一、简介
二、
Context
中关于外部存储的
重要函数
public abstract File getExternalCacheDir ()
Returns the absolute path to the directory on the external filesystem (that is somewhere on Environment.getExternalStorageDirectory() where the application can place cache files it owns.
This is like getCacheDir() in that these files will be deleted when the application is uninstalled, however there are some important differences:
该函数像getCacheDir() 一样，保存在该目录下的文件会在卸载该应用程序时被删除。然而又有以下几点不同：
- The platform does not monitor the space available in external storage, and thus will not automatically delete these files. Note that you should be managing the maximum space you will use for these anyway, just like with
getCacheDir(). 系统并不会监视外部存储的可用容量。因此程序员应该自己管理其占用的最大空间，自己做文件的清理机制
- External files are not always available: they will disappear if the user mounts the external storage on a computer or removes it. See the APIs on
Environment for information in the storage state.
- There is no security enforced with these files. All applications can read and write files placed here. 系统对该目录下的文件并没做安全访问机制，所有的应用程序都可以读写该目录下的文件。
Returns
- Returns the path of the directory holding application cache files on external storage. Returns null if external storage is not currently mounted so it could not ensure the path exists; you will need to call this method again when it is available.
public abstract File getExternalFilesDir (String type)
Returns the absolute path to the directory on the external filesystem (that is somewhere on Environment.getExternalStorageDirectory()) where the application can place persistent files it owns. These files are private to the applications, and not typically visible to the user as media.
该目录下的文件对其应用程序是私有的。其目录下的文件也不会被当做多媒体文件而为用户所见
This is like getFilesDir() in that these files will be deleted when the application is uninstalled, however there are some important differences:
该函数像 getFilesDir() 一样，保存在该目录下的文件会在卸载该应用程序时被删除。然而又有以下几点不同：
- External files are not always available: they will disappear if the user mounts the external storage on a computer or removes it. See the APIs on
Environment for information in the storage state.
- There is no security enforced with these files. All applications can read and write files placed here. 系统对该目录下的文件并没做安全访问机制，所有的应用程序都可以读写该目录下的文件。
Here is an example of typical code to manipulate a file in an application's private storage:
void
createExternalStoragePrivateFile
()
{
/* Create a path where we will place our private file on external
storage.
*/
File
file
=
new
File
(
getExternalFilesDir
(
null
),
"DemoFile.jpg"
);
try
{
/* Very simple code to copy a picture from the application's
resource into the external file. Note that this code does
no error checking, and assumes the picture is small (does not
try to copy it in chunks). Note that if external storage is
not currently mounted this will silently fail.
*/
InputStream
is
=
getResources
().
openRawResource
(
R
.
drawable
.
balloons
);
OutputStream
os
=
new
FileOutputStream
(
file
);
byte
[]
data
=
new
byte
[
is
.
available
()];
is
.
read
(
data
);
os
.
write
(
data
);
is
.
close
();
os
.
close
();
}
catch
(
IOException
e
)
{
/* Unable to create file, likely because external storage is
not currently mounted.
*/
Log
.
w
(
"ExternalStorage"
,
"Error writing "
+
file
,
e
);
}
}
void
deleteExternalStoragePrivateFile
()
{
/* Get path for the file on external storage. If external
storage is not currently mounted this will fail.
*/
File
file
=
new
File
(
getExternalFilesDir
(
null
),
"DemoFile.jpg"
);
if
(
file
!=
null
)
{
file
.
delete
();
}
}
boolean
hasExternalStoragePrivateFile
()
{
/* Get path for the file on external storage. If external
storage is not currently mounted this will fail.
*/
File
file
=
new
File
(
getExternalFilesDir
(
null
),
"DemoFile.jpg"
);
if
(
file
!=
null
)
{
return
file
.
exists
();
}
return
false
;
}
If you supply a non-null type to this function, the returned file will be a path to a sub-directory of the given type. Though these files are not automatically scanned by the media scanner, you can explicitly add them to the media database with MediaScannerConnection.scanFile. Note that this is not the same asEnvironment.getExternalStoragePublicDirectory(), which provides directories of media shared by all applications. The directories returned here are owned by the application, and their contents will be removed when the application is uninstalled. UnlikeEnvironment.getExternalStoragePublicDirectory(), the directory returned here will be automatically created for you.
Here is an example of typical code to manipulate a picture in an application's private storage and add it to the media database:
void
createExternalStoragePrivatePicture
()
{
/* Create a path where we will place our picture in our own private
pictures directory. Note that we don't really need to place a
picture in DIRECTORY_PICTURES, since the media scanner will see
all media in these directories; this may be useful with other
media types such as DIRECTORY_MUSIC however to help it classify
your media for display to the user.
*/
File
path
=
getExternalFilesDir
(
Environment
.
DIRECTORY_PICTURES
);
File
file
=
new
File
(
path
,
"DemoPicture.jpg"
);
try
{
/* Very simple code to copy a picture from the application's
resource into the external file. Note that this code does
no error checking, and assumes the picture is small (does not
try to copy it in chunks). Note that if external storage is
not currently mounted this will silently fail.
*/
InputStream
is
=
getResources
().
openRawResource
(
R
.
drawable
.
balloons
);
OutputStream
os
=
new
FileOutputStream
(
file
);
byte
[]
data
=
new
byte
[
is
.
available
()];
is
.
read
(
data
);
os
.
write
(
data
);
is
.
close
();
os
.
close
();
/* Tell the media scanner about the new file so that it is
immediately available to the user.
*/
MediaScannerConnection
.
scanFile
(
this
,
new
String
[]
{
file
.
toString
()
},
null
,
new
MediaScannerConnection
.
OnScanCompletedListener
()
{
public
void
onScanCompleted
(
String
path
,
Uri
uri
)
{
Log
.
i
(
"ExternalStorage"
,
"Scanned "
+
path
+
":"
);
Log
.
i
(
"ExternalStorage"
,
"-> uri="
+
uri
);
}
});
}
catch
(
IOException
e
)
{
/* Unable to create file, likely because external storage is
not currently mounted.
*/
Log
.
w
(
"ExternalStorage"
,
"Error writing "
+
file
,
e
);
}
}
void
deleteExternalStoragePrivatePicture
()
{
/* Create a path where we will place our picture in the user's
public pictures directory and delete the file. If external
storage is not currently mounted this will fail.
*/
File
path
=
getExternalFilesDir
(
Environment
.
DIRECTORY_PICTURES
);
if
(
path
!=
null
)
{
File
file
=
new
File
(
path
,
"DemoPicture.jpg"
);
file
.
delete
();
}
}
boolean
hasExternalStoragePrivatePicture
()
{
/* Create a path where we will place our picture in the user's
public pictures directory and check if the file exists. If
external storage is not currently mounted this will think the
picture doesn't exist.
*/
File
path
=
getExternalFilesDir
(
Environment
.
DIRECTORY_PICTURES
);
if
(
path
!=
null
)
{
File
file
=
new
File
(
path
,
"DemoPicture.jpg"
);
return
file
.
exists
();
}
return
false
;
}
Returns
- Returns the path of the directory holding application files on external storage. Returns null if external storage is not currently mounted so it could not ensure the path exists; you will need to call this method again when it is available.
该函数返回的地址将是如下形式：/mnt/sdcard/Android/data/com.lenovo.robin/files
其中为context所对应的应用程序的包名。
三、
Environment
中
关于
外部存储的
重要函数
public static File getExternalStorageDirectory ()
Gets the Android external storage directory. This directory may not currently be accessible if it has been mounted by the user on their computer, has been removed from the device, or some other problem has happened. You can determine its current state with getExternalStorageState().
Note: don't be confused by the word "external" here. This directory can better be thought as media/shared storage. It is a filesystem that can hold a relatively large amount of data and that is shared across all applications (does not enforce permissions). Traditionally this is an SD card, but it may also be implemented as built-in storage in a device that is distinct from the protected internal storage and can be mounted as a filesystem on a computer.
In devices with multiple "external" storage directories (such as both secure app storage and mountable shared storage), this directory represents the "primary" external storage that the user will interact with.
Applications should not directly use this top-level directory, in order to avoid polluting the user's root namespace. Any files that are private to the application should be placed in a directory returned by Context.getExternalFilesDir, which the system will take care of deleting if the application is uninstalled. Other shared files should be placed in one of the directories returned by getExternalStoragePublicDirectory(String).
该函数现在已经不合时宜，在API Level 8后，对于应用程序的私有文件应该放在Context.getExternalFilesDir目录下，非私有的（shared）的文件应该放在目录下Environment提供的函数getExternalStoragePublicDirectory(String)所指定的目录下
Here is an example of typical code to monitor the state of external storage:
BroadcastReceiver
mExternalStorageReceiver
;
boolean
mExternalStorageAvailable
=
false
;
boolean
mExternalStorageWriteable
=
false
;
void
updateExternalStorageState
()
{
String
state
=
Environment
.
getExternalStorageState
();
if
(
Environment
.
MEDIA_MOUNTED
.
equals
(
state
))
{
mExternalStorageAvailable
=
mExternalStorageWriteable
=
true
;
}
else
if
(
Environment
.
MEDIA_MOUNTED_READ_ONLY
.
equals
(
state
))
{
mExternalStorageAvailable
=
true
;
mExternalStorageWriteable
=
false
;
}
else
{
mExternalStorageAvailable
=
mExternalStorageWriteable
=
false
;
}
handleExternalStorageState
(
mExternalStorageAvailable
,
mExternalStorageWriteable
);
}
void
startWatchingExternalStorage
()
{
mExternalStorageReceiver
=
new
BroadcastReceiver
()
{
@Override
public
void
onReceive
(
Context
context
,
Intent
intent
)
{
Log
.
i
(
"test"
,
"Storage: "
+
intent
.
getData
());
updateExternalStorageState
();
}
};
IntentFilter
filter
=
new
IntentFilter
();
filter
.
addAction
(
Intent
.
ACTION_MEDIA_MOUNTED
);
filter
.
addAction
(
Intent
.
ACTION_MEDIA_REMOVED
);
registerReceiver
(
mExternalStorageReceiver
,
filter
);
updateExternalStorageState
();
}
void
stopWatchingExternalStorage
()
{
unregisterReceiver
(
mExternalStorageReceiver
);
public static File getExternalStoragePublicDirectory (String type)
Get a top-level public external storage directory for placing files of a particular type. This is where the user will typically place and manage their own files, so you should be careful about what you put here to ensure you don't erase their files or get in the way of their own organization.
Here is an example of typical code to manipulate a picture on the public external storage:
void
createExternalStoragePublicPicture
()
{
/* Create a path where we will place our picture in the user's
public pictures directory. Note that you should be careful about
what you place here, since the user often manages these files. For
pictures and other media owned by the application, consider
Context.getExternalMediaDir().
*/
File
path
=
Environment
.
getExternalStoragePublicDirectory
(
Environment
.
DIRECTORY_PICTURES
);
File
file
=
new
File
(
path
,
"DemoPicture.jpg"
);
try
{
// Make sure the Pictures directory exists.
path.mkdirs();
/* Very simple code to copy a picture from the application's
resource into the external file. Note that this code does
no error checking, and assumes the picture is small (does not
try to copy it in chunks). Note that if external storage is
not currently mounted this will silently fail.
*/
InputStream
is
=
getResources
().
openRawResource
(
R
.
drawable
.
balloons
);
OutputStream
os
=
new
FileOutputStream
(
file
);
byte
[]
data
=
new
byte
[
is
.
available
()];
is
.
read
(
data
);
os
.
write
(
data
);
is
.
close
();
os
.
close
();
/* Tell the media scanner about the new file so that it is
immediately available to the user.
*/
MediaScannerConnection
.
scanFile
(
this
,
new
String
[]
{
file
.
toString
()
},
null
,
new
MediaScannerConnection
.
OnScanCompletedListener
()
{
public
void
onScanCompleted
(
String
path
,
Uri
uri
)
{
Log
.
i
(
"ExternalStorage"
,
"Scanned "
+
path
+
":"
);
Log
.
i
(
"ExternalStorage"
,
"-> uri="
+
uri
);
}
});
}
catch
(
IOException
e
)
{
/* Unable to create file, likely because external storage is
not currently mounted.
*/
Log
.
w
(
"ExternalStorage"
,
"Error writing "
+
file
,
e
);
}
}
void
deleteExternalStoragePublicPicture
()
{
/* Create a path where we will place our picture in the user's
public pictures directory and delete the file. If external
storage is not currently mounted this will fail.
*/
File
path
=
Environment
.
getExternalStoragePublicDirectory
(
Environment
.
DIRECTORY_PICTURES
);
File
file
=
new
File
(
path
,
"DemoPicture.jpg"
);
file
.
delete
();
}
boolean
hasExternalStoragePublicPicture
()
{
/* Create a path where we will place our picture in the user's
public pictures directory and check if the file exists. If
external storage is not currently mounted this will think the
picture doesn't exist.
*/
File
path
=
Environment
.
getExternalStoragePublicDirectory
(
Environment
.
DIRECTORY_PICTURES
);
File
file
=
new
File
(
path
,
"DemoPicture.jpg"
);
return
file
.
exists
();
Returns
- Returns the File path for the directory. Note that this directory may not yet exist, so you must make sure it exists before using it such as with
File.mkdirs().
对于
Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MOVIES).getAbsolutePath()
返回的将是
/mnt/sdcard/Movies
public static String getExternalStorageState ()
返回值可以为Environment的以下常量之一