Java 为什么Getter和Setter在Android中不适用于Arraylist

我是Android新手。我有两个类，我在一个类中生成一个ArrayList，并使用setter方法将其传递给另一个类

问题：我希望listview仅在arraylist中收到数据后显示，而arraylist是在单击按钮后出现的。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

类别1:SearchComponents 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：

---

您正在创建另一个SearchComponents实例，需要使用传递给Components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);
}

---

为了让另一个类可以访问属性或方法，它必须是公共的

请参阅w3schools.com上的此文档

---

因此，在类1中的setter方法中，来自类2的数据显示为变量this.foodlist。这不会在整个课程中设置this.foodlist的值吗？为什么getter方法不显示数据？

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);
}