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[操作系统]android 数据文件存取至储存卡


来自:http://blog.csdn.net/jianghuiquan/article/details/8569233

<??><LinearLayout  ="http://schemas.android.com/apk/res/android"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:orientation="vertical" >  <Button    android:id="@+id/save"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text="保存数据(File)" />  <Button    android:id="@+id/read"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text="读取数据(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";  @Override  protected 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;        //判断外部存储卡是否存在        if(!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){          Toast.makeText(getApplicationContext(), "读取失败,SD存储卡不存在!", Toast.LENGTH_LONG).show();          return;        }        //初始化File        String path=Environment.getExternalStorageDirectory().toString()            +File.separator            +"genwoxue"            +File.separator            +FILENAME;        file=new File(path);        //如果当前文件的父文件夹不存在,则创建genwoxue文件夹        if(!file.getParentFile().exists())          file.getParentFile().mkdirs();        //写文件        try {          ps = new PrintStream(new FileOutputStream(file));          ps.println("跟我学网址:www.genwoxue.com");          ps.println("");          ps.println("电子邮件: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();        //判断外部存储卡是否存在        if(!Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){          Toast.makeText(getApplicationContext(), "读取失败,SD存储卡不存在!", Toast.LENGTH_LONG).show();          return;        }        //初始化File        String 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;        }        //读取文件内容        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();        }      }    });  }}

权限

<??><manifest ="http://schemas.android.com/apk/res/android"  package="com.example.yanlei.wifi" >  <!-- 在SDCard中创建与删除文件权限 -->  <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>  <!-- 往SDCard写入数据权限 -->  <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />  <application    android:allowBackup="true"    android:icon="@mipmap/ic_launcher"    android:label="@string/app_name"    android:theme="@style/AppTheme" >    <activity      android: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" />