Add writeContent

[jfaltis]

This PR adds the functionality to write content to a URI.

[espresso3389]

The PR does not make sense to me.
I think the plugin is to resolve the URL content but not to generate some.
Could you please explain more about your use case?

[jfaltis]

If you target Android 11 you won't be able to freely access the external storage of the Android device (https://developer.android.com/about/versions/11/privacy/storage). You will have to use the Storage Access Framework which allows the user to pick a folder in the external storage to which the app will be granted access to.

To write to a file you have to use the ContentResolver with openFileDescriptor to be able to get a reference to an OutputStream. https://developer.android.com/training/data-storage/shared/documents-files

This plugin was the only plugin I found which was related to the ContentResolver. Since you can only pass specific data types between flutter and the native code (https://docs.flutter.dev/development/platform-integration/platform-channels?tab=type-mappings-java-tab) you cannot expose the file descriptor to flutter (from my understanding). Therefore I implemented a method which just writes bytes to a file.

I totally see your point about how the ContentResolver is just responsible for resolving content. I don't know if it might be possible to expose the file descriptor and use it in dart or if this piece of code I have written is better suited for a storage access framework flutter library like https://github.com/lakscastro/shared-storage or https://github.com/ivehement/saf

[espresso3389]

OK, it's not a major usage of content provider but it may be neccesary on certain situation.

[espresso3389]

0.1.0 is released now!