Question

我一直在关注this教程，为我的Android应用程序执行SQLite的CRUD操作。这些是我的代码

ScheduleSQLiteHelper.java

package com.skery.letspark.database;


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

import com.skery.letspark.entities.Schedule;

import java.util.LinkedList;
import java.util.List;

public class ScheduleSQLiteHelper extends SQLiteOpenHelper {
    // Database version
    private static final int DATABASE_VERSION = 1;

    // Database name =
    private static final String DATABASE_NAME = "LetsParkDB";

    // Schedule table name
    private static final String TABLE_SCHEDULE = "Schedule";

    // Schedule table column names
    private static final String SCHEDULE_ID = "scheduleID";
    private static final String SCHEDULE_TIME = "scheduleTime";
    private static final String SCHEDULE_DATE = "scheduleDate";
    private static final String SCHEDULE_NAME = "scheduleName";
    private static final String SCHEDULE_DESC = "scheduleDesc";
    private static final String ROUTE_ID = "routeID";

    private static final String[] COLUMNS  = {SCHEDULE_ID, SCHEDULE_TIME, SCHEDULE_DATE, SCHEDULE_NAME, SCHEDULE_DESC
    , ROUTE_ID};

    public ScheduleSQLiteHelper(Context context){
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db){
        // SQL statement to create the schedule table
        String CREATE_SCHEDULE_TABLE = " CREATE TABLE Schedule ( " +
                "scheduleID INTEGER PRIMARY KEY AUTOINCREMENT, " +
                "scheduleTime TEXT, " +
                "scheduleDate TEXT, " +
                "scheduleName TEXT, " +
                "scheduleDesc TEXT, " +
                "routeID INTEGER )";

        // create schedule table
        db.execSQL(CREATE_SCHEDULE_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // Drop older schedule table if existed
        db.execSQL("DROP TABLE IF EXISTS Schedule");

        // Create fresh schedule table
        this.onCreate(db);
    }

    // add schedule
    public void addSchedule(Schedule schedule){
        // for logging
        Log.d("addSchedule", schedule.toString());

        // 1. get reference to writable DB
        SQLiteDatabase db = this.getWritableDatabase();

        // 2. create content values to add key column/value
        ContentValues values = new ContentValues();
        values.put(SCHEDULE_TIME, schedule.getScheduleTime());
        values.put(SCHEDULE_DATE, schedule.getScheduleDate());
        values.put(SCHEDULE_NAME, schedule.getScheduleName());
        values.put(SCHEDULE_DESC, schedule.getScheduleDescription());
        values.put(ROUTE_ID, schedule.getRouteId());

        // 3. insert
        db.insert(TABLE_SCHEDULE, //table
                    null, //nullColumnHack
                    values);

        // 4. close
        db.close();
    }

    // get schedule by id
    public Schedule getSchedule(int scheduleID){

        // 1. get reference to readable DB
        SQLiteDatabase db = this.getReadableDatabase();

        // 2. build query
        Cursor cursor =
                db.query(TABLE_SCHEDULE,
                        COLUMNS,
                        "scheduleID = ?",
                        new String[] {String.valueOf(scheduleID)},
                        null, // group by
                        null, // having
                        null, // order by
                        null); // limit

        // 3. navigate through results
        if(cursor!= null)
            cursor.moveToFirst();

        // 4. build schedule object
        Schedule schedule = new Schedule();
        schedule.setScheduleId(Integer.parseInt(cursor.getString(0)));
        schedule.setScheduleTime(cursor.getString(1));
        schedule.setScheduleDate(cursor.getString(2));
        schedule.setScheduleName(cursor.getString(3));
        schedule.setScheduleDescription(cursor.getString(4));
        schedule.setRouteId(Integer.parseInt(cursor.getString(5)));

        // log
        Log.d("getBook(" + scheduleID + ")", schedule.toString());

        return schedule;
    }

    // get all schedules
    public List<Schedule> getAllSchedules(){
        List<Schedule> schedules = new LinkedList<Schedule>();

        // 1. build query
        String query = "SELECT * FROM " + TABLE_SCHEDULE;

        // 2. get reference to writable db
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(query, null);

        // 3. go over each row, build book and add items to object
        Schedule schedule = null;
        if(cursor.moveToFirst()) {
            do{
                schedule = new Schedule();
                schedule.setScheduleId(Integer.parseInt(cursor.getString(0)));
                schedule.setScheduleTime(cursor.getString(1));
                schedule.setScheduleDate(cursor.getString(2));
                schedule.setScheduleName(cursor.getString(3));
                schedule.setScheduleDescription(cursor.getString(4));
                schedule.setRouteId(Integer.parseInt(cursor.getString(5)));

                // add schedule object to list
                schedules.add(schedule);
            } while (cursor.moveToNext());
        }

        Log.d("getAllSchedules()", schedules.toString());

        return schedules;
    }

    // update schedule
    public int updateSchedule(Schedule schedule){
        // 1. get reference to writable DB
        SQLiteDatabase db = this.getWritableDatabase();

        // 2. create contentvalues to add
        ContentValues values = new ContentValues();
        values.put("scheduleTime", schedule.getScheduleTime());
        values.put("scheduleDate", schedule.getScheduleDate());
        values.put("scheduleName", schedule.getScheduleName());
        values.put("scheduleDesc", schedule.getScheduleDescription());
        values.put("routeID", schedule.getRouteId());

        // 3. update row
        int i = db.update(TABLE_SCHEDULE, // table
         values, //
         SCHEDULE_ID+" = ?",
                new String[]{String.valueOf(schedule.getScheduleId())});

        // 4. close
        db.close();

        return i;
    }


}

安排实体，Schedule.java

package com.skery.letspark.entities;


public class Schedule {

private int scheduleId;
private String scheduleTime;
private String scheduleDate;
private String scheduleName;
private String scheduleDescription;
private int routeId;

public Schedule(){}

public Schedule(String scheduleTime, String scheduleDate, String scheduleName, String scheduleDescription, int routeId){
    super();
    this.scheduleTime = scheduleTime;
    this.scheduleDate = scheduleDate;
    this.scheduleName = scheduleName;
    this.scheduleDescription = scheduleDescription;
    this.routeId = routeId;
}

public int getScheduleId() {
    return scheduleId;
}

public void setScheduleId(int scheduleId) {
    this.scheduleId = scheduleId;
}

public String getScheduleTime() {
    return scheduleTime;
}

public void setScheduleTime(String scheduleTime) {
    this.scheduleTime = scheduleTime;
}

public String getScheduleDate() {
    return scheduleDate;
}

public void setScheduleDate(String scheduleDate) {
    this.scheduleDate = scheduleDate;
}

public String getScheduleName() {
    return scheduleName;
}

public void setScheduleName(String scheduleName) {
    this.scheduleName = scheduleName;
}

public String getScheduleDescription() {
    return scheduleDescription;
}

public void setScheduleDescription(String scheduleDescription) {
    this.scheduleDescription = scheduleDescription;
}

public int getRouteId() {
    return routeId;
}

public void setRouteId(int routeId) {
    this.routeId = routeId;
}
}

以及我如何在活动中执行它：

btnSaveSchedule.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // schedule items
            String scheduleName =  etScheduleName.getText().toString();
            String scheduleDesc = etScheduleDesc.getText().toString();
            String scheduleDate = Day + " " + selectedMonth + " " + Year;
            tpScheduleTime.clearFocus();
            int hour = tpScheduleTime.getCurrentHour();
            int minute = tpScheduleTime.getCurrentMinute();
            String scheduleTime = hour + ":" + minute;
            //int routeID = Integer.parseInt(tvAppliedRoute.getText().toString());

            int routeID = 12345;
            ScheduleSQLiteHelper db = new ScheduleSQLiteHelper(PlannerNewScheduleActivity.this);
            db.addSchedule(new Schedule(scheduleTime, scheduleDate, scheduleName, scheduleDesc,routeID));
        }
    });

但是，我的log cat中出现了一个java null指针异常。我尝试将db.open()添加到我的代码中，但它显示语法错误。任何澄清都会非常有用，谢谢！

Android SQLite添加操作空指针异常

0 个答案: