记住账号密码（本地存储）

1.activity_main.xml

<?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"
    tools:context=".MainActivity">


    <ImageView
        android:id="@+id/iv"
        android:layout_width="70dp"
        android:layout_height="70dp"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="40dp"
        android:background="@drawable/dongman"/>

    <LinearLayout
        android:id="@+id/ll_number"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/iv"
        android:layout_centerVertical="true"
        android:layout_marginTop="15dp"
        android:layout_marginLeft="10dp"
        android:layout_marginRight="10dp"
        android:layout_marginBottom="5dp"
        android:background="#ffffff">

        <TextView
            android:id="@+id/tv_number"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="10dp"
            android:text="账号"
            android:textColor="#000"
            android:textSize="20sp"/>
        <EditText
            android:id="@+id/et_number"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="5dp"
            android:background="@null"
            android:padding="10dp"/>
    </LinearLayout>


    <LinearLayout
        android:id="@+id/ll_password"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/ll_number"
        android:layout_centerVertical="true"
        android:layout_marginTop="15dp"
        android:layout_marginLeft="10dp"
        android:layout_marginRight="10dp"
        android:layout_marginBottom="5dp"
        android:background="#ffffff">

        <TextView
            android:id="@+id/tv_password"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="10dp"
            android:text="密码"
            android:textColor="#000"
            android:textSize="20sp"/>
        <EditText
            android:id="@+id/et_password"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginLeft="5dp"
            android:background="@null"
            android:padding="10dp"/>
    </LinearLayout>
    <Button
        android:id="@+id/btn_login"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/ll_password"
        android:layout_marginLeft="10dp"
        android:layout_marginRight="10dp"
        android:layout_marginTop="30dp"
        android:text="登录"
        android:background="#3C8DC4"
        android:textSize="20sp"/>


</RelativeLayout>

2.MainActivity.java主页内容

package com.example.remembernp;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import java.util.Map;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private EditText etNumber;
    private EditText etPassword;
    private Button btnLogin;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button btn = (Button)findViewById(R.id.btn_login);
        Map<String,String> userInfo = SaveFile.getUserInfo(this);
        initView();
        if(userInfo != null){
            etNumber.setText(userInfo.get("number"));
            etPassword.setText(userInfo.get("password"));
        }
    }

    private void  initView(){
        etNumber = (EditText)findViewById(R.id.et_number);
        etPassword = (EditText)findViewById(R.id.et_password);
        btnLogin = (Button)findViewById(R.id.btn_login);
        btnLogin.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        //单击事件，获取账号密码
        String number = etNumber.getText().toString().trim();
        String password = etPassword.getText().toString().trim();
        //检查账号密码是否正确
        if(TextUtils.isEmpty(number)){
            Toast.makeText(this, "请输入账号", Toast.LENGTH_SHORT).show();
            return;
        }
        if(TextUtils.isEmpty(password)){
            Toast.makeText(this, "请输入密码", Toast.LENGTH_SHORT).show();
            return;
        }
        //否则登录成功
        Toast.makeText(this, "登录成功", Toast.LENGTH_SHORT).show();
        //保存信息
        boolean isSaveSuccess = SaveFile.saveUserInfo(this,number,password);
        if(isSaveSuccess){
            Toast.makeText(this, "保存成功", Toast.LENGTH_SHORT).show();
        }else{
            Toast.makeText(this, "保存失败", Toast.LENGTH_SHORT).show();
        }
    }
}

3.创建一个保存文件的类

package com.example.remembernp;

import android.content.Context;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.util.HashMap;
import java.util.Map;

public class SaveFile {
    //把账号密码保存在data.txt文件中
    public static boolean saveUserInfo(Context context, String number, String password){
        try{
            FileOutputStream fos = context.openFileOutput("data.txt",Context.MODE_PRIVATE);
            fos.write((number + ":" + password).getBytes());
            fos.close();
            return true;
        }catch (Exception e){
            e.printStackTrace();
            return false;
        }
    }
    //从data.txt中去获取刚刚保存的账号密码
    public static Map<String,String> getUserInfo(Context context) {
        String content = "";
        try {
            FileInputStream fis = context.openFileInput("data.txt");
            byte[] buffer = new byte[fis.available()];
            fis.read(buffer);//读取
            content = new String(buffer);
            Map<String ,String > userMap = new HashMap<String, String>();
            String[] infos = content.split(":");
            userMap.put("number",infos[0]);
            userMap.put("password",infos[1]);
            fis.close();
            return userMap;
        }catch (Exception e){
            e.printStackTrace();
            return null;
        }

    }
}