Android开发学习之路--数据持久化之初体验

时间:2021-12-01 16:06:14

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:

Android开发学习之路--数据持久化之初体验

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

Android开发学习之路--数据持久化之初体验

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)

Android开发学习之路--数据持久化之初体验

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:

Android开发学习之路--数据持久化之初体验

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:

Android开发学习之路--数据持久化之初体验

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:

Android开发学习之路--数据持久化之初体验

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

Android开发学习之路--数据持久化之初体验

导出后打开文件可以查看内容如下:

Android开发学习之路--数据持久化之初体验

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:

Android开发学习之路--数据持久化之初体验

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。

Android开发学习之路--数据持久化之初体验

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:

Android开发学习之路--数据持久化之初体验

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

Android开发学习之路--数据持久化之初体验

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:

Android开发学习之路--数据持久化之初体验

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:

Android开发学习之路--数据持久化之初体验

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:

Android开发学习之路--数据持久化之初体验

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》