（1）说明:操作SD卡上的文件需要加入以下权限

 在SD卡上创建和删除文件权限

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

在SD卡上写入数据的权限
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

在sd卡上的文件操作和我上一篇文章差不多，如果有不懂的可以看我的上一篇文章

android 读写文件示例

http://blog.csdn.net/liuzuyi200/article/details/25049183

只不过多加了判断SD卡是否存在的方法

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

（2）布局文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <RelativeLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical" >

        <TextView
            android:id="@+id/label_01"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/name"
            android:textSize="20dp" />

        <EditText
            android:id="@+id/filename"
            android:layout_width="160dp"
            android:layout_height="wrap_content"
            android:layout_alignTop="@id/label_01"
            android:layout_toRightOf="@id/label_01" />
    </RelativeLayout>

    <TextView
        android:id="@+id/label_02"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/neirong" />

    <EditText
        android:id="@+id/content"
        android:layout_width="fill_parent"
        android:layout_height="120px"
        android:ems="10" >

        <requestFocus />
    </EditText>

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal" >

        <Button
            android:id="@+id/savebutton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:gravity="right"
            android:text="@string/save" />

        <Button
            android:id="@+id/readbutton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:gravity="right"
            android:text="@string/read" />
    </LinearLayout>

    <TextView
        android:id="@+id/textcontent"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="0.10" />

</LinearLayout>

（3）代码

package com.liuzuyi.file;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import android.os.Build;

public class MainActivity extends Activity {

	private  EditText filename;
	private  EditText context;
	private TextView textcontent;
	private static final String TAG="simplefile";
	
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		filename=(EditText)this.findViewById(R.id.filename);
		context=(EditText)this.findViewById(R.id.content);
		textcontent=(TextView)this.findViewById(R.id.textcontent);
		Button savebtn=(Button)this.findViewById(R.id.savebutton);
		Button viewbtn=(Button)this.findViewById(R.id.readbutton);
		savebtn.setOnClickListener(l);
		viewbtn.setOnClickListener(l);

	}
   private View.OnClickListener l =new OnClickListener() {
	public void onClick(View v) {
	
		 Button button =(Button)v;
		 //过滤掉开头结尾的空格
		 String namestr = filename.getText().toString().trim();
		 String contentstr =context.getText().toString();
		 
		 switch ( button.getId() ) {
		case R.id.savebutton:
			String resid_s ="success";
			OutputStream fileos = null;
			try {
				if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))
				  {
					FileOutputStream outstream = new FileOutputStream("/sdcard/"+namestr+".txt");
					outstream.write(contentstr.getBytes() );
					outstream.close();
				  }
				else
					return ;
			} catch (Exception e) {
				 resid_s = "faile";
				 e.printStackTrace();
			}
			Toast.makeText(MainActivity.this,  resid_s,Toast.LENGTH_LONG).show();
			Log.i(TAG, namestr);
			Log.i(TAG, contentstr);
			break;
		case R.id.readbutton:
			String resid_v ="success";
			InputStream filsIs= null;
			String contentst = null;
			try {
				if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))
				  {
					File SDCardDir=Environment.getExternalStorageDirectory();
					File saveFile = new File(SDCardDir,namestr+".txt");
					FileInputStream instream = new FileInputStream(saveFile);
					ByteArrayOutputStream Ostream = new ByteArrayOutputStream();
					
					byte[] buffer = new byte[1024];
					int len = -1;
					  while( (len = instream.read(buffer)) != -1 )
					    {
						  Ostream.write(buffer,0,len);
						  }
					  contentst = Ostream.toString();
					  Ostream.close();
					  instream.close(); 
				  }
				else
				{
					Toast.makeText(MainActivity.this, "SD卡不存在", Toast.LENGTH_LONG).show();
				}
			
			} catch (Exception e) {
				 resid_v ="faile";
				 e.printStackTrace();
				
			}
			textcontent.setText( contentst);
			Log.i(TAG, contentst);
			Toast.makeText(MainActivity.this, resid_v,Toast.LENGTH_LONG).show();
			Log.i(TAG,namestr);
			break;
		}
	  }
    };
}