<?xml version="1.0" encoding="utf-8"?><LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical" ><Buttonandroid:id="@+id/save"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="保存數據(File)" /><Buttonandroid:id="@+id/read"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="讀取數據(File)" /></LinearLayout> package com.example.yanlei.wifi;import android.os.Bundle;import android.os.Environment;import android.support.v7.app.AppCompatActivity;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.Toast;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.PrintStream;import java.util.Scanner;public class MainActivity extends AppCompatActivity {private Button btnSave=null;private Button btnRead=null;private File file=null;private static final String FILENAME="data.txt";@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);btnSave=(Button)super.findViewById(R.id.save);btnRead=(Button)super.findViewById(R.id.read);btnSave.setOnClickListener(new OnClickListener(){public void onClick(View v){PrintStream ps=null;//判斷外部存儲卡是否存在if(!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){Toast.makeText(getApplicationContext(), "讀取失敗，SD存儲卡不存在！", Toast.LENGTH_LONG).show();return;}//初始化FileString path=Environment.getExternalStorageDirectory().toString()+File.separator+"genwoxue"+File.separator+FILENAME;file=new File(path);//如果當前文件的父文件夾不存在，則創建genwoxue文件夾if(!file.getParentFile().exists())file.getParentFile().mkdirs();//寫文件try {ps = new PrintStream(new FileOutputStream(file));ps.println("跟我學網址：www.genwoxue.com");ps.println("");ps.println("電子郵件：hello@genwoxue.com");} catch (FileNotFoundException e) {e.printStackTrace();}finally{ps.close();}Toast.makeText(getApplicationContext(), "保存成功！", Toast.LENGTH_LONG).show();}});btnRead.setOnClickListener(new OnClickListener(){public void onClick(View v){StringBuffer info=new StringBuffer();//判斷外部存儲卡是否存在if(!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){Toast.makeText(getApplicationContext(), "讀取失敗，SD存儲卡不存在！", Toast.LENGTH_LONG).show();return;}//初始化FileString path=Environment.getExternalStorageDirectory().toString()+File.separator+"genwoxue"+File.separator+FILENAME;file=new File(path);if(!file.exists()){Toast.makeText(getApplicationContext(), "文件不存在！", Toast.LENGTH_LONG).show();return;}//讀取文件內容Scanner scan=null;try {scan=new Scanner(new FileInputStream(file));while(scan.hasNext()){info.append(scan.next()).append("☆☆☆/n");}Toast.makeText(getApplicationContext(), info.toString(), Toast.LENGTH_LONG).show();} catch (FileNotFoundException e) {e.printStackTrace();}finally{scan.close();}}});}}

<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.example.yanlei.wifi" ><!-- 在SDCard中創建與刪除文件權限 --><uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/><!-- 往SDCard寫入數據權限 --><uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /><applicationandroid:allowBackup="true"android:icon="@mipmap/ic_launcher"android:label="@string/app_name"android:theme="@style/AppTheme" ><activityandroid:name=".MainActivity"android:label="@string/app_name" ><intent-filter><action android:name="android.intent.action.MAIN" /><category android:name="android.intent.category.LAUNCHER" /></intent-filter></activity></application></manifest><uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/><uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />