Android——几种数据存储应用浅谈

（1）android中的数据存储主要有五种方式：

        第一种、sharedPreferences存储数据，

适用范围：保存少量的数据，且这些数据的格式非常简单：字符串型、基本类型的值。比如应用程序的各种配置信息（如是否打开音效、是否使用震动效果、小游戏的玩家积分等），解锁口 令密码等

    核心原理：保存基于XML文件存储的key-value键值对数据，通常用来存储一些简单的配置信息。通过DDMS的File Explorer面板，展开文件浏览树,很明显SharedPreferences数据总是存储在/data/data/<package name>/shared_prefs目录下。SharedPreferences对象本身只能获取数据而不支持存储和修改,存储修改是通过SharedPreferences.edit()获取的内部接口Editor对象实现。 SharedPreferences本身是一 个接口，程序无法直接创建SharedPreferences实例，只能通过Context提供的getSharedPreferences(String name, int mode)方法来获取SharedPreferences实例，该方法中name表示要操作的xml文件名，第二个参数具体如下：

                 Context.MODE_PRIVATE: 指定该SharedPreferences数据只能被本应用程序读、写。

                 Context.MODE_WORLD_READABLE:  指定该SharedPreferences数据能被其他应用程序读，但不能写。

                 Context.MODE_WORLD_WRITEABLE:  指定该SharedPreferences数据能被其他应用程序读，写

Editor有如下主要重要方法：

                 SharedPreferences.Editor clear():清空SharedPreferences里所有数据

                 SharedPreferences.Editor putXxx(String key , xxx value): 向SharedPreferences存入指定key对应的数据，其中xxx 可以是boolean,float,int等各种基本类型据

                 SharedPreferences.Editor remove(): 删除SharedPreferences中指定key对应的数据项

                 boolean commit(): 当Editor编辑完成后，使用该方法提交修改

下面是具体的demo，登录注册通过sharedPreferences保存注册数据到user.xml文件中，通过sharedPerferences的contains方法验证用户是否存在，截图如下

具体实现代码如下：

package com.example.shareperferencesdemo1;

import android.app.Activity;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {
	EditText edtName, edtPwd;
	Button btnLogin, btnRegister;
	SharedPreferences sp;
	Editor editor;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		edtName = (EditText) findViewById(R.id.editText1);
		edtPwd = (EditText) findViewById(R.id.editText2);
		btnLogin = (Button) findViewById(R.id.button1);
		btnRegister = (Button) findViewById(R.id.button2);
		//实例化sharedperferences对象
		sp = getSharedPreferences("user", Activity.MODE_PRIVATE);

		btnLogin.setOnClickListener(new View.OnClickListener() {

			@Override
			public void onClick(View v) {
				String uName=edtName.getText().toString();
				String uPwd=edtPwd.getText().toString();
				if(uName.equals("")||uPwd.equals("")){
					Toast.makeText(MainActivity.this, "用户名或密码不能为空", 2000).show();
				}else{
					//如果sharedpreferences中用户名已经存在
					if(sp.contains(uName)){
						//调用sharedpferences对象的getString（键值对）方法判断是否存在用户
						if(uPwd.equals(sp.getString(uName,uPwd))){
							Toast.makeText(MainActivity.this, "登录成功",2000 ).show();
						}else{
							Toast.makeText(MainActivity.this, "登录失败",2000).show();
						}
					}
				}
			}
		});
		btnRegister.setOnClickListener(new View.OnClickListener() {

			@Override
			public void onClick(View v) {
				if (edtName.getText().toString().equals("") || edtPwd.getText().toString().equals("")) {
					Toast.makeText(MainActivity.this, "用户名或者密码不能为空！", 2000).show();
				} else {
					String name = edtName.getText().toString();
					String pwd = edtPwd.getText().toString();
					if (sp.contains(name)) {
						Toast.makeText(MainActivity.this, "用户已存在", 2000).show();
					} else {
						//获取edit对象
						editor = sp.edit();
						//向user文件中添加用户信息键值对
						editor.putString(name, pwd);
						//添加数据
						editor.commit();
						Toast.makeText(MainActivity.this, "注册成功", 2000).show();
					}
				}
			}
		});
	}

}

（2）文件存储

文件如果不放在sdcrad中则存在data/data目录下，如果文件要放在SDCard中，则首先要判断SDCard是否存在，如果存在，要获取SDCard文件对象，代码为

if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
			//存在的情况
                    //Environment.getExternalStorageState(),获取SDCard的状态
			//获取sdcard的文件对象
			File sdCard=Environment.getExternalStorageDirectory();
			
		}                                

还需要在注册文件中声明对Sdcard的读写权限

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />

效果图

代码如下：

package com.example.filestoragedemo;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.RandomAccessFile;
import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
	private TextView tvContext;
	private EditText edtContext;
	private Button btnWrite;
	private Button btnRead;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		// 关联控件
		tvContext = (TextView) findViewById(R.id.txtContext);
		edtContext = (EditText) findViewById(R.id.edtContext);
		btnWrite = (Button) findViewById(R.id.btnWrite);
		btnRead = (Button) findViewById(R.id.btnRead);

		btnWrite.setOnClickListener(new View.OnClickListener() {

			@Override
			public void onClick(View v) {
				String str = edtContext.getText().toString();
				try {
					writeFile(str);
					edtContext.setText("");
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		});

		btnRead.setOnClickListener(new View.OnClickListener() {

			@Override
			public void onClick(View v) {
				try {
					String str=readFile();
					tvContext.setText(str);
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		});

	}

	// 写入文件的方法
	public void writeFile(String str) throws IOException {
		// 将文件写到sdcard中
		// 首先判断sdcard是否存在
		if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
			// 存在的情况
			// 获取sdcard的文件对象
			File sdCard = Environment.getExternalStorageDirectory();
			// 创建文件
			File file = new File(sdCard.getAbsolutePath() + "/abc.txt");
			// 随机流
			RandomAccessFile rf = new RandomAccessFile(file, "rw");
			// 将文件指针放到末尾
			rf.seek(file.length());
			// 写入文件
			rf.write(str.getBytes());
			// 关闭随机流
			rf.close();
		} else {
			Toast.makeText(MainActivity.this, "请插入内存卡", 2000).show();
		}
	}

	public String readFile() throws IOException {
		// 将文件写到sdcard中
		// 首先判断sdcard是否存在
		if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
			// 存在的情况
			// 获取sdcard的文件对象
			File sdCard = Environment.getExternalStorageDirectory();
			// 创建文件
			File file = new File(sdCard.getAbsolutePath() + "/abc.txt");
			//将文件转化为字节流
			FileInputStream fs = new FileInputStream(file);
			// 将字节流转化为字符流
			BufferedReader bf = new BufferedReader(new InputStreamReader(fs));
			StringBuffer sb = new StringBuffer();
			String line = null;
			// 读取
			while ((line = bf.readLine()) != null) {
				sb.append(line);
			}
			bf.close();
			fs.close();
			return sb.toString();
		} else {
			Toast.makeText(MainActivity.this, "请插入内存卡", 2000).show();
			return null;
		}
	}
}

（3）sqlite 数据存储

SQLite是轻量级嵌入式数据库引擎，它支持 SQL 语言，并且只利用很少的内存就有很好的性能。现在的主流移动设备像Android、iPhone等都使用SQLite作为复杂数据的存储引擎，在我们为移动设备开发应用程序时，也许就要使用到SQLite来存储我们大量的数据，所以我们就需要掌握移动设备上的SQLite开发技巧，SQLiteDatabase类为我们提供了很多种方法。

要使用sqlite数据存储需要创建一个继承于SQLiteOpenHelper的类，该类封装了sqlite和android之间的驱动，所以我们不用向在java中一样要加载数据库驱动。

下面用一个学生信息demo，来实现学生的增删改查，demo的界面如下

首先建一个student实体类，代码如下

package com.example.androidsqlitedemo;

import java.io.Serializable;

public class Student implements Serializable{
	private int id;
	private String name;
	private String sex;
	private int age;
	public Student(){
		
	}
	public Student(int id){
		super();
		this.id = id;
	}
	public Student(String name, String sex, int age) {
		super();
		this.name = name;
		this.sex = sex;
		this.age = age;
	}
	public Student(int id, String name, String sex, int age) {
		super();
		this.id = id;
		this.name = name;
		this.sex = sex;
		this.age = age;
	}
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	

}

　　数据库操作类

package com.example.androidsqlitedemo;

import java.util.ArrayList;
import java.util.List;

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

public class MyDB extends SQLiteOpenHelper {

	public MyDB(Context context){
		super(context, "myDB.db", null, 1);
	}
	public MyDB(Context context, String name, CursorFactory factory, int version) {
		super(context, "myDB.db", null, 1);
	}

	@Override
	public void onCreate(SQLiteDatabase db) {
		//建表
		String sql="create table student(id Integer primary key not null,name varchar(20),sex varchar,age Integer)";
		db.execSQL(sql);
	}

	@Override
	public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

	}
	//根据学号验证学生是否存在
	public Boolean isStudentExit(Student student){
		SQLiteDatabase db = this.getWritableDatabase();
		String sql="select * from student where id='"+student.getId()+"'";
		Cursor cursor = db.rawQuery(sql, null);
		if(cursor.getCount()==0){
			return false;
		}else{
			return true;
		}
	}
	//添加数据
	public void insertStudent(Student student){
		SQLiteDatabase db = this.getWritableDatabase();
		String sql="insert into student(name,sex,age) values (?,?,?)";
		db.execSQL(sql,new Object[]{student.getName(),student.getSex(),student.getAge()});
		db.close();//关闭数据库
	}
	//删除数据
	public void deleteStudent(Student student){
		SQLiteDatabase db = this.getWritableDatabase();
		String sql="delete from student where id=?";
		db.execSQL(sql, new Object[]{student.getId()});
		db.close();
	}
	//修改学生信息
	public void updateStudent(Student student){
		SQLiteDatabase db = this.getWritableDatabase();
		String sql="update student set name=?,sex=?,age=? where id=?";
		db.execSQL(sql, new Object[]{student.getName(),student.getSex(),student.getAge(),student.getId()});
		db.close();
	}
	//查一个学生的信息
	public Student getStudent(int id){
		Student student=new Student();
		SQLiteDatabase db = this.getWritableDatabase();
		String sql="select * from student where id='"+id+"'";
		Cursor cursor = db.rawQuery(sql, null);
		while(cursor.moveToNext()){
			String name=cursor.getString(1);
			String sex=cursor.getString(2);
			int age=cursor.getInt(3);
			student.setId(id);
			student.setName(name);
			student.setSex(sex);
			student.setAge(age);
		}
		return student;
	}
	//查询所有学生的信息
	public ArrayList<Student> getAllStudent(){
		ArrayList<Student> list=new ArrayList<Student>();
		SQLiteDatabase db = this.getWritableDatabase();
		String sql="select * from student";
		Cursor cursor = db.rawQuery(sql, null);
		while (cursor.moveToNext()) {
			int id=cursor.getInt(0);
			String name = cursor.getString(1);
			String sex = cursor.getString(2);
			int age = cursor.getInt(3);
			list.add(new Student(id,name, sex, age));
		}
		return list;
		
	}


}

　　主界面的后台代码

package com.example.androidsqlitedemo;



import java.io.Serializable;
import java.util.ArrayList;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {

	private EditText edtId,edtName,edtSex,edtAge;
	private Button btnAdd,btnDelete,btnUpdate,btnFind,btnFindAll;
	private MyDB mydata;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		edtId=(EditText) findViewById(R.id.edtId);
		edtName=(EditText) findViewById(R.id.edtName);
		edtSex=(EditText) findViewById(R.id.edtSex);
		edtAge=(EditText) findViewById(R.id.edtAge);
		btnAdd=(Button)findViewById(R.id.btnAdd);
		btnDelete=(Button)findViewById(R.id.btnDelete);
		btnUpdate=(Button)findViewById(R.id.btnUpdate);
		btnFind=(Button)findViewById(R.id.btnFind);
		btnFindAll=(Button)findViewById(R.id.btnFindAll);
		mydata=new MyDB(MainActivity.this);
		
		btnAdd.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				//edtId.setEnabled(false);
				if(edtName.getText().toString().equals("")||edtAge.getText().toString().equals("")||edtSex.getText().equals("")){
					Toast.makeText(MainActivity.this, "学生信息不能为空", 2000).show();
				}else{
					String name=edtName.getText().toString();
					String sex=edtSex.getText().toString();
					int age=Integer.parseInt(edtAge.getText().toString());
					//Log.i("key", age+"");
					Student student=new Student(name, sex, age);
					mydata.insertStudent(student);
					Toast.makeText(MainActivity.this, "添加成功", 2000).show();
					edtAge.setText("");
					edtName.setText("");
					edtSex.setText("");
				}
			}
		});
		btnDelete.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				if(edtId.getText().toString().equals("")){
					Toast.makeText(MainActivity.this, "请输入要删除学生的学号", 2000).show();
				}else{
					int id=Integer.parseInt(edtId.getText().toString());
					Student student=new Student(id);
					if(mydata.isStudentExit(student)){
						mydata.deleteStudent(student);
						edtId.setText("");
						Toast.makeText(MainActivity.this, "删除成功", 2000).show();
					}else{
						Toast.makeText(MainActivity.this, "要删除的学生不存在", 2000).show();
					}
				}
			}
		});
		btnUpdate.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				if(edtId.getText().toString().equals("")){
					Toast.makeText(MainActivity.this, "请输入要修改学生信息的学号", 2000).show();
				}else{
					int id=Integer.parseInt(edtId.getText().toString());
					Student student=new Student(id);
					if(mydata.isStudentExit(student)){
						if(edtAge.getText().toString().equals("")||edtName.getText().toString().equals("")||edtSex.getText().toString().equals("")){
							Toast.makeText(MainActivity.this, "要修改的学生信息不能为空", 2000).show();
						}
						else{
							String name=edtName.getText().toString();
							String sex=edtSex.getText().toString();
							int age=Integer.parseInt(edtAge.getText().toString());
							Student stu=new Student(id, name, sex, age);
							mydata.updateStudent(stu);
							Toast.makeText(MainActivity.this, "修改成功", 2000).show();
						}
					}else{
						Toast.makeText(MainActivity.this, "该学生不存在，请重新输入学号", 2000).show();
					}
				}
			}
		});
		btnFind.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				if(edtId.getText().toString().equals("")){
					Toast.makeText(MainActivity.this, "请输入要查找学生的学号", 2000).show();
				}else{
					int id=Integer.parseInt(edtId.getText().toString());
					//Log.i("key", id+"");
					Student stu=new Student(id);
					if(mydata.isStudentExit(stu)){
						Student student=mydata.getStudent(id);
						edtName.setText(student.getName().toString());
						edtAge.setText(student.getAge()+"");
						edtSex.setText(student.getSex().toString());
					}else{
						Toast.makeText(MainActivity.this, "改学生不存在，请重新输入学号", 2000).show();
					}
				}
			}
		});
		btnFindAll.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				ArrayList<Student> list=mydata.getAllStudent();
				Bundle bundle=new Bundle();
				//这里list里面存储的student要实现Serializable接口菜可以被传递
				bundle.putSerializable("list", (Serializable)list);
				Intent intent=new Intent(MainActivity.this,StudentInfo.class);
				intent.putExtras(bundle);
				startActivity(intent);
				Log.i("list", "success");
			}
		});
	}

}

　　传递参数后的第二个界面代码

package com.example.androidsqlitedemo;

import java.util.ArrayList;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.ListView;

public class StudentInfo extends Activity {
	private ListView lvStudent;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.student);
		lvStudent=(ListView) findViewById(R.id.lvStudent);
		Intent intent=getIntent();
		ArrayList<Student> list =(ArrayList<Student>) intent.getSerializableExtra("list");
		lvStudent.setAdapter(new MyAdapter(this, list));
	}
}

　　listView适配器代码

package com.example.androidsqlitedemo;

import java.util.ArrayList;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class MyAdapter extends BaseAdapter {
	private Context context;
	private ArrayList<Student> list;
	

	public MyAdapter(Context context, ArrayList<Student> list) {
		super();
		this.context = context;
		this.list = list;
	}

	@Override
	public int getCount() {
		return list.size();
	}

	@Override
	public Object getItem(int position) {
		return position;
	}

	@Override
	public long getItemId(int position) {
		return position;
	}

	@Override
	public View getView(int position, View view, ViewGroup parent) {
		ViewHolder holder;
		if(view==null){
			holder=new ViewHolder();
			view=LayoutInflater.from(context).inflate(R.layout.item, null);
			holder.txtID=(TextView) view.findViewById(R.id.tvID);
			holder.txtName=(TextView) view.findViewById(R.id.tvName);
			holder.txtSex=(TextView) view.findViewById(R.id.tvSex);
			holder.txtAge=(TextView) view.findViewById(R.id.tvAge);
			view.setTag(holder);
		}
		else{
			holder=(ViewHolder) view.getTag();
		}
		holder.txtID.setText(list.get(position).getId()+"");
		holder.txtName.setText(list.get(position).getName().toString());
		holder.txtSex.setText(list.get(position).getSex().toString());
		holder.txtAge.setText(list.get(position).getAge()+"");
		return view;
	}
	private final class ViewHolder{
		TextView txtID;
		TextView txtName;
		TextView txtSex;
		TextView txtAge;
	}

}

　　android与sqlite中游标cursor对象类似于dataset对象，其主要的方法有

1 c.move(int offset); //以当前位置为参考,移动到指定行  
 2 c.moveToFirst();    //移动到第一行  
 3 c.moveToLast();     //移动到最后一行  
 4 c.moveToPosition(int position); //移动到指定行  
 5 c.moveToPrevious(); //移动到前一行  
 6 c.moveToNext();     //移动到下一行  
 7 c.isFirst();        //是否指向第一条  
 8 c.isLast();     //是否指向最后一条  
 9 c.isBeforeFirst();  //是否指向第一条之前  
10 c.isAfterLast();    //是否指向最后一条之后  
11 c.isNull(int columnIndex);  //指定列是否为空(列基数为0)  
12 c.isClosed();       //游标是否已关闭  
13 c.getCount();       //总数据项数  
14 c.getPosition();    //返回当前游标所指向的行数  
15 c.getColumnIndex(String columnName);//返回某列名对应的列索引值  
16 c.getString(int columnIndex);   //返回当前行指定列的值 

（4）contentprovider存储数据

（5）网络存储数据