Android初学者//为什么我的变量在我应该填充后都为0

Question

我刚刚从原来的帖子中编辑了这篇文章，因为我可以缩小问题范围，但不想为它打开额外的帖子。

我想要什么我有一个活动，在该活动中，我将数据从房屋生成到阵列中。然后，在打开另一个活动时，数据应用于显示它。

我的问题数据生成正确，我可以在日志中看到它是在我想访问它之前生成的。访问时，它仍然不会显示我的数据。

我的代码

Houses.java(我生成Houses并使用下面给出的答案来尝试获取我的数据(

public class Houses{
int[][] NewHouseProps = new int[20][10];
int[][] HouseProps;
public Houses(){
}
public ArrayList<Integer> getClasses()
{
ArrayList<Integer> classes = new ArrayList<>();
Log.d("Test","ID: "+3+" CLASS: "+NewHouseProps[3][0]);
Log.d("Test","ID: "+4+" CLASS: "+NewHouseProps[4][0]);
for(int id=0 ; id<=8; id++) {
classes.add(NewHouseProps[id][0]);
Log.d("getClasses","Classes: "+NewHouseProps[id][0]);
Log.d("getClasses!!!!!!!!!", "List: "+classes.get(id));
}
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;
Log.d("ID: ", Integer.toString(id));
Log.d("CLASS: ",Integer.toString(NewHouseProps[id][0]));
Log.d("PRICE: ", Integer.toString(NewHouseProps[id][1]));
}
}
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;
}

BuyHouseActivity.java(此处应访问并显示数据(

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));
}
List<Integer> images = new ArrayList<>();
images.add(R.drawable.apartment);
images.add(R.drawable.townhouse);
images.add(R.drawable.bungalow);
images.add(R.drawable.villa);
ViewPager viewPager = findViewById(R.id.vpPager);
viewPager.setAdapter(new MyViewPagerAdapter(getSupportFragmentManager(), images));
}

protected class MyViewPagerAdapter extends FragmentStatePagerAdapter {
private List<Integer> imageList;
MyViewPagerAdapter(FragmentManager fm, List<Integer> images) {
super(fm);
imageList = images;
}
@Override
public int getCount() {
return imageList.size();
}
@Override
public Fragment getItem(int position) {
return FragmentBuyHouse.newInstance(imageList.get(position));
}
}

我的日志这些是我的日志的结果，它们如您所见：正在生成访问

我希望你能帮助我，告诉我我做错了什么和/或忘记了什么。

Answer 1

发生这种情况是因为您使用的是一个空列表。看

在您的FragmentBuyHouse中，您调用：

BuyHousesActivity bha = new BuyHousesActivity();
List<Integer> classes = bha.classes;

但当您实例化new BuyHouseActivity()时，它会初始化数组，而不包含任何数据。看你的课BuyHouseActivity

List<Integer> classes = new ArrayList<>();

在您的实现中，您在方法onCreate()中填充它的数组classes，该方法在您安装类时未被调用。这是因为第46行出现错误。

您需要像使用Bundle一样通过参数传递数据。

解决方案2

您可以创建一个静态方法来返回类：

更改BuyHousesActivity:

public class BuyHousesActivity extends FragmentActivity {
List<Integer> classes = new ArrayList<>();
private ViewPager mPager;
private PagerAdapter mPagerAdapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
// Houses h = new Houses(); //Activity where my Houses get generated
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_buy_houses);
Log.d("1. Step", "!!!!!!!!!!!!!!!!!!!!!!");
//   for(int id=0; id<=8;id++){
//       classes.add(h.NewHouseProps[id][0]);
//       Log.d("Klasse: ", Integer.toString(h.NewHouseProps[id][0]));
//   }
//   Log.d("2. Step", "!!!!!!!!!!!!!!!!!!!!!!");
/*
classes.add(R.drawable.apartment); //Class 0
classes.add(R.drawable.townhouse); //Class 1
classes.add(R.drawable.bungalow); //Class 2
classes.add(R.drawable.villa); //Class 3
*/
mPager = findViewById(R.id.vpPager);
mPagerAdapter = new ViewPagerAdapter(getSupportFragmentManager(), classes);
mPager.setAdapter(mPagerAdapter);

}

public static ArrayList<Integer> getClasses()
{
Houses h = new Houses();
classes = new ArrayList<>();
for(int id=0 ; id<=8; id++) {
classes.add(h.NewHouseProps[id][0]);
}
return classes;
}

@Override
public void onBackPressed() {
//ViewPager Last Page or Back
if (mPager.getCurrentItem() == 0) {
super.onBackPressed();
} else {
mPager.setCurrentItem(mPager.getCurrentItem() - 1);
}
}

你想要像FragmentBuyHouse那样的课程

public class FragmentBuyHouse extends Fragment {
private int[] imageResId;
private int fragnumber;
BuyHousesActivity bha = new BuyHousesActivity();
List<Integer> classes = bha.getClasses();
...
}