Android-彻底理解文件存储

参考：https://developer.android.com/training/basics/data-storage/files.html#WriteInternalStorage

 

All Android devices have two file storage areas: "internal" and "external" storage. These names come from the early days of Android, when most devices offered built-in non-volatile memory (internal storage), plus a removable storage medium such as a micro SD card (external storage). Some devices divide the permanent storage space into "internal" and "external" partitions, so even without a removable storage medium, there are always two storage spaces and the API behavior is the same whether the external storage is removable or not. The following lists summarize the facts about each storage space.

 

总结：

1. Internal storage：
   1. 只有当前app可以访问；
   2. 卸载时删除；
   3. getFileDir()，返回/data/data/com.dhn.test/files
   4. getCacheDir()，返回 /data/data/com.dhn.test/cache
2. External storage：
   1. public:
      1. 所有app都可以访问
      2. 卸载时保留
      3. Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC)：返回/storage/emulated/0/Music
   2. private:
      1. 所有app都可以访问
      2. 卸载时会删除
      3. getExternalFilesDir(Environment.DIRECTORY_MUSIC)：返回/storage/emulated/0/Android/data/com.dhn.test/files/Music
3. 注意点：无论使用public还是private的External storage时，使用api提供的常量作为目录名（DIRECTORY_RINGTONES），这样会被系统识别为铃声，而不是音乐。
4. 实验：

   // /storage/emulated/0
   // sc卡根路径，卸载时会保留
   File f1 = Environment.getExternalStorageDirectory();
   Log.e("Main", f1.getAbsolutePath());
   
   // /storage/emulated/0/Music
   File f2 = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC);
   Log.e("Main", f2.getAbsolutePath());
   
   // /data/data/com.dhn.test/files
   File f3 = getFilesDir();
   Log.e("Main", f3.getAbsolutePath());
   
   File f4 = getCacheDir();
   Log.e("Main", f4.getAbsolutePath());
   
   // /storage/emulated/0/Android/data/com.dhn.test/files/Music
   // 在SD卡中，卸载时会被删除
   File f5 = getExternalFilesDir(Environment.DIRECTORY_MUSIC);
   Log.e("Main", f5.getAbsolutePath());