(1)使用Activity的openFileOutput()方法,存放些小文件还行。SDCard存放大文件,SDCard看做U盘或移动硬盘。
(2)注意:在程序中访问SDCard,需要申请访问SDCard的权限。
在AndroidManifest.xml中加入访问SDCard的权限如下:
<!-- 在SDCard中创建与删除文件权限 -->
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
<!-- 往SDCard写入数据权限 -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
(3) 要往SDCard存放文件,程序必须先判断手机是否装有SDCard,并且可以进行读写。
if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){ File sdCardDir = Environment.getExternalStorageDirectory();//获取SDCard目录 File saveFile = new File(sdCardDir, “ljq.txt”); FileOutputStream outStream = new FileOutputStream(saveFile); outStream.write("abc".getBytes()); outStream.close(); }
Environment.getExternalStorageState()方法用于获取SDCard的状态,如果手机装有SDCard,并且可以进行读写,那么方法返回的状态等于Environment.MEDIA_MOUNTED。
Environment.getExternalStorageDirectory()方法用于获取SDCard的目录,
(4)要获取SDCard的目录,你也可以这样写:
File sdCardDir = new File("/mnt/sdcard"); //获取SDCard目录
File saveFile = new File(sdCardDir, "ljq.txt");
//上面两句代码可以合成一句: File saveFile = new File("/mnt/sdcard/ljq.txt");
FileOutputStream outStream = new FileOutputStream(saveFile);
outStream.write("abc".getBytes());
outStream.close();
案例
main.xml布局文件
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent" > <!-- 相对布局 --> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="wrap_content"> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/filename" android:id="@+id/filenameLable" /> <EditText android:layout_width="250px" android:layout_height="wrap_content" android:layout_toRightOf="@id/filenameLable" android:layout_alignTop="@id/filenameLable" android:layout_marginLeft="10px" android:text="ljq.txt" android:id="@+id/filename" /> </RelativeLayout> <TextView android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/content" /> <EditText android:layout_width="fill_parent" android:layout_height="wrap_content" android:minLines="3" android:id="@+id/content" /> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="wrap_content"> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/button" android:id="@+id/button" /> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_toRightOf="@id/button" android:layout_alignTop="@id/button" android:layout_marginLeft="10px" android:minLines="3" android:text="@string/readButton" android:id="@+id/readButton" /> </RelativeLayout> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/resultView" /> </LinearLayout>
strings.xml
<?xml version="1.0" encoding="utf-8"?> <resources> <string name="hello">Hello World, FileActivity!</string> <string name="app_name">数据保存</string> <string name="filename">文件名称</string> <string name="content">文件内容</string> <string name="button">保存</string> <string name="readButton">读取内容</string> <string name="error">保存失败</string> <string name="success">保存成功</string> </resources>
FileService工具类
package com.ljq.service; import java.io.ByteArrayOutputStream; import java.io.InputStream; import java.io.OutputStream; public class FileService { /** * 保存数据 * * @param outputStream * @param content * @throws Exception */ public static void save(OutputStream outputStream, String content) throws Exception { outputStream.write(content.getBytes()); outputStream.close(); } /** * 读取数据 * * @param inputStream * @return * @throws Exception */ public static String read(InputStream inputStream) throws Exception { ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream(); // 往内存写数据 byte[] buffer = new byte[1024]; // 缓冲区 int len = -1; while ((len = inputStream.read(buffer)) != -1) { byteArrayOutputStream.write(buffer, 0, len); } byte[] data = byteArrayOutputStream.toByteArray(); // 存储数据 byteArrayOutputStream.close(); inputStream.close(); return new String(data); } }
SdcardActivity类
public class SdcardActivity extends Activity { private final String TAG = "FileActivity"; private EditText filenameText; private TextView resultView; private EditText contentText; public void onCreate(Bundle savedInstanceState){ super.onCreate(savedInstanceState); setContentView(R.layout.main); filenameText=(EditText)this.findViewById(R.id.filename); contentText = (EditText)this.findViewById(R.id.content); resultView = (TextView)this.findViewById(R.id.resultView); Button saveButton = (Button)this.findViewById(R.id.saveButton); saveButton.setOnClickListener(listener); Button readButton = (Button)this.findViewById(R.id.readButton); readButton.setOnClickListener(listener); } private View.OnClickListener listener=new View.OnClickListener() { public void onClick(View v) { // TODO Auto-generated method stub Button button=(Button)v; String filename=filenameText.getText().toString(); // Environment.getExternalStorageDirectory()等价于new File("/sdcard")---->获取sdcard目录 //File file = new File("/sdcard" + filename); File file=new File(Environment.getExternalStorageDirectory(),filename); switch(button.getId()){ case R.id.saveButton: int resId = R.string.success; String content=contentText.getText().toString(); if(Environment.getExternalStorageDirectory().equals(Environment.MEDIA_MOUNTED)){ try{ FileOutputStream fileOutputStream=new FileOutputStream(file); FileService.save(fileOutputStream, content); }catch(Exception e){ Log.e(TAG, e.toString()); resId = R.string.error; } Toast.makeText(SdcardActivity.this, resId, Toast.LENGTH_LONG).show(); } else{ Toast.makeText(SdcardActivity.this, "sdcard不存在或写保护", Toast.LENGTH_LONG).show(); } break; case R.id.readButton: try{ InputStream inputStream=new FileInputStream(file); String result=FileService.read(inputStream); resultView.setText(result); }catch(Exception e){ Log.e(TAG, e.toString()); e.printStackTrace(); } break; } } }; }
清单文件
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.ljq.sdcard" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".SdcardActivity" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion="7" /> <!-- 在SDCard中创建与删除文件权限 --> <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" /> <!-- 往SDCard写入数据权限 --> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> </manifest>
运行结果