Android api file delete

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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Android File IO Tutorial with Internal and External Storage

In this tutorial I will cover how to create files in various methods in Android such as Internal Storage, External Storage, the MediaStore API and the Storage Access Framework.

I will explain the differences between each of these file storage methods and provide some context on when to use each.

I will also cover some details on the Scoped Storage privacy feature released in Android 10 and enhanced in Android 11 for files created by your app in external storage.

I will share code samples in this tutorial and I have also published all the code from this tutorial in the GitHub repository in the link below.

Android Internal File Storage Tutorial

This section of the post contains a tutorial on how to use internal storage in Android. We will cover the following topics in our tutorial on the use of internal storage in Android.

• What is Internal Storage in Android?
• How to Create a Text File Programmatically in Internal Storage in Android
• How to Write Text to a File Programmatically in Internal Storage in Android
• How to Read Text from a File Programmatically in Internal Storage in Android
• How to Delete a Text File Programmatically from Internal Storage in Android
• How to View Files in Internal Storage using the Android Device File Explorer
• How to Remove Files from Internal Storage using the Android Storage Utility

Please see a screen capture below of the Android app of what we will be creating in this tutorial.

What is Internal Storage in Android?

Internal Storage in Android is used for storing files that are only visible to your app. No permissions are required to read or write files to internal storage for your app. If your app is uninstalled with files in internal storage, these files will be deleted as a part of the uninstallation process.

Files in internal storage in Android can either be persistent files or cache files.

Cache files are stored in internal storage as temporary files, they will get deleted when the user uninstalls the app but they can also be deleted before then by the Android system clearing space in storage or by deleting the cache file programmatically. Unlike cache files, persistent files in internal storage cannot be deleted by the Android system automatically.

How to Create a Text File Programmatically in Internal Storage in Android

To create a text file programmatically in internal storage in Android we will be using the File class from the java.io.File package.

In the code sample I have created, I am allowing the user to enter the name of the file inside an EditText as well as allowing them to use a ToggleButton to choose if they want a persistent file or a cache file to be created in internal storage.

We will use the File constructor and provide two parameters, the first is of the data type File which refers to the directory where the File we create will reside and the second parameter is of the data type String which will be the name of the file.

For persistent files in internal storage we need to use the “files” directory inside the internal storage directory. To obtain this directory use the getFilesDir() method on the application context which will return a File object pointing the “files” directory.

For cache files in internal storage we need to use the “cache” directory inside the internal storage directory. To obtain this directory use the getCacheDir() method on the application context which will return a File object pointing the “cache” directory.

Before we create the file, I will first check whether it already exists using the exists() method on the File object which will return true if the File already exists or false if it does not exist.

If the file doesn’t exist, I will proceed to create the file using the createNewFile() method on the File object.

Please see the code excerpt below for programmatically creating either a persistent or cache file in internal storage in Android.

How to Write Text to a File Programmatically in Internal Storage in Android

To write text to a file residing in the internal storage of our app programmatically we will be using the FileOutputStream class from the java.io.FileOutputStream package.

In our code sample, we will be writing the file name that has been entered in the EditText by the user and will determine if the file is a persistent file or a cache file based on the checked status of the ToggleButton.

Also in our code sample, the user will enter the text they wish to write into the file in an EditText and select the “Write File” button when they are ready to write the text to the file.

To set up the FileOutputStream for writing the text to the file, we will first check if the file is a persistent file or cache file in internal storage.

If it is a persistent file then we will set up the FileOutputStream using the openFileOutput(String, int) method on the application context passing the file name and the Context.MODE_PRIVATE flag as parameters. The Context.MODE_PRIVATE flag for the file creation mode means the created file can only be accessed by the calling application.

If the file is a cache file then we will set up the FileOutputStream by passing a File object pointing to the cache file as a parameter to the FileOutputStream constructor.

Then to write the text to the file using the FileOutputStream we will call the write(byte[]) method by passing a byte array as a parameter that consists of the text from the file contents EditText encoded using the UTF-8 format into a byte array.

Please see the code excerpt below for programmatically writing text to either a persistent or cache file in internal storage in Android.

How to Read Text from a File Programmatically in Internal Storage in Android

To read the text from a file residing in the internal storage of our app programmatically we will be using the FileInputStream class from the java.io.FileInputStream package.

In our code sample, we will overwrite the file contents EditText with the text read from the file entered into file name EditText when the user selects the “Read File” button.

To set up the FileInputStream for reading the text from the file, we will first check if the file is a persistent file or a cache file in internal storage.

If it is a persistent file then we will set up the FileInputStream using the openFileInput(String) method on the application context passing the file name as a parameter.

If the file is a cache file then we will set up the FileInputStream by passing a File object pointing to the cache file as a parameter to the FileInputStream constructor.

Then we create will an InputStreamReader from the FileInputStream and use that to create a BufferedReader which allows us to read from the file one line at a time. We will create an empty ArrayList of Strings to store each line of text from the file.

Next we will use the BufferedReader inside a while loop to extract each line of text one at a time until there is no more text. Each line of text read using the BufferedReader will be inserted into the ArrayList sequentially.

Once all of the lines of text have been read from the file we will use the join(…) method from the TextUtils class to create a single String of text by joining all of the lines of text in the ArrayList together with a new line character between all lines of text. This will allow the text to be formatted correctly when displayed in the EditText containing the file contents.

Please see the code excerpt below for programmatically reading text from a either a persistent or cache file in internal storage in Android.

How to Delete a Text File Programmatically from Internal Storage in Android

To delete a file residing in the internal storage of our app programmatically we will be using the File class from the java.io.File package.

First we will create File object pointing the File we want to delete by using the file name entered by the user and selecting the appropriate file directory based on whether the file is a persistent file or a cache file.

Then we will use the exists() method on the File object to confirm that it exists, and if it does exist we will proceed to delete using the delete() method on the File object.

Please see the code excerpt below for programmatically deleting either a persistent or cache file in internal storage in Android.

How to View Files in Internal Storage using the Android Device File Explorer

The Device File Explorer is a tool available in Android Studio that allows you to view all of the files on the Android device connected to Android Studio.

The Device File Explorer can be used to read both the persistent and cache files inside internal storage of your Android app.

To access the Device File Explorer in Android Studio select the “View” menu, hover over “Tool Windows” and select the “Device File Explorer” menu item.

The Device File Explorer will load on the right side of Android Studio and will display a file tree of all of the directories and files on the Android device.

To locate persistent files in internal storage of your app navigate through to the following directory.

data/data/ /files

To locate cache files in internal storage of your app navigate through to the following directory.

data/data/ /cache

You can also open any file to read inside Android Studio by double clicking on the file name.

How to Remove Files from Internal Storage using the Android Storage Utility

It is possible to use a storage utility an Android device to remove persistent and cache files from the internal storage of your app.

In the storage utility shown in the GIF below. The total amount of storage used by your Android app broken down by the App size, User data and Cache is shown along with a button to “Clear storage” and a button to “Clear cache”.

Selecting the “Clear storage” button will delete all persistent and cache files from the internal storage of your app.

Selecting the “Clear cache” button will delete only the cache files from the internal storage of your app leaving the persistent files in internal storage.

Android External File Storage Tutorial

What is External Storage in Android?

In Android External Storage is used for storing files that other apps are able to access. External storage is better for storing larger files that need to be shared with other apps.

Files in external storage can be app specific, meaning that when the app is uninstalled these files in external storage will be deleted. App specific files in external storage can be persistent files or cache files.

For Android 4.4 (API level 19) and higher, no storage related permissions are required to access app specific directories with external storage.

For apps the target Android 10 (API level 29) or higher, a new feature called scoped storage is applied by default to external storage which will prevent other apps from accessing your app specific files in external storage.

To learn more about scoped storage check out the YouTube video below.

Media files such as images, audio and video can be exposed to other apps in external storage through the use of the Android MediaStore API.

Other files you want to share to other apps in external storage such as documents can be shared using the Storage Access Framework.

How to Store Persistent and Cache Files in External Storage in Android

App specific persistent files in external storage reside in a directory accessible using the getExternalFileDirs() method.

App specific cache files in external storage reside in a directory accessible using the getExternalCacheDirs() method.

The code sample below contains code for writing a persistent file or a cache file into external storage in Android.

The code sample below contains code for reading a persistent file or a cache file from external storage in Android.

Below is a screenshot of an Android app creating a persistent file in app specific external storage.

Below is a screenshot of the Device File Explorer in Android Studio showing the persistent file created in app specific external storage.

Below is a screenshot of an Android app creating a cache file in app specific external storage.

Below is a screenshot of the Device File Explorer in Android Studio showing the cache file created in app specific external storage.

How to Store Media Files in External Storage in Android

Media files such as images, videos and audio can be shared in external storage with other apps using the Android Media Store API providing they have the READ_EXTERNAL_STORAGE permission. Media files shared using the Media Store API will not be deleted when the app is uninstalled.

On Android 10 (API level 29) or higher, READ_EXTERNAL_STORAGE or WRITE_EXTERNAL_STORAGE permissions are required to access media files created by other apps via the Media Store API. On Android 9 (API level 28) or lower permissions are required for accessing all media files via the Media Store API.

To demonstrate how to storage media files in external storage in Android using the MediaStore API, I created a sample app that loads an image from the internet using the Glide library then stores it into the Pictures directory in external storage using the MediaStore API for images.

The app also will display a RecyclerView in a grid layout of all images in the Pictures directory retrieved using the MediaStore API.

If you would like to learn more about how to set up and use Glide for image loading in your Android app including how to download the Glide using Gradle and how to set up the manifest to include internet permissions, check out the tutorial I wrote on how to use Glide at the link below.

For this section of the tutorial first we will be creating a class modelling an image retrieved from the Media Store API. See the code sample for the Image class below.

Next we will be creating a RecyclerViewHolder class for the Image to display the Image in the RecyclerView. See the code sample for the ImageViewHolder class below which sets the name of the Image in the TextView and loads the ImageView with Glide inside the bind(Image) method.

For the next step we will create a RecyclerViewAdapter for the RecyclerView. See the code sample for the GalleryRecyclerAdapter class below.

In the final step in this section of the tutorial we will create an Activity class that includes code for inserting an Image into the Media Store API and querying Images from the Media Store API into the RecyclerViewAdapter to be shown in the RecyclerView.

How to Store Documents in External Storage in Android

Documents and other files can be shared with other apps in external storage using the Storage Access Framework.

No permissions are required read or write files in external storage to the Storage Access Framework. Files created using your app via the Storage Access Framework will not automatically be deleted when you uninstall your app.

Please see the code sample for the activity class below that can read and write files to external storage using the Storage Access Framework.

See the screen capture below showing the user experience of creating and writing to a text document generating using the Storage Access Framework.

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