SD卡读写之FileNotFoundException: /storage/emulated/0object.txt: open failed: ENOENT (No such file or dir

读写sd卡中的文件按照如下步骤：1调用Environment的getExternalStorageState（）方法判断手机上是否插入了sd卡，并且应用程序具有读写SD卡的能力

//如果手机已经插入了SD卡，且具有读写sd卡的能力，下面的语句将会返回true

Environment.getExternalStorageState().equals(Envronment.MEDIA_MOUNTED)

2）调用environment的getExternalStorageDIrectory（）方法获取外部存储器，也就是SD卡的目录

3）使用FileInputStream、FileOUtputStream FileReader或者FileWriter来读写sd卡中的文件

注册权限

<--!在SD卡中创建与删除文件权限-->

<uses-permission android:name="android.permission.MOUNT_FORMAT_FILESYSTEMS"/>
<--!向SD卡写入数据的权限--->
<uses-permission android:name="androd.permission.WRITE_EXTERNAL_STORAGE"/>
<--!读取数据的权限--->
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

实例代码：

有两个EditText 和两个Button组件，text_Write用于写入数据，Button（write）组件用于读取text_Write中的数据并写入/storage/emulated/0/object.txt 文件中；

Button（read）组件用于从SD卡的/storage/emulated/0/object.txt中读取数据，并显示在text_Read组件中。

<span style="font-size:18px;"><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:orientation="vertical"    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.example.sdcard03.MainActivity$PlaceholderFragment" >    <EditText                android:id="@+id/text_Write"        android:layout_width="match_parent"        android:layout_height="45dp"         />    <EditText        android:id="@+id/text_Read"        android:layout_width="match_parent"        android:layout_height="45dp"         />    <Button         android:id="@+id/read"        android:layout_height="wrap_content"        android:layout_width="match_parent"        android:text="read"/>     <Button         android:id="@+id/write"        android:layout_height="wrap_content"        android:layout_width="match_parent"        android:text="write"/>    </LinearLayout></span>

主程序：

<span style="font-size:18px;">package com.example.sdcard03;import java.io.BufferedReader;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStreamReader;import android.app.Activity;import android.os.Bundle;import android.os.Environment;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;import android.widget.Toast;public class MainActivity extends Activity {private EditText read_Text;private EditText write_Text;private Button read;private Button write;private String fileName = <span style="color:#FF6666;">"/object.txt";</span>@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.fragment_main);read = (Button) findViewById(R.id.read);write = (Button) findViewById(R.id.write);read_Text = (EditText) findViewById(R.id.text_Read);write_Text = (EditText) findViewById(R.id.text_Write);read.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubString s = readFromSdcard();read_Text.setText(s);}});// ------------------------write.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubString s2 = write_Text.getText().toString();writeToSdcard(s2);}});}public String readFromSdcard() {if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {try {File sdPath = Environment<span style="color:#FF0000;">.getExternalStorageDirectory()</span>;<span style="color:#6633FF;">System.out.println(sdPath.toString());</span>FileInputStream fis = new FileInputStream(sdPath.<span style="color:#FF0000;">getCanonicalFile()</span>.toString() + fileName);<span style="color:#3366FF;">System.out.println(sdPath.getCanonicalFile().toString());</span>BufferedReader br = new BufferedReader(new InputStreamReader(fis));StringBuilder sb = new StringBuilder("");String line = null;while ((line = br.readLine()) != null) {sb.append(line);}fis.close();br.close();return sb.toString();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}return null;}// -------------------------------------------------------public void writeToSdcard(String s) {if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {File sdCardDir = Environment.getExternalStorageDirectory();try {File file = new File(sdCardDir.getCanonicalPath() + fileName);FileOutputStream fos = new FileOutputStream(file);fos.write(s.getBytes());fos.close();} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}}else {Toast.makeText(MainActivity.this, "sd卡异常", Toast.LENGTH_LONG).show();}}}</span>

几点注意：1 不要忘记注册权限

2，

<span style="font-size:18px;">File sdPath = Environment<span style="color:#FF0000;">.getExternalStorageDirectory()</span>;中getExternalStorageDirectory()方法返回的是什么？</span><pre name="code" class="java"><span style="font-size:18px;">sdPath.<span style="color:#FF0000;">getCanonicalFile()</span>.toString()方法返回的是什么？通过上面两行蓝色输出语句可以在logcat中看到返回的都是/storage/emulated/0   注意在0后面没有“/”反斜杠，所以我们在最初声明字符串常量filName时</span><pre name="code" class="java"><span style="font-size:18px;">private String fileName = <span style="color:#FF6666;">"/object.txt";object前有反斜杠，也就是代表了路径</span></span><pre name="code" class="java"><pre name="code" class="java">/storage/emulated/0<span style="color:#FF6666;">/object.txt</span> 。如果我们最初在声明fileName时不加反斜杠就变成了/storage/emulated/0<span style="color:#FF6666;">object.txt</span>，这个路径是不合法的，不存在程序会报错03-15 15:07:39.440: W/System.err(26730): java.io.FileNotFoundException: /storage/emulated/0object.txt: open failed: ENOENT (No such file or directory)<pre name="code" class="java"><pre name="code" class="java"><pre name="code" class="java">