Geteilte Datei anfordern
Mit Sammlungen den Überblick behalten
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Wenn eine App auf eine Datei zugreifen möchte, die von einer anderen App freigegeben wurde, wird die anfragende App (der Client)
sendet normalerweise eine Anfrage an die App, die die Dateien freigibt (den Server). In den meisten Fällen
startet ein Activity
in der Server-App, das die Dateien anzeigt, die freigegeben werden können.
Der Nutzer wählt eine Datei aus, woraufhin die Server-App den Inhalts-URI der Datei an den
Client-App.
In dieser Lektion erfahren Sie, wie eine Client-App eine Datei von einer Server-App anfordert, die
Inhalts-URI aus der Server-App und öffnet die Datei mit dem Inhalts-URI.
Anfrage für die Datei senden
Zum Anfordern einer Datei von der Server-App ruft die Client-App auf
startActivityForResult
mit einem
Intent
mit der Aktion, z. B.
ACTION_PICK
und einen MIME-Typ, den die Client-App
die Sie bewältigen können.
Das folgende Code-Snippet zeigt beispielsweise, wie ein
Intent
an eine Server-App, um den
Activity
beschrieben unter Datei freigeben:
Kotlin
class MainActivity : Activity() {
private lateinit var requestFileIntent: Intent
private lateinit var inputPFD: ParcelFileDescriptor
...
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
requestFileIntent = Intent(Intent.ACTION_PICK).apply {
type = "image/jpg"
}
...
}
...
private fun requestFile() {
/**
* When the user requests a file, send an Intent to the
* server app.
* files.
*/
startActivityForResult(requestFileIntent, 0)
...
}
...
}
Java
public class MainActivity extends Activity {
private Intent requestFileIntent;
private ParcelFileDescriptor inputPFD;
...
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
requestFileIntent = new Intent(Intent.ACTION_PICK);
requestFileIntent.setType("image/jpg");
...
}
...
protected void requestFile() {
/**
* When the user requests a file, send an Intent to the
* server app.
* files.
*/
startActivityForResult(requestFileIntent, 0);
...
}
...
}
Auf die angeforderte Datei zugreifen
Die Server-App sendet den Inhalts-URI der Datei in einem
Intent
Diese Intent
wird an den Client übergeben.
durch onActivityResult()
überschrieben wird. Einmal
die Client-App den Inhalts-URI der Datei hat, kann sie auf die Datei zugreifen, indem sie
FileDescriptor
Die Dateisicherheit wird bei diesem Vorgang nur gewahrt, wenn Sie den Inhalts-URI richtig parsen
die die Client-App erhält. Achten Sie beim Parsen von Inhalten darauf, dass dieser URI nicht auf
nicht auf das vorgesehene Verzeichnis.
Es wird versucht, einen Pfaddurchlauf zu erstellen.
Nur die Client-App sollte Zugriff auf die Datei erhalten und nur die von der
Server-App. Berechtigungen sind temporär. Sobald der Aufgabenstapel der Client-App fertig ist,
auf die Datei kann nicht mehr außerhalb der Server-App zugegriffen werden.
Das nächste Snippet zeigt, wie die Client-App
Intent
wird von der Server-App gesendet und wie die Client-App die
FileDescriptor
mithilfe des Inhalts-URI:
Kotlin
/*
* 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.
*/
public override fun onActivityResult(requestCode: Int, resultCode: Int, returnIntent: Intent) {
// If the selection didn't work
if (resultCode != Activity.RESULT_OK) {
// Exit without doing anything else
return
}
// Get the file's content URI from the incoming Intent
returnIntent.data?.also { returnUri ->
/*
* 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.
*/
inputPFD = try {
/*
* Get the content resolver instance for this context, and use it
* to get a ParcelFileDescriptor for the file.
*/
contentResolver.openFileDescriptor(returnUri, "r")
} catch (e: FileNotFoundException) {
e.printStackTrace()
Log.e("MainActivity", "File not found.")
return
}
// Get a regular file descriptor for the file
val fd = inputPFD.fileDescriptor
...
}
}
Java
/*
* 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.
*/
inputPFD = 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 = inputPFD.getFileDescriptor();
...
}
}
Die Methode openFileDescriptor()
gibt ParcelFileDescriptor
für die Datei zurück. Über dieses Objekt
App ein FileDescriptor
-Objekt erhält, mit dem sie dann die Datei lesen kann.
Weitere Informationen finden Sie hier:
Alle Inhalte und Codebeispiele auf dieser Seite unterliegen den Lizenzen wie im Abschnitt Inhaltslizenz beschrieben. Java und OpenJDK sind Marken oder eingetragene Marken von Oracle und/oder seinen Tochtergesellschaften.
Zuletzt aktualisiert: 2025-07-27 (UTC).
[[["Leicht verständlich","easyToUnderstand","thumb-up"],["Mein Problem wurde gelöst","solvedMyProblem","thumb-up"],["Sonstiges","otherUp","thumb-up"]],[["Benötigte Informationen nicht gefunden","missingTheInformationINeed","thumb-down"],["Zu umständlich/zu viele Schritte","tooComplicatedTooManySteps","thumb-down"],["Nicht mehr aktuell","outOfDate","thumb-down"],["Problem mit der Übersetzung","translationIssue","thumb-down"],["Problem mit Beispielen/Code","samplesCodeIssue","thumb-down"],["Sonstiges","otherDown","thumb-down"]],["Zuletzt aktualisiert: 2025-07-27 (UTC)."],[],[],null,["# Requesting a shared file\n\nWhen an app wants to access a file shared by another app, the requesting app (the client)\nusually sends a request to the app sharing the files (the server). In most cases, the request\nstarts an [Activity](/reference/android/app/Activity) in the server app that displays the files it can share.\nThe user picks a file, after which the server app returns the file's content URI to the\nclient app.\n\n\nThis lesson shows you how a client app requests a file from a server app, receives the file's\ncontent URI from the server app, and opens the file using the content URI.\n\nSend a request for the file\n---------------------------\n\n\nTo request a file from the server app, the client app calls\n[startActivityForResult](/reference/android/app/Activity#startActivityForResult(android.content.Intent, int)) with an\n[Intent](/reference/android/content/Intent) containing the action such as\n[ACTION_PICK](/reference/android/content/Intent#ACTION_PICK) and a MIME type that the client app\ncan handle.\n\n\nFor example, the following code snippet demonstrates how to send an\n[Intent](/reference/android/content/Intent) to a server app in order to start the\n[Activity](/reference/android/app/Activity) described in [Sharing a file](/training/secure-file-sharing/share-file#SendURI): \n\n### Kotlin\n\n```kotlin\nclass MainActivity : Activity() {\n private lateinit var requestFileIntent: Intent\n private lateinit var inputPFD: ParcelFileDescriptor\n ...\n override fun onCreate(savedInstanceState: Bundle?) {\n super.onCreate(savedInstanceState)\n setContentView(R.layout.activity_main)\n requestFileIntent = Intent(Intent.ACTION_PICK).apply {\n type = \"image/jpg\"\n }\n ...\n }\n ...\n private fun requestFile() {\n /**\n * When the user requests a file, send an Intent to the\n * server app.\n * files.\n */\n startActivityForResult(requestFileIntent, 0)\n ...\n }\n ...\n}\n```\n\n### Java\n\n```java\npublic class MainActivity extends Activity {\n private Intent requestFileIntent;\n private ParcelFileDescriptor inputPFD;\n ...\n @Override\n protected void onCreate(Bundle savedInstanceState) {\n super.onCreate(savedInstanceState);\n setContentView(R.layout.activity_main);\n requestFileIntent = new Intent(Intent.ACTION_PICK);\n requestFileIntent.setType(\"image/jpg\");\n ...\n }\n ...\n protected void requestFile() {\n /**\n * When the user requests a file, send an Intent to the\n * server app.\n * files.\n */\n startActivityForResult(requestFileIntent, 0);\n ...\n }\n ...\n}\n```\n\nAccess the requested file\n-------------------------\n\n\nThe server app sends the file's content URI back to the client app in an\n[Intent](/reference/android/content/Intent). This [Intent](/reference/android/content/Intent) is passed to the client\napp in its override of [onActivityResult()](/reference/android/app/Activity#onActivityResult(int, int, android.content.Intent)). Once\nthe client app has the file's content URI, it can access the file by getting its\n[FileDescriptor](/reference/java/io/FileDescriptor).\n\n\nFile security is preserved in this process only as long as you properly parse the content URI\nthat the client app receives. When parsing content, you must ensure that this URI does not point\nto anything outside of the intended directory, ensuring that no\n[path traversal](/privacy-and-security/risks/path-traversal) is being attempted.\nOnly the client app should gain access to the file, and only for the permissions granted by the\nserver app. Permissions are temporary, so once the client app's task stack is finished, the\nfile is no longer accessible outside the server app.\n\n\nThe next snippet demonstrates how the client app handles the\n[Intent](/reference/android/content/Intent) sent from the server app, and how the client app gets the\n[FileDescriptor](/reference/java/io/FileDescriptor) using the content URI: \n\n### Kotlin\n\n```kotlin\n/*\n * When the Activity of the app that hosts files sets a result and calls\n * finish(), this method is invoked. The returned Intent contains the\n * content URI of a selected file. The result code indicates if the\n * selection worked or not.\n */\npublic override fun onActivityResult(requestCode: Int, resultCode: Int, returnIntent: Intent) {\n // If the selection didn't work\n if (resultCode != Activity.RESULT_OK) {\n // Exit without doing anything else\n return\n }\n // Get the file's content URI from the incoming Intent\n returnIntent.data?.also { returnUri -\u003e\n /*\n * Try to open the file for \"read\" access using the\n * returned URI. If the file isn't found, write to the\n * error log and return.\n */\n inputPFD = try {\n /*\n * Get the content resolver instance for this context, and use it\n * to get a ParcelFileDescriptor for the file.\n */\n contentResolver.openFileDescriptor(returnUri, \"r\")\n } catch (e: FileNotFoundException) {\n e.printStackTrace()\n Log.e(\"MainActivity\", \"File not found.\")\n return\n }\n\n // Get a regular file descriptor for the file\n val fd = inputPFD.fileDescriptor\n ...\n }\n}\n```\n\n### Java\n\n```java\n /*\n * When the Activity of the app that hosts files sets a result and calls\n * finish(), this method is invoked. The returned Intent contains the\n * content URI of a selected file. The result code indicates if the\n * selection worked or not.\n */\n @Override\n public void onActivityResult(int requestCode, int resultCode,\n Intent returnIntent) {\n // If the selection didn't work\n if (resultCode != RESULT_OK) {\n // Exit without doing anything else\n return;\n } else {\n // Get the file's content URI from the incoming Intent\n Uri returnUri = returnIntent.getData();\n /*\n * Try to open the file for \"read\" access using the\n * returned URI. If the file isn't found, write to the\n * error log and return.\n */\n try {\n /*\n * Get the content resolver instance for this context, and use it\n * to get a ParcelFileDescriptor for the file.\n */\n inputPFD = getContentResolver().openFileDescriptor(returnUri, \"r\");\n } catch (FileNotFoundException e) {\n e.printStackTrace();\n Log.e(\"MainActivity\", \"File not found.\");\n return;\n }\n // Get a regular file descriptor for the file\n FileDescriptor fd = inputPFD.getFileDescriptor();\n ...\n }\n }\n```\n\n\nThe method [openFileDescriptor()](/reference/android/content/ContentResolver#openFileDescriptor(android.net.Uri, java.lang.String))\nreturns a [ParcelFileDescriptor](/reference/android/os/ParcelFileDescriptor) for the file. From this object, the client\napp gets a [FileDescriptor](/reference/java/io/FileDescriptor) object, which it can then use to read the file.\n\nFor additional related information, refer to:\n\n- [Intents and Intent Filters](/guide/components/intents-filters)\n- [Retrieving Data from the Provider](/guide/topics/providers/content-provider-basics#SimpleQuery)"]]