Null pointer exception in parsing JSON (only in some cases)-CodePudding

I'm using this code to parse a json file and change some items in de app I build:

 fun fetchJson() {

        if (isNetworkAvailable()) {

            val request = Request.Builder().url(stationAPPJsonURL).build()

            client.newCall(request).enqueue(object : Callback {

                override fun onResponse(call: Call, response: Response) {
    
                    val body = response.body?.string()

                    val gson = GsonBuilder().create()

                    try {

                        val stationAPP = gson.fromJson(body, StationAPP::class.java)

                        //ACTIE
                        actie_zichtbaar = stationAPP.actie_zichtbaar
                        actie_img = stationAPP.actie_img
                        actie_url = stationAPP.actie_url

... I left out some code

                    catch (error: JsonParseException) {

                        runOnUiThread {

                            val toast = Toast.makeText(applicationContext, "Problem loading JSON.\nFunctionality may be limited for a while.", Toast.LENGTH_SHORT)

                            val view = toast.view!!.findViewById<TextView>(android.R.id.message)
                            toast?.let { view.gravity = Gravity.CENTER }
                            toast.setGravity(Gravity.CENTER, 0, 0)
                            toast.show()

                        }

                    }

               }

                override fun onFailure(call: Call, e: IOException) {
                runOnUiThread {

                    val toast = Toast.makeText(applicationContext, "Problem loading JSON.\nFunctionality may be limited for a while.", Toast.LENGTH_SHORT)

                    val view = toast.view!!.findViewById<TextView>(android.R.id.message)
                    view?.let { view.gravity = Gravity.CENTER }
                    toast.setGravity(Gravity.CENTER, 0, 0)
                    toast.show() --> line 1390!!

                }

            }

         }

  }

I see in the logs in Google Play Console that sometime this part of the code crashes (4%). I've no clue why? I tested it on several devices and no errors at all.

Who can help me out here?

Is it possible That: val stationAPP = gson.fromJson(body, StationAPP::class.java) throws no exception but that somehow the json file is loaded with some errors in it? And therefor some items are null?

Thanks for you help ;)

Update: this is the error it produces:

Exception java.lang.NullPointerException:
  at com.familiekoning.grolloo.MainActivity$fetchJson$1.onFailure$lambda-10 (MainActivity.kt:1390)
  at com.familiekoning.grolloo.MainActivity$fetchJson$1.$r8$lambda$lczurdfMtnZdFDn9iwHvPqw9_Pg
  at com.familiekoning.grolloo.MainActivity$fetchJson$1$$ExternalSyntheticLambda8.run
  at android.os.Handler.handleCallback (Handler.java:938)
  at android.os.Handler.dispatchMessage (Handler.java:99)
  at android.os.Looper.loop (Looper.java:250)
  at android.app.ActivityThread.main (ActivityThread.java:7806)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:592)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:958)

CodePudding user response：

This is going to be a guess but if you see !! anywhere and you have NullPointerException. You are very close to certain that it is the culprit. If you want a different Toast appearance there are NPE safe ways.

Relying on stuff that is android.id.x is not safe because it might be very much OEM dependent.

CodePudding user response：

I changed:

val toast = Toast.makeText(applicationContext, "Problem loading JSON.\nFunctionality may be limited for a while.", Toast.LENGTH_SHORT)

            val view = toast.view!!.findViewById<TextView>(android.R.id.message)
            view?.let { view.gravity = Gravity.CENTER }
            toast.setGravity(Gravity.CENTER, 0, 0)
            toast.show()

to:

val toast = Toast.makeText(applicationContext, "Problem loading JSON.\nFunctionality may be limited for a while.", Toast.LENGTH_SHORT)

            toast.setGravity(Gravity.CENTER, 0, 0)
            toast.show()

That fixed the problem.