为什么 Getter 和 Setter 不适用于 Android 中的 Arraylist

Question

我是安卓新手。 我有 2 个类，我在一个类中生成一个 ArrayList 并使用 setter 方法将它传递给另一个类。

问题：我希望仅在单击按钮后发生的 arraylist 中接收到数据后才显示列表视图。 我无法访问 getter 方法的返回结果，也无法访问 getter 方法中的任何其他变量。

第 1 类：搜索成分（getFoodlist、setFoodlist）

public class SearchIngredients extends AppCompatActivity {

//UI
EditText enter_ingredients;
Button search_ingredients, search_recipe;
ListView ingredient_display;


//Variables
private Recipe displayRecipe;
private Instructions instructions;
private ArrayList<String> foodlist;
private JSONArray foodArray;
private ArrayList<String> ingredientList;
private IngredientAdapter ingredientAdapter;
private JSONArray jsonArray;
private boolean stats = false;
String TAG = "SearchIngredients";
public SharedPreferences preferences;
public SharedPreferences.Editor editor;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_search);

    //UI
    enter_ingredients = findViewById(R.id.enter_ingredients);
    ingredient_display = findViewById(R.id.ingredient_display);
    search_ingredients = findViewById(R.id.search_ingredients);
    search_recipe = findViewById(R.id.search_recipe);

    // variables
    foodlist = new ArrayList<String>();
    foodArray = new JSONArray();
    ingredientList = new ArrayList<String>();
    jsonArray = new JSONArray();
    preferences = this.getSharedPreferences("dataStatus", MODE_PRIVATE);
    editor  = preferences.edit();

    //click functionality
    search_recipe.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            String food = enter_ingredients.getText().toString();

            if (food.equals("")) {
                enter_ingredients.setError("Enter the ingredients before searching");
            } else {

                getIngredients(food);
            }

        }
    });

  
}

public void getIngredients(String food) {
    Ingredients methods = new Ingredients(SearchIngredients.this);
    String url = methods.SearchIngredientURL(food);
    methods.JsonRequest(url);

}

//Getter and Setter
public ArrayList<String> getFoodlist() {
    Log.d("foodArrayGetList", "" + foodlist); // after setting the value still the value is null
    return this.foodlist;
}

public void setFoodlist(ArrayList<String> foodlist) {  //setting the value for foodlist from Class 2
    this.foodlist = new ArrayList<>();
    this.foodlist = foodlist;
    Log.d("foodArraySetList", "" + this.foodlist);
}
}

第 2 类：

public class Ingredients {
private Context context;
private ArrayList<String> newData;
private JSONArray foodArray;
private ArrayList<String> ingredientsList;

//constructor
public Ingredients(Context context) {
    this.context = context;
    this.newData = new ArrayList<String>();
    this.foodArray = new JSONArray();
    this.ingredientsList = new ArrayList<String>();
}


//JSON Object Request
//GET Method from API
public void JsonRequest(String url) {
    final SearchIngredients searchIngredients = new SearchIngredients();
    JsonArrayRequest arrayRequest = new JsonArrayRequest(
            Request.Method.GET,
            url,
            null,
            new Response.Listener<JSONArray>() {
                @Override
                public void onResponse(JSONArray response) {
                    try {
                        setFoodArray(response);
                        Log.d("foodArrayIn", "" + foodArray);
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                    try {
                        newData = savedData(response);
                        searchIngredients.setFoodlist(newData); // calling the setter function of Class 1
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }

            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    Log.e("Rest Error Recipe", error.toString());
                }
            }

    );
    RequestQueue requestQueue = Volley.newRequestQueue(context);
    requestQueue.add(arrayRequest);
}

public ArrayList<String> savedData(JSONArray response) throws JSONException {
    for (int i = 0; i < response.length(); i++) {
        JSONObject jsonObject = response.getJSONObject(i);

        //Parse JSON data
        String name = (jsonObject.getString("name"));
        IngredientName ingredientName = new IngredientName(name);
        Log.d("ingredientName", "" + ingredientName.getName());

        ingredientsList.add(ingredientName.getName());

    }
    Log.d("SearchIngre", "" + ingredientsList.toString());
    this.setNewData(ingredientsList);
    return ingredientsList;
}

//TODO: Change the Log e.
//IngredientName in JSON Format
public String JsonReturn() {
    SearchGSON searchGSON = new SearchGSON(context, "Bread, Butter");
    Log.e("GSONresult", searchGSON.toString());

    return searchGSON.toString();
}

//Getter and Setter
public JSONArray getFoodArray() {
    Log.d("foodArraygetI", "" + this.foodArray);
    return this.foodArray;
}

public void setFoodArray(JSONArray foodArray) throws JSONException {
    for (int i = 0; i < foodArray.length(); i++) {
        this.foodArray.put(foodArray.get(i));
    }
    Log.d("foodArraySetClass", "" + this.foodArray);

}
public ArrayList<String> getNewData() {
    Log.d("newDataSet", "" + this.foodArray);
    return this.newData;
}

public void setNewData(ArrayList<String> newData) {

    this.newData = newData;
    Log.d("newDataSet", "" + this.foodArray);
}
}

Answer 1

您正在创建SearchIngredients另一个实例，您需要使用传递给Ingredients构造函数的实例

public class Ingredients {
private SearchIngredients searchIngredients;
private ArrayList<String> newData;
private JSONArray foodArray;
private ArrayList<String> ingredientsList;

//constructor
public Ingredients(SearchIngredients searchIngredients) {
    this.searchIngredients = searchIngredients;
    this.newData = new ArrayList<String>();
    this.foodArray = new JSONArray();
    this.ingredientsList = new ArrayList<String>();
}


//JSON Object Request
//GET Method from API
public void JsonRequest(String url) {
    //REMOVE THIS final SearchIngredients searchIngredients = new SearchIngredients();
    JsonArrayRequest arrayRequest = new JsonArrayRequest(
            Request.Method.GET,
            url,
            null,
            new Response.Listener<JSONArray>() {
                @Override
                public void onResponse(JSONArray response) {
                    try {
                        setFoodArray(response);
                        Log.d("foodArrayIn", "" + foodArray);
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                    try {
                        newData = savedData(response);
                        searchIngredients.setFoodlist(newData); // calling the setter function of Class 1
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }

            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    Log.e("Rest Error Recipe", error.toString());
                }
            }

    );
    RequestQueue requestQueue = Volley.newRequestQueue(searchIngredients);
    requestQueue.add(arrayRequest);
}

Answer 2

为了让另一个类可以访问一个属性或方法，它必须是公共的。

请参阅 w3schools.com 上的此文档

https://www.w3schools.com/java/java_modifiers.asp