填充的ArrayList引发OutOfBounds异常

时间：2018-11-02 21:47:35

标签： android

我的应用
我想制作一个简单的游戏开始。为此，我生成了房屋，然后希望将其显示给玩家。

我的问题
当我尝试访问应存储房屋类别的ArrayList时，出现异常（请参见下文）。在调试器中，我可以看到在尝试访问类之前已正确生成了类。

我的代码
Houses.java（这是我在App启动时生成我的房屋，然后尝试访问它们的地方）

  public class Houses{

    ArrayList<Integer> classes = new ArrayList<>();
    int[][] NewHouseProps = new int[20][10];
    int[][] HouseProps;

    public Houses(){
    }

    public ArrayList<Integer> getClasses()
    {
        for(int id=0;id<=8;id++){
            Log.d("getClasses()","ID: "+id+" CLASSES: "+classes.get(id)); //Exception
        }
        return classes;
    }

    public void GenerateHouses(){
        Log.d("Generate Houses","!!");
        for(int id=0; id<=8; id++){
                Random r = new Random();
                int h_class, garage = 0, rooms = 0, furn = 0, balkon = 0, pool = 0;
                h_class = r.nextInt(4); //Klasse
                if(h_class == 0){
                    rooms = r.nextInt(4)+1;
                    balkon = r.nextInt(1);
                }else if(h_class == 1){
                    rooms = r.nextInt(3)+3;
                    garage = r.nextInt(1)+1;
                    pool = r.nextInt(1);
                    balkon = r.nextInt(2);
                }else if(h_class == 2){
                    rooms = r.nextInt(3)+2;
                    garage = r.nextInt(2)+2;
                    pool = r.nextInt(1);
                }else if(h_class == 3){
                    rooms = r.nextInt(8)+6;
                    garage = r.nextInt(6)+4;
                    pool = r.nextInt(1);
                    balkon = r.nextInt(3);
                }
                furn = r.nextInt(1);

                int price = GenerateHousePrice(id, h_class, garage, rooms, furn, balkon, pool);
                NewHouseProps[id][0] = h_class;
                NewHouseProps[id][1] = price;
                NewHouseProps[id][2] = rooms;
                NewHouseProps[id][3] = furn;
                NewHouseProps[id][4] = balkon;
                NewHouseProps[id][5] = pool;
                NewHouseProps[id][6] = garage;
                classes.add(h_class);
                Log.d("GenerateHouses","ID: "+id+" CLASS: "+h_class);
                Log.d("GenerateHouses","CLASSES: "+classes.get(id));
                Log.d("GenerateHouses","PROPS: "+NewHouseProps[id][0]);
        }
    }

public int GenerateHousePrice(int id, int h_class, int garage, int rooms, int furn, int balkon, int pool){

    int price = 0, pricep = 0;
    Random r = new Random();
    if(h_class == 0){
        price = r.nextInt(150000)+50000; // 50 - 200 tausend
        price += rooms * 7500;
    }
    else if(h_class == 1){
        price = r.nextInt(165000)+85000; //85 - 250 tausend
        price += rooms * 12500;
    }
    else if(h_class == 2){
        price = r.nextInt(300000)+100000; //100 - 400 tausnd
        price += rooms * 20000;
    }
    else if(h_class == 3){
        price = r.nextInt(800000)+500000; // 500 - 1.3 Mill.
        price += rooms * 15000;
    }

    if(garage > 0){
        pricep += price*0.20;
        pricep += garage * 500;
    }
    if(furn == 1){
        pricep += price*0.25;
    }
    if(balkon > 0){
        pricep += price*0.1;
        pricep += balkon*500;
    }
    if(pool == 1){
        pricep += 20000;
    }
    price += pricep;
    return price;
}

}

BuyHousesActivity（这是我要显示它的位置，当我尝试获取类时会崩溃）

public class BuyHousesActivity extends FragmentActivity {


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_buy_houses);
    Houses h = new Houses();
    ArrayList<Integer> classes = h.getClasses();
    for(int id=0;id<=8;id++){
        Log.d("OnCreate Classes: ","Classes: "+classes.get(id)); //Exception
    }

    ViewPager viewPager = findViewById(R.id.vpPager);
    viewPager.setAdapter(new MyViewPagerAdapter(getSupportFragmentManager(), classes));

}



protected class MyViewPagerAdapter extends FragmentStatePagerAdapter {
    int clicker = 0;
    private List<Integer> pclasses;
    private ArrayList<Integer> threeclasses;

    MyViewPagerAdapter(FragmentManager fm, ArrayList<Integer> classes) {
        super(fm);
        pclasses = classes;

        if(clicker == 0){
            for(int id=0;id<=2;id++) {
                threeclasses.add(classes.get(id));
            }
        }else if(clicker == 1){
            for(int id=3;id<=5;id++) {
                threeclasses.add(classes.get(id));
            }
        }else if(clicker == 2){
            for(int id=6;id<=8;id++){
                threeclasses.add(classes.get(id));
            }
            clicker = 0;
            return;
        }
        clicker++;
        return;
    }

    @Override
    public int getCount() {
        return pclasses.size()/3;
    }

    @Override
    public Fragment getItem(int position) {
        return FragmentBuyHouse.newInstance(threeclasses);
    }
}

例外情况（上面标记的行）：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: at.simonic.realtoroffice, PID: 4913
java.lang.RuntimeException: Unable to start activity ComponentInfo{at.simonic.realtoroffice/at.simonic.realtoroffice.BuyHousesActivity}: java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
 Caused by: java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
    at java.util.ArrayList.get(ArrayList.java:437)
    at at.simonic.realtoroffice.BuyHousesActivity.onCreate(BuyHousesActivity.java:31)
    at android.app.Activity.performCreate(Activity.java:7136)
    at android.app.Activity.performCreate(Activity.java:7127)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
    at android.os.Handler.dispatchMessage(Handler.java:106) 
    at android.os.Looper.loop(Looper.java:193) 
    at android.app.ActivityThread.main(ActivityThread.java:6669) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 

我希望您能帮助我了解数据丢失的过程，并帮助我了解其背后的问题。

1 个答案:

答案 0 :(得分：0)

您没有在GenerateHouses类构造函数上调用Houses。检查您的BuyHousesActivity onCreate。您正在做的是：

Houses h = new Houses(); // This will create an new object

在此对象的构造函数中，您什么也不做：

public Houses(){}

因此，该对象classes参数在您访问时将为空：

ArrayList<Integer> classes = h.getClasses();

这就是您得到例外的原因。

因此解决方案是其中之一：

  1. 在GenerateHouses对象构造函数中调用Houses
  2. 在访问GenerateHouses变量之前调用classes
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