Android开发学习之路--数据持久化之初体验

    上班第一天，虽然工作上处于酱油模式，但是学习上依旧不能拉下，接着学习android开发吧，这里学习数据持久化的

知识。

    其实数据持久化就是数据可以保存起来，一般我们保存数据都是以文件，或者数据库的形式保存的，android程序也有

文件和数据库的保存，此外还有一种叫做SharedPreference存储，也就是键值对，一般用过ios的dictionary或者

hashmap就会知道这个功能。下面学习下android中的这三种存储数据的方式。

    首先是文件存储的方式。新建工程FileTest，然后编写代码saveToFile方法，代码如下：

package com.example.jared.filetest;

import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import java.io.BufferedWriter;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;

public class MainActivity extends AppCompatActivity {

    private FileOutputStream fs = null;
    private BufferedWriter out = null;
    private static String file_name = "file_test1";
    private static String file_data = "Save something int the file!";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        saveToFile(file_name, file_data);
    }

    public void saveToFile(String name, String data) {
        try {
            fs = openFileOutput(name, Context.MODE_PRIVATE);
            out = new BufferedWriter(new OutputStreamWriter(fs));
            out.write(data);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if(out != null) {
                    out.close();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

    这里的fs是以MODE_PRIVATE的方式打开一个文件，然后通过io流来操作，因为是写文件，所以这里是OutputStream

最后调用write方法把数据写到文件中去，然后在结束的时候close文件。这里在onCreate中就把信息存储到了文件中了。

    运行后可以通过DDMS来查看文件，关于android studio的ddms如下图：

    打开后，在File Explorer中的data->data->com.example.jared.filetest->files下面就会新建一个file_test1的文件

    导出这个文件，然后查看下内容如下所示：（这个内容在模拟器里面，所以不能直接访问，需要导出，当然也可以把

现有的文件导入进去，上图的➕➖符号的左边的两个图标就是导入和导出的文件的按钮）

    可以看到文件内容就是我们所需要的。能把数据存储到文件中，那么必须得把存入的数据读取出来，要不然也没有多

大意义，其实读取和存储差不多，这里在实现个readFromFile方法吧。这里结合下一个场景，比如我们在输入帐号的时

候不小心按了back，那么我们输入的信息就会全没有了，此时如果我们输入的信息还保存着的话，那么用户体验会非常

的好。这里结合readFromFile和saveToFile方法还有前面学的布局。修改MainActivity代码如下：

package com.example.jared.filetest;

import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.EditText;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class MainActivity extends AppCompatActivity {

    private FileOutputStream fs = null;
    private BufferedWriter out = null;
    private FileInputStream fs_in = null;
    private BufferedReader input = null;

    private static String file_name = "file_test1";
    private static String file_data = "Save something int the file!";

    private EditText account;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //saveToFile(file_name, file_data);
        account = (EditText)findViewById(R.id.account);
        String account_read = readFromFile(file_name);
        if(!account_read.isEmpty()) {
            account.setText(account_read);
            account.setSelection(account_read.length());
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        String account_write = account.getText().toString();
        saveToFile(file_name, account_write);
    }

    public void saveToFile(String name, String data) {
        try {
            fs = openFileOutput(name, Context.MODE_PRIVATE);
            out = new BufferedWriter(new OutputStreamWriter(fs));
            out.write(data);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if(out != null) {
                    out.close();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public String readFromFile(String name) {
        StringBuffer stringBuffer = new StringBuffer();
        try {
            fs_in = openFileInput(name);
            input = new BufferedReader(new InputStreamReader(fs_in));
            String line = "";
            while((line = input.readLine()) != null) {
                stringBuffer.append(line);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (input != null) {
                try {
                    input.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
        return stringBuffer.toString();
    }
}

    这里的readFromFile和saveToFile差不多，添加了edittext，用来输入帐号，在onDestdroy方法中存储了当前输入的信

息，然后在onCreate方法中重新load这些信息。布局文件如下：

<?xml version="1.0" encoding="utf-8"?>
<TableLayout
    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"
    tools:context="com.example.jared.filetest.MainActivity">

    <TableRow>
        <TextView
            android:text="账号"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="22dp"/>
        <EditText
            android:id="@+id/account"
            android:hint="请输入账号"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"/>
    </TableRow>

</TableLayout>

    这里布局就不多讲了，运行输入test，然后退出，然后再进入，一直是刚输入的信息：

    接着我们学习SharedPreferences的方式。依旧刚才的例子，这里不再新建工程了，再加上密码，和性别的选项，布

局和效果如下：

<?xml version="1.0" encoding="utf-8"?>
<TableLayout
    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:layout_margin="10dp"
    android:stretchColumns="1"
    tools:context="com.example.jared.filetest.MainActivity">

    <TableRow>
        <TextView
            android:text="账号:"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="22sp"/>
        <EditText
            android:id="@+id/account"
            android:hint="请输入账号"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
    </TableRow>

    <TableRow>
        <TextView 
            android:text="密码:"
            android:layout_height="wrap_content"
            android:layout_weight="wrap_content"
            android:textSize="22sp"/>
        <EditText
            android:id="@+id/password"
            android:hint="请输入密码"
            android:layout_height="wrap_content"
            android:layout_width="wrap_content" />
    </TableRow>
    
    <TableRow>
        <TextView
            android:text="性别:"
            android:layout_height="wrap_content"
            android:layout_weight="wrap_content"
            android:textSize="22sp"/>
        
        <RadioGroup 
            android:id="@+id/sex"
            android:layout_height="wrap_content"
            android:layout_width="wrap_content"
            android:orientation="horizontal" >
            
            <RadioButton 
                android:id="@+id/sex_man"
                android:layout_height="wrap_content"
                android:layout_width="wrap_content"
                android:text="男"/>
            <RadioButton
                android:id="@+id/sex_woman"
                android:layout_height="wrap_content"
                android:layout_width="wrap_content"
                android:text="女"/>
        </RadioGroup>
    </TableRow>
    <TableRow>
        <Button 
            android:id="@+id/login"
            android:layout_height="wrap_content"
            android:layout_width="wrap_content"
            android:text="登陆"
            android:layout_span="2"/>
    </TableRow>
</TableLayout>

    运行效果如下所示：

    接着我们来使用SharedPreferences来存储我们输入的内容吧。这里用了radiobutton，因为性别是唯一的，所以用了

RadioGroup，代码可以参考上面的，其实和一般的控件也差不多，只是有些特殊的属性。

    下面简单实现下保存的功能，代码如下：

package com.example.jared.filetest;

import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioGroup;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class MainActivity extends AppCompatActivity {

    private Button login;
    private EditText account_edit;
    private EditText password_edit;
    private RadioGroup sex_radio;

    private String accountData = null;
    private String passwordData = null;
    private String sexData = null;
    private String file_name = "person";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        account_edit = (EditText)findViewById(R.id.account);
        password_edit = (EditText)findViewById(R.id.password);

        sex_radio = (RadioGroup)findViewById(R.id.sex);
        sex_radio.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(RadioGroup radioGroup, int i) {
                int radioButtonId = radioGroup.getCheckedRadioButtonId();
                switch (radioButtonId){
                    case R.id.sex_man:
                        sexData = "man";
                        break;
                    case R.id.sex_woman:
                        sexData = "woman";
                        break;
                    default:
                        sexData = "null";
                        break;
                }
            }
        });

        login = (Button)findViewById(R.id.login);
        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                accountData = account_edit.getText().toString();
                passwordData = password_edit.getText().toString();
                saveToSharedP(file_name, accountData, passwordData, sexData);
            }
        });
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
    }

    public void saveToSharedP(String name, String account, String password, String sex) {
        SharedPreferences.Editor editor = getSharedPreferences(name, MODE_PRIVATE).edit();
        editor.putString("Account", account);
        editor.putString("Password", password);
        editor.putString("Sex", sex);
        editor.commit();
    }
｝

    然后运行程序，点击登陆按钮：

    在data->data->com.example.jared.filetest->shared_prefs下面就存储了一个名为person.xml的文件。

    导出后打开文件可以查看内容如下：

    

    可以看出，我们要保存的数据都已经存储到一个xml文件中了。下面就来实现读取的功能了。 修改代码如下：

package com.example.jared.filetest;

import android.content.Context;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioGroup;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class MainActivity extends AppCompatActivity {

    private Button login;
    private EditText account_edit;
    private EditText password_edit;
    private RadioGroup sex_radio;

    private String accountData = null;
    private String passwordData = null;
    private String sexData = null;
    private String file_name = "person";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        account_edit = (EditText)findViewById(R.id.account);
        password_edit = (EditText)findViewById(R.id.password);

        sex_radio = (RadioGroup)findViewById(R.id.sex);
        sex_radio.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(RadioGroup radioGroup, int i) {
                int radioButtonId = radioGroup.getCheckedRadioButtonId();
                switch (radioButtonId){
                    case R.id.sex_man:
                        sexData = "man";
                        break;
                    case R.id.sex_woman:
                        sexData = "woman";
                        break;
                    default:
                        sexData = "null";
                        break;
                }
            }
        });

        readFromSharedp(file_name);
        account_edit.setText(accountData);
        password_edit.setText(passwordData);
        if(sexData.equals("man")) {
            sex_radio.check(R.id.sex_man);
        } else if(sexData.equals("woman")) {
            sex_radio.check(R.id.sex_woman);
        }
        
        login = (Button)findViewById(R.id.login);
        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                accountData = account_edit.getText().toString();
                passwordData = password_edit.getText().toString();
                saveToSharedP(file_name, accountData, passwordData, sexData);
            }
        });
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
    }

    public void saveToSharedP(String name, String account, String password, String sex) {
        SharedPreferences.Editor editor = getSharedPreferences(name, MODE_PRIVATE).edit();
        editor.putString("Account", account);
        editor.putString("Password", password);
        editor.putString("Sex", sex);
        editor.commit();
    }

    public void readFromSharedp(String name) {
        SharedPreferences sharedP = getSharedPreferences(name, MODE_PRIVATE);
        accountData = sharedP.getString("Account", "");
        passwordData = sharedP.getString("Password", "");
        sexData = sharedP.getString("Sex", "");
    }
｝

    然后运行后重新输入另一组账号密码，运行后，back退出，再打开app后可以发现还是保存着数据：

    最后学习数据库的方式，android数据库是sqlite3，sqlite3是开源库，记得在linux上用过，调用接口，然后通过sql语

句来实现，android这里也是基本类型，只不过在上层封装了一些api而已。对于数据库主要的操作就是CRUD，也就是

增加，查询，更新和删除这几个操作。

    增(create)：create tbl ...；

    查(Retrieve)：select ＊from tbl；

    改(update)：update tbl ... set ...；

    删(delete)：delete from tbl where ...。

    下面对于增查改删都做一些例子。首先是增，新建工程dbtest。创建mydbhelper继承sqliteopenhelper，代码如下：

package com.example.jared.dbtest;

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

/**
 * Created by jared on 16/2/14.
 */
public class MyDBHelper extends SQLiteOpenHelper {
    public static final String CREATE_PERSON =
              "create table person ("
            + "id integer primary key autoincrement, "
            + "name text, "
            + "age integer, "
            + "height real, "
            + "sex text)";

    private Context mContext;

    public MyDBHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
        mContext = context;
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        sqLiteDatabase.execSQL(CREATE_PERSON);
        Toast.makeText(mContext, "Create table person success", Toast.LENGTH_LONG).show();
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {

    }
}

    这里当创建数据库的时候会调用onCreate方法。这里创建了一个person表。表中有主键id自增，姓名，年龄，身高，

性别等。然后修改layout，代码如下：

<?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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.example.jared.dbtest.MainActivity">

    <Button
        android:id="@+id/createDB"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="创建数据库" />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        <Button
            android:id="@+id/addData"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="添加数据"/>
        <Button
            android:id="@+id/updateData"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="更新数据"/>
        <Button
            android:id="@+id/delData"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="删除数据"/>
        <Button
            android:id="@+id/queryData"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="查询数据"/>
    </LinearLayout>


</LinearLayout>

    然后修改MainActivity的代码：

package com.example.jared.dbtest;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private Button createDb;

    private MyDBHelper myDBHelper;

    private static final String dbName = "PersonStore.db";
    private static final int version = 1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myDBHelper = new MyDBHelper(this, dbName, null, version);

        createDb = (Button)findViewById(R.id.createDB);
        createDb.setOnClickListener(new myOnClickListener());
    }

    private class myOnClickListener implements View.OnClickListener {
        @Override
        public void onClick(View view) {
            switch (view.getId()){
                case R.id.createDB:
                    myDBHelper.getWritableDatabase();
                    break;
                default:
                    break;
            }
        }
    }
}

    运行按创建数据库的按钮，就可以创建数据库了。

    

    接着我们通过adb来进入模拟器的终端，执行adb shell。在android 

studio的软件，在左下角有terminal终端里面执行，进入root后进到对应的文件夹下面：

    然后执行sqlite3 PersonStore.db，再执行.table，在执行.schema，如下所示：

    具体的sqlite3命令可以通过.help查看。

    由上可知数据库创建成功，那么如果需要更新数据库，需要怎么做呢？这里有onUpgrade方法，如果version版本变化

了，原来是1，后来升级为2了，那么就会调用这个方法，而在这个方法中，可以drop原有的table，再调用onCreate方法

去创建。修改MyDBHelper如下：

package com.example.jared.dbtest;

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

/**
 * Created by jared on 16/2/14.
 */
public class MyDBHelper extends SQLiteOpenHelper {
    public static final String CREATE_PERSON =
              "create table person ("
            + "id integer primary key autoincrement, "
            + "name text, "
            + "age integer, "
            + "height real, "
            + "sex text)";

    public static final  String CREATE_TEACHER =
            "create table teacher ("
            + "id integer primary key autoincrement, "
            + "class text )";

    private Context mContext;

    public MyDBHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
        mContext = context;
    }

    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        sqLiteDatabase.execSQL(CREATE_PERSON);
        sqLiteDatabase.execSQL(CREATE_TEACHER);
        Toast.makeText(mContext, "Create table person success", Toast.LENGTH_LONG).show();
    }

    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
        sqLiteDatabase.execSQL("drop table if exists person");
        sqLiteDatabase.execSQL("drop table if exists teacher");
        onCreate(sqLiteDatabase);
    }
}

    运行后，通过adb查看相应目录下的文件，并通过sqlite3命令可以查看对应的table有两个，一个是person，另一个是

teacher。

    接下来添加数据。修改MainActivity代码如下：

package com.example.jared.dbtest;

import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private Button createDb;
    private Button addDataToDb;

    private MyDBHelper myDBHelper;

    private static final String dbName = "PersonStore.db";
    private static final int version = 2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myDBHelper = new MyDBHelper(this, dbName, null, version);

        createDb = (Button)findViewById(R.id.createDB);
        createDb.setOnClickListener(new myOnClickListener());

        addDataToDb = (Button)findViewById(R.id.addData);
        addDataToDb.setOnClickListener(new myOnClickListener());
    }

    private class myOnClickListener implements View.OnClickListener {
        @Override
        public void onClick(View view) {
            switch (view.getId()){
                case R.id.createDB:
                    myDBHelper.getWritableDatabase();
                    break;
                case R.id.addData:
                    addDataToPerson("xiao ming", 20, 172.5, "man");
                    addDataToPerson("xiao hong", 22, 160.3, "woman");
                    addDataToPerson("xiao li", 25, 180.5, "man");
                    break;
                default:
                    break;
            }
        }
    }

    public void addDataToPerson(String name, int age, double height, String sex) {
        SQLiteDatabase db = myDBHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("name", name);
        values.put("age", age);
        values.put("height", height);
        values.put("sex", sex);
        db.insert("person", null, values);
    }
}

    运行后点击添加数据按钮，这里会添加3条数据。通过命令行查看数据库信息如下：

    从上图可知已经添加了3条数据了，添加数据成功了。

    接着我们如果我们发现小明又长高了，从原来的172.5到了175了，那么我们来更新下xiao ming的身高。修改

MainActivity代码：

package com.example.jared.dbtest;

import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private Button createDb;
    private Button addDataToDb;
    private Button updateToDb;

    private MyDBHelper myDBHelper;

    private static final String dbName = "PersonStore.db";
    private static final int version = 2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myDBHelper = new MyDBHelper(this, dbName, null, version);

        createDb = (Button)findViewById(R.id.createDB);
        createDb.setOnClickListener(new myOnClickListener());

        addDataToDb = (Button)findViewById(R.id.addData);
        addDataToDb.setOnClickListener(new myOnClickListener());

        updateToDb = (Button)findViewById(R.id.updateData);
        updateToDb.setOnClickListener(new myOnClickListener());

    }

    private class myOnClickListener implements View.OnClickListener {
        @Override
        public void onClick(View view) {
            switch (view.getId()){
                case R.id.createDB:
                    myDBHelper.getWritableDatabase();
                    break;
                case R.id.addData:
                    addDataToPerson("xiao ming", 20, 172.5, "man");
                    addDataToPerson("xiao hong", 22, 160.3, "woman");
                    addDataToPerson("xiao li", 25, 180.5, "man");
                    break;
                case R.id.updateData:
                    updateHeight("xiao ming", 175.0);
                    break;
                default:
                    break;
            }
        }
    }

    public void updateHeight(String name, double height) {
        SQLiteDatabase db = myDBHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("height", height);
        db.update("person", values, "name = ?", new String[] {name});
    }

    public void addDataToPerson(String name, int age, double height, String sex) {
        SQLiteDatabase db = myDBHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("name", name);
        values.put("age", age);
        values.put("height", height);
        values.put("sex", sex);
        db.insert("person", null, values);
    }
}

    运行后点击更新数据按钮，然后通过命令行查看如下：

    xiao ming的身高已经更新为175.0了，更新的数据已经OK了。

    如果我们发现多录入了xiao li，其实xiao li已经录入过了，那么得删除掉它，接着来删除吧，代码如下：

package com.example.jared.dbtest;

import android.content.ContentValues;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private Button createDb;
    private Button addDataToDb;
    private Button updateToDb;
    private Button delToDb;

    private MyDBHelper myDBHelper;

    private static final String dbName = "PersonStore.db";
    private static final int version = 2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myDBHelper = new MyDBHelper(this, dbName, null, version);

        createDb = (Button)findViewById(R.id.createDB);
        createDb.setOnClickListener(new myOnClickListener());

        addDataToDb = (Button)findViewById(R.id.addData);
        addDataToDb.setOnClickListener(new myOnClickListener());

        updateToDb = (Button)findViewById(R.id.updateData);
        updateToDb.setOnClickListener(new myOnClickListener());

        delToDb = (Button)findViewById(R.id.delData);
        delToDb.setOnClickListener(new myOnClickListener());

    }

    private class myOnClickListener implements View.OnClickListener {
        @Override
        public void onClick(View view) {
            switch (view.getId()){
                case R.id.createDB:
                    myDBHelper.getWritableDatabase();
                    break;
                case R.id.addData:
                    addDataToPerson("xiao ming", 20, 172.5, "man");
                    addDataToPerson("xiao hong", 22, 160.3, "woman");
                    addDataToPerson("xiao li", 25, 180.5, "man");
                    break;
                case R.id.updateData:
                    updateHeight("xiao ming", 175.0);
                    break;
                case R.id.delData:
                    deleteByName("xiao li");
                    break;
                default:
                    break;
            }
        }
    }

    public void deleteByName(String name) {
        SQLiteDatabase db = myDBHelper.getWritableDatabase();
        db.delete("Person", "name = ?", new String[]{name});
    }

    public void updateHeight(String name, double height) {
        SQLiteDatabase db = myDBHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("height", height);
        db.update("person", values, "name = ?", new String[] {name});
    }

    public void addDataToPerson(String name, int age, double height, String sex) {
        SQLiteDatabase db = myDBHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("name", name);
        values.put("age", age);
        values.put("height", height);
        values.put("sex", sex);
        db.insert("person", null, values);
    }
}

    运行代码后点击删除数据按钮，然后通过命令行如下图：

    由上可知xiao li已经被删除了。

    最后来使用下查询，比如我们要查看年龄大于21岁的人的信息。 代码如下：

package com.example.jared.dbtest;

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private static final String TAB = "DBTest";
    private Button createDb;
    private Button addDataToDb;
    private Button updateToDb;
    private Button delToDb;
    private Button queryToDb;

    private MyDBHelper myDBHelper;

    private static final String dbName = "PersonStore.db";
    private static final int version = 2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myDBHelper = new MyDBHelper(this, dbName, null, version);

        createDb = (Button)findViewById(R.id.createDB);
        createDb.setOnClickListener(new myOnClickListener());

        addDataToDb = (Button)findViewById(R.id.addData);
        addDataToDb.setOnClickListener(new myOnClickListener());

        updateToDb = (Button)findViewById(R.id.updateData);
        updateToDb.setOnClickListener(new myOnClickListener());

        delToDb = (Button)findViewById(R.id.delData);
        delToDb.setOnClickListener(new myOnClickListener());

        queryToDb = (Button)findViewById(R.id.queryData);
        queryToDb.setOnClickListener(new myOnClickListener());

    }

    private class myOnClickListener implements View.OnClickListener {
        @Override
        public void onClick(View view) {
            switch (view.getId()){
                case R.id.createDB:
                    myDBHelper.getWritableDatabase();
                    break;
                case R.id.addData:
                    addDataToPerson("xiao ming", 20, 172.5, "man");
                    addDataToPerson("xiao hong", 22, 160.3, "woman");
                    addDataToPerson("xiao li", 25, 180.5, "man");
                    break;
                case R.id.updateData:
                    updateHeight("xiao ming", 175.0);
                    break;
                case R.id.delData:
                    deleteByName("xiao li");
                    break;
                case R.id.queryData:
                    queryByAge(21);
                    break;
                default:
                    break;
            }
        }
    }

    public void queryByAge(int age) {
        SQLiteDatabase db = myDBHelper.getWritableDatabase();
        Cursor cursor = db.rawQuery("select * from person where age > ?", new String[]{String.valueOf(age)});
        while(cursor.moveToNext()){
            int id = cursor.getInt(cursor.getColumnIndex("id"));
            String name = cursor.getString(cursor.getColumnIndex("name"));
            int age1 = cursor.getInt(cursor.getColumnIndex("age"));
            double height = cursor.getDouble(cursor.getColumnIndex("height"));
            String sex = cursor.getString(cursor.getColumnIndex("sex"));
            Log.d(TAB, "id:"+id + "| name:"+name + "| age:"+age1 + "| height:"+height + "| sex:"+sex);
        }
    }

    public void deleteByName(String name) {
        SQLiteDatabase db = myDBHelper.getWritableDatabase();
        db.delete("Person", "name = ?", new String[]{name});
    }

    public void updateHeight(String name, double height) {
        SQLiteDatabase db = myDBHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("height", height);
        db.update("person", values, "name = ?", new String[] {name});
    }

    public void addDataToPerson(String name, int age, double height, String sex) {
        SQLiteDatabase db = myDBHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("name", name);
        values.put("age", age);
        values.put("height", height);
        values.put("sex", sex);
        db.insert("person", null, values);
    }
}

    运行效果如下：

02-14 09:14:59.100 29182-29182/com.example.jared.dbtest D/DBTest: id:2| name:xiao hong| age:22| height:160.3| sex:woman

    显然年龄为20的xiao ming没有打印出来，我们需要查找的是年龄大于21岁的人，在数据库中就是xiao hong了。这里的查找直接用的sql语句，其实还是sql语句比较直接明了。关于数据库基本也学到了这里。

附：参考《第一行代码》