为什么我的公共变量显示为“'this'is not available”？

Question

I am trying to populate a listview with data from a database but it won't allow me to assign a string variable.

i have read some other articles on this but i cannot for the life of me figure out why my variable is shown as " 'this' is not available " When i use the debugger.

public class InventoryActivity extends AppCompatActivity
{
private RecyclerView varRecyclerView;
private RecyclerView.Adapter varAdapter;
private RecyclerView.LayoutManager varLayoutManager;

private static String URL_FindInventory = "MyPHPFile";

//IM TRYING TO SET THESE TWO VARIABLES
public String itemOneName, itemOneEffect;

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_inventory);

    String characterID = getIntent().getStringExtra("characterID");

    ArrayList<LayoutItem> inventoryList = new ArrayList<>();

    FindInventory(characterID);

    inventoryList.add(new LayoutItem(R.drawable.ic_add_circle, itemOneName, itemOneEffect));
    inventoryList.add(new LayoutItem(R.drawable.ic_add_circle, "Item Two Name", "Item Two's Effect"));

    varRecyclerView = findViewById(R.id.recyclerView);
    varRecyclerView.setHasFixedSize(true);
    varLayoutManager = new LinearLayoutManager(this);
    varAdapter = new LayoutAdapter(inventoryList);

    varRecyclerView.setLayoutManager(varLayoutManager);
    varRecyclerView.setAdapter(varAdapter);
}


private void FindInventory(final String characterID)
{
    StringRequest stringRequest = new StringRequest(Request.Method.POST, URL_FindInventory,
            new Response.Listener<String>()
            {
                @Override
                public void onResponse(String response)
                {
                    try
                    {
                        JSONObject jsonObject = new JSONObject(response);

                        String result = jsonObject.getString("result");

                        if (result != null)
                        {
                            JSONArray jsonArray = jsonObject.getJSONArray("result");

                            for(int i = 0; i < jsonArray.length(); i++)
                            {
                                JSONObject object = jsonArray.getJSONObject(i);

           //IM TRYING TO USE THESE TWO VARIABLES TO SET THE PUBLIC ONES.
                                String itemName = object.getString("Name").trim(); // this has a value of "Cap of Thinking"
                                String itemEffect = object.getString("Effect").trim(); // this has a value of "Helps the user to think +2 Intelligence"

                                itemOneName = itemName;  // THIS IS SHOWN AS "ItemOneName = 'this' is not available "
                                itemOneEffect = itemEffect; // THIS IS SHOWN AS "ItemOneEffect = 'this' is not available "

                            }

                        }
                        else if ((result.equals("error")))
                        {
                            Toast.makeText(InventoryActivity.this, "Cannot find Inventory", Toast.LENGTH_LONG).show();
                        }
                    } catch (JSONException e)
                    {
                        e.printStackTrace();
                        Toast.makeText(InventoryActivity.this, "Exception Error " + e.toString(), Toast.LENGTH_LONG).show();

                    }
                }
            },
            new Response.ErrorListener()
            {
                @Override
                public void onErrorResponse(VolleyError error) {
                    Toast.makeText(InventoryActivity.this, "Error " + error.toString(), Toast.LENGTH_LONG).show();
                }
            }) {
        @Override
        protected Map<String, String> getParams() throws AuthFailureError {
            Map<String, String> params = new HashMap<>();
            params.put("characterid", characterID);

            return params;
        }
    };
    RequestQueue requestQueue = Volley.newRequestQueue(this);
    requestQueue.add(stringRequest);

}

When I'm trying to set the value of the 2 public strings they are being set as null, I can't for the life of me figure out why it won't allow me to set there value to the variables I read from the JSON object.

Answer 1

They are null because your web request happens after you added the items to the lists.

Make inventoryList a field and remove the two string fields you're trying to set

Move the two inventoryList.add methods into the onResponse, then you need to notify the RecyclerView adapter that new data needs to be displayed

Answer 2

The reason they are null is because when the compiler executes below two lines(let's call it line 1 and line 2):

FindInventory(characterID);//line 1

inventoryList.add(new LayoutItem(R.drawable.ic_add_circle, itemOneName, itemOneEffect));//line 2

-At line 1, the method gets executed asynchronously(means that it will not block the execution of line 2, line 2 will be executed either after or before line 1). This causes the variables itemOneName and itemOneEffect to be null, since line 2 was executed before line 1, remember line 1 and line 2 are being executed in parallel or same time.

To fix this:

-You have to do below:

inventoryList.add(new LayoutItem(R.drawable.ic_add_circle, itemOneName, itemOneEffect));
inventoryList.add(new LayoutItem(R.drawable.ic_add_circle, "Item Two Name", "Item Two's Effect"));

...and other dependencies

After you invoke these lines within onResponse():

String itemName = object.getString("Name").trim(); // this has a value of "Cap of Thinking"
String itemEffect = object.getString("Effect").trim();