Question

我有以下活动，它是MainActivity的独立类

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，我进行了以下调用以获取活动

Calculation_getInventory.getInstance().getInventory();

我的问题是如何将CalculationList从Calculation_getInventory传递给Calculation？

Answer 1

不完全确定你想在这里实现什么，但是getInventory（）应该返回值，而不是：

public void getInventory()

应该是：

public ArrayList getInventory()

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;
}

Answer 2

您的getInventory()没有返回任何内容。设置为返回值ArrayList并让它返回列表。

示例

你有：

public void getStuff() { int ret = 6; }

将其转换为：

public int getStuff() { int ret = 6; return ret; }

在您的其他课程中，您可以在课程对象上调用getStuff()，如下所示：

int stuff = YourClass.getInstance().getStuff();

Answer 3

只需为Calculation_getInventory类创建一个InventoryList作为全局，并添加一个getter settter方法。

public class Calculation_getInventory {
List InventoryList = new ArrayList(); // create global var of list
SQLiteDatabase db;
private static Calculation_getInventory _instance = null;

// call this method to get arraylist /list of inventory
public List getInventoryList()
{
    if(InventoryList==null)
          return new ArrayList();
    InventoryList;
}

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(); comment this line and declare globally
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");

 }
}

现在只需使用Calculation_getInventory对象

调用此方法

Calculation_getInventory i=Calculation_getInventory.getInstance().getInventory();
List list=i.getInventoryList();

Android - 从其他Activity中检索ArrayList

3 个答案: