How to Store Large Blobs in an Android Content Provider

How to store large blobs in an android content provider?

The solution phreed gives in the bottom half of question is basically correct. I'll try to add some more details here.

When you do getContentResolver().openInputStream(...), content resolver will go to your content provider and call its openFile method. This is how the openFile looks in ContentProvider.java:

public ParcelFileDescriptor openFile(Uri uri, String mode)
     throws FileNotFoundException {
 throw new FileNotFoundException("No files supported by provider at "
         + uri);
}

So this explains where the "No files supported ..." error exactly comes from! You get around this by overriding openFile method in your subclass and providing your own implementation. It's neat: you get perfect control of where your files get placed when any client does openInputStream or openOutputStream.

Code sample in phreed's question gives a hint how the implementation could look like. Here's my slightly modified version which also creates directories and files as needed. I'm novice at this stuff so this might not be the optimal way of doing things, but it gives an idea. For one thing, it should probably check if external storage is available.

@Override
public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {
    File root = new File(Environment.getExternalStorageDirectory(), 
            "/Android/data/com.example.myapp/cache");
    root.mkdirs();
    File path = new File(root, uri.getEncodedPath());
    // So, if the uri was content://com.example.myapp/some/data.xml,
    // we'll end up accessing /Android/data/com.example.myapp/cache/some/data.xml

    int imode = 0;
    if (mode.contains("w")) {
            imode |= ParcelFileDescriptor.MODE_WRITE_ONLY;
            if (!path.exists()) {
                try {
                    path.createNewFile();
                } catch (IOException e) {
                    // TODO decide what to do about it, whom to notify...
                    e.printStackTrace();
                }
            }
    }
    if (mode.contains("r")) imode |= ParcelFileDescriptor.MODE_READ_ONLY;
    if (mode.contains("+")) imode |= ParcelFileDescriptor.MODE_APPEND;        

    return ParcelFileDescriptor.open(path, imode);
}

Passing binary blob through a content provider

You won't be able to use a MatrixCursor to send the byte array. This is because it depends on AbstractCursor#fillWindow method which fills the CursorWindow using Object#toString. So what is happening is that the byte array toString method is being called and it's storing that instead of the contents of the byte array which is what you want. The only way around this I can see is to implement your own Cursor that will fill the CursorWindow appropriately for a byte array.

Storing file in Android Database (Custom Content Provider) using _data field - v1.6

To see where "No files supported by provider at..." comes from, have a look here. The situation there seems very similar with the one you've described.

In short, your content provider (or some of its superclasses) needs to override and implement openFile method. That error is raised by the default "not implemented--back off!" code in ContentProvider.java.

I find it helpful to peek at underlying source code of the framework when I get stuck, since documentation is sometimes a bit lacking.

How to pass binary data between two apps using Content Provider?

Why not giving the data as Base64 string?

Content provider file storage No Such file or directory

I had a similar problem to this. In your emulator, if the folder corresponding to Environment.getDataDirectory() does not exist then you will get an exception. You need to manually create the folder first (not by the code) through either the terminal or adb. Once you do that, try running your code again and it should work.

Content Provider commons

Should we use Content Provider, when data are not meant to be shared across applications?

Content Provider is one of the good features to share data among applications or activities within applications.
If you want to use content provider for your application and don't want to share then you can use content provider and it is really nice abstraction if you use content provider.

When having multiple data tables connected together, should we create single Provider for
every data type, or can we use single provider for all of them?

For different tables I think you have to create different content provider.In Android there are different content provider for different tables and database.So better you create
separate content provider for all the tables.

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