Java Android Studio-ClassCastException错误？

我想很快提到这是一个家庭作业，但我只是在寻找方向。我的教授以前没有应用过SQLite，所以他不确定该怎么做。该类正在执行SharedReference（我无法获取），但这是用于存储待办事项列表数据的另一个选项

现在，当我点击按钮“添加”AddDo类下的任务时，它抛出以下错误：

编辑：这是实际按钮的类。这是我的主要任务列表所在的位置，因为XML已经准备好接收数据，并且有一个用于添加新任务的按钮

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


    Button addMainTask = (Button) findViewById(R.id.addMainTask);

    addMainTask.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View view) {
            //This is being flagged as of now because the class type IS not Activity, but serializable.
            startActivity(new Intent(main.this, AddDo.class));

        }
    });

这是我的类，用于添加任务（这处于早期阶段）：

这是我的DBHandler：

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

import net.example.name.dotoday.AddDo;

import java.util.ArrayList;
import java.util.List;

public class DBHelper extends SQLiteOpenHelper {

    private static final String TAG = "DbHelper";

    // Database Info
    private static final String TheDB = "TheDB";
    private static final int DATABASE_VERSION = 1;

    //DB Table Names
    private static final String TABLE_ParentTask = "ParentTask";
    private static final String TABLE_SubTask = "SubTask";


    //ParentTask Table Columns
    private static final String parentIDColumn = "_parentID";
    private static final String taskTitleColumn = "_taskTitle";
    private static final String statusColumn = "_status";
    private static final String dueDateColumn = "_dueDate";
    private static final String completedColumn = "_completedTask"; //When completion is 100%
    private static final String calculatedProgressColumn = "_calculatedProgress"; //LONG VALUE WHEN CONVERTED.

    //SubTask Table Columns
    private static final String foreignkeyColumn = "_foreignkey";
    private static final String childIDColumn = "_childID";
    private static final String subTaskDescColumn = "_subTaskDesc";
    private static final String subCompletedColumn = "_subCompleted"; // BOOL for individual tasks -- may not be implemented


    /*  -- Here comes the real fun, ya'll! -- */

    private static DBHelper mDbHelper;


    public static synchronized DBHelper getInstance(Context context) {
        // Use the application context, which will ensure that you
        // don't accidentally leak an Activity's context.

        if (mDbHelper == null) {
            mDbHelper = new DBHelper(context.getApplicationContext());
        }
        return mDbHelper;
    }


    /**
     * Constructor should be private to prevent direct instantiation.
     * Make a call to the static method "getInstance()" instead.
     */
    private DBHelper(Context context) {
        super(context, TheDB, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_ParentTask_TABLE = "CREATE TABLE " + TABLE_ParentTask +
                "(" +
                parentIDColumn + " INTEGER PRIMARY KEY ," +
                taskTitleColumn + " TEXT," +
                statusColumn + " BOOL," +
                dueDateColumn+ " TEXT," +
                completedColumn + " BOOL," +
                calculatedProgressColumn + " REAL" +
                ")";

        //CREATE THE PHYSICAL TABLE
        db.execSQL(CREATE_ParentTask_TABLE);

        /*String CREATE_SubTask_TABLE = "CREATE TABLE " + TABLE_SubTask +
                "(" +
                childID + " INTEGER PRIMARY KEY ," +
                foreignkey + " INT," +
                subTaskDesc + " TEXT," +
                subCompleted + " BOOL" +
                ")";

        //CREATE THE PHYSICAL TABLE
        db.execSQL(CREATE_SubTask_TABLE);*/
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        if (oldVersion != newVersion) {
            // Simplest implementation is to drop all old tables and recreate them
            db.execSQL("DROP TABLE IF EXISTS " + TABLE_ParentTask);
            db.execSQL("DROP TABLE IF EXISTS " + TABLE_SubTask);

            onCreate(db);
        }
    }

    public void insertTaskDetails(AddDo userData) {

        SQLiteDatabase db = getWritableDatabase();

        db.beginTransaction();

        try {
            ContentValues values = new ContentValues();
            values.put(parentIDColumn, userData.doParentID);
            values.put(taskTitleColumn, userData.doTaskTitle);
            values.put(statusColumn, userData.doStatus);
            values.put(dueDateColumn, userData.doDueDate);
            values.put(completedColumn, userData.doCompletedTask);
            values.put(calculatedProgressColumn, userData.doCalculatedProgress);

            db.insertOrThrow(TABLE_ParentTask, null, values);
            db.setTransactionSuccessful();
        } catch (SQLException e) {
            e.printStackTrace();
            Log.d(TAG, "Error while trying to add post to database");
        } finally {

            db.endTransaction();
        }


    }

   /*
   fetch all data from UserTable
    */

    public List<AddDo> getAllMainTasks() {

        List<AddDo> usersdetail = new ArrayList<>();

        String USER_DETAIL_SELECT_QUERY = "SELECT * FROM " + TABLE_ParentTask;

        SQLiteDatabase db = getReadableDatabase();
        Cursor cursor = db.rawQuery(USER_DETAIL_SELECT_QUERY, null);

        try {
            if (cursor.moveToFirst()) {
                do {
                    AddDo userData = new AddDo();
                    userData.doParentID = cursor.getString(cursor.getColumnIndex(parentIDColumn));
                    userData.doTaskTitle = cursor.getString(cursor.getColumnIndex(taskTitleColumn));
                    userData.doStatus = cursor.getString(cursor.getColumnIndex(statusColumn));
                    userData.doDueDate = cursor.getString(cursor.getColumnIndex(dueDateColumn));
                    userData.doCompletedTask = cursor.getString(cursor.getColumnIndex(completedColumn));
                    userData.doCalculatedProgress = cursor.getString(cursor.getColumnIndex(calculatedProgressColumn));

                    usersdetail.add(userData);

                } while (cursor.moveToNext());
            }
        } catch (Exception e) {
            Log.d(TAG, "Error while trying to get posts from database");
        } finally {
            if (cursor != null && !cursor.isClosed()) {
                cursor.close();
            }
        }

        return usersdetail;

    }

    /*
   Delete single row from ParentTask
     */
    void deleteRow(String name) {
        SQLiteDatabase db = getWritableDatabase();


        try {
            db.beginTransaction();
            db.execSQL("delete from " + TABLE_ParentTask + " where parentid ='" + parentIDColumn + "'");
            db.setTransactionSuccessful();
        } catch (SQLException e) {
            Log.d(TAG, "Error while trying to delete task detail");
        } finally {
            db.endTransaction();
        }


    }
}

导入android.content.ContentValues；
导入android.content.Context；
导入android.database.Cursor；
导入android.database.SQLException；
导入android.database.sqlite.SQLiteDatabase；
导入android.database.sqlite.SQLiteOpenHelper；
导入android.util.Log；
导入net.example.name.dotoday.AddDo；
导入java.util.ArrayList；
导入java.util.List；
公共类DBHelper扩展了SQLiteOpenHelper{
私有静态最终字符串TAG=“DbHelper”；
//数据库信息
私有静态最终字符串TheDB=“TheDB”；
私有静态最终int数据库_VERSION=1；
//数据库表名
私有静态最终字符串表\u ParentTask=“ParentTask”；
私有静态最终字符串表_SubTask=“SubTask”；
//ParentTask表列
私有静态最终字符串parentIDColumn=“\u parentID”；
私有静态最终字符串taskTitleColumn=“\u taskTitle”；
私有静态最终字符串statusColumn=“\u status”；
私有静态最终字符串dueDateColumn=“\u dueDate”；
私有静态最终字符串completedColumn=“\u completedTask”//完成为100%时
私有静态最终字符串calculatedProgressColumn=“\u calculatedProgress”//转换时的长值。
//子任务表列
私有静态最终字符串foreignkeyColumn=“\u foreignkey”；
私有静态最终字符串childIDColumn=“\u childID”；
私有静态最终字符串subtaskdescolumn=“_subTaskDesc”；
私有静态最终字符串subCompletedColumn=“\u subCompleted”//BOOL用于单个任务--可能未实现
/*——真正的乐趣来了，你会的！——*/
私有静态DBHelper-mDbHelper；
公共静态同步DBHelper getInstance（上下文）{
//使用应用程序上下文，这将确保
//不要意外泄露活动的上下文。
如果（mDbHelper==null）{
mDbHelper=new DBHelper（context.getApplicationContext（））；
}
返回mDbHelper；
}
/**
*构造函数应该是私有的，以防止直接实例化。
*改为调用静态方法“getInstance（）”。
*/
私有DBHelper（上下文）{
super（上下文，TheDB，null，数据库版本）；
}
@凌驾
public void onCreate（SQLiteDatabase db）{
字符串CREATE\u ParentTask\u TABLE=“CREATE TABLE”+TABLE\u ParentTask+
"(" +
parentIDColumn+“整数主键，”+
taskTitleColumn+“文本，”+
statusColumn+“BOOL，”+
dueDateColumn+“文本，”+
completedColumn+“BOOL，”+
calculatedProgressColumn+“REAL”+
")";
//创建物理表
execSQL（创建父任务表）；
/*字符串CREATE_SubTask_TABLE=“CREATE TABLE”+TABLE_SubTask+
"(" +
childID+“整数主键，”+
外键+“INT，”+
subTaskDesc+“文本，”+
子完成+“BOOL”+
")";
//创建物理表
execSQL（创建子任务表）*/
}
@凌驾
public void onUpgrade（SQLiteDatabase db，int-oldVersion，int-newVersion）{
如果（旧版本！=新版本）{
//最简单的实现是删除所有旧表并重新创建它们
db.execSQL（“如果存在删除表”+表\u ParentTask）；
db.execSQL（“如果存在删除表”+表_子任务）；
onCreate（db）；
}
}
public void insertTaskDetails（AddDo userData）{
SQLiteDatabase db=getWritableDatabase（）；
db.beginTransaction（）；
试一试{
ContentValues=新的ContentValues（）；
value.put（parentIDColumn，userData.doParentID）；
value.put（tasktilecolumn，userData.doTaskTitle）；
value.put（statusColumn，userData.doStatus）；
value.put（dueDateColumn，userData.doDueDate）；
value.put（completedColumn、userData.doccompletedtask）；
value.put（calculatedProgressColumn，userData.doCalculatedProgress）；
db.insertOrThrow（表_ParentTask，null，值）；
db.setTransactionSuccessful（）；
}捕获（SQLE异常）{
e、 printStackTrace（）；
Log.d（标记“尝试将post添加到数据库时出错”）；
}最后{
db.endTransaction（）；
}
}
/*
从UserTable获取所有数据
*/
公共列表getAllMainTasks（）{
List usersdetail=new ArrayList（）；
字符串USER\u DETAIL\u SELECT\u QUERY=“SELECT*FROM”+表\u ParentTask；
SQLiteDatabase db=getReadableDatabase（）；
Cursor Cursor=db.rawQuery（用户详细信息选择查询，空）；
试一试{
if（cursor.moveToFirst（））{
做{
AddDo userData=new AddDo（）；
userData.doParentID=cursor.getString（cursor.getColumnIndex（parentIDColumn））；
userData.doTaskTitle=cursor.getString（cursor.getColumnIndex（taskTitleColumn））；
userData.doStatus=cursor.getString（cursor.getColumnIndex（statusColumn））；
userData.doDueDate=cursor.getString（cursor.getColu
    package net.example.name.dotoday;

import java.io.Serializable;

public class AddDo implements Serializable {

    //This is what will be transferred to the actual DB when I make a task.
    public String doParentID, doTaskTitle, doStatus, doDueDate, doCompletedTask, doCalculatedProgress = "";

}

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

import net.example.name.dotoday.AddDo;

import java.util.ArrayList;
import java.util.List;

public class DBHelper extends SQLiteOpenHelper {

    private static final String TAG = "DbHelper";

    // Database Info
    private static final String TheDB = "TheDB";
    private static final int DATABASE_VERSION = 1;

    //DB Table Names
    private static final String TABLE_ParentTask = "ParentTask";
    private static final String TABLE_SubTask = "SubTask";


    //ParentTask Table Columns
    private static final String parentIDColumn = "_parentID";
    private static final String taskTitleColumn = "_taskTitle";
    private static final String statusColumn = "_status";
    private static final String dueDateColumn = "_dueDate";
    private static final String completedColumn = "_completedTask"; //When completion is 100%
    private static final String calculatedProgressColumn = "_calculatedProgress"; //LONG VALUE WHEN CONVERTED.

    //SubTask Table Columns
    private static final String foreignkeyColumn = "_foreignkey";
    private static final String childIDColumn = "_childID";
    private static final String subTaskDescColumn = "_subTaskDesc";
    private static final String subCompletedColumn = "_subCompleted"; // BOOL for individual tasks -- may not be implemented


    /*  -- Here comes the real fun, ya'll! -- */

    private static DBHelper mDbHelper;


    public static synchronized DBHelper getInstance(Context context) {
        // Use the application context, which will ensure that you
        // don't accidentally leak an Activity's context.

        if (mDbHelper == null) {
            mDbHelper = new DBHelper(context.getApplicationContext());
        }
        return mDbHelper;
    }


    /**
     * Constructor should be private to prevent direct instantiation.
     * Make a call to the static method "getInstance()" instead.
     */
    private DBHelper(Context context) {
        super(context, TheDB, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_ParentTask_TABLE = "CREATE TABLE " + TABLE_ParentTask +
                "(" +
                parentIDColumn + " INTEGER PRIMARY KEY ," +
                taskTitleColumn + " TEXT," +
                statusColumn + " BOOL," +
                dueDateColumn+ " TEXT," +
                completedColumn + " BOOL," +
                calculatedProgressColumn + " REAL" +
                ")";

        //CREATE THE PHYSICAL TABLE
        db.execSQL(CREATE_ParentTask_TABLE);

        /*String CREATE_SubTask_TABLE = "CREATE TABLE " + TABLE_SubTask +
                "(" +
                childID + " INTEGER PRIMARY KEY ," +
                foreignkey + " INT," +
                subTaskDesc + " TEXT," +
                subCompleted + " BOOL" +
                ")";

        //CREATE THE PHYSICAL TABLE
        db.execSQL(CREATE_SubTask_TABLE);*/
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        if (oldVersion != newVersion) {
            // Simplest implementation is to drop all old tables and recreate them
            db.execSQL("DROP TABLE IF EXISTS " + TABLE_ParentTask);
            db.execSQL("DROP TABLE IF EXISTS " + TABLE_SubTask);

            onCreate(db);
        }
    }

    public void insertTaskDetails(AddDo userData) {

        SQLiteDatabase db = getWritableDatabase();

        db.beginTransaction();

        try {
            ContentValues values = new ContentValues();
            values.put(parentIDColumn, userData.doParentID);
            values.put(taskTitleColumn, userData.doTaskTitle);
            values.put(statusColumn, userData.doStatus);
            values.put(dueDateColumn, userData.doDueDate);
            values.put(completedColumn, userData.doCompletedTask);
            values.put(calculatedProgressColumn, userData.doCalculatedProgress);

            db.insertOrThrow(TABLE_ParentTask, null, values);
            db.setTransactionSuccessful();
        } catch (SQLException e) {
            e.printStackTrace();
            Log.d(TAG, "Error while trying to add post to database");
        } finally {

            db.endTransaction();
        }


    }

   /*
   fetch all data from UserTable
    */

    public List<AddDo> getAllMainTasks() {

        List<AddDo> usersdetail = new ArrayList<>();

        String USER_DETAIL_SELECT_QUERY = "SELECT * FROM " + TABLE_ParentTask;

        SQLiteDatabase db = getReadableDatabase();
        Cursor cursor = db.rawQuery(USER_DETAIL_SELECT_QUERY, null);

        try {
            if (cursor.moveToFirst()) {
                do {
                    AddDo userData = new AddDo();
                    userData.doParentID = cursor.getString(cursor.getColumnIndex(parentIDColumn));
                    userData.doTaskTitle = cursor.getString(cursor.getColumnIndex(taskTitleColumn));
                    userData.doStatus = cursor.getString(cursor.getColumnIndex(statusColumn));
                    userData.doDueDate = cursor.getString(cursor.getColumnIndex(dueDateColumn));
                    userData.doCompletedTask = cursor.getString(cursor.getColumnIndex(completedColumn));
                    userData.doCalculatedProgress = cursor.getString(cursor.getColumnIndex(calculatedProgressColumn));

                    usersdetail.add(userData);

                } while (cursor.moveToNext());
            }
        } catch (Exception e) {
            Log.d(TAG, "Error while trying to get posts from database");
        } finally {
            if (cursor != null && !cursor.isClosed()) {
                cursor.close();
            }
        }

        return usersdetail;

    }

    /*
   Delete single row from ParentTask
     */
    void deleteRow(String name) {
        SQLiteDatabase db = getWritableDatabase();


        try {
            db.beginTransaction();
            db.execSQL("delete from " + TABLE_ParentTask + " where parentid ='" + parentIDColumn + "'");
            db.setTransactionSuccessful();
        } catch (SQLException e) {
            Log.d(TAG, "Error while trying to delete task detail");
        } finally {
            db.endTransaction();
        }


    }
}

Unable to instantiate activity 
ComponentInfo{net.example.name.dotoday/net.name.example.dotoday.AddDo}:
java.lang.ClassCastException: net.example.name.dotoday.AddDo cannot be cast to android.app.Activity 

Android is unable to create an object of Activity , 
the reason is related with AddDo class 
android can't convert AddDo class to Activity because AddDo is not a child of
Activity but android need an activity parent-child relationship 
between AddDo and Activity 

class Addo  extends AppCompactActivity

class Data implements Serializable 
{
 public String doParentID, doTaskTitle, doStatus, doDueDate, doCompletedTask, doCalculatedProgress = "";

  public Data (){} // suitable default and parameterized constructor  

  .. fields and getter and setters
}

public class AddDo extends Activity implements Serializable {