Android save on device

Saving Files

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Android uses a file system that’s similar to disk-based file systems on other platforms. This lesson describes how to work with the Android file system to read and write files with the File APIs.

A File object is suited to reading or writing large amounts of data in start-to-finish order without skipping around. For example, it’s good for image files or anything exchanged over a network.

This lesson shows how to perform basic file-related tasks in your app. The lesson assumes that you are familiar with the basics of the Linux file system and the standard file input/output APIs in java.io .

Choose Internal or External Storage

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.

• It’s always available.
• Files saved here are accessible by only your app by default.
• When the user uninstalls your app, the system removes all your app’s files from internal storage.

Internal storage is best when you want to be sure that neither the user nor other apps can access your files.

• It’s not always available, because the user can mount the external storage as USB storage and in some cases remove it from the device.
• It’s world-readable, so files saved here may be read outside of your control.
• When the user uninstalls your app, the system removes your app’s files from here only if you save them in the directory from getExternalFilesDir() .

External storage is the best place for files that don’t require access restrictions and for files that you want to share with other apps or allow the user to access with a computer.

Tip: Although apps are installed onto the internal storage by default, you can specify the android:installLocation attribute in your manifest so your app may be installed on external storage. Users appreciate this option when the APK size is very large and they have an external storage space that’s larger than the internal storage. For more information, see App Install Location.

Obtain Permissions for External Storage

To write to the external storage, you must request the WRITE_EXTERNAL_STORAGE permission in your manifest file:

Caution: Currently, all apps have the ability to read the external storage without a special permission. However, this will change in a future release. If your app needs to read the external storage (but not write to it), then you will need to declare the READ_EXTERNAL_STORAGE permission. To ensure that your app continues to work as expected, you should declare this permission now, before the change takes effect.

However, if your app uses the WRITE_EXTERNAL_STORAGE permission, then it implicitly has permission to read the external storage as well.

You don’t need any permissions to save files on the internal storage. Your application always has permission to read and write files in its internal storage directory.

Save a File on Internal Storage

When saving a file to internal storage, you can acquire the appropriate directory as a File by calling one of two methods:

getFilesDir() Returns a File representing an internal directory for your app. getCacheDir() Returns a File representing an internal directory for your app’s temporary cache files. Be sure to delete each file once it is no longer needed and implement a reasonable size limit for the amount of memory you use at any given time, such as 1MB. If the system begins running low on storage, it may delete your cache files without warning.

To create a new file in one of these directories, you can use the File() constructor, passing the File provided by one of the above methods that specifies your internal storage directory. For example:

Alternatively, you can call openFileOutput() to get a FileOutputStream that writes to a file in your internal directory. For example, here’s how to write some text to a file:

Or, if you need to cache some files, you should instead use createTempFile() . For example, the following method extracts the file name from a URL and creates a file with that name in your app’s internal cache directory:

Note: Your app’s internal storage directory is specified by your app’s package name in a special location of the Android file system. Technically, another app can read your internal files if you set the file mode to be readable. However, the other app would also need to know your app package name and file names. Other apps cannot browse your internal directories and do not have read or write access unless you explicitly set the files to be readable or writable. So as long as you use MODE_PRIVATE for your files on the internal storage, they are never accessible to other apps.

Save a File on External Storage

Because the external storage may be unavailable—such as when the user has mounted the storage to a PC or has removed the SD card that provides the external storage—you should always verify that the volume is available before accessing it. You can query the external storage state by calling getExternalStorageState() . If the returned state is equal to MEDIA_MOUNTED , then you can read and write your files. For example, the following methods are useful to determine the storage availability:

Although the external storage is modifiable by the user and other apps, there are two categories of files you might save here:

Public files Files that should be freely available to other apps and to the user. When the user uninstalls your app, these files should remain available to the user.

For example, photos captured by your app or other downloaded files.

Private files Files that rightfully belong to your app and should be deleted when the user uninstalls your app. Although these files are technically accessible by the user and other apps because they are on the external storage, they are files that realistically don’t provide value to the user outside your app. When the user uninstalls your app, the system deletes all files in your app’s external private directory.

For example, additional resources downloaded by your app or temporary media files.

If you want to save public files on the external storage, use the getExternalStoragePublicDirectory() method to get a File representing the appropriate directory on the external storage. The method takes an argument specifying the type of file you want to save so that they can be logically organized with other public files, such as DIRECTORY_MUSIC or DIRECTORY_PICTURES . For example:

If you want to save files that are private to your app, you can acquire the appropriate directory by calling getExternalFilesDir() and passing it a name indicating the type of directory you’d like. Each directory created this way is added to a parent directory that encapsulates all your app’s external storage files, which the system deletes when the user uninstalls your app.

For example, here’s a method you can use to create a directory for an individual photo album:

If none of the pre-defined sub-directory names suit your files, you can instead call getExternalFilesDir() and pass null . This returns the root directory for your app’s private directory on the external storage.

Remember that getExternalFilesDir() creates a directory inside a directory that is deleted when the user uninstalls your app. If the files you’re saving should remain available after the user uninstalls your app—such as when your app is a camera and the user will want to keep the photos—you should instead use getExternalStoragePublicDirectory() .

Regardless of whether you use getExternalStoragePublicDirectory() for files that are shared or getExternalFilesDir() for files that are private to your app, it’s important that you use directory names provided by API constants like DIRECTORY_PICTURES . These directory names ensure that the files are treated properly by the system. For instance, files saved in DIRECTORY_RINGTONES are categorized by the system media scanner as ringtones instead of music.

Query Free Space

If you know ahead of time how much data you’re saving, you can find out whether sufficient space is available without causing an IOException by calling getFreeSpace() or getTotalSpace() . These methods provide the current available space and the total space in the storage volume, respectively. This information is also useful to avoid filling the storage volume above a certain threshold.

However, the system does not guarantee that you can write as many bytes as are indicated by getFreeSpace() . If the number returned is a few MB more than the size of the data you want to save, or if the file system is less than 90% full, then it’s probably safe to proceed. Otherwise, you probably shouldn’t write to storage.

Note: You aren’t required to check the amount of available space before you save your file. You can instead try writing the file right away, then catch an IOException if one occurs. You may need to do this if you don’t know exactly how much space you need. For example, if you change the file’s encoding before you save it by converting a PNG image to JPEG, you won’t know the file’s size beforehand.

Delete a File

You should always delete files that you no longer need. The most straightforward way to delete a file is to have the opened file reference call delete() on itself.

If the file is saved on internal storage, you can also ask the Context to locate and delete a file by calling deleteFile() :

Note: When the user uninstalls your app, the Android system deletes the following:

• All files you saved on internal storage
• All files you saved on external storage using getExternalFilesDir() .

However, you should manually delete all cached files created with getCacheDir() on a regular basis and also regularly delete other files you no longer need.

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How to save data in an android app

I recently coded an Android app. It’s just a simple app that allows you to keep score of a basketball game with a few simple counter intervals. I’m getting demand to add a save feature, so you can save your scores and then load them back up. Currently, when you stop the app, your data is lost. So what I was wondering is what I would have to add to have the app save a label (score) and then load it back up. Thanks guys sorry I don’t know much about this stuff.

12 Answers 12

You have two options, and I’ll leave selection up to you.

This is a framework unique to Android that allows you to store primitive values (such as int , boolean, and String , although strictly speaking String isn’t a primitive) in a key-value framework. This means that you give a value a name, say, «homeScore» and store the value to this key.

This, in my opinion, is what you might be looking for. You can store anything you want to a file, so this gives you more flexibility. However, the process can be trickier because everything will be stored as bytes, and that means you have to be careful to keep your read and write processes working together.

Now, you can also look into External Storage, but I don’t recommend that in this particular case, because the external storage might not be there later. (Note that if you pick this, it requires a permission)

OP is asking for a «save» function, which is more than just preserving data across executions of the program (which you must do for the app to be worth anything.)

I recommend saving the data in a file on the sdcard which allows you to not only recall it later, but allows the user to mount the device as an external drive on their own computer and grab the data for use in other places.

So you really need a multi-point system:

1) Implement onSaveInstanceState() . In this method, you’re passed a Bundle, which is basically like a dictionary. Store as much information in the bundle as would be needed to restart the app exactly where it left off. In your onCreate() method, check for the passed-in bundle to be non-null, and if so, restore the state from the bundle.

2) Implement onPause() . In this method, create a SharedPreferences editor and use it to save whatever state you need to start the app up next time. This mainly consists of the users’ preferences (hence the name), but anything else relavent to the app’s start-up state should go here as well. I would not store scores here, just the stuff you need to restart the app. Then, in onCreate() , whenever there’s no bundle object, use the SharedPreferences interface to recall those settings.

3a) As for things like scores, you could follow Mathias’s advice above and store the scores in the directory returned in getFilesDir() , using openFileOutput() , etc. I think this directory is private to the app and lives in main storage, meaning that other apps and the user would not be able to access the data. If that’s ok with you, then this is probably the way to go.

3b) If you do want other apps or the user to have direct access to the data, or if the data is going to be very large, then the sdcard is the way to go. Pick a directory name like com/user1446371/basketballapp/ to avoid collisions with other applications (unless you’re sure that your app name is reasonably unique) and create that directory on the sdcard. As Mathias pointed out, you should first confirm that the sdcard is mounted.

I recommend simple CSV files for your data, so that other applications can read them easily.

Obviously, you’ll have to write activities that allow «save» and «open» dialogs. I generally just make calls to the openintents file manager and let it do the work. This requires that your users install the openintents file manager to make use of these features, however.

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How to save data on your Android device in 5 different ways

Let’s get real for a second: mobile data is expensive, and it can get eaten up quickly by many different apps and performance issues that drain data without you even realizing it.

Fortunately, there are plenty of ways to cut back on your data usage on an Android device.

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How to save data on your Android device

Here are five ways you can save data on your Android device.

Connect to Wi-Fi frequently

The easiest way to save data on your Android device is to connect to Wi-Fi as often as possible to avoid using unnecessary data. If you’re doing something on your Android device that requires a lot of data, like streaming videos or performing app updates, connected to Wi-Fi will save you a lot of data in the long run.

Use streaming apps in moderation

If an app you’re using streams video, music, or even just large photos, the app is going to eat up a lot of your data. You’re better off using heavy-data apps like Spotify, YouTube, or Netflix on a computer instead of your Android device, or limit their use to times when your Android device has a secure Wi-Fi connection.

Limit data usage for specific apps

Limiting the data usage for specific apps can also help save data in the long run. This involves disabling the feature that allows an app to use data while it’s running in the background of your phone, even if you aren’t using the app.

1. In your Android device’s Settings app, tap on «Apps.»

2. Tap on the app that you want to limit data for.

3. Tap «Mobile data.»

4. If background data usage is enabled, the slider next to «Allow background data usage» will be white and blue. To disable this feature so that you save data, tap on the slider so that it turns only white.

Set a data limit for your Android device

Getting into more extreme measures, you might find it helpful to set a limit on the amount of data your Android device uses. You can do this in your device’s Settings.

1. Open your Android device’s Settings app.

2. Tap on «Connections.»

3. Tap on «Data usage.»

4. Tap on «Mobile data usage.»

5. Tap on the gear icon in the upper-right corner of the screen.

From there, you can set a data warning so that you know when you’re running out of data, or set a complete limit on mobile data usage, so that your device stops using data after a certain point until your next billing cycle.

Turn on data saver mode

When all else fails, there’s always data saver mode. This mode will completely stop all of your Android’s data usage by disallowing all apps to run background data. As you might expect, this can sometimes affect various apps’ functionality.

1. Open the Settings app on your Android device.

2. Tap «Connections.»

3. Tap «Data usage.»

4. Tap «Data saver.»

5. If data saver mode is off, the slider will be white. To turn data saver mode on, tap on the slider so that it turns white and blue.

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