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

读写sd卡中的文件依照例如以下步骤：1调用Environment的getExternalStorageState（）方法推断手机上是否插入了sd卡。而且应用程序具有读写SD卡的能力

//假设手机已经插入了SD卡，且具有读写sd卡的能力。以下的语句将会返回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卡的文件夹

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

注冊权限

<--!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 文件里。

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>

	@Override
	protected 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() {

			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				String s = readFromSdcard();
				read_Text.setText(s);

			}
		});
		// ------------------------
		write.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				String 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 block
				e.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 block
				e.printStackTrace();
			}

		}

		else {
			Toast.makeText(MainActivity.this, "sd卡异常", Toast.LENGTH_LONG)
					.show();
		}

	}
}
</span>

几点注意：1 不要忘记注冊权限

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能够在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> 。假设我们最初在声明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">