Android中Toast因null不显示的问题排查与解决求助

程序在模拟器中可正常启动且无崩溃，但点击四个按钮中的任意一个，本该从listings.csv获取对应房产价格并显示Toast，现在毫无反应。尝试过通过ID判断按钮（例如id == R.id.button3），但始终无法满足property != null的条件，模拟器通知已开启。

相关代码 #

MainActivity.java #

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends Activity implements View.OnClickListener {
   
    private Listing listing;

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

        listing = new Listing();
        listing.loadProperties("listings.csv");

        Button button3 = findViewById(R.id.button3);
        Button button4 = findViewById(R.id.button4);
        Button button5 = findViewById(R.id.button5);
        Button button6 = findViewById(R.id.button6);

        button3.setOnClickListener(this);
        button4.setOnClickListener(this);
        button5.setOnClickListener(this);
        button6.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        Button clickedButton = (Button) view;
        String location = clickedButton.getText().toString();
        Property property = listing.getProperty(location);

        if (property != null) {
            String priceText = "Price: $" + property.getPrice();
            Toast.makeText(this, priceText, Toast.LENGTH_SHORT).show();
        }
    }
}

Property.java #

public abstract class Property {
    private String ID;
    private String location;
    private double price;

    public Property(String ID, String location, double price) {
        this.ID = ID;
        this.location = location;
        this.price = price;
    }

    public String getID() { return ID; }
    public void setID(String ID) { this.ID = ID; }
    public String getLocation() { return location; }
    public void setLocation(String location) { this.location = location; }
    public double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }

    @Override
    public String toString() {
        return "ID: " + ID + "\nLocation: " + location + "\nPrice: " + price;
    }
}

CommercialProperty.java #

public class CommercialProperty extends Property {
    private String zone;
    private int numUnits;
    private int numParkingSpots;

    public CommercialProperty(String ID, String location, double price, String zone, int numUnits, int numParkingSpots) {
        super(ID, location, price);
        this.zone = zone;
        this.numUnits = numUnits;
        this.numParkingSpots = numParkingSpots;
    }

    public String getZone() { return zone; }
    public void setZone(String zone) { this.zone = zone; }
    public int getNumUnits() { return numUnits; }
    public void setNumUnits(int numUnits) { this.numUnits = numUnits; }
    public int getNumParkingSpots() { return numParkingSpots; }
    public void setNumParkingSpots(int numParkingSpots) { this.numParkingSpots = numParkingSpots; }

    @Override
    public String toString() {
        return super.toString() + "\nZone: " + zone + "\nUnits: " + numUnits + "\nParking Spots: " + numParkingSpots;
    }
}

ResidentialProperty.java #

public class ResidentialProperty extends Property {
    private double annualHoaFees;
    private int numBedrooms;
    private double numBathrooms;

    public ResidentialProperty(String ID, String location, double price, double annualHoaFees, int numBedrooms, double numBathrooms) {
        super(ID, location, price);
        this.annualHoaFees = annualHoaFees;
        this.numBedrooms = numBedrooms;
        this.numBathrooms = numBathrooms;
    }

    public double getAnnualHoaFees() { return annualHoaFees; }
    public void setAnnualHoaFees(double annualHoaFees) { this.annualHoaFees = annualHoaFees; }
    public int getNumBedrooms() { return numBedrooms; }
    public void setNumBedrooms(int numBedrooms) { this.numBedrooms = numBedrooms; }
    public double getNumBathrooms() { return numBathrooms; }
    public void setNumBathrooms(double numBathrooms) { this.numBathrooms = numBathrooms; }

    @Override
    public String toString() {
        return super.toString() + "\nAnnual HOA Fees: " + annualHoaFees + "\nBedrooms: " + numBedrooms + "\nBathrooms: " + numBathrooms;
    }
}

Listing.java #

import java.util.ArrayList;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class Listing {
   
    private ArrayList<Property> properties;

    public Listing() {
        properties = new ArrayList<>();
    }

    public void loadProperties(String fileName) {
        try (BufferedReader br = new BufferedReader(new FileReader("listings.csv"))) {
            String line;
            while ((line = br.readLine()) != null) {
                String[] data = line.split(" ");
                if (data.length >= 6) {
                    String ID = data[0];
                    String location = data[1] + " " + data[2] + " " + data[3];
                    double price = Double.parseDouble(data[4]);

                    if (ID.startsWith("rp")) {
                        double annualHoaFees = Double.parseDouble(data[5]);
                        int numBedrooms = Integer.parseInt(data[6]);
                        double numBathrooms = Double.parseDouble(data[7]);
                        ResidentialProperty rp = new ResidentialProperty(ID, location, price, annualHoaFees, numBedrooms, numBathrooms);
                        properties.add(rp);
                    } else if (ID.startsWith("cp")) {
                        String zone = data[5];
                        int numUnits = Integer.parseInt(data[6]);
                        int numParkingSpots = Integer.parseInt(data[7]);
                        CommercialProperty cp = new CommercialProperty(ID, location, price, zone, numUnits, numParkingSpots);
                        properties.add(cp);
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public Property getProperty(String address) {
        for (Property prop : properties) {
            if (prop.getLocation().equals(address)) {
                return prop;
            }
        }
        return null;
    }
}

问题根源及修复方案 #

1. 文件读取路径错误（核心问题） #

Android应用无法直接通过new FileReader("listings.csv")读取根目录文件，必须将listings.csv放在项目的src/main/assets目录下，同时修改Listing类的文件读取逻辑：

import android.content.Context;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Listing {
    private ArrayList<Property> properties;
    private Context context;

    public Listing(Context context) {
        properties = new ArrayList<>();
        this.context = context;
    }

    public void loadProperties(String fileName) {
        try (BufferedReader br = new BufferedReader(new InputStreamReader(context.getAssets().open(fileName)))) {
            String line;
            // 跳过CSV表头（如果有表头的话）
            br.readLine();
            while ((line = br.readLine()) != null) {
                // 标准CSV用逗号分割，替换原有的空格分割
                String[] data = line.split(",");
                // 严格判断数据长度，避免数组越界
                if (data.length >= 8) {
                    String ID = data[0].trim();
                    String location = data[1].trim();
                    double price = Double.parseDouble(data[2].trim());

                    if (ID.startsWith("rp")) {
                        double annualHoaFees = Double.parseDouble(data[3].trim());
                        int numBedrooms = Integer.parseInt(data[4].trim());
                        double numBathrooms = Double.parseDouble(data[5].trim());
                        properties.add(new ResidentialProperty(ID, location, price, annualHoaFees, numBedrooms, numBathrooms));
                    } else if (ID.startsWith("cp")) {
                        String zone = data[3].trim();
                        int numUnits = Integer.parseInt(data[4].trim());
                        int numParkingSpots = Integer.parseInt(data[5].trim());
                        properties.add(new CommercialProperty(ID, location, price, zone, numUnits, numParkingSpots));
                    }
                }
            }
        } catch (IOException | NumberFormatException e) {
            e.printStackTrace();
        }
    }

    // 增加获取所有房产的方法，用于调试
    public ArrayList<Property> getProperties() {
        return properties;
    }

    public Property getProperty(String address) {
        for (Property prop : properties) {
            if (prop.getLocation().equals(address)) {
                return prop;
            }
        }
        return null;
    }
}

2. 修改MainActivity中Listing的初始化 #

// 在MainActivity的onCreate方法中
listing = new Listing(this);
listing.loadProperties("listings.csv");

3. 验证按钮文本与CSV数据的一致性 #

确保按钮上的文本和CSV文件中location字段完全一致（包括大小写、空格），同时在onClick中增加调试逻辑，定位问题：

import android.util.Log;

// 在MainActivity的onClick方法中
@Override
public void onClick(View view) {
    Button clickedButton = (Button) view;
    String location = clickedButton.getText().toString();
    Log.d("MainActivity", "当前点击按钮文本：" + location);
    
    Property property = listing.getProperty(location);

    if (property != null) {
        String priceText = "Price: $" + property.getPrice();
        Toast.makeText(this, priceText, Toast.LENGTH_SHORT).show();
    } else {
        Toast.makeText(this, "未找到对应房产", Toast.LENGTH_SHORT).show();
        // 打印所有已加载的房产地址，方便对比
        for (Property p : listing.getProperties()) {
            Log.d("MainActivity", "已加载地址：" + p.getLocation());
        }
    }
}

4. 修正CSV文件格式 #

使用标准CSV格式（逗号分割），示例如下：

rp001,123 Main St,500000,1200,3,2.0
cp001,456 Business Rd,1200000,Commercial,4,10

内容的提问来源于stack exchange，提问作者Burger290