无法使用SQLite数据库查询填充ListView

Question

我是Android开发的完整新手。我的目的是创建一个应用程序，该应用将用EditText收集的用户输入存储到SQLite数据库中，然后将其显示为Next Activity作为listView。还涉及一些按钮，其中一些是多余的，因为该应用仍处于早期阶段。

构建Gradle时，没有错误，logcat似乎对整个事情都完全可以。麻烦的第一个迹象是检查不包括任何.db文件或数据库目录的/data/data/[projectname]文件夹。我已经设法使活动之间的过渡完美无缺，但是由于我的项目中没有数据库，所以没有任何数据库可以填充ListView。

我正在寻求一些帮助确定我的代码问题。

主动脉：

package com.example.peroalex.trackofworkinghours;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
public class MainActivity extends AppCompatActivity {
    MyDatabaseHelper databaseHelper;
    Button ADD, DISPLAY, DELETE, MODIFY;
    EditText DESCRIPTION, LOCATION, START, FINISH, COMMENT, ID;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ADD = (Button) findViewById(R.id.addButton);
        DISPLAY = (Button) findViewById(R.id.displayButton);
        DELETE = (Button) findViewById(R.id.deleteButton);
        MODIFY = (Button) findViewById(R.id.modifyButton);
        DESCRIPTION = (EditText) findViewById(R.id.descriptionEdit);
        LOCATION = (EditText) findViewById(R.id.locationEdit);
        START = (EditText) findViewById(R.id.startEdit);
        FINISH = (EditText) findViewById(R.id.finishEdit);
        COMMENT = (EditText) findViewById(R.id.commentEdit);
        ID = (EditText) findViewById(R.id.idEdit);
        databaseHelper = new MyDatabaseHelper(this, null, null, 1);
        ADD.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                databaseAddData();
            }
        });
    }
    public void databaseAddData() {
        String addDSC = DESCRIPTION.getText().toString();
        String addLOC = LOCATION.getText().toString();
        String addSTR = START.getText().toString();
        String addFNS = FINISH.getText().toString();
        String addCOM = COMMENT.getText().toString();
        databaseHelper.addData(addDSC, addLOC, addSTR, addFNS, addCOM);
    }
    public void Action (View view) {
        Intent intent = new Intent(MainActivity.this, showRecords.class);
        startActivity(intent);
    }
}

mydatabasehelper：

package com.example.peroalex.trackofworkinghours;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
/**
 * Created by peroalex on 4/1/18.
 */
public class MyDatabaseHelper extends SQLiteOpenHelper {
    //Define database properties
    private static final int database_version = 1;
    private static final String database_name = "DatabaseRecords.db";
    private static final String table_name = "tasks";
    private static final String column_id = "_id";
    private static final String column_desc = "description";
    private static final String column_loc = "location";
    private static final String column_strt = "start";
    private static final String column_fnsh = "finish";
    private static final String column_comm = "comment";

    public MyDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
    super(context, database_name, factory, database_version);
    }
    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
    //This code will be executed when creating a database, it includes the SQLite query which initiates a table
    String query = " CREATE TABLE " + table_name + " ( "
            + column_id + " INTEGER PRIMARY KEY AUTOINCREMENT, "
            + column_desc + " TEXT "
            + column_loc + " TEXT "
            + column_strt + " TEXT "
            + column_fnsh + " TEXT "
            + column_comm + " TEXT " + ");";
    sqLiteDatabase.execSQL(query);
    }

    //This method is used for deleting data according to given ID
    public void removeData(Integer ID) {
    SQLiteDatabase sqLiteDatabase = getWritableDatabase();
    sqLiteDatabase.execSQL("DELETE FROM " + table_name + " WHERE " + column_id + " = " + ID + ";");
    sqLiteDatabase.close();
    }
    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
    sqLiteDatabase.execSQL("DROP TABLE IF EXISTS " + table_name);
    onCreate(sqLiteDatabase);
    }
    //This method is used for adding data to the SQLite database
    public void addData(String dsc, String loc, String st, String fi, String comm) {
    SQLiteDatabase sqLiteDatabase = getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(column_desc, dsc);
    values.put(column_loc, loc);
    values.put(column_strt, st);
    values.put(column_fnsh, fi);
    values.put(column_comm, comm);
    sqLiteDatabase.insert(table_name, null, values);
    sqLiteDatabase.close();
    }
    public Cursor getData() {
    SQLiteDatabase sqLiteDatabase = this.getWritableDatabase();
    Cursor data = sqLiteDatabase.rawQuery("SELECT * FROM " + table_name, null);
    return data;
    }
}

showRecords：

package com.example.peroalex.trackofworkinghours;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import java.util.ArrayList;

/**
 * Created by peroalex on 4/2/18.
 */
public class showRecords extends AppCompatActivity {
    ListView listView;
    MyDatabaseHelper myDatabaseHelper;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_show_records);
    listView = (ListView) findViewById(R.id.displayDBListview);
    myDatabaseHelper = new MyDatabaseHelper(this, null, null, 1);
    displayDB();
    }
    public void displayDB() {
    Cursor data = myDatabaseHelper.getData();
    ArrayList<String> listData = new ArrayList<>();
    while (data.moveToNext()) {
        listData.add(data.getString(1));
    }
    ListAdapter adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, listData);
    listView.setAdapter(adapter);
    }
}

activity_main：

    <?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.peroalex.trackofworkinghours.MainActivity">
    <EditText
    android:id="@+id/descriptionEdit"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:drawableStart="@drawable/ic_description_black_24dp"
    android:ems="10"
    android:fontFamily="serif"
    android:hint="@string/description"
    android:inputType="text"
    android:textAlignment="center"
    android:textSize="16sp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.052" />
    <EditText
    android:id="@+id/locationEdit"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:drawableStart="@drawable/ic_location_on_black_24dp"
    android:ems="10"
    android:fontFamily="serif"
    android:hint="@string/location"
    android:inputType="text"
    android:textAlignment="center"
    android:textSize="16sp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.14" />
    <EditText
    android:id="@+id/startEdit"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:drawableStart="@drawable/ic_work_black_24dp"
    android:ems="10"
    android:fontFamily="serif"
    android:hint="@string/start"
    android:inputType="time"
    android:textAlignment="center"
    android:textSize="16sp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.249" />
    <EditText
    android:id="@+id/finishEdit"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:drawableStart="@drawable/ic_work_black_24dp"
    android:ems="10"
    android:fontFamily="serif"
    android:hint="@string/finish"
    android:inputType="time"
    android:textAlignment="center"
    android:textSize="16sp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.337" />
    <EditText
    android:id="@+id/commentEdit"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:drawableStart="@drawable/ic_comment_black_24dp"
    android:ems="10"
    android:fontFamily="serif"
    android:hint="@string/comments"
    android:inputType="textMultiLine"
    android:textAlignment="center"
    android:textSize="16sp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.448" />
    <Button
    android:id="@+id/addButton"
    style="@android:style/Widget.Holo.Button"
    android:layout_width="90sp"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:text="@string/add"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.297"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.628" />
    <Button
    android:id="@+id/deleteButton"
    style="@android:style/Widget.Holo.Button.Borderless"
    android:layout_width="80sp"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:text="@string/delete"
    android:textColor="@android:color/black"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.291"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.934" />
    <Button
    android:id="@+id/displayButton"
    style="@android:style/Widget.Holo.Button"
    android:layout_width="90sp"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:text="@string/display"
    android:onClick="Action"
    android:textColor="@android:color/white"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.702"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.628" />
    <Button
    android:id="@+id/modifyButton"
    style="@android:style/Widget.Holo.Button.Borderless"
    android:layout_width="80sp"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:text="@string/modify"
    android:textColor="@android:color/black"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintHorizontal_bias="0.708"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.934" />
    <TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:text="@string/insert_an_id_to_either_modify_or_delete_the_query"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.731" />
    <EditText
    android:id="@+id/idEdit"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    android:ems="10"
    android:drawableStart="@drawable/ic_update_black_24dp"
    android:fontFamily="serif"
    android:hint="@string/id"
    android:inputType="text"
    android:textAlignment="center"
    android:textSize="16sp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    app:layout_constraintVertical_bias="0.829" />
</android.support.constraint.ConstraintLayout>

activity_show_records：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <ListView
    android:id="@+id/displayDBListview"
    android:layout_width="344dp"
    android:layout_height="551dp"
    android:layout_marginBottom="8dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

Answer 1

创建数据库的查询不正确。您忘记了在TEXT之后添加,，因此您的数据库从未创建。看看下面的代码

String query = " CREATE TABLE " + table_name + " ("
    + column_id + " INTEGER PRIMARY KEY AUTOINCREMENT, "
    + column_desc + " TEXT,"
    + column_loc + " TEXT,"
    + column_strt + " TEXT,"
    + column_fnsh + " TEXT,"
    + column_comm + " TEXT" + ");";
    sqLiteDatabase.execSQL(query);
}