Android：保护现场的三种方法

方法一：用SharedPreferences

输出页面代码：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.hzyc.tf61.lesson11savedata.MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="登录"
        android:id="@+id/textView"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="90dp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="un："
        android:id="@+id/un1"
        android:layout_below="@+id/textView"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginTop="48dp" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/un"
        android:layout_alignBottom="@+id/un1"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:layout_toRightOf="@+id/un1"
        android:layout_toEndOf="@+id/un1" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="pw:"
        android:id="@+id/textView2"
        android:layout_centerVertical="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/pw"
        android:layout_alignBottom="@+id/textView2"
        android:layout_alignLeft="@+id/un"
        android:layout_alignStart="@+id/un"
        android:layout_alignRight="@+id/un"
        android:layout_alignEnd="@+id/un" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="存"
        android:id="@+id/login"
        android:layout_marginTop="84dp"
        android:layout_below="@+id/pw"
        android:layout_alignLeft="@+id/pw"
        android:layout_alignStart="@+id/pw" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="取"
        android:id="@+id/read"
        android:layout_alignTop="@+id/login"
        android:layout_alignRight="@+id/pw"
        android:layout_alignEnd="@+id/pw" />
</RelativeLayout>

java代码：

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

public class MainActivity extends AppCompatActivity {

    private Button button;
    private Button read;
    private EditText un;
    private EditText pw;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        button = (Button) findViewById(R.id.login);
        read = (Button) findViewById(R.id.read);
        un = (EditText) findViewById(R.id.un);
        pw = (EditText) findViewById(R.id.pw);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String unV = un.getText().toString().trim();
                String pwV = pw.getText().toString().trim();

                SharedPreferences sharedPreferences = getSharedPreferences("data1",1);//xml
                SharedPreferences.Editor editor =  sharedPreferences.edit();

                editor.putString("un",unV);
                editor.putString("pw",pwV);

                editor.putString("un","asd");//修改
                //editor.remove("pw");//删除   根据key删除数据


               boolean bol =  editor.commit();

            }
        });

        read.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                SharedPreferences sharedPreferences = getSharedPreferences("data1",1);//xml
                String unV = sharedPreferences.getString("un","no");
                String pwV = sharedPreferences.getString("pw","no");
                Log.i("message",unV+"-"+pwV);
            }
        });
    }
}

方法二：使用IO流

java代码如下：

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

import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;

public class Main2Activity extends AppCompatActivity {

    private Button save;
    private Button read;
    private EditText un;
    private EditText pw;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        save = (Button) findViewById(R.id.save);
        read = (Button) findViewById(R.id.read);
        un = (EditText) findViewById(R.id.un);
        pw = (EditText) findViewById(R.id.pw);

        save.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String unV = un.getText().toString().trim();
                String pwV = pw.getText().toString().trim();

                //准备输出流  并创建文件
                try {
                    FileOutputStream fileOutputStream = openFileOutput("data2",2);//txt
                    String info = unV+"-"+pwV;
                    fileOutputStream.write(info.getBytes());//往目标写数据

                    fileOutputStream.close();

                } catch (Exception e) {
                    e.printStackTrace();
                }

            }
        });

        read.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                try {
                    FileInputStream fileInputStream = openFileInput("data2");
                    byte[] bytes = new byte[1024];
                    int len = fileInputStream.read(bytes);

                    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
                    byteArrayOutputStream.write(bytes,0,len);

                    String receive = new String(byteArrayOutputStream.toString());

                    Log.i("接收的数据message",receive);
                    fileInputStream.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

方法三：Sqlite 微型数据存储方案
内存比较小 联系人这种才会用 安卓系统自带的数据库 存储在内存中 exe

Sqlite每一个app内置一个 属于系统

要使用Sqlite 需要创建 new 自己的库

1.创建一个类 继承SQLiteOpenHelper
2.创建表
MySqlite代码如下：

  public class MySqlite extends SQLiteOpenHelper{
    public MySqlite(Context context, int version) {
        super(context, "lesson11", null, version);
    }

    //创建表
    //当你初始化库的时候就会调用该方法  而且只调用一次
    @Override
    public void onCreate(SQLiteDatabase sqLiteDatabase) {
        Log.i("meaage","@@@@@@@@");
        //id 主键  类型  不再是int  必须用Integer   自增不用auto_increment  用autoincrement
        String sql = "create table user (id Integer primary key autoincrement,un varchar(10))";
        sqLiteDatabase.execSQL(sql);
    }

    //更新表结构
    //当版本号更改时，会调用更新方法
    @Override
    public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i1) {
        Log.i("meaage","####");
        String sql = "alter table user add pw varchar(10)";
        sqLiteDatabase.execSQL(sql);
    }
}

Main3Activity代码

 public class Main3Activity extends AppCompatActivity {
        private Button save;
        private Button read;
        private EditText un;
        private EditText pw;
        private int version = 3;//只能从小到大写1~     版本号只能越来越大
    
        private SQLiteDatabase sqLiteDatabase;
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main3);
    
            save = (Button) findViewById(R.id.save);
            read = (Button) findViewById(R.id.read);
            un = (EditText) findViewById(R.id.un);
            pw = (EditText) findViewById(R.id.pw);
    
            save.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    String unV = un.getText().toString().trim();
                    String pwV = pw.getText().toString().trim();
    
                    MySqlite mySqlite = new MySqlite(Main3Activity.this,version);
                    sqLiteDatabase = mySqlite.getReadableDatabase();//库才会创建完并且创建表
    
                    boolean bol = false;
                    sqLiteDatabase.execSQL("insert into user (un,pw) values ('"+unV+"','"+pwV+"')");
    
                    bol = true;
                }
            });
    
            read.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    MySqlite mySqlite = new MySqlite(Main3Activity.this,version);
                    sqLiteDatabase = mySqlite.getReadableDatabase();//库才会创建完并且创建表
    
                    //Cursor 游标   同resultSet  rs
                    Cursor c = sqLiteDatabase.rawQuery("select * from user",null);//第二个参数是给？赋值
                    c.moveToNext();//相当于rs.next();
                   String info =  c.getString(1);//根据列的索引取值  从0开始
                    Log.i("meaage",info);
                    String name = c.getColumnName(0);//
                    Log.i("meaage",name);
    
    
                }
            });
        }
    }