从Firestore取数据填充ListView时出现非法参数异常求助

Hey, let's break down what's going wrong here and fix it step by step.

错误根源分析 #

The error java.lang.IllegalArgumentException: n <= 0: 0 is happening because you're calling randomGenerator.nextInt(randomPlaceList.size()) when randomPlaceList is empty (size = 0). The Random.nextInt(int n) method requires n to be greater than 0, so passing 0 triggers this exception.

Looking at your code, there are several critical issues in the loop where you're building the random place list, plus a few other minor bugs across your files:

• You're using the empty randomPlaceList to generate random indexes instead of the populated placesList
• There's a type mismatch: you're trying to assign an int (random index) to a String variable, then add that String to a List<Places> (this should be a compile error, likely a typo when pasting code)
• You're initializing the adapter and setting it on the ListView inside the loop, which is inefficient and unnecessary
• Your adapter class name doesn't match what you're using in the activity
• The Places entity is missing the image field and its getter/setter (required for your adapter's Glide call)
• Syntax error and incorrect intent extra retrieval in Card_activity

修正后的完整代码 #

1. ListViewPlaces 主活动

public class ListViewPlaces extends AppCompatActivity {
    FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
    CollectionReference placesRef = rootRef.collection("Places");

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_list_view_places);

        placesRef.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
            @Override
            public void onComplete(@NonNull Task<QuerySnapshot> task) {
                if (task.isSuccessful()) {
                    List<Places> placesList = new ArrayList<>();
                    for (DocumentSnapshot document : task.getResult()) {
                        Places places = document.toObject(Places.class);
                        placesList.add(places);
                    }

                    if (placesList.size() > 0) {
                        int placeCount = placesList.size();
                        System.out.println(placesList.size());
                        Random randomGenerator = new Random();
                        List<Places> randomPlaceList = new ArrayList<>();

                        // 最多生成3个随机地点，如果总地点数不足3则取全部
                        int itemsToAdd = Math.min(3, placeCount);
                        for (int i = 0; i < itemsToAdd; i++) {
                            // 使用已填充的placesList的size生成有效索引
                            int randomIndex = randomGenerator.nextInt(placeCount);
                            randomPlaceList.add(placesList.get(randomIndex));
                        }

                        // 循环结束后一次性初始化适配器并设置到ListView
                        ListView mListView = findViewById(R.id.place_list);
                        PlaceAdapter placesAdapter = new PlaceAdapter((ArrayList<Places>) randomPlaceList, getApplicationContext());
                        mListView.setAdapter(placesAdapter);

                        // 添加点击事件跳转到Card_activity
                        mListView.setOnItemClickListener((parent, view, position, id) -> {
                            Places selectedPlace = randomPlaceList.get(position);
                            Intent intent = new Intent(ListViewPlaces.this, Card_activity.class);
                            intent.putExtra("name", selectedPlace.getName());
                            startActivity(intent);
                        });
                    } else {
                        // 处理Firestore未加载到任何数据的情况
                        Toast.makeText(ListViewPlaces.this, "未找到任何地点数据", Toast.LENGTH_SHORT).show();
                    }
                } else {
                    // 处理Firestore数据获取失败的情况
                    Toast.makeText(ListViewPlaces.this, "加载地点失败: " + task.getException().getMessage(), Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}

2. Places 实体类

public class Places {
    private String name;
    private String image; // 补充适配器需要的image字段

    // Firestore要求的空构造函数
    public Places() {}

    public Places(String name, String image) {
        this.name = name;
        this.image = image;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getImage() {
        return image;
    }

    public void setImage(String image) {
        this.image = image;
    }
}

3. PlaceAdapter 适配器

class PlaceAdapter extends ArrayAdapter<Places> {
    private ArrayList<Places> dataSet;
    Context mContext;

    private static class ViewHolder {
        TextView name_text;
        ImageView image_text;
    }

    public PlaceAdapter(ArrayList<Places> dataSet, Context context) {
        super(context, R.layout.item_list, dataSet);
        this.dataSet = dataSet;
        this.mContext = context;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Places places = getItem(position);
        ViewHolder viewHolder;
        final View result;

        if (convertView == null) {
            viewHolder = new ViewHolder();
            LayoutInflater inflater = LayoutInflater.from(getContext());
            convertView = inflater.inflate(R.layout.item_list, parent, false);
            viewHolder.name_text = convertView.findViewById(R.id.text_image_id);
            viewHolder.image_text = convertView.findViewById(R.id.image_id);
            result = convertView;
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
            result = convertView;
        }

        viewHolder.name_text.setText(places.getName());
        Glide.with(getContext()).load(places.getImage()).into(viewHolder.image_text);

        return convertView;
    }
}

4. Card_activity 跳转目标活动

public class Card_activity extends AppCompatActivity implements View.OnClickListener {
    TextView mTextView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.massive_places);

        mTextView = findViewById(R.id.head_name);
        // 修正语法错误和intent extra获取方式
        String name = getIntent().getStringExtra("name");
        mTextView.setText(name);
    }

    @Override
    public void onClick(View v) {
        // 这里可以实现你需要的点击逻辑
    }
}

关键修复总结 #

• 替换randomGenerator.nextInt(randomPlaceList.size())为randomGenerator.nextInt(placeCount)，使用已填充的placesList的大小生成有效索引
• 修复了向randomPlaceList添加元素时的类型不匹配问题
• 将适配器初始化逻辑移到循环外部，避免重复创建和设置
• 补充了Places实体类缺失的字段和方法，适配适配器的需求
• 修正了Card_activity中的语法错误和intent数据获取方式
• 添加了Firestore数据加载失败和空数据的错误处理

内容的提问来源于stack exchange，提问作者Spike Johnson