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 plaincopyprint?

1. <!-- 在SDCard中创建与删除文件权限 -->  
2.   
3. <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />  
4.   
5. <!-- 往SDCard中写入数据权限 -->  
6.   
7. <uses-permission android: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

[java] view plaincopyprint?

1. package com.jiahui.sdcarddemo;  
2.   
3. import java.io.File;  
4. import java.io.FileInputStream;  
5. import java.io.FileNotFoundException;  
6. import java.io.FileOutputStream;  
7. import java.io.IOException;  
8. import java.io.InputStream;  
9. import java.io.OutputStream;  
10. import java.io.RandomAccessFile;  
11.   
12. import android.app.Activity;  
13. import android.os.Bundle;  
14. import android.os.Environment;  
15. import android.view.View;  
16. import android.widget.Button;  
17. import android.widget.EditText;  
18. import android.widget.TextView;  
19.   
20. public class SDCardDemoActivity extends Activity {  
21.   
22.     private Button btnWrite, btnRead;  
23.     private EditText edtContent;  
24.     private TextView tvResult;  
25.     private static final String FILE_NAME = "test.txt";  
26.   
27.     public void onCreate(Bundle savedInstanceState) {  
28.         super.onCreate(savedInstanceState);  
29.         setContentView(R.layout.main);  
30.         edtContent = (EditText) this.findViewById(R.id.edtContent);  
31.         tvResult = (TextView) this.findViewById(R.id.tvResult);  
32.   
33.         btnRead = (Button) this.findViewById(R.id.btnRead);  
34.         btnWrite = (Button) this.findViewById(R.id.btnWrite);  
35.         btnWrite.setOnClickListener(new View.OnClickListener() {  
36.             @Override  
37.             public void onClick(View v) {  
38.                 System.out.println("往SDCard里写数据");  
39.                 // 先判断是否有SDCard  
40.                 System.out.println("Environment.getExternalStorageState():"  
41.                         + Environment.getExternalStorageState());  
42.                 System.out.println("Environment.MEDIA_MOUNTED:"  
43.                         + Environment.MEDIA_MOUNTED);  
44.                 if (Environment.getExternalStorageState().equals(  
45.                         Environment.MEDIA_MOUNTED)) {  
46.   
47.                     String content = edtContent.getText().toString();  
48.   
49.                     try {  
50.   
51.                         // 获取SDcard路径  
52.                         File sdCardDir = Environment  
53.                                 .getExternalStorageDirectory();  
54.   
55.                         // SDCard目录：/mnt/sdcard  
56.                         String sdcardPath = sdCardDir.getAbsolutePath();  
57.                         System.out.println("sdCardDir.getAbsolutePath()"  
58.                                 + sdCardDir.getAbsolutePath());  
59.   
60.                         File file = new File(sdCardDir, FILE_NAME);  
61.                         // File file = new File(sdcardPath  
62.                         // + File.separator + FILE_NAME);  
63.                         // 以指定文件创建RandomAccessFile对象  
64.                         RandomAccessFile raf = new RandomAccessFile(file, "rw");  
65.                         // 将文件记录指针移动最后  
66.                         raf.seek(file.length());  
67.                         // 输出文件内容  
68.                         raf.write(content.getBytes());  
69.                         raf.close();  
70.   
71.                     } catch (Exception e) {  
72.                         // TODO: handle exception  
73.                     }  
74.                 }  
75.             }  
76.         });  
77.         btnRead.setOnClickListener(new View.OnClickListener() {  
78.   
79.             @Override  
80.             public void onClick(View v) {  
81.   
82.                 if (Environment.getExternalStorageState().equals(  
83.                         Environment.MEDIA_MOUNTED)) {  
84.                     // 获取SDcard路径   
85.   
86.                     StringBuilder sb = new StringBuilder();  
87.                     try {  
88.                         File sdCardDir = Environment  
89.                                 .getExternalStorageDirectory();  
90.                         File file = new File(sdCardDir, FILE_NAME);  
91.   
92.                         InputStream inputStream = new FileInputStream(file);  
93.                         int len = 0;  
94.                         byte[] buffer = new byte[1024];  
95.                         while ((len = inputStream.read(buffer)) != -1) {  
96.   
97.                             sb.append(new String(buffer, 0, len));  
98.                         }  
99.                         tvResult.setText(sb.toString());  
100.                         // 关闭流   
101.                         inputStream.close();  
102.   
103.                     } catch (Exception e) {  
104.                         // TODO Auto-generated catch block  
105.                         e.printStackTrace();  
106.                     }  
107.                 }  
108.   
109.             }  
110.         });  
111.   
112.     }  
113. }  

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 plaincopyprint?

1. <!-- 在SDCard中创建与删除文件权限 -->  
2.   
3. <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />  
4.   
5. <!-- 往SDCard中写入数据权限 -->  
6.   
7. <uses-permission android: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