android之外部文件存储和读取

时间：2022-08-06 16:01:04

这次借用上次读写内部存储的代码，只是对将更换文件的读写路径即可。这里需要对获取SDcard的读写权限。

一、AndroidManifest.xml

这里增加了对外部存储设备的读写权限

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="xidian.dy.com.chujia">

    <application

        android:allowBackup="true"

        android:icon="@mipmap/ic_launcher"

        android:label="@string/app_name"

        android:supportsRtl="true"

        android:theme="@style/AppTheme">

        <activity android:name=".MainActivity">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

    </application>

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

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

</manifest>

二、activity_main.xml

<?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:paddingBottom="@dimen/activity_vertical_margin"

    android:paddingLeft="@dimen/activity_horizontal_margin"

    android:paddingRight="@dimen/activity_horizontal_margin"

    android:paddingTop="@dimen/activity_vertical_margin"

    android:orientation="vertical"

    tools:context="xidian.dy.com.chujia.MainActivity">

    <EditText

        android:id="@+id/username"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:hint="请输入用户名"/>

    <EditText

        android:id="@+id/password"

        android:inputType="textPassword"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:hint="请输入密码"/>

    <RelativeLayout

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:orientation="horizontal">

        <CheckBox

            android:id="@+id/remember"

            android:layout_width="wrap_content"

            android:layout_height="wrap_content"

            android:text="记住用户名和密码"

            android:layout_centerVertical="true"/>

        <Button

            android:id="@+id/login"

            android:layout_alignParentRight="true"

            android:layout_width="wrap_content"

            android:layout_height="wrap_content"

            android:text="登录"/>

    </RelativeLayout>

</LinearLayout>

三、MainActivity.java

package xidian.dy.com.chujia;

import android.os.Environment;

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.CheckBox;

import android.widget.EditText;

import java.io.BufferedReader;

import java.io.BufferedWriter;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStreamReader;

import java.io.OutputStreamWriter;

import java.io.PrintWriter;

public class MainActivity extends AppCompatActivity {

    private EditText etUsername;

    private EditText etPassword;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        Button bt = (Button) findViewById(R.id.login);

        etUsername = (EditText) findViewById(R.id.username);

        etPassword = (EditText) findViewById(R.id.password);

        if (bt != null)

            bt.setOnClickListener(new View.OnClickListener() {

                @Override

                public void onClick(View v) {

                    String username = null;

                    String password = null;

                    if (etUsername != null)

                        username = etUsername.getText().toString();

                    if (etPassword != null)

                        password = etPassword.getText().toString();

                    Log.e("Login", "登录成功");

                    CheckBox cb = (CheckBox) findViewById(R.id.remember);

                    if (cb != null && cb.isChecked()) {
　　　　　　　　　　　　　　 //这里获取sd卡的目录

                        File file = new File(Environment.getExternalStorageDirectory(), "info.txt");

                        PrintWriter pw;

                        try {

                            pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file))));

                            pw.println(username);

                            pw.println(password);

                            pw.close();

                        } catch (FileNotFoundException e) {

                            e.printStackTrace();

//                            Log.e("MainActivity", "file not found");

                        }

                    }

                }

            });

        this.readAccount();

    }

    public void readAccount() {

        File file = new File(Environment.getExternalStorageDirectory(), "info.txt");

        if (file.exists()) {

            try {

                BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));

                String str = br.readLine();

                if (etUsername != null)

                    etUsername.setText(str);

                str = br.readLine();

                if (etPassword != null)

                    etPassword.setText(str);

                br.close();

            } catch (IOException e) {

                e.printStackTrace();

            }

        }

    }

}

四、SDcard外部存储检查

在实际开发中，我们在对SDcard进行操作的时候一定先要检查手机是否有SDcard。然后才能对SD进行读写操作。

if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){

   //TODO

}

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