如何从列表视图中从 sqlite 检索数据单击并查看不同的活动 android studio

Question

我是 android studio 的新手，我正在尝试制作一个出勤移动应用程序，其中： - 我可以添加学生并查看添加的学生列表 - 添加事件并查看添加的事件列表 - 在我有一个微调器、自动完成文本视图和一个按钮的地方添加出勤率。在微调器上，事件名称是从 SQLite 数据库表中检索的。在自动完成文本视图中，学生的姓氏也在 SQLite DB 中的表中检索。

我的问题是我不知道如何查看出席该活动的学生名单。当我单击事件列表视图时，我希望它这样做，新活动将打开并显示所有在场的学生。

我的学生表有 StudentID（主键、自动增量）、姓氏、名字、年份。 事件表有EventId（主键，自增），事件名称，日期，时间。 考勤表：考勤ID（主键，自增），事件名，学生姓。

非常感谢你们的帮助。这是我的代码。

ViewEvents.java

package com.example.acer.finals;

import android.content.Intent;
import android.database.Cursor;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.Toast;

import java.util.ArrayList;

public class ViewEvents extends AppCompatActivity{

    DatabaseHelper myDB;
    private ListView mylistView;

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

        mylistView = (ListView) findViewById(R.id.listView3);
        myDB = new DatabaseHelper(this);

        populateEventView();
    }

    private void populateEventView()
    {
        ArrayList<String> theList = new ArrayList<>();
        Cursor data = myDB.getEventsList();
        int numRows = data.getCount();
        if(numRows == 0)
        {
            Toast.makeText(ViewEvents.this, "Event List Empty!", Toast.LENGTH_LONG).show();
        }
        else {
            while (data.moveToNext()) {
                theList.add("Event Name: " + data.getString(1) + "\nDate: " + data.getString(2) + "\nTime: " + data.getString(3));
            }
        }
        ListAdapter listAdapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, theList);
        mylistView.setAdapter(listAdapter);

        //set an onItemClickListener to the ListView
        mylistView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {
                String ename = adapterView.getItemAtPosition(i).toString();

                Cursor data = myDB.getEventName(ename);
                Intent intent = new Intent(ViewEvents.this, Load_Attendance.class);
                startActivity(intent);

            }
        });
    }

}

AddAttendance.java

    package com.example.acer.finals;


import android.database.Cursor;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.Toast;

import java.util.ArrayList;

public class AddAttendance extends AppCompatActivity {
    Spinner spnrEvent;
    Button btnSave;
    AutoCompleteTextView autoCtv;

    DatabaseHelper myDB;
    ArrayList<String> names = new ArrayList<String>();
    ArrayList<String> all_Lname = new ArrayList<String>();
    ArrayAdapter<String> adapter;
    ArrayAdapter<String> AllNames_adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_attendance);
        spnrEvent = (Spinner) findViewById(R.id.spnrEvent);
        btnSave = (Button) findViewById(R.id.btnSave);
        autoCtv = (AutoCompleteTextView) findViewById(R.id.autoCtv);

        //ADAPTER
        adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, names);
        myDB = new DatabaseHelper(this);

        final Cursor event = myDB.getAllEvents();
        while(event.moveToNext())
        {
            String name = event.getString(1);
            names.add(name);
        }
        spnrEvent.setAdapter(adapter);

        //================================================

        all_Lname = myDB.getAll_Lname();
        AllNames_adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, all_Lname);
        autoCtv.setAdapter(AllNames_adapter);

        //================================================

        btnSave.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                String evname = spnrEvent.getSelectedItem().toString();
                String lastname = autoCtv.getText().toString();

                if(evname.length() != 0 && lastname.length() != 0){
                    createAttendance(evname,lastname);
                    spnrEvent.setSelection(0);
                    autoCtv.setText("");
                }else{
                    Toast.makeText(AddAttendance.this,"You must put something in the text field!",Toast.LENGTH_LONG).show();
                }
            }
        });

    }
    public void createAttendance(String evname, String lastname){
        boolean insertData = myDB.createAttendanceTB(evname,lastname);

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

Load_Attendance.java

    package com.example.acer.finals;

import android.database.Cursor;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.Toast;

import java.util.ArrayList;

public class Load_Attendance extends AppCompatActivity {
    DatabaseHelper myDB;
    private ListView attendance_list;

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

        attendance_list = (ListView) findViewById(R.id.attendance_list);
        myDB = new DatabaseHelper(this);

        populateListViewAttendance();

    }

    private void populateListViewAttendance()
    {
        String name= "";
        ArrayList<String> theList = new ArrayList<>();
        Cursor data = myDB.getEventAttendance(name);
        int numRows = data.getCount();
        if(numRows == 0)
        {
            Toast.makeText(Load_Attendance.this, "Attendance List Empty!", Toast.LENGTH_LONG).show();
        }
        else {
            while(data.moveToNext())
            {
                theList.add(data.getString(1));
            }
        }
        ListAdapter listAdapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, theList);
        attendance_list.setAdapter(listAdapter);

    }
}

DatabaseHelper.java

    package com.example.acer.finals;

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

import java.util.ArrayList;

/**
 * Created by acer on 12/3/2017.
 */
public class DatabaseHelper extends SQLiteOpenHelper {

    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "Finals";

    // Table Names
    private static final String StudentInfo = "StudentInfo";
    private static final String EventTB= "EventTB";
    private static final String AttendanceTB = "AttendanceTB";

    // StudentInfo Table - column names
    private static final String StudentID = "StudentID";
    private static final String LastName = "LastName";
    private static final String FirstName = "FirstName";
    private static final String Year = "Year";

    // TAGS Table - column names
    private static final String EventID = "EventID";
    private static final String EventName = "EventName";
    private static final String EDate = "EDate";
    private static final String Time = "Time";

    // NOTE_TAGS Table - column names
    private static final String AttendanceID = "AttendanceID";
    private static final String Event_Name = "EventName";
    private static final String Student_Lname = "Student_Lname";


    public DatabaseHelper(Context context){
        super(context,DATABASE_NAME, null, DATABASE_VERSION);
    }
    // Table Create Statements
    // createStudentInfo table create statement
    private static final String createStudentInfo = "CREATE TABLE " + StudentInfo + "("
            + StudentID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
            + LastName + " TEXT,"
            + FirstName + " TEXT,"
            + Year + " TEXT " + ")";

    // createEventTB table create statement
    private static final String createEventTB = "CREATE TABLE " + EventTB + "("
            + EventID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
            + EventName + " TEXT,"
            + EDate + " TEXT,"
            + Time + " TEXT " + ")";

    // AttendanceTB table create statement
    private static final String createAttendanceTB = "CREATE TABLE " + AttendanceTB + "("
            + AttendanceID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
            + Event_Name + " TEXT,"
            + Student_Lname + " TEXT "+ ")";


    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(createStudentInfo);
        db.execSQL(createEventTB);
        db.execSQL(createAttendanceTB);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int i, int i1) {
        // on upgrade drop older tables
        db.execSQL("DROP TABLE IF EXISTS " + createStudentInfo);
        db.execSQL("DROP TABLE IF EXISTS " + createEventTB);
        db.execSQL("DROP TABLE IF EXISTS " + createAttendanceTB);

        // create new tables
        onCreate(db);
    }

    public boolean createStudentInfo(String lname, String fname, String year)
    {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(LastName,lname);
        contentValues.put(FirstName,fname);
        contentValues.put(Year, year);

        long result  = db.insert(StudentInfo, null, contentValues);

        if(result == -1){
            return false;
        }else{
            return true;
        }
    }

    public boolean createEventTB(String ename, String edate, String time)
    {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(EventName,ename);
        contentValues.put(EDate,edate);
        contentValues.put(Time,time);

        long result  = db.insert(EventTB, null, contentValues);

        if(result == -1){
            return false;
        }else{
            return true;
        }
    }

    public boolean createAttendanceTB(String evname, String lastname)
    {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(Event_Name,evname);
        contentValues.put(Student_Lname,lastname);

        long result  = db.insert(AttendanceTB, null, contentValues);

        if(result == -1){
            return false;
        }else{
            return true;
        }
    }

    //returns all data from StudentInfo db
    public Cursor getStudentsList() {
        SQLiteDatabase db = this.getWritableDatabase();
        String query = "SELECT * FROM " + StudentInfo;
        Cursor data = db.rawQuery(query, null);
        return data;
    }
    //returns all events list
    public Cursor getEventsList() {
        SQLiteDatabase db = this.getWritableDatabase();
        String query = "SELECT * FROM " + EventTB;
        Cursor data = db.rawQuery(query, null);
        return data;
    }

    //Returns only the ID that matches the name passed in
    public Cursor getEventName(String ename){
        SQLiteDatabase db = this.getWritableDatabase();
        String query = "SELECT * FROM " + AttendanceTB +
                " WHERE " + EventName + " = '" + ename + "'";
        Cursor data = db.rawQuery(query, null);
        return data;
    }

    //Returns only the ID that matches the name passed in
    public Cursor getEventAttendance(String name){
        SQLiteDatabase db = this.getReadableDatabase();
        String query = "SELECT * " + Student_Lname + " FROM " + AttendanceTB +
                " WHERE " + EventName + " = '" + name + "'";
        Cursor data = db.rawQuery(query, null);
        return data;
    }

    //GET ALL Events
    public Cursor getAllEvents()
    {
        SQLiteDatabase db = this.getWritableDatabase();
        String[] columns={EventID,EventName};
        return db.query(EventTB, columns, null, null, null, null, null);
    }

    //spinner
    public ArrayList<String> getAll_Lname()
    {
        ArrayList<String> all_Lname = new ArrayList<String>();

        SQLiteDatabase db = this.getReadableDatabase();
        String query = "SELECT DISTINCT " + LastName + " FROM " + StudentInfo;
        Cursor data = db.rawQuery(query, null);

        if (data.getCount() > 0)
        {
            data.moveToFirst();
        }
        while(!data.isAfterLast())
        {
            all_Lname.add(data.getString(0));
            data.moveToNext();
        }
        return all_Lname;
    }
}

activity_viewevents.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:layout_width="match_parent"
        android:layout_height="400dp"
        android:id="@+id/listView3"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_margin="20dp" />

</RelativeLayout>

acivity_addattendance.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:text="Choose Event :"
        android:id="@+id/textView15"
        android:textSize="22sp"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginLeft="20dp"
        android:layout_marginTop="50dp" />

    <Spinner
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/spnrEvent"
        android:layout_gravity="right"
        android:clickable="false"
        android:layout_below="@+id/textView15"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="20dp"
        android:layout_marginLeft="20dp"
        android:layout_marginRight="20dp" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="SAVE"
        android:id="@+id/btnSave"
        android:textSize="25sp"
        android:layout_marginTop="45dp"
        android:layout_below="@+id/autoCtv"
        android:layout_alignLeft="@+id/autoCtv"
        android:layout_alignStart="@+id/autoCtv"
        android:layout_alignRight="@+id/autoCtv"
        android:layout_alignEnd="@+id/autoCtv"
        android:background="@color/material_deep_teal_500"
        android:textColor="@color/primary_text_default_material_dark" />

    <AutoCompleteTextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/autoCtv"
        android:layout_marginTop="50dp"
        android:textSize="20sp"
        android:visibility="visible"
        android:layout_below="@+id/spnrEvent"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:hint="Last Name"
        android:layout_marginLeft="20dp"
        android:layout_marginRight="20dp" />

</RelativeLayout>

activity_loadattendance.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/attendance_list" />
</LinearLayout>

Answer 1

当您单击一个事件时，您会提取被单击事件的事件名称。然后，您想要启动一个活动，但将事件名称传递给该活动。

您可以通过添加 Intent Extra 来做到这一点，例如:-

            Intent intent = new Intent(ViewEvents.this, Load_Attendance.class);
            intent.putExtra("EVENT_NAME",ename); //<<<<<<<< ADD this Line
            startActivity(intent);

那么 Load_Attendance 可能是：-

public class Load_Attendance extends AppCompatActivity {
    DatabaseHelper myDB;
    private ListView attendance_list;

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

        attendance_list = (ListView) findViewById(R.id.attendance_list);
        myDB = new DatabaseHelper(this);

        populateListViewAttendance(getIntent().getStringExtra("EVENT_NAME")); //<<<<<<<< invoke with retrieved event name

    }

    private void populateListViewAttendance(String name) //<<<<<<<< added parameter
    {
        ArrayList<String> theList = new ArrayList<>();
        Cursor data = myDB.getEventAttendance(name);
        int numRows = data.getCount();
        if(numRows == 0)
        {
            Toast.makeText(Load_Attendance.this, "Attendance List Empty!", Toast.LENGTH_LONG).show();
        }
        else {
            while(data.moveToNext())
            {
                theList.add(data.getString(1));
            }
        }
        ListAdapter listAdapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, theList);
        attendance_list.setAdapter(listAdapter);

    }
}

//<<<<<<<< 表示更改/添加的代码行

请注意，这尚未经过测试，并假定现有代码正在运行，可能存在奇怪的错误。

附：你应该在完成后关闭游标。

---

由于一连串的失败，在 cmets 之后进行编辑。

以下是基于您的代码的代码，但简化为您想要的关于此问题的基础知识。

这是一个事件列表显示在一个列表视图中，单击一个项目会生成一个参与者列表。

但是，这都是在同一个活动中完成的，点击事件的参与者会在日志中列出。简而言之，这验证了上述答案中提供的基本过程是否有效，而您遇到的问题很可能是由于您在数据库中拥有的数据。

代码

activity_main.xml :-

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="acer.com.finals.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"/>

    <ListView
        android:id="@+id/EventsList"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
    >
    </ListView>
</LinearLayout>

DatabaseHelper.java

public class DatabaseHelper extends SQLiteOpenHelper {

    // Database Version
    private static final int DATABASE_VERSION = 1;

    // Database Name
    private static final String DATABASE_NAME = "Finals";

    // Table Names
    private static final String StudentInfo = "StudentInfo";
    private static final String EventTB= "EventTB";
    private static final String AttendanceTB = "AttendanceTB";

    // StudentInfo Table - column names
    private static final String StudentID = "StudentID";
    private static final String LastName = "LastName";
    private static final String FirstName = "FirstName";
    private static final String Year = "Year";

    // TAGS Table - column names
    private static final String EventID = "EventID";
    private static final String EventName = "EventName";
    private static final String EDate = "EDate";
    private static final String Time = "Time";

    // NOTE_TAGS Table - column names
    private static final String AttendanceID = "AttendanceID";
    private static final String Event_Name = "EventName";
    private static final String Student_Lname = "Student_Lname";


    public DatabaseHelper(Context context){
        super(context,DATABASE_NAME, null, DATABASE_VERSION);
    }
    // Table Create Statements
    // createStudentInfo table create statement
    private static final String createStudentInfo = "CREATE TABLE " + StudentInfo + "("
            + StudentID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
            + LastName + " TEXT,"
            + FirstName + " TEXT,"
            + Year + " TEXT " + ")";

    // createEventTB table create statement
    private static final String createEventTB = "CREATE TABLE " + EventTB + "("
            + EventID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
            + EventName + " TEXT,"
            + EDate + " TEXT,"
            + Time + " TEXT " + ")";

    // AttendanceTB table create statement
    private static final String createAttendanceTB = "CREATE TABLE " + AttendanceTB + "("
            + AttendanceID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
            + Event_Name + " TEXT,"
            + Student_Lname + " TEXT "+ ")";


    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(createStudentInfo);
        db.execSQL(createEventTB);
        db.execSQL(createAttendanceTB);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int i, int i1) {
        // on upgrade drop older tables
        db.execSQL("DROP TABLE IF EXISTS " + StudentInfo);
        db.execSQL("DROP TABLE IF EXISTS " + EventTB);
        db.execSQL("DROP TABLE IF EXISTS " + AttendanceTB);

        // create new tables
        onCreate(db);
    }

    public boolean createStudentInfo(String lname, String fname, String year)
    {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(LastName,lname);
        contentValues.put(FirstName,fname);
        contentValues.put(Year, year);

        long result  = db.insert(StudentInfo, null, contentValues);

        if(result == -1){
            return false;
        }else{
            return true;
        }
    }

    public boolean createEventTB(String ename, String edate, String time)
    {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(EventName,ename);
        contentValues.put(EDate,edate);
        contentValues.put(Time,time);

        long result  = db.insert(EventTB, null, contentValues);

        if(result == -1){
            return false;
        }else{
            return true;
        }
    }

    public boolean createAttendanceTB(String evname, String lastname)
    {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(Event_Name,evname);
        contentValues.put(Student_Lname,lastname);

        long result  = db.insert(AttendanceTB, null, contentValues);

        if(result == -1){
            return false;
        }else{
            return true;
        }
    }

    //returns all data from StudentInfo db
    public Cursor getStudentsList() {
        SQLiteDatabase db = this.getWritableDatabase();
        String query = "SELECT * FROM " + StudentInfo;
        Cursor data = db.rawQuery(query, null);
        return data;
    }
    //returns all events list
    public Cursor getEventsList() {
        SQLiteDatabase db = this.getWritableDatabase();
        String query = "SELECT * FROM " + EventTB;
        Cursor data = db.rawQuery(query, null);
        return data;
    }

    //Returns only the ID that matches the name passed in
    public Cursor getEventName(String ename){
        SQLiteDatabase db = this.getWritableDatabase();
        String query = "SELECT * FROM " + AttendanceTB +
                " WHERE " + EventName + " = '" + ename + "'";
        Cursor data = db.rawQuery(query, null);
        return data;
    }

    //Returns only the ID that matches the name passed in
    public Cursor getEventAttendance(String name){
        SQLiteDatabase db = this.getReadableDatabase();
        String query = "SELECT *  FROM " + AttendanceTB +
                " WHERE " + EventName + " = '" + name + "'";
        Cursor data = db.rawQuery(query, null);
        return data;
    }

    //GET ALL Events
    public Cursor getAllEvents()
    {
        SQLiteDatabase db = this.getWritableDatabase();
        String[] columns={EventID,EventName};
        return db.query(EventTB, columns, null, null, null, null, null);
    }

    //spinner
    public ArrayList<String> getAll_Lname()
    {
        ArrayList<String> all_Lname = new ArrayList<String>();

        SQLiteDatabase db = this.getReadableDatabase();
        String query = "SELECT DISTINCT " + LastName + " FROM " + StudentInfo;
        Cursor data = db.rawQuery(query, null);

        if (data.getCount() > 0)
        {
            data.moveToFirst();
        }
        while(!data.isAfterLast())
        {
            all_Lname.add(data.getString(0));
            data.moveToNext();
        }
        return all_Lname;
    }
}

请注意，虽然这相似，但有 2) 重要更改：-

• 1 onUpgrade 方法不是连接表创建 SQL，而是连接相应的表名。原来的onUpgrade 方法会失败。

• 2 根据答案和 cmets，getEventAttendance 方法已被修改为以 eventname 作为参数并从出席表中选择所有列。

MainActivity.java

公共类 MainActivity 扩展 AppCompatActivity {

DatabaseHelper dbhelper;
ListAdapter mEventListAdapter;
ArrayList<String> mEventList;
ListView mEventsListView;

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

    mEventsListView = this.findViewById(R.id.EventsList);

    dbhelper = new DatabaseHelper(this);

    dbhelper.getWritableDatabase().delete("EventTB",null,null);
    dbhelper.getWritableDatabase().delete("StudentInfo", null,null);
    dbhelper.getWritableDatabase().delete("AttendanceTB", null,null);

    dbhelper.createEventTB("The Main Event","31/12/2017","10:30");
    dbhelper.createEventTB("The Normal Event","31/12/2017","10:30");
    dbhelper.createEventTB("The Minor Event","31/12/2017","10:30");

    dbhelper.createStudentInfo("Bloggs","Fred","2017");
    dbhelper.createStudentInfo("Smith","Tom", "2016");
    dbhelper.createStudentInfo("Thomas","John","2015");


    dbhelper.createAttendanceTB("The Main Event","Bloggs");
    dbhelper.createAttendanceTB("The Main Event", "Smith");
    dbhelper.createAttendanceTB("The Normal Event","Thomas");
    dbhelper.createAttendanceTB("The Minor Event","Thomas");
    dbhelper.createAttendanceTB("The Minor Event","Smith");

    Cursor csr = dbhelper.getEventsList();
    mEventList = new ArrayList<>();
    while (csr.moveToNext()) {
        mEventList.add(csr.getString(1));
    }
    mEventListAdapter = new ArrayAdapter<>(this,android.R.layout.simple_list_item_1,mEventList);
    mEventsListView.setAdapter(mEventListAdapter);
    mEventsListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            String eventname = parent.getItemAtPosition(position).toString();
            Log.d("EVLIST_ITEMCLCK","You clicked Item at Position " + position + " and extracted Event name as " + eventname);
            logEventAttendance(eventname);
        }
    });
}

private void logEventAttendance(String eventname) {

    Cursor csr = dbhelper.getEventAttendance(eventname);
    Log.d("EVATTEND","Number of attendance rows extracted is " + csr.getCount());
    while (csr.moveToNext()) {
        Log.d("EVATTEND", "Attendee is " + csr.getString(2) + " at Event " + csr.getString(1));
    }
}

}

这个：-

• 1) 进行非常普通的初始化，然后通过它的 ID 获取 ListView。
• 2) 创建数据库助手的实例，清空 3 个表（数据库和表将在应用程序的第一次运行时创建）。
• 3) 添加 3 个事件。
• 4) 添加 3 名学生。
• 5) 在活动中添加出席人数请注意，活动名称和学生姓氏必须与相应的活动名称和学生姓名完全匹配
  • 请注意，使用名称作为引用是有限制的，例如您不能使用学生的 Tom Smith 和 Fred Smith，因为您使用姓氏作为参考。
  • 通常 ID 用于在表之间引用/链接列。
• 6) 获取 EventList 并将其转换为 ArrayList。
• 7) 设置 ListAdapter 以使用事件名称的 ArrayList。
• 8) 将适配器绑定到 ListView

• 9) 向列表视图添加一个 onItemClick 侦听器。

• 10) 单击项目时，事件的出席行数会显示在日志中，并且会为每个（如果有）创建一个日志条目。

输出

以下是上面依次点击每一项后的输出：-

12-12 04:58:53.014 2860-2860/acer.com.finals D/EVLIST_ITEMCLCK: You clicked Item at Position 0 and extracted Event name as The Main Event
12-12 04:58:53.014 2860-2860/acer.com.finals D/EVATTEND: Number of attendance rows extracted is 2
12-12 04:58:53.014 2860-2860/acer.com.finals D/EVATTEND: Attendee is Bloggs at Event The Main Event
12-12 04:58:53.014 2860-2860/acer.com.finals D/EVATTEND: Attendee is Smith at Event The Main Event


12-12 04:58:54.192 2860-2860/acer.com.finals D/EVLIST_ITEMCLCK: You clicked Item at Position 1 and extracted Event name as The Normal Event
12-12 04:58:54.193 2860-2860/acer.com.finals D/EVATTEND: Number of attendance rows extracted is 1
12-12 04:58:54.193 2860-2860/acer.com.finals D/EVATTEND: Attendee is Thomas at Event The Normal Event


12-12 04:58:55.477 2860-2860/acer.com.finals D/EVLIST_ITEMCLCK: You clicked Item at Position 2 and extracted Event name as The Minor Event
12-12 04:58:55.478 2860-2860/acer.com.finals D/EVATTEND: Number of attendance rows extracted is 2
12-12 04:58:55.478 2860-2860/acer.com.finals D/EVATTEND: Attendee is Thomas at Event The Minor Event
12-12 04:58:55.478 2860-2860/acer.com.finals D/EVATTEND: Attendee is Smith at Event The Minor Event

请注意，这是为了补充答案。