Google去年11月正式发布了Android 4.4,代号为KitKat(奇巧,雀巢的一款巧克力品牌),该系统带来了诸多新的特性。
但需要注意的是,该系统可能会让你之前一直正常使用的SD卡变为无用的“摆设”,因为根据新版本的API改进,应用程序将不能再往SD卡中写入文件。
来看Android开发者网站的“外部存储技术信息”文档中的描述:
引用
WRITE_EXTERNAL_STORAGE只为设备上的主要外部存储授予写权限,应用程序无法将数据写入二级外部存储设备,除非指定了应用程序允许访问的特定的目录。
这目前只影响双存储设备,如果你的设备有内部存储空间,即通常所说的机身存储(这就是指主要外部存储),那么你的SD卡就是一个二级外部存储设备。
在Android 4.4中,如果你同时使用了机身存储和SD卡,那么应用程序将无法在SD卡中创建、修改、删除数据。比如,你无法使用文件管理器通过无线网络从电脑往SD卡中复制文件了。但是应用程序仍然可以往主存储的任意目录中写入数据,不受任何限制。
Google表示,这样做的目的是,通过这种方式进行限制,系统可以在应用程序被卸载后清除遗留文件。
目前三星已经通过OTA向部分手机发送了Android 4.4的更新,已经有Note3用户抱怨FX文件管理器现在不能往SD卡中复制内容了。
解决办法
获得系统的ROOT权限是一个解决方法。
很显然,这是针对用户的解决办法,但是并不是所有的用户都愿意进行ROOT,那么需要SD卡写入权限的开发者该如何做呢?
XDA论坛已经有大神给出了解决方案——在应用中嵌入一段代码,这段代码作用是在Android 4.4+设备上,如果其他方式写入失败,则将数据写入二级存储设备。
详细方案:http://forum.xda-developers.com/showthread.php?p=50008987
- /*
- * Copyright (C) 2014 NextApp, Inc.
- *
- * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS"
- * BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language
- * governing permissions and limitations under the License.
- */
- package nextapp.mediafile;
- import java.io.File;
- import java.io.IOException;
- import java.io.OutputStream;
- import android.content.ContentResolver;
- import android.content.ContentValues;
- import android.net.Uri;
- import android.provider.MediaStore;
- /**
- * Wrapper for manipulating files via the Android Media Content Provider. As of Android 4.4 KitKat, applications can no longer write
- * to the "secondary storage" of a device. Write operations using the java.io.File API will thus fail. This class restores access to
- * those write operations by way of the Media Content Provider.
- *
- * Note that this class relies on the internal operational characteristics of the media content provider API, and as such is not
- * guaranteed to be future-proof. Then again, we did all think the java.io.File API was going to be future-proof for media card
- * access, so all bets are off.
- *
- * If you're forced to use this class, it's because Google/AOSP made a very poor API decision in Android 4.4 KitKat.
- * Read more at https://plus.google.com/+TodLiebeck/posts/gjnmuaDM8sn
- *
- * Your application must declare the permission "android.permission.WRITE_EXTERNAL_STORAGE".
- */
- public class MediaFile {
- private final File file;
- private final ContentResolver contentResolver;
- private final Uri filesUri;
- private final Uri imagesUri;
- public MediaFile(ContentResolver contentResolver, File file) {
- this.file = file;
- this.contentResolver = contentResolver;
- filesUri = MediaStore.Files.getContentUri("external");
- imagesUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
- }
- /**
- * Deletes the file. Returns true if the file has been successfully deleted or otherwise does not exist. This operation is not
- * recursive.
- */
- public boolean delete()
- throws IOException {
- if (!file.exists()) {
- return true;
- }
- boolean directory = file.isDirectory();
- if (directory) {
- // Verify directory does not contain any files/directories within it.
- String[] files = file.list();
- if (files != null && files.length > 0) {
- return false;
- }
- }
- String where = MediaStore.MediaColumns.DATA + "=?";
- String[] selectionArgs = new String[] { file.getAbsolutePath() };
- // Delete the entry from the media database. This will actually delete media files (images, audio, and video).
- contentResolver.delete(filesUri, where, selectionArgs);
- if (file.exists()) {
- // If the file is not a media file, create a new entry suggesting that this location is an image, even
- // though it is not.
- ContentValues values = new ContentValues();
- values.put(MediaStore.Files.FileColumns.DATA, file.getAbsolutePath());
- contentResolver.insert(imagesUri, values);
- // Delete the created entry, such that content provider will delete the file.
- contentResolver.delete(filesUri, where, selectionArgs);
- }
- return !file.exists();
- }
- public File getFile() {
- return file;
- }
- /**
- * Creates a new directory. Returns true if the directory was successfully created or exists.
- */
- public boolean mkdir()
- throws IOException {
- if (file.exists()) {
- return file.isDirectory();
- }
- ContentValues values;
- Uri uri;
- // Create a media database entry for the directory. This step will not actually cause the directory to be created.
- values = new ContentValues();
- values.put(MediaStore.Files.FileColumns.DATA, file.getAbsolutePath());
- contentResolver.insert(filesUri, values);
- // Create an entry for a temporary image file within the created directory.
- // This step actually causes the creation of the directory.
- values = new ContentValues();
- values.put(MediaStore.Files.FileColumns.DATA, file.getAbsolutePath() + "/temp.jpg");
- uri = contentResolver.insert(imagesUri, values);
- // Delete the temporary entry.
- contentResolver.delete(uri, null, null);
- return file.exists();
- }
- /**
- * Returns an OutputStream to write to the file. The file will be truncated immediately.
- */
- public OutputStream write()
- throws IOException {
- if (file.exists() && file.isDirectory()) {
- throw new IOException("File exists and is a directory.");
- }
- // Delete any existing entry from the media database.
- // This may also delete the file (for media types), but that is irrelevant as it will be truncated momentarily in any case.
- String where = MediaStore.MediaColumns.DATA + "=?";
- String[] selectionArgs = new String[] { file.getAbsolutePath() };
- contentResolver.delete(filesUri, where, selectionArgs);
- ContentValues values = new ContentValues();
- values.put(MediaStore.Files.FileColumns.DATA, file.getAbsolutePath());
- Uri uri = contentResolver.insert(filesUri, values);
- if (uri == null) {
- // Should not occur.
- throw new IOException("Internal error.");
- }
- return contentResolver.openOutputStream(uri);
- }
- }