argument("user_dob")

But the following error is thrown: Kotlin: Type mismatch: inferred type is String? but String was expected

Note: When I was sending the map data to the MethodChannel, it was accidentally being sent as a String. To follow THIS method through, please make sure that a Map object is implemented in passing the data.

Solution

When getting method argument from method channel of Flutter the data that comes in, is a json formatted String.

You can simply call call.argument, and it will return a Nullable string.

In your case you requested for a String which in Kotlin is Nun-null String object, but the returned value of call.argument might not exists in the json and be null. So you must get a String? instead which is a Nullable String.

Update

Check and make sure channel is able to pass data to the native.

In flutter:

static const MethodChannel _channel = const MethodChannel('NAME');

And in native code:

val channel = MethodChannel(registrar.messenger(), "NAME");

TL; DR

In Kotlin use Nullable object for data that can be null.

val userDOB : String? = call.argument("user_dob")

And use it with ?. (Null safe)