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Background
Accessing documents and other files from shared storage (including external and cloud storage).
In the past, we used to be able to access files on external storage directly using FileSystemStorage, but more recent android versions block this, requiring you to use their Shared Document APIs. a.k.a Share Files API and Storage Access Framework.
On Android devices from version 4.4 and above, apps can use the Storage Access Framework to let users choose documents and files for the app without needing special permissions. This enhances user privacy and control, and the accessed files remain on the device even after uninstalling the app.
The new Codename One Shared Files Library provides a wrapper over the Android shared files API to allow your Codename One apps to read and write shared files (i.e. files accessible to other apps).
This is a clean, secure and well-supported way to save and open files that could also be accessed by other applications.
Basic Usage
This API provides two abstractions:
1. SharedFile – Represents a single file or directory.
2. SharedFileManager – Provides access to the shared file system. Includes UI abstractions to select directories and files.
First step is to request access to a file:
// Open a directory
// Will open a file chooser for user to access a directory
SharedFileManager.getInstance().openDirectory().ready(sharedDirectory -> {
// sharedDirectory is a SharedFile object
});
// Open a file
SharedFileManager.getInstance().openFile().ready(sharedFile -> {
// sharedFile is a SharedFile object
});
// Open file of specific type
SharedFileManager.getInstance().openFile("text/plain").ready(sharedFile -> {
// sharedFile is a SharedFile object
});
Reading and Writing Files
Use SharedFile.openInputStream() and SharedFile.openOutputStream(String mimetype) for reading and writing files.
E.g.
String textContents = Util.readToString(sharedFile.openInputStream());
textContents += "Modified";
try (OutputStream output = sharedFile.openOutputStream(sharedFile.getMimetype())) {
output.write(textContents.getBytes("UTF-8"));
}
Creating New Files
1. Open a directory
2. Call directory.getChild(relativePath) to get reference to file.
3. Call child.openOutputStream(mimetype)
Bookmarking For Later Use
By default, the files you obtain will no be accessible the next time you load the app. You need to create a bookmarked file which will provide you with a persistent path that you can use to access the file.
1. Use SharedFile.createBookmark() to create a bookmark.
2. Use SharedFile.deleteBookmark() do remove a bookmark.
3. Use SharedFile.isBookmark() to check if the file is a bookmarked file.
4. Use SharedFileManager.openBookmark(String) to open a file given its bookmarked path. (i.e. bookmarkedFile.getPath())
5. Use SharedFileManager.getBookmarks() for a list of all current bookmarks.
Installation
Add the following maven dependency to your common/pom.xml file
<dependency>
<groupId>com.codenameone</groupId>
<artifactId>sharedfiles-lib</artifactId>
<version>0.1.0</version>
<type>pom</type>
</dependency>
2 Comments
Thanks for this. And good to see blogs returning after a while.
Thanks @Steve Hannah. This is awesome. Very useful… As @Wits ICT has said, glad to see you guys back. Hopefully you, Chen and Shai and the rest of the cn1 family still have good stuff in store.