Android--数据持久化

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。