Why my data class giving null values unless i applied default on it?

Question

I am trying to show data from the server using data class of kotlin. It's almost working fine but some case whenever I fetch a response I don't know why it is still giving null values unless I add a default value ("") for msg.

This is my data class

data class ViewcardModel(
        val msg: String = "",  // here is default values
        val cartcnt: String = "",
        val order_total: Int = 0,
        val status: Boolean = false          
)

This is my response from server

{
  status = false  // server response
}

What you would like you `msg` property value to be if the server does not return it? — miensol, Sep 05 '18 at 06:29

score 0 · Answer 1 · answered Sep 05 '18 at 06:48

0

You're probably using something like GSON to instantiate the instances of your model. These tools use reflection to create instances, and therefore the default parameter value of your primary constructor will never take effect (since it's never called).

What you need is the same as what this question is about:

Setting Default value to a variable when deserializing using gson

A custom deserializer is probably what you'll end up with.

answered Sep 05 '18 at 06:48

zsmb13

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i already use this situation (according to my question) in another activity it is working fine so i cannot say that this is GSON reflection problem. – chari sharma Sep 05 '18 at 07:03
Are you sure you're creating the models the same way? Any chance that those other properties are primitives, and they only have their default values based on Java behavior and not because of what you're assigning to them? If the instances are created via reflection, booleans will be false by default, number types 0, etc. – zsmb13 Sep 05 '18 at 08:45
in my previous case, I assigned empty string ("") and whenever server does not respond the same key as i defined default ("") string then i got empty string if i fetch from this data class. That is the role of data-class but this time i don't know. – chari sharma Sep 05 '18 at 11:56

score 0 · Answer 2 · answered Sep 05 '18 at 07:01

0

You should pass the value into data class like this

  val s= ViewcardModel(status=false)
  println(s.toString())
  val s1= ViewcardModel(msg="hello",status=false)
  println(s1.toString())

output

ViewcardModel(msg=, cartcnt=, order_total=0, status=false)
ViewcardModel(msg=hello, cartcnt=, order_total=0, status=false)

answered Sep 05 '18 at 07:01

sasikumar

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my data is coming from server like: override fun onSuccess(body: T?) { val viewcardmodel = body as ViewcardModel } – chari sharma Sep 05 '18 at 07:11

Why my data class giving null values unless i applied default on it?

2 Answers2