文件存储

Context类中提供了一个openFileOutput()方法，可以用于将数据存储到指定文件中。
第一个参数是文件名
第二个参数是文件的操作模式

文件默认会存储到/data/data/package name/files/目录下

MainActivity.java

package com.zhoujian.persistentdata;

import android.content.Context;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
import android.widget.EditText;
import android.widget.Toast;
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 EditText edit;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        edit = (EditText) findViewById(R.id.edit);
        String inputText = loadData();
        if (!TextUtils.isEmpty(inputText))
        {
            edit.setText(inputText);
            edit.setSelection(inputText.length());
            Toast.makeText(this, "恢复数据成功", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    protected void onDestroy()
    {
        super.onDestroy();
        String inputText = edit.getText().toString();
        saveData(inputText);
    }

    public void saveData(String inputText)
    {
        FileOutputStream out = null;
        BufferedWriter writer = null;
        try
        {
            //MODE_PRIVATE:默认模式，表示当指定同样文件名的时候，所写的内容将会覆盖原文件中的内容
            //MODE_APPEND:表示如果文件存在，就往文件里追加内容，不存在就创建
            out = openFileOutput("file", Context.MODE_PRIVATE);
            writer = new BufferedWriter(new OutputStreamWriter(out));
            writer.write(inputText);
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
        finally
        {
            try {
                if (writer != null) {
                    writer.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public String loadData()
    {
        FileInputStream in = null;
        BufferedReader reader = null;
        StringBuilder sb = new StringBuilder();
        try
        {
            in = openFileInput("file");
            reader = new BufferedReader(new InputStreamReader(in));
            String line = "";
            while ((line = reader.readLine()) != null)
            {
                sb.append(line);
            }
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
        finally
        {
            if (reader != null)
            {
                try
                {
                    reader.close();
                }
                catch (IOException e)
                {
                    e.printStackTrace();
                }
            }
        }
        return sb.toString();
    }
}

Demo下载：https://github.com/zeke123/PersistentData

SharedPreferences 存储

SharedPreferences是采用键值对的方式存储数据的

点击CheckBox，用SharedPreferences存储数据，记住用户名和密码

LoginActivity.java


package com.zhoujian.sharedPreferences;

import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;

public class LoginActivity extends BaseActivity
{

    private SharedPreferences pref;

    private SharedPreferences.Editor editor;

    private EditText mAccount;

    private EditText mPassword;

    private Button login;

    private CheckBox mCheckBox;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login);
        pref = PreferenceManager.getDefaultSharedPreferences(this);
        mAccount = (EditText) findViewById(R.id.account);
        mPassword = (EditText) findViewById(R.id.password);
        mCheckBox = (CheckBox) findViewById(R.id.remember_pass);
        login = (Button) findViewById(R.id.login);
        boolean isRemember = pref.getBoolean("remember_password", false);
        if (isRemember) {
            // 将账号和密码都设置到文本框中
            String account = pref.getString("account", "");
            String password = pref.getString("password", "");
            mAccount.setText(account);
            mPassword.setText(password);
            mCheckBox.setChecked(true);
        }
        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String account = mAccount.getText().toString();
                String password = mPassword.getText().toString();
                // 如果账号是123456且密码是123456，就认为登录成功
                if (account.equals("123456") && password.equals("123456")) {
                    editor = pref.edit();
                    if (mCheckBox.isChecked()) {
                        // 检查复选框是否被选中
                        editor.putBoolean("remember_password", true);
                        editor.putString("account", account);
                        editor.putString("password", password);
                    } else {
                        editor.clear();
                    }
                    editor.apply();
                    Intent intent = new Intent(LoginActivity.this, MainActivity.class);
                    startActivity(intent);
                    finish();
                } else {
                    Toast.makeText(LoginActivity.this, "账号或者密码错误", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}

Demo下载：https://github.com/zeke123/SharedPreferences

SQLite数据库存储

创建数据库

在mac上查看数据库的工具：SQLPro for SQLite

数据库文件位于：/data/data/package name/databases/目录下

MyDatabaseHelper.java

package com.zhoujian.sqlitedemo;

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

public class MyDatabaseHelper extends SQLiteOpenHelper {


    private Context mContext;

    //integer：表示整型
    //text:表示文本型
    //real:表示浮点型
    //blob:表示二进制类型

    public static final String CREATE_BOOK = "create table Book ("
            + "id integer primary key autoincrement, "
            + "author text, "
            + "price real, "
            + "pages integer, "
            + "name text)";

    public static final String CREATE_CATEGORY = "create table Category ("
            + "id integer primary key autoincrement, "
            + "category_name text, "
            + "category_code integer)";



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

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_BOOK);
        db.execSQL(CREATE_CATEGORY);
        Toast.makeText(mContext, "创建数据库成功", Toast.LENGTH_SHORT).show();
    }

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

        //当数据库升级的时候，如果表存在，会先删除表，然后重新创建
        db.execSQL("drop table if exists Book");
        db.execSQL("drop table if exists Category");
        onCreate(db);
    }

}

增删改查

MainActivity.java

package com.zhoujian.sqlitedemo;

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;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity
{

    private MyDatabaseHelper dbHelper;
    private SQLiteDatabase mDb;
    private Button mCreateDatabase;
    private Button mAddData;
    private Button mQueryButton;
    private Button mDeleteButton;
    private Button mUpdateData;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        dbHelper = new MyDatabaseHelper(this, "Book.db", null, 1);
        initViews();
        clickEvents();
    }

    private void initViews()
    {
        mCreateDatabase = (Button) findViewById(R.id.create_database);
        mAddData = (Button) findViewById(R.id.add_data);
        mQueryButton = (Button) findViewById(R.id.query_data);
        mDeleteButton = (Button) findViewById(R.id.delete_data);
        mUpdateData = (Button) findViewById(R.id.update_data);
    }
    private void clickEvents()
    {
        mCreateDatabase.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //getReadableDatabase():如果磁盘已满，将以只读的方式打开数据库
                //getWritableDatabase():如果磁盘已满，将出现异常

                mDb = dbHelper.getWritableDatabase();
            }
        });

        mAddData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(mDb!=null){
                    ContentValues values = new ContentValues();
                    // 插入第一条数据
                    values.put("name", "Android开发艺术探索");
                    values.put("author", "任玉刚");
                    values.put("pages", 494);
                    values.put("price", 65.5);
                    mDb.insert("Book", null, values);
                    values.clear();
                    // 插入第二条数据
                    values.put("name", "第一行代码");
                    values.put("author", "郭霖");
                    values.put("pages", 510);
                    values.put("price", 75);
                    mDb.insert("Book", null, values);
                    values.clear();
                    // 插入第三条数据
                    values.put("name", "疯狂Android讲义");
                    values.put("author", "李刚");
                    values.put("pages", 580);
                    values.put("price", 85);
                    mDb.insert("Book", null, values);


                    Toast.makeText(MainActivity.this, "添加数据成功", Toast.LENGTH_SHORT).show();
                }else {
                    Toast.makeText(MainActivity.this, "请先创建数据库", Toast.LENGTH_SHORT).show();
                }
            }
        });

        mUpdateData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(mDb!=null){

                    //把Android开发艺术探索这本书的价格改为70
                    ContentValues values = new ContentValues();
                    values.put("price", 70);
                    mDb.update("Book", values, "name = ?", new String[] { "Android开发艺术探索" });
                    Toast.makeText(MainActivity.this, "更新数据成功", Toast.LENGTH_SHORT).show();
                }else {
                    Toast.makeText(MainActivity.this, "请先创建数据库", Toast.LENGTH_SHORT).show();
                }
            }
        });

        mDeleteButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(mDb!=null){
                    //删除页数大于500的书籍
                    mDb.delete("Book", "pages > ?", new String[] { "500" });
                    Toast.makeText(MainActivity.this, "删除数据成功", Toast.LENGTH_SHORT).show();
                }else {
                    Toast.makeText(MainActivity.this, "请先创建数据库", Toast.LENGTH_SHORT).show();
                }
            }
        });

        mQueryButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if(mDb!=null){

                    // 查询Book表中所有的数据
                    Cursor cursor = mDb.query("Book", null, null, null, null, null, null);
                    if (cursor.moveToFirst()) {
                        do {
                            // 遍历Cursor对象，取出数据并打印
                            String name = cursor.getString(cursor.getColumnIndex("name"));
                            String author = cursor.getString(cursor.getColumnIndex("author"));
                            int pages = cursor.getInt(cursor.getColumnIndex("pages"));
                            double price = cursor.getDouble(cursor.getColumnIndex("price"));
                            Log.d("MainActivity", "书籍的名字： " + name);
                            Log.d("MainActivity", "书籍的作者： " + author);
                            Log.d("MainActivity", "书籍的页数： " + pages);
                            Log.d("MainActivity", "书籍的价格：" + price);
                        } while (cursor.moveToNext());
                    }
                    cursor.close();
                    Toast.makeText(MainActivity.this, "查询数据成功", Toast.LENGTH_SHORT).show();
                }else {
                    Toast.makeText(MainActivity.this, "请先创建数据库", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}

Demo下载：https://github.com/zeke123/SqliteDemo