Android sd相关笔记 - Android4.4上应用写sd卡问题

Android sd卡笔记

1. Environment.getExternalStorageDirectory() 的使用
(1)Environment.getExternalStorageDirectory()在部分手机中获取到的是内部存储路径,而不是sd卡路径，如三星手机等
(2).如果系统设置了优先存储在内置存储中，那么Environment.getExternalStorageDirectory()获取到的也是内部存储路径
(3)Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)在没有sd的部分手机

(Environment.getExternalStorageDirectory()指向内部路径时)上也返回true

//此方法不知是否可行，没有大量手机测试
public static boolean externalMemoryAvailable(final Context context) {
File[] list = context.getExternalCacheDirs();
boolean hasSd = list != null && list.length > 1;
return Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED) && hasSd;
}

那么如何正确获取手机存储位置路径呢，这里附上链接:
http://blog.fidroid.com/post/android/ru-he-zheng-que-huo-de-androidnei-wai-sdqia-lu-jing     (sd卡路径获取)
http://www.cnblogs.com/bluestorm/p/3694921.html    (/storage/sdcard， /sdcard， /mnt/sdcard 三者的区别)
http://www.cnblogs.com/yejiurui/p/3421314.html   (android中的目录结构介绍)

2. 在sd卡根目录下创建目录(部分手机)失败
因为在 Android4.4新版本中，Google针对外卡写权限增加了CTS用例，对外卡的写操作增加了限制，由此导致部分开发者的应用可能存在外卡写权限兼容性问题。
Android4.4对外卡的写操作进行增加了如下两条限制：
（1）通过用户态文件系统fuse对外卡的写权限进行了限制；

• 用户只能在外卡Android/data/<package-name>/目录下进行写操作。
• 拥有WRITE_MEDIA_STORAGE权限（仅特权用户才能申请这个权限）的用户才能对整个外卡进行写操作。

（2）Android4.4的MediaProvider不允许对外卡进行任何写操作。

注意:随着应用的卸载，Android/data/<package-name>/目录也会被删除

参考:
http://developer.huawei.com/devunion/ui/newsDetail.html?news=/devunion/news/n_00033.html
http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2014/1027/1849.html      (Android 外部存储权限分析)
https://developer.android.com/training/articles/scoped-directory-access.html

3. 在sd卡的Android/data/<package-name>/目录下mkdirs()失败(部分手机)
本人经过多次尝试，终于成功了，做法是:
(1)mContext.getExternalFilesDir(null).getAbsolutePath();//要先执行该方法，后面才能创建目录，否则失败
个人猜测是新建了Android/data/<package-name>/目录
(2)然后再调用mkdirs()

4. getExternalFilesDir(null)及getExternalFilesDirs(null)
getExternalFilesDir(null)返回的是SdCard/Android/data/应用包名/files或者内置存储路径/Android/data/应用包名/files
getExternalFilesDirs(null)返回的是内置和sd卡的/Android/data/应用包名/files

测试:

private void getDir(){
    	Context context = getApplicationContext();
    	Log.e(TAG, "getCacheDir():" + context.getCacheDir().getAbsolutePath());
    	Log.e(TAG, "getExternalCacheDir():" + context.getExternalCacheDir().getAbsolutePath());
    	print("getExternalCacheDirs():", context.getExternalCacheDirs());
    	Log.e(TAG, "getFilesDir:" + context.getFilesDir().getAbsolutePath());
    	Log.e(TAG, "getExternalFilesDir(null):" + context.getExternalFilesDir(null).getAbsolutePath());
    	print("getExternalFilesDirs(null):", context.getExternalFilesDirs(null));
    	
    	Log.e(TAG, "getObbDir:" + context.getObbDir().getAbsolutePath());
    	print("getObbDirs():", context.getObbDirs());
    	
    	Log.e(TAG, "Environment.getDataDirectory():" + Environment.getDataDirectory());
    	Log.e(TAG, "Environment.getDownloadCacheDirectory():" + Environment.getDownloadCacheDirectory());
    	Log.e(TAG, "Environment.getRootDirectory():" + Environment.getRootDirectory());
    }
    
    private void print(String tag, File[] list){
    	if(list == null){
    		Log.e(TAG, tag + "null or list.length == 0");
    	}else{
    		int i = 0;
    		for(File f : list){
    			if(f != null){
	    			i++;
	    			Log.e(TAG, tag + " " + i + " " + f.getAbsolutePath());
    			}
    		}
    	}
    }

(1)有sd卡

08-24 14:10:23.666: E/DirDemo(26722): getCacheDir():/data/data/应用包名/cache
08-24 14:10:23.666: E/DirDemo(26722): getExternalCacheDir():/storage/emulated/0/Android/data/应用包名/cache
08-24 14:10:23.666: E/DirDemo(26722): getExternalCacheDirs(): 1 /storage/emulated/0/Android/data/应用包名/cache(内部存储)
08-24 14:10:23.666: E/DirDemo(26722): getExternalCacheDirs(): 2 /storage/sdcard1/Android/data/应用包名/cache
08-24 14:10:23.666: E/DirDemo(26722): getFilesDir:/data/data/应用包名/files
08-24 14:10:23.666: E/DirDemo(26722): getExternalFilesDir(null):/storage/emulated/0/Android/data/应用包名/files
08-24 14:10:23.667: E/DirDemo(26722): getExternalFilesDirs(null): 1 /storage/emulated/0/Android/data/应用包名/files
08-24 14:10:23.667: E/DirDemo(26722): getExternalFilesDirs(null): 2 /storage/sdcard1/Android/data/应用包名/files
08-24 14:10:23.667: E/DirDemo(26722): getObbDir:/storage/emulated/0/Android/obb/应用包名
08-24 14:10:23.667: E/DirDemo(26722): getObbDirs(): 1 /storage/emulated/0/Android/obb/应用包名
08-24 14:10:23.667: E/DirDemo(26722): getObbDirs(): 2 /storage/sdcard1/Android/obb/应用包名
08-24 14:10:23.667: E/DirDemo(26722): Environment.getDataDirectory():/data
08-24 14:10:23.667: E/DirDemo(26722): Environment.getDownloadCacheDirectory():/cache
08-24 14:10:23.667: E/DirDemo(26722): Environment.getRootDirectory():/system

(2)无sd卡

08-24 14:22:39.862: E/DirDemo(6457): getCacheDir():/data/data/应用包名/cache
08-24 14:22:39.873: E/DirDemo(6457): getExternalCacheDir():/storage/emulated/0/Android/data/应用包名/cache
08-24 14:22:39.881: E/DirDemo(6457): getExternalCacheDirs(): 1 /storage/emulated/0/Android/data/应用包名/cache
08-24 14:22:39.882: E/DirDemo(6457): getFilesDir:/data/data/应用包名/files
08-24 14:22:39.890: E/DirDemo(6457): getExternalFilesDir(null):/storage/emulated/0/Android/data/应用包名/files
08-24 14:22:39.895: E/DirDemo(6457): getExternalFilesDirs(null): 1 /storage/emulated/0/Android/data/应用包名/files
08-24 14:22:39.903: E/DirDemo(6457): getObbDir:/storage/emulated/0/Android/obb/应用包名
08-24 14:22:39.907: E/DirDemo(6457): getObbDirs(): 1 /storage/emulated/0/Android/obb/应用包名
08-24 14:22:39.907: E/DirDemo(6457): Environment.getDataDirectory():/data
08-24 14:22:39.907: E/DirDemo(6457): Environment.getDownloadCacheDirectory():/cache
08-24 14:22:39.907: E/DirDemo(6457): Environment.getRootDirectory():/system