Android之Android的数据存储--SD卡
上一节我们学习了Android的数据存储采用File,但是这样的数据是存储在应用程序内的,那么也就是说这样的存储的文件大小还是有一定要限制的,有时候我们需要存储更大的文件,比如电影等,这就用到了我们的SDSard存储卡。Android也为我们提供了SDCard的一些相关操作。Environment这个类就可以实现这个功能。
Environmet类
常用常量
String MEDIA_MOUNTED | 当前Android的外部存储器可读可写 |
String MEDIA_MOUNTED_READ_ONLY | 当前Android的外部存储器只读 |
常用方法
方法名称 | 描述 |
public static File getDataDirectory () | 获得Android下的data文件夹的目录 |
public static File getDownloadCacheDirectory () | 获得Android Download/Cache 内容的目录 |
public static File getExternalStorageDirectory () | 获得Android外部存储器也就是SDCard的目录 |
public static String getExternalStorageState () | 获得Android外部存储器的当前状态 |
public static File getRootDirectory () | 获得Android下的root文件夹的目录 |
要想实现对SDCard的读取操作,只需要按以下几个步骤就行:
1、 先判断这台手机设备上是否有SDCard且具有读写SDCard的权限
Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)
2、 调用Environment.getExternalStorageDirectory()获得到外部存储器的目录
3、 使用IO流对外部存储器进行文件的读写
4、 别忘记了要在AndroidMainfest.xml中添加权限哦
特别声明:以下操作必须要在如下权限下完成:
[html] view plain copy print ?- <!--在SDCard中创建与删除文件权限-->
- <uses-permissionandroid:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
- <!--往SDCard中写入数据权限-->
- <uses-permissionandroid:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<!-- 在SDCard中创建与删除文件权限 --> <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" /> <!-- 往SDCard中写入数据权限 --> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
实例:读写SDCard上的文件
- packagecom.jiahui.sdcarddemo;
- importjava.io.File;
- importjava.io.FileInputStream;
- importjava.io.FileNotFoundException;
- importjava.io.FileOutputStream;
- importjava.io.IOException;
- importjava.io.InputStream;
- importjava.io.OutputStream;
- importjava.io.RandomAccessFile;
- importandroid.app.Activity;
- importandroid.os.Bundle;
- importandroid.os.Environment;
- importandroid.view.View;
- importandroid.widget.Button;
- importandroid.widget.EditText;
- importandroid.widget.TextView;
- publicclassSDCardDemoActivityextendsActivity{
- privateButtonbtnWrite,btnRead;
- privateEditTextedtContent;
- privateTextViewtvResult;
- privatestaticfinalStringFILE_NAME="test.txt";
- publicvoidonCreate(BundlesavedInstanceState){
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- edtContent=(EditText)this.findViewById(R.id.edtContent);
- tvResult=(TextView)this.findViewById(R.id.tvResult);
- btnRead=(Button)this.findViewById(R.id.btnRead);
- btnWrite=(Button)this.findViewById(R.id.btnWrite);
- btnWrite.setOnClickListener(newView.OnClickListener(){
- @Override
- publicvoidonClick(Viewv){
- System.out.println("往SDCard里写数据");
- //先判断是否有SDCard
- System.out.println("Environment.getExternalStorageState():"
- +Environment.getExternalStorageState());
- System.out.println("Environment.MEDIA_MOUNTED:"
- +Environment.MEDIA_MOUNTED);
- if(Environment.getExternalStorageState().equals(
- Environment.MEDIA_MOUNTED)){
- Stringcontent=edtContent.getText().toString();
- try{
- //获取SDcard路径
- FilesdCardDir=Environment
- .getExternalStorageDirectory();
- //SDCard目录:/mnt/sdcard
- StringsdcardPath=sdCardDir.getAbsolutePath();
- System.out.println("sdCardDir.getAbsolutePath()"
- +sdCardDir.getAbsolutePath());
- Filefile=newFile(sdCardDir,FILE_NAME);
- //Filefile=newFile(sdcardPath
- //+File.separator+FILE_NAME);
- //以指定文件创建RandomAccessFile对象
- RandomAccessFileraf=newRandomAccessFile(file,"rw");
- //将文件记录指针移动最后
- raf.seek(file.length());
- //输出文件内容
- raf.write(content.getBytes());
- raf.close();
- }catch(Exceptione){
- //TODO:handleexception
- }
- }
- }
- });
- btnRead.setOnClickListener(newView.OnClickListener(){
- @Override
- publicvoidonClick(Viewv){
- if(Environment.getExternalStorageState().equals(
- Environment.MEDIA_MOUNTED)){
- //获取SDcard路径
- StringBuildersb=newStringBuilder();
- try{
- FilesdCardDir=Environment
- .getExternalStorageDirectory();
- Filefile=newFile(sdCardDir,FILE_NAME);
- InputStreaminputStream=newFileInputStream(file);
- intlen=0;
- byte[]buffer=newbyte[1024];
- while((len=inputStream.read(buffer))!=-1){
- sb.append(newString(buffer,0,len));
- }
- tvResult.setText(sb.toString());
- //关闭流
- inputStream.close();
- }catch(Exceptione){
- //TODOAuto-generatedcatchblock
- e.printStackTrace();
- }
- }
- }
- });
- }
- }
package com.jiahui.sdcarddemo;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.io.RandomAccessFile;import android.app.Activity;import android.os.Bundle;import android.os.Environment;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.TextView;public class SDCardDemoActivity extends Activity {private Button btnWrite, btnRead;private EditText edtContent;private TextView tvResult;private static final String FILE_NAME = "test.txt";public void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);edtContent = (EditText) this.findViewById(R.id.edtContent);tvResult = (TextView) this.findViewById(R.id.tvResult);btnRead = (Button) this.findViewById(R.id.btnRead);btnWrite = (Button) this.findViewById(R.id.btnWrite);btnWrite.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {System.out.println("往SDCard里写数据");// 先判断是否有SDCardSystem.out.println("Environment.getExternalStorageState():"+ Environment.getExternalStorageState());System.out.println("Environment.MEDIA_MOUNTED:"+ Environment.MEDIA_MOUNTED);if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {String content = edtContent.getText().toString();try {// 获取SDcard路径File sdCardDir = Environment.getExternalStorageDirectory();// SDCard目录:/mnt/sdcardString sdcardPath = sdCardDir.getAbsolutePath();System.out.println("sdCardDir.getAbsolutePath()"+ sdCardDir.getAbsolutePath());File file = new File(sdCardDir, FILE_NAME);// File file = new File(sdcardPath// + File.separator + FILE_NAME);// 以指定文件创建RandomAccessFile对象RandomAccessFile raf = new RandomAccessFile(file, "rw");// 将文件记录指针移动最后raf.seek(file.length());// 输出文件内容raf.write(content.getBytes());raf.close();} catch (Exception e) {// TODO: handle exception}}}});btnRead.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {// 获取SDcard路径StringBuilder sb = new StringBuilder();try {File sdCardDir = Environment.getExternalStorageDirectory();File file = new File(sdCardDir, FILE_NAME);InputStream inputStream = new FileInputStream(file);int len = 0;byte[] buffer = new byte[1024];while ((len = inputStream.read(buffer)) != -1) {sb.append(new String(buffer, 0, len));}tvResult.setText(sb.toString());// 关闭流inputStream.close();} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}}});}}
实现效果
用File Explorer可以看到如下图一样的效果:
开发注意事项:
1、 一定不能忘记添加权限
[html] view plain copy print ?- <!--在SDCard中创建与删除文件权限-->
- <uses-permissionandroid:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
- <!--往SDCard中写入数据权限-->
- <uses-permissionandroid:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<!-- 在SDCard中创建与删除文件权限 --> <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" /> <!-- 往SDCard中写入数据权限 --> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
2、 要判断一下是否插入SD卡和是否具有读写的能力:
Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)
如需转载引用请注明出处:http://blog.csdn.net/jiahui524
源代码下载:http://download.csdn.net/download/jiahui524/3799819
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