android studio SQLite Database小例

##简述
SQLiteDatabase是一个可以进行增(Create)、查(Retrieve)、改(Update)、删(Delete)数据，即CRUD操作的类。
下面教程将向你展示如何使用SQLiteDatabase在Android中实现CRUD操作。

工具使用：
Android studio 1.1.0

TODO
在这个教程中，我们将创建一个app，允许对一个student表进行增查改删的数据操作。
很容易吗？是的，如果你知道怎样做的话 :)

##表结构
这个student表将用于存储学生的详细数据，为了简单，只创建3个域，如下图：

id是主键，允许自增

##页面布局
创建两个页面布局，第一个页面展示所有学生名字，如下图：

第二个页面是学生的详细信息的页面，用户点击listview的每个item时，将会进入这个页面，如下图：

##布局实现
1.新建一个SQLiteDemo的project;
2.实现第一个页面布局activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent"   android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Add"
        android:id="@+id/btnAdd"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
       />
    <ListView
        android:id="@android:id/list"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/btnAdd"
        />
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="List All"
        android:id="@+id/btnGetAll"
        android:layout_alignParentBottom="true"
        android:layout_toRightOf="@+id/btnAdd"/>
</RelativeLayout>

你需要修改ListView的id为 android:id=”@+id/listView” 如果你选择继承ListActivity在你的Activity类，否则将会出错；content必须有一个ListView，它的id的属性是‘android.R.id.list’

3.创建另一个activity，StudentDetail.java，其布局为第二个页面activity_student_detail.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context="cn.cfanr.sqlitedemo.StudentDetail">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Name"
        android:id="@+id/tvName"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="30dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Email"
        android:id="@+id/tvEmail"
        android:layout_below="@id/tvName"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="30dp" />
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Age"
        android:id="@+id/tvAge"
        android:layout_below="@id/tvEmail"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="30dp" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/etName"
        android:inputType="textPersonName"
        android:ems="10"
        android:layout_above="@id/tvEmail"
        android:layout_toRightOf="@id/tvName"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true" />


    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/etEmail"
        android:layout_toRightOf="@id/tvEmail"
        android:inputType="textEmailAddress"
        android:ems="10"
        android:layout_above="@id/tvAge"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/etAge"
        android:inputType="number"
        android:ems="10"
        android:layout_alignBottom="@id/tvAge"
        android:layout_alignLeft="@id/etEmail"
        android:layout_alignStart="@id/etEmail"
        android:layout_alignRight="@id/etEmail"
        android:layout_alignEnd="@id/etEmail"
        />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/btnClose"
        android:text="Close"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/btnSave"
        android:text="Save"
        android:layout_alignParentBottom="true"
        android:layout_toLeftOf="@id/btnClose"/>

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/btnDelete"
        android:text="Delete"
        android:layout_alignParentBottom="true"
        android:layout_toLeftOf="@id/btnSave"/>
</RelativeLayout>

4.当用户点击ListView的item时展示学生的详细信息的activity，所以我们需要一个特殊的id来检索学生的详细信息，并且这个id必须来自ListView，可以通过两个方法实现：

• 最简单的方法，可以放id和name进listview的item中，展示给用户（不好的UI设计），当用户点击选中item时，将检索的记录传递到StudentDetail.java的activity。
• 创建一个layout作为listview的item，通过item中包含学生的id（不过设置成隐藏）来检索学生的详细信息；

采用第二种方法，创建一个新的layout，view_student_entry.xml，代码如下：

<?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">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/student_Id"
        android:visibility="gone"/>

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingLeft="6dip"
        android:paddingTop="6dip"
        android:textSize="22sp"
        android:textStyle="bold"/>
</LinearLayout>

##编码
1.创建Student类

package cn.cfanr.sqlitedemo;

/**
 * Created by ifanr on 2015/3/29.
 */
public class Student {
    //表名
    public static final String TABLE="Student";

    //表的各域名
    public static final String KEY_ID="id";
    public static final String KEY_name="name";
    public static final String KEY_email="email";
    public static final String KEY_age="age";

    //属性
    public int student_ID;
    public String name;
    public String email;
    public int age;
}

2.为了创建表，需要使用到SQLiteDatabase类（实现CRUD操作）和SQLiteOpenHelper（用于数据库的创建和版本管理），下面先创建一个DBHelper类

package cn.cfanr.sqlitedemo;

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

/**
 * Created by ifanr on 2015/3/29.
 */
public class DBHelper extends SQLiteOpenHelper {
    //数据库版本号
    private static final int DATABASE_VERSION=4;

    //数据库名称
    private static final String DATABASE_NAME="crud.db";

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        //创建数据表
        String CREATE_TABLE_STUDENT="CREATE TABLE "+ Student.TABLE+"("
                +Student.KEY_ID+" INTEGER PRIMARY KEY AUTOINCREMENT ,"
                +Student.KEY_name+" TEXT, "
                +Student.KEY_age+" INTEGER, "
                +Student.KEY_email+" TEXT)";
        db.execSQL(CREATE_TABLE_STUDENT);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        //如果旧表存在，删除，所以数据将会消失
        db.execSQL("DROP TABLE IF EXISTS "+ Student.TABLE);

        //再次创建表
        onCreate(db);
    }
}

3.新建StudentRepo类，编写CRUD函数。

package cn.cfanr.sqlitedemo;

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

import java.util.ArrayList;
import java.util.HashMap;

/**
 * Created by ifanr on 2015/3/29.
 */
public class StudentRepo {
    private DBHelper dbHelper;

    public StudentRepo(Context context){
        dbHelper=new DBHelper(context);
    }

    public int insert(Student student){
        //打开连接，写入数据
        SQLiteDatabase db=dbHelper.getWritableDatabase();
        ContentValues values=new ContentValues();
        values.put(Student.KEY_age,student.age);
        values.put(Student.KEY_email,student.email);
        values.put(Student.KEY_name,student.name);
        //
        long student_Id=db.insert(Student.TABLE,null,values);
        db.close();
        return (int)student_Id;
    }

    public void delete(int student_Id){
        SQLiteDatabase db=dbHelper.getWritableDatabase();
        db.delete(Student.TABLE,Student.KEY_ID+"=?", new String[]{String.valueOf(student_Id)});
        db.close();
    }
    public void update(Student student){
        SQLiteDatabase db=dbHelper.getWritableDatabase();
        ContentValues values=new ContentValues();

        values.put(Student.KEY_age,student.age);
        values.put(Student.KEY_email,student.email);
        values.put(Student.KEY_name,student.name);

        db.update(Student.TABLE,values,Student.KEY_ID+"=?",new String[] { String.valueOf(student.student_ID) });
        db.close();
    }

    public ArrayList<HashMap<String, String>> getStudentList(){
        SQLiteDatabase db=dbHelper.getReadableDatabase();
        String selectQuery="SELECT "+
                Student.KEY_ID+","+
                Student.KEY_name+","+
                Student.KEY_email+","+
                Student.KEY_age+" FROM "+Student.TABLE;
        ArrayList<HashMap<String,String>> studentList=new ArrayList<HashMap<String, String>>();
        Cursor cursor=db.rawQuery(selectQuery,null);

        if(cursor.moveToFirst()){
            do{
                HashMap<String,String> student=new HashMap<String,String>();
                student.put("id",cursor.getString(cursor.getColumnIndex(Student.KEY_ID)));
                student.put("name",cursor.getString(cursor.getColumnIndex(Student.KEY_name)));
                studentList.add(student);
            }while(cursor.moveToNext());
        }
        cursor.close();
        db.close();
        return studentList;
    }

    public Student getStudentById(int Id){
        SQLiteDatabase db=dbHelper.getReadableDatabase();
        String selectQuery="SELECT "+
                Student.KEY_ID + "," +
                Student.KEY_name + "," +
                Student.KEY_email + "," +
                Student.KEY_age +
                " FROM " + Student.TABLE
                + " WHERE " +
                Student.KEY_ID + "=?";
        int iCount=0;
        Student student=new Student();
        Cursor cursor=db.rawQuery(selectQuery,new String[]{String.valueOf(Id)});
        if(cursor.moveToFirst()){
            do{
                student.student_ID =cursor.getInt(cursor.getColumnIndex(Student.KEY_ID));
                student.name =cursor.getString(cursor.getColumnIndex(Student.KEY_name));
                student.email  =cursor.getString(cursor.getColumnIndex(Student.KEY_email));
                student.age =cursor.getInt(cursor.getColumnIndex(Student.KEY_age));
            }while(cursor.moveToNext());
        }
        cursor.close();
        db.close();
        return student;
    }
}

4.用户点击item，进入的详细页面StudentDetail

package cn.cfanr.sqlitedemo;

import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;


public class StudentDetail extends ActionBarActivity implements View.OnClickListener {

    private Button btnSave,btnDelete;
    private Button btnClose;
    private EditText etName;
    private EditText etEmail;
    private EditText etAge;
    private int _student_id=0;

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

        btnSave = (Button) findViewById(R.id.btnSave);
        btnDelete = (Button) findViewById(R.id.btnDelete);
        btnClose = (Button) findViewById(R.id.btnClose);

        etName = (EditText) findViewById(R.id.etName);
        etEmail = (EditText) findViewById(R.id.etEmail);
        etAge = (EditText) findViewById(R.id.etAge);

        btnSave.setOnClickListener(this);
        btnDelete.setOnClickListener(this);
        btnClose.setOnClickListener(this);

        _student_id =0;
        Intent intent = getIntent();
        _student_id =intent.getIntExtra("student_Id", 0);
        StudentRepo repo = new StudentRepo(this);
        Student student = new Student();
        student = repo.getStudentById(_student_id);

        etAge.setText(String.valueOf(student.age));
        etName.setText(student.name);
        etEmail.setText(student.email);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_student_detail, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onClick(View v) {
        if(v==findViewById(R.id.btnSave)){
            StudentRepo repo=new StudentRepo(this);
            Student student=new Student();
            student.age=Integer.parseInt(etAge.getText().toString());
            student.email=etEmail.getText().toString();
            student.name=etName.getText().toString();
            student.student_ID=_student_id;

            if(_student_id==0){
                _student_id=repo.insert(student);
                Toast.makeText(this,"New Student Insert",Toast.LENGTH_SHORT).show();
            }else{
                repo.update(student);
                Toast.makeText(this,"Student Record updated",Toast.LENGTH_SHORT).show();
            }
        }else if (v== findViewById(R.id.btnDelete)){
            StudentRepo repo = new StudentRepo(this);
            repo.delete(_student_id);
            Toast.makeText(this, "Student Record Deleted", Toast.LENGTH_SHORT);
            finish();
        }else if (v== findViewById(R.id.btnClose)){
            finish();
        }
    }
}

5.在MainActivity实现获取学生列表和跳转到StudentDetail页面

package cn.cfanr.sqlitedemo;

import android.app.ListActivity;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.HashMap;


public class MainActivity extends ListActivity implements android.view.View.OnClickListener {

    private Button btnAdd,btnGetAll;
    private TextView student_Id;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btnAdd = (Button) findViewById(R.id.btnAdd);
        btnAdd.setOnClickListener(this);

        btnGetAll = (Button) findViewById(R.id.btnGetAll);
        btnGetAll.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        if (v== findViewById(R.id.btnAdd)){

            Intent intent = new Intent(this,StudentDetail.class);
            intent.putExtra("student_Id",0);
            startActivity(intent);

        }else {

            StudentRepo repo = new StudentRepo(this);

            ArrayList<HashMap<String, String>> studentList =  repo.getStudentList();
            if(studentList.size()!=0) {
                ListView lv = getListView();
                lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> parent, View view,int position, long id) {
                        student_Id = (TextView) view.findViewById(R.id.student_Id);
                        String studentId = student_Id.getText().toString();
                        Intent objIndent = new Intent(getApplicationContext(),StudentDetail.class);
                        objIndent.putExtra("student_Id", Integer.parseInt( studentId));
                        startActivity(objIndent);
                    }
                });
                ListAdapter adapter = new SimpleAdapter( MainActivity.this,studentList, R.layout.view_student_entry, new String[] { "id","name"}, new int[] {R.id.student_Id, R.id.student_name});
                setListAdapter(adapter);
            }else{
                Toast.makeText(this, "No student!", Toast.LENGTH_SHORT).show();
            }

        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

6.运行结果如下：

参考http://instinctcoder.com/android-studio-sqlite-database-example/

另外，SQLite的详细资料，Android中SQLite应用详解