I used to use the path="/sdcard/myapp" to save data.
However,the compiler suggests me to use Environment.getExternalStorageDirectory() instead of hardcode "/sdcard"
My Question is:
If I do this, would the users of myapp lost their data when they updates？
AND, if true , how to prevent？
Sometimes, certain device manufacturers might use a different path for the external storage. Some devices might not have external storage at all and consider a part of their onboard storage as external storage. At other times, "/sdcard" might be mapped to another storage area as well.
So it is generally not considered wise to use "/sdcard".
On the other hand, Environment.getExternalStorageDirectory() is a system API and will always be supported by all device manufacturers. It will always correctly map to the storage area which is meant to be used as external storage for that particular device. So you can use this safely whenever you need a reference to the external storage directory.
Not all devices have sdcard. Some have build in storage like tablets. Therefore you should using the external storage directory.
Could be that it is directory mapped to /sdcard but could be some other directory/mount.
To answer your question: no, they will not loose there data.
Related
I have some downloadable content (e.g.:game character image) in a app, in iOS they are saved to path NSCachesDirectory, which I follows the guidelines of iOS that downloadable content should be saved in NSCachesDirectory, which is a cache directory. I am struggling if I should save the files to getCacheDir() in android side.
At first I think the cache folder in iOS should be equivalent (or similar) to the one in android, but after looking at some doc I doubt if they are functionally identical:
1.iOS suggest some downloadable content to save in cache folder, such content is more persist temporary file in tmp. But in android, the doc says getCacheDir() should store cache files rather than persist files, it makes me suspect android cache folder works more like the tmp folder in iOS
2.I cannot find any size limit guideline on iOS cache file, but android side says it should have reasonable size limit, say 1 MB (and I think my content would be far more than 1 MB, say 50 to 100 MB).
So my question is, are iOS cache folder works functionally equivalent to cache folder in android? Is it correct to use getCacheDir() at android side at the place that I use NSCachesDirectory in iOS side? if not,which path should I use at android side when I use NSCachesDirectory at iOS side?
No, iOS cache folder doesn't works functionally equivalent to cache
folder in android.
For more details of all the data-storage options of Android have a look at official docs here.
In Android for storing large amount of data you can go with either Internal or external data-storage options, Also you can make your data private on Internal or external data-storage options if you need so.
Internal storage
Each application has its own private internal storage to save files. This is the kind of storage to use if the user shouldn’t be able to modify the file from outside your application, and if other application shouldn’t be able to access those files. Since the internal storage is private to your application, the files will be deleted if your application is uninstalled. The internal storage is also where your application is installed by default, so your files will always be available. On some older or cheaper devices the internal storage is quite limited, so you need to be careful about the size of the data you save if you need to support those devices.
You should never hardcode the path to the storage directories, since the directory may changes depending on the version of the Android OS used. Also, Android 4.4 introduces the concept of multiple users : in that case, the internal and external storage depend on the user logged in and the files of the other users will be invisible. Here are some of the methods used to get the paths to the internal storage:
android.content.Context.getFilesDir(): returns a java.io.File object representing the root directory of the internal storage for your application from the current context.
android.content.Context.getDir(String name, Context.MODE_PRIVATE): returns a java.io.File object representing the directory name in the internal storage, creating the directory if it does not exists. The second parameter can also be used to set the directory to MODE_WORLD_READABLE or MODE_WORLD_WRITABLE so it is visible by all the other applications, but this is is risky security-wise and was deprecated in API level 17 (Android 4.2).
android.content.Context.getCacheDir(): returns a java.io.File object representing the internal cache directory for the application. This is mean for small files (the documentation suggests no more that 1MB total) that can be deleted at any time when the system needs more storage. There is no guarantee that the cache will be cleared, so you must also clear those files manually when they are not needed anymore.
As you can see, the files are represented by the File object from the java.io namepace: there is no file object specific to the Android SDK and the standard Java APIs for reading and writing files are used. Also, there is no specific application permission to set in the Android manifest to use the internal storage since it is already private to the application.
External storage
In addition of the internal storage, there is an external storage space shared by all the applications that is kept when your application is uninstalled. This is the storage that is shown when using a file explorer application and when the device is plugged in your computer. It may be implemented as a SD card that can be removed or as a partition of the built-in storage in the device, so your application should be able to work even if the card is removed or changed. To check the current state of the external storage, you can call the getExternalStorageState() method.
On device with many users (starting with Android 4.4), the external storage is specific to the current user and files for other users can’t be accessed. Also, there may be more than one external storage if the device has a built-in external storage which is a partition on the internal memory and a SD card: in that case, the built-in storage is the primary external storage. Reading files from the external storage requires the READ_EXTERNAL_STORAGE permission and writing or reading files requires the WRITE_EXTERNAL_STORAGE permission.
Here are the methods you should use to call to get the directories of the primary external storage:
android.os.Environment.getExternalStorageDirectory(): returns a java.io.File object representing the root directory of the primary external storage of the device that is shared by all applications.
android.os.Environment.getExternalStoragePublicDirectory(): returns a java.io.File object representing a public directory for files of a particular type on the primary external storage of the device. For example, you can get the path to the public music directory by calling Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC) or the public pictures directory by calling Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).
android.content.Context.getExternalFilesDir(): returns a java.io.File representing the root directory of the primary external storage specific to your application, which is under the directory returned by getExternalStorageDirectory(). Unlike the other directories of the external storage, the files you store in that folder will be deleted when your application is uninstalled. So, if you need to store files that are only needed by your application you should use this folder. Also, there is no specific permission needed for the application to read or write to its own external storage starting with Android 4.4, but with older versions your application needs the READ_EXTERNAL_STORAGE or WRITE_EXTERNAL_STORAGE permission.
android.content.Context.getExternalFilesDirs(): returns an array of java.io.File representing the root directories of all the external storage directories that can be used by your application with the primary external storage as the first directory in the array. All those directories works the same as the primary storage returned by the getExternalFilesDir() method. If the device has a built-in storage as the primary external storage and a SD card as a secondary external storage, this is the only way to get the path to the SD card. This method was introduced in Android 4.4, before that it was impossible to get the path to the secondary storage.
android.content.Context.getExternalCacheDir(): returns a java.io.File object representing the cache of the application on the primary external storage. This cache is not visible to the user and is deleted when the application is uninstalled. There is no mechanism in the Android SDK to delete files in the cache directory, so you need to manage your cache to keep it to a reasonable maximum size. Starting with Android 4.4, the application does not need permission to access its own cache, but with older versions your application needs the READ_EXTERNAL_STORAGE or WRITE_EXTERNAL_STORAGE permission.
I read alot about KITKAT and the prevention of writing to the secondary external sdcard.
It seems to be a new policy from google. I also read about storing the app's data under /externalsdcard/Android/data/.
Now my question, because I can't reproduce or test:
If the app is not allowed to write data directly under
< secundary external sdcard >, Will it then be possible to store the app's data under < secundary external sdcard >/Android/data/< app package name > ?
If possible. Could someone share a codesample ?
Never assume the removable secondary storage is larger than primar internal. On most modern devices internal storage can be up to 64 GB, but SD Card can be as small as 1 MB large (if user inserted small old card).
There is no way to distinguish which one is "external" using current APIs.
So the right way is using Context.getExternalFilesDirs() which returns all external storages to which you can store application-specific files without any permissions.
Use StatFs to find the largest storage available, and write data into it.
final File[] dirs = context.getExternalFilesDirs(null); //null means default type
//find a dir that has most of the space and save using StatFs
As the documentation says,
Returns absolute paths to application-specific directories on all external storage devices where the application can place persistent files it owns. These files are internal to the application, and not typically visible to the user as media.
This is like getFilesDir() in that these files will be deleted when the application is uninstalled, however there are some important differences:
External files are not always available: they will disappear if the user mounts the external storage on a computer or removes it.
There is no security enforced with these files.
External storage devices returned here are considered a permanent part of the device, including both emulated external storage and physical media slots, such as SD cards in a battery compartment. The returned paths do not include transient devices, such as USB flash drives.
An application may store data on any or all of the returned devices. For example, an app may choose to store large files on the device with the most available space, as measured by StatFs.
No permissions are required to read or write to the returned paths; they are always accessible to the calling app. Write access outside of these paths on secondary external storage devices is not available.
The first path returned is the same as getExternalFilesDir(String). Returned paths may be null if a storage device is unavailable.
So I'm testing an app on a galaxy s3 on 4.1 and an older phone that runs 2.3. Neither phone has an sdcard in it but when I use Environment.getExternalStorageDirectory().getAbsolutePath() on my galaxy s3 it directs me to a folder called sdcard0 within a folder called storage. When I run it on the older phone it gives me the path mnt/sdcard/ and the sdcard folder is read only.
I am trying to create a folder in these directories. I can do it on my s3 but not on my older phone.
Is there something similar to the storage folder I'm missing on the older phone or can I write to the sdcard folder when there is no sd card present?
EDIT: I have the external write permissions in my manifest
On some phones, as the documentation suggests, the word external is not to be taken all too serious:
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.
You can check if the storage is really external or not, using the Environment.isExternalStorageRemovable()-method. If it's not removable, you should always be able to write to it (given that you have the permissions declared).
If it is however removable, you'll need to check it's current state with Environment.getExternalStorageState(). Here's a quick example of how to use it:
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state)) {
// We can read and write!
} else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
// Mounted read only...
} else {
// Something is wrong...
}
So in these cases, you can write to the external storage.
Important: As the documentation specifies at multiple points, the above methods work for the primary external storage. Some devices (like the Motorola Xoom) have both an internal "external" storage, and an SD-Card.
There seems to be no "generalized" way to access the "secondary external storage" on such devices, although there is a standard now, introduced with Android 4.2
Devices may contain multiple instances of external storage, but
currently only the primary external storage is exposed to developers through API.
[...]
Starting in Android 4.2, devices can support multiple users, and
external storage must meet the following constraints:
[...]
Secondary external storage must not be writable by apps.
It seems to depend on the vendor which storage (internal or real external) is considered the primary one. Not much you can do here (without things getting messy...)
If there is no external storage present, you can use your applications Internal Storage, or the caching directory, depending on what kind of data you're storing.
how can I get the path for the folder where my app can save large JPG files?. getExternalStorageDirectory() works fine only when SD Card is present, but what happens when SD is removed or the harware don't have SD Card slot.
thanks
You can use the getFilesDir() method of a Context. From a context you can also use methods to get the cache directory, external cache directory, and the external files directory. An Activity is also a context, so you can use these methods from inside one.
The getFilesDir() method gives you the folder where your files will be accessible only from your application and will be always available. However, you should use the cache directory instead, when possible. This way you will avoid making the system run out of space.
EDIT:
My answer: Almost always a device will either have an SD card or built-in external storage. When it's built-in, it's still called external storage. To check whether the external storage is removable (SD card) or built-in you can use isExternalStorageRemovable() in Environment.
Basically, you shouldn't place large files on the internal memory. There is no public folder in the internal memory. If a device doesn't have external storage, it's simply not capable of doing certain things. Simple as that. So one option you have when there is no external storage is to inform the user about it and ask them to insert a card. You don't have to handle this case, let the user handle it.
The answer you asked for: Try using getDir(String name, int mode) and/or openFileOutput(String name, int mode) of a Context object, and for mode use MODE_WORLD_READABLE or MODE_WORLD_WRITEABLE. Also check Using the Internal Storage.
You are facing intended limitations of the platform that are there for the good of everyone.
You could either require external directory to exist, or you can store to the internal directory. If you choose to permit both, I suggest you store a flag in internal space to indicate that you've stored something externally, so that if external storage is not present you can take appropriate action.
As you are Saving Large JPG files, its is better to save it in external storage because Phone has very small internal memory and its all effect the performance of phone.
I currently use Environment.getExternalStorageDirectory() to obtain a location where I can store some data temporarily and then after being used gets deleted. This data can range from 1-100MB.
This works fine but on some cases the state of the external storage is removed or unmounted etc... and I can't access to store my data...
My question is what could be a good fallback solution when this storage is not available?
I'm targeting Android 1.6 and greater.
Note that you should not use the path returned by Environment.getExternalStorageDirectory() directly:
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).
Use the path returned by getFilesDir() to store files private to your app on the internal storage, or getExternalFilesDir() to store on the external storage.
If you're storing data temporarily, consider using the cache directories.
These files will be ones that get deleted first when the device runs
low on storage.
Use the methods: getCacheDir() or getExternalCacheDir() on the external filesystem. Read the documentation for important differences between them.
If the size of the data to be stored is not large, you'd be better off using the internal storage. Otherwise, you'll have to managing the complexity of detecting if external storage is available, falling backing to internal storage if not.