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diff --git a/docs/html/training/secure-file-sharing/request-file.jd b/docs/html/training/secure-file-sharing/request-file.jd new file mode 100644 index 0000000..116701d --- /dev/null +++ b/docs/html/training/secure-file-sharing/request-file.jd @@ -0,0 +1,147 @@ +page.title=Requesting a Shared File + +trainingnavtop=true +@jd:body + + +<div id="tb-wrapper"> +<div id="tb"> + +<h2>This lesson teaches you to</h2> +<ol> + <li><a href="#SendRequest">Send a Request for the File</a></li> + <li><a href="#OpenFile">Access the Requested File</a> +</ol> + +<h2>You should also read</h2> +<ul> + <li> + <a href="{@docRoot}guide/components/intents-filters.html">Intents and Intent Filters</a> + </li> + <li> + <a href="{@docRoot}guide/topics/providers/content-provider-basics.html#SimpleQuery" + >Retrieving Data from the Provider</a> + </li> +</ul> + +</div> +</div> + +<p> + When an app wants to access a file shared by another app, the requesting app (the client) + usually sends a request to the app sharing the files (the server). In most cases, the request + starts an {@link android.app.Activity} in the server app that displays the files it can share. + The user picks a file, after which the server app returns the file's content URI to the + client app. +</p> +<p> + This lesson shows you how a client app requests a file from a server app, receives the file's + content URI from the server app, and opens the file using the content URI. +</p> + +<h2 id="SendRequest">Send a Request for the File</h2> +<p> + To request a file from the server app, the client app calls + {@link android.app.Activity#startActivityForResult startActivityForResult} with an + {@link android.content.Intent} containing the action such as + {@link android.content.Intent#ACTION_PICK ACTION_PICK} and a MIME type that the client app + can handle. +</p> +<p> + For example, the following code snippet demonstrates how to send an + {@link android.content.Intent} to a server app in order to start the + {@link android.app.Activity} described in <a href="share-file.html#SendURI" + >Sharing a File</a>: +</p> +<pre> +public class MainActivity extends Activity { + private Intent mRequestFileIntent; + private ParcelFileDescriptor mInputPFD; + ... + @Override + protected void onCreate(Bundle savedInstanceState) { + super.onCreate(savedInstanceState); + setContentView(R.layout.activity_main); + mRequestFileIntent = new Intent(Intent.ACTION_PICK); + mRequestFileIntent.setType("image/jpg"); + ... + } + ... + protected void requestFile() { + /** + * When the user requests a file, send an Intent to the + * server app. + * files. + */ + startActivityForResult(mRequestFileIntent, 0); + ... + } + ... +} +</pre> +<h2 id="OpenFile">Access the Requested File</h2> +<p> + The server app sends the file's content URI back to the client app in an + {@link android.content.Intent}. This {@link android.content.Intent} is passed to the client + app in its override of {@link android.app.Activity#onActivityResult onActivityResult()}. Once + the client app has the file's content URI, it can access the file by getting its + {@link java.io.FileDescriptor}. +</p> +<p> +<p> + File security is preserved in this process because the content URI is the only piece of data + that the client app receives. Since this URI doesn't contain a directory path, the client app + can't discover and open any other files in the server app. Only the client app gets access to + the file, and only for the permissions granted by the server app. The permissions are temporary, + so once the client app's task stack is finished, the file is no longer accessible outside the + server app. +</p> +<p> + The next snippet demonstrates how the client app handles the + {@link android.content.Intent} sent from the server app, and how the client app gets the + {@link java.io.FileDescriptor} using the content URI: +</p> +<pre> + /* + * When the Activity of the app that hosts files sets a result and calls + * finish(), this method is invoked. The returned Intent contains the + * content URI of a selected file. The result code indicates if the + * selection worked or not. + */ + @Override + public void onActivityResult(int requestCode, int resultCode, + Intent returnIntent) { + // If the selection didn't work + if (resultCode != RESULT_OK) { + // Exit without doing anything else + return; + } else { + // Get the file's content URI from the incoming Intent + Uri returnUri = returnIntent.getData(); + /* + * Try to open the file for "read" access using the + * returned URI. If the file isn't found, write to the + * error log and return. + */ + try { + /* + * Get the content resolver instance for this context, and use it + * to get a ParcelFileDescriptor for the file. + */ + mInputPFD = getContentResolver().openFileDescriptor(returnUri, "r"); + } catch (FileNotFoundException e) { + e.printStackTrace(); + Log.e("MainActivity", "File not found."); + return; + } + // Get a regular file descriptor for the file + FileDescriptor fd = mInputPFD.getFileDescriptor(); + ... + } + } +</pre> +<p> + The method {@link android.content.ContentResolver#openFileDescriptor openFileDescriptor()} + returns a {@link android.os.ParcelFileDescriptor} for the file. From this object, the client + app gets a {@link java.io.FileDescriptor} object, which it can then use to read the file. +</p> |