java - Android - 从其他 Activity 检索 ArrayList

Question

我有以下 Activity，它是一个独立于 MainActivity 的类

public class Calculation_getInventory {
SQLiteDatabase db;
private static Calculation_getInventory _instance = null;
public static Calculation_getInventory getInstance(){
    if(_instance == null)
        _instance= new Calculation_getInventory();
    return _instance;
  }
  private Calculation_getInventory(){} 

  public void getInventory() {
    db = SQLiteDatabase.openDatabase("/data/data/com.sjhdevelopment.shaunharrison.myejuiceapp/databases/EJuiceData.db", null, 0);
    Cursor c = db.rawQuery("SELECT * FROM Inventory", null);
    List InventoryList = new ArrayList();
    if (c.moveToFirst()) {
        do {
            Double amountLeft = Double.parseDouble(c.getString(4));
            if (amountLeft != 0) {
                InventoryList.add(c.getString(1));
            }
        } while (c.moveToNext());
    }
    java.util.Collections.sort(InventoryList);
    InventoryList.add(0, "No Selection");

  }
}

在我的计算类(MainActivity)中，我进行了以下调用来获取 Activity

Calculation_getInventory.getInstance().getInventory();

我的问题是如何将 ArrayList 从 Calculation_getInventory 传递到 Calculation？

Answer 1

不完全确定您想在这里实现什么，但 getInventory() 应该返回值，而不是:

public void getInventory()

应该是:

public ArrayList getInventory()

并且应该返回InventoryList

public ArrayList getInventory() {
    db = SQLiteDatabase.openDatabase("/data/data/com.sjhdevelopment.shaunharrison.myejuiceapp/databases/EJuiceData.db", null, 0);
    Cursor c = db.rawQuery("SELECT * FROM Inventory", null);
    List InventoryList = new ArrayList();
    if (c.moveToFirst()) {
        do {
            Double amountLeft = Double.parseDouble(c.getString(4));
            if (amountLeft != 0) {
                InventoryList.add(c.getString(1));
            }
        } while (c.moveToNext());
    }
    java.util.Collections.sort(InventoryList);
    InventoryList.add(0, "No Selection");

    return InventoryList;
}