为什么即使我反对，II也会得到零点异常？

Question

How do I safeguard against null points? I tried this way:

var spr = context.getSharedPreferences("FAV", Context.MODE_PRIVATE)
var emptyArray: JsonArray = jsonArray()
var myjson = spr.getString("KEY", null)

//GET JSON FROM SHARED PREFERENCE

Log.d("TAG", "NOT NULL")
if(myjson != null) {
    var parsedFavFromJson = Gson().fromJson<List<String>>(myjson)
    //PARSE FROM JSON TO ARRAY

    for (i in parsedFavFromJson) {
        emptyArray.add(i)
        Log.d("TAG", "" + i)

        if (i == recipeArray!![counterX].recipeKey!!) {
            Picasso.with(context)
                    .load(R.drawable.fav_icon_60at3x).into(favMarkerButton)
            Log.d("TAG", "Match " + i)
        } else {
            Log.d("TAG", "WAS NULL")
            Picasso.with(context)
                    .load(R.drawable.fav_unclicked_icon60at3x).into(favMarkerButton)
        }
    }
}

I have clearly stated the conditional if(myjson != null) , still it pass through and crash with the error message java.lang.IllegalStateException: fromJson(json, typeToken<T>()) must not be null . There is no clear indication where the error actually occur - it actually points to an empty code line! If I remove the code above, things are working fine. I also tried using:

var myjson = spr.getString("KEY", null).let {

...and so on, with the same result. Am I missing something here?

UPDATE I checked variable myjson and it is clearly null . Question is why the conditional if(myjson != null) passed...

Answer 1

In short, you're missing the question mark.

You expect that in block:

spr.getString("KEY", null).let { it }

Won't be null? That's incorrect.

Correct syntax is

spr.getString("KEY", null)?.let { it }

Easy to miss.

Same goes for working with nested JSONs. You should never use bang-bang ( !! ) in Kotlin. Use the safe syntax instead:

recipeArray?[counterX].recipeKey