多列 ListView 显示零而不是数据库值

Question

I'm making a speedometer app in android studio and everytime the user goes over the saved speed limit his current speed, longitude, latitude and time should be stored in a database. The user would then be able to view the entries in a list. I've created everythinf but the listview(which has 4 columns using an adapter) only shows zeros instead of the database values.

DATABASE HELPER

package com.mortoglou.speedometer;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

import android.database.sqlite.SQLiteOpenHelper;

import androidx.annotation.Nullable;

public class DatabaseHelper extends SQLiteOpenHelper {
    public static final String DATABASE_NAME = "limits_list_final.db";
    public static final String TABLE_NAME = "limits_list";
    public static final String COL1 = "ID";
    public static final String COL2 = "SPEED";
    public static final String COL3 = "LONGITUDE";
    public static final String COL4 = "LATITUDE";
    public static final String COL5 = "TIMESTAMP";


    public DatabaseHelper(@Nullable Context context) {
        super(context, DATABASE_NAME, null, 3);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTable = "CREATE TABLE " + TABLE_NAME + " (ID INTEGER PRIMARY KEY AUTOINCREMENT, " +
                " SPEED TEXT, LONGITUDE TEXT, LATITUDE TEXT, TIMESTAMP TEXT)";
        db.execSQL(createTable);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS TABLE_NAME");
        onCreate(db);
    }

    public boolean addData(float curSpeed, double longitude, double latitude, long timestamp){
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(COL2, curSpeed);
        contentValues.put(COL3, longitude);
        contentValues.put(COL4, latitude);
        contentValues.put(COL5, timestamp);


        long result = db.insert(TABLE_NAME, null, contentValues);
        if (result == -1) {
            return false;
        } else {
            return true;
        }
    }

    public Cursor getListContents(){
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor data = db.rawQuery("SELECT * FROM " + TABLE_NAME, null);
        return data;
    }

}

MAIN ACTIVITY

'package com.mortoglou.speedometer;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.pm.PackageManager;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
import android.Manifest;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements LocationListener, PopUP.PopUpListener {

    private TextView textView;
    private String savedSpeedText;
    private Button updateSpeedButton;
    private Button checkLimits;

    DatabaseHelper myDB;

    public double longi;
    public int ch = 1; //choice
    public float savedSpeed;
    public static final String SHARED_PREFS = "sharedprefs";
    public static final String SAVED_SPEED = "savedspeed";

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

        textView = (TextView) findViewById(R.id.textView5);
        updateSpeedButton = (Button) findViewById(R.id.button);
        checkLimits = (Button) findViewById(R.id.button2);

        myDB = new DatabaseHelper(this);

        updateSpeedButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                popUp();


            }
        });

        checkLimits.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //setContentView(R.layout.speed_limits);
                Intent intent = new Intent(MainActivity.this, LimitsList.class);
                startActivity(intent);
            }
        });

        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.ACCESS_FINE_LOCATION)
                != PackageManager.PERMISSION_GRANTED) {

            int MY_PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION = 0;
            ActivityCompat.requestPermissions(this,
                    new String[]{Manifest.permission.ACCESS_FINE_LOCATION},
                    MY_PERMISSIONS_REQUEST_ACCESS_FINE_LOCATION);
        }

        LocationManager lm = (LocationManager) this.getSystemService(Context.LOCATION_SERVICE);
        lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);

        // this.onLocationChanged(null);
        //savedSpeed();
        loadSpeed();
        updateSpeed();
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.speed_menu, menu);
        return true;
    }


    @Override
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {

        switch (item.getItemId()) {
            case R.id.speed1:
                ch = 1; // choice 1 = m/s
                return true;
            case R.id.speed2:
                ch = 2; // choice 2 = km/h
                return true;
        }
        return super.onOptionsItemSelected(item);
    }


    @Override
    public void onLocationChanged(Location location) {

        TextView txt = (TextView) this.findViewById(R.id.textView2);
        float curSpeed = location.getSpeed();
        double longitude = location.getLongitude();
        double latitude = location.getLatitude();
        long timestamp = location.getTime();

        if (location == null) {
            txt.setText("NO LOCATION FOUND");
        } else {
            if (curSpeed > 0) {
                if (ch == 1) {
                    txt.setText(String.format(curSpeed + "m/s"));

                } else if (ch == 2) {
                    txt.setText(String.format(curSpeed * 3.6 + "km/h"));
                }
            } else {
                txt.setText("-");
            }
            speedLimit(curSpeed, longi, latitude, timestamp);
        }


    }

    public void savedSpeed() {
        SharedPreferences sharedPreferences = getSharedPreferences(SHARED_PREFS, MODE_PRIVATE);
        SharedPreferences.Editor editor = sharedPreferences.edit();

        editor.putFloat(SAVED_SPEED, savedSpeed);
        editor.apply();

    }

    public void loadSpeed() {
        SharedPreferences sharedPreferences = getSharedPreferences(SHARED_PREFS, MODE_PRIVATE);

        savedSpeedText = String.valueOf(sharedPreferences.getFloat(SAVED_SPEED, 0));

    }

    public void updateSpeed() {
        textView.setText(savedSpeedText);

    }

    public void popUp() {
        PopUP popUP = new PopUP();
        popUP.show(getSupportFragmentManager(), "pop up");
    }

    public void speedLimit(float curSpeed, double longitude, double latitude, long timestamp) {
        if (curSpeed > savedSpeed) {
            Toast.makeText(this, "Ayo you goin too fast", Toast.LENGTH_SHORT).show();
            AddData(curSpeed, longi, latitude, timestamp);

        }

    }


    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {

    }

    @Override
    public void onProviderEnabled(String provider) {

    }

    @Override
    public void onProviderDisabled(String provider) {

    }

    @Override
    public void passText(float speedText) {
        savedSpeed = speedText;
        savedSpeed();
        loadSpeed();
        updateSpeed();
    }

    public void AddData(float curSpeed, double longitude, double latitude, long time) {
        boolean insertData = myDB.addData(curSpeed, longitude, latitude, time);

        if (insertData == true) {
            Toast.makeText(MainActivity.this, "Successfully Entered Data!", Toast.LENGTH_LONG).show();
        } else {
            Toast.makeText(MainActivity.this, "Something went wrong :(.", Toast.LENGTH_LONG).show();
        }
    }
}

(to view content)

    package com.mortoglou.speedometer;

import android.database.Cursor;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.Toast;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import java.util.ArrayList;

public class LimitsList extends AppCompatActivity {

    DatabaseHelper myDB;
    ArrayList<Entry> entryList;
    ListView listView;
    Entry entry;


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

        //listView = (ListView) findViewById(R.id.limits_list);
        myDB = new DatabaseHelper(this);

        //populate an ArrayList<String> from the database and then view it
        entryList = new ArrayList<>();
        Cursor data = myDB.getListContents();
        if (data.getCount() == 0) {
            Toast.makeText(this, "There are no contents in this list!", Toast.LENGTH_LONG).show();
        } else {
            int i=0;
            while(data.moveToNext()){
                entry = new Entry(data.getFloat(1),data.getDouble(2),data.getDouble(3), data.getLong(4));
                entryList.add(entry);
                //System.out.println(data.getFloat(1)+" "+data.getDouble(2)+" "+data.getDouble(3), data.getLong(4));
                System.out.println(entryList.get(i).getSpeed());
                i++;
            }
            LimitsAdapter adapter = new LimitsAdapter(this, R.layout.final_list_adapter, entryList);
            listView = findViewById(R.id.limits_list);
            listView.setAdapter(adapter);
        }
    }
}

ENTRY

    package com.mortoglou.speedometer;

public class Entry {

    private float Speed;
    private double Longitude;
    private double Latitude;
    private long Time;



    public Entry(float speed, double longitude, double latitude, long time){
        speed = Speed;
        longitude = Longitude;
        latitude = Latitude;
        time = Time;
    }

    public float getSpeed() {
        return Speed;
    }

    public void setSpeed(float speed) {
        Speed = speed;
    }

    public double getLongitude() {
        return Longitude;
    }

    public void setLongitude(double longitude) {
        Longitude = longitude;
    }

    public double getLatitude() {
        return Latitude;
    }

    public void setLatitude(double latitude) {
        Latitude = latitude;
    }

    public long getTime() {
        return Time;
    }

    public void setTime(long time) {
        Time = time;
    }
}

ADAPTER

    package com.mortoglou.speedometer;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

import java.util.ArrayList;

public class LimitsAdapter extends ArrayAdapter<Entry> {

    private LayoutInflater mInflater;
    private ArrayList<Entry> entries;
    private int mViewResourceId;


    public LimitsAdapter(Context context, int textViewResourceId, ArrayList<Entry> entries) {
        super(context, textViewResourceId, entries);
        this.entries = entries;
        mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        mViewResourceId = textViewResourceId;
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        convertView = mInflater.inflate(mViewResourceId, null);

        Entry entry = entries.get(position);


        TextView speed = (TextView) convertView.findViewById(R.id.speed);
        TextView longitude = (TextView) convertView.findViewById(R.id.longitude);
        TextView latitude = (TextView) convertView.findViewById(R.id.latitude);
        TextView timestamp = (TextView) convertView.findViewById(R.id.timestamp);
        speed.setText(Float.toString(entry.getSpeed()));
        longitude.setText(Double.toString((entry.getLongitude())));
        latitude.setText(Double.toString((entry.getLatitude())));
        timestamp.setText(Long.toString(entry.getTime()));


        return convertView;
    }

}

Answer 1

I believe your issue is with the constructor for the Entry object.

You have :-

public Entry(float speed, double longitude, double latitude, long time){
    speed = Speed;
    longitude = Longitude;
    latitude = Latitude;
    time = Time;
}

which is setting/overwriting the values passed to the constructor with the values held in the Object's variables which will be the default value (0) for the type of the variable, as no value has been assigned.

• Default Values

  It's not always necessary to assign a value when a field is declared. Fields that are declared but not initialized will be set to a reasonable default by the compiler. Generally speaking, this default will be zero or null, depending on the data type. Relying on such default values, however, is generally considered bad programming style.

  The following chart summarizes the default values for the above data types.

   Data Type Default Value (for fields) byte 0 short 0 int 0 long 0L float 0.0f double 0.0d char '\' String (or any object) null boolean false

  Primitive Data Types

You should be setting the Object's variables with the values passed. So use :-

public Entry(float speed, double longitude, double latitude, long time){
    Speed = speed;
    Longitude = longitude;
    Latitude = latitude;
    Time = time;
}