[Interest] Android-6 File Opening Permissions

[Robert Iakobashvili]

Hi,
Replying to my own email hoping it will help somebody
not to waist time.

The issue was related to Android-6 and above file treatment permissions.

It is well covered by the excellent link below:
http://www.bytran.org/androidmpermissions.htm

IMHO, I would believe that it could be explained in Qt-documentation
for Android-Extras - note for the maintainer. Thanks.

Kind regards,
Robert


On Thu, Mar 23, 2017 at 7:23 PM, Robert Iakobashvili
<coroberti at gmail.com> wrote:
> Hello,
>
> Qt-5.7, Nexus-7, Android-6, API 25 or 22.
>
> 1. Running Intent from Qt widget app to ask for a new file rather in a
> standard way works properly:
>
> QAndroidJniObject intent("android/content/Intent");
> QAndroidJniObject ACTION_CREATE_DOCUMENT =
> QAndroidJniObject::fromString("android.intent.action.CREATE_DOCUMENT");
>
>         if (ACTION_CREATE_DOCUMENT.isValid() && intent.isValid())
>         {
>             intent.callObjectMethod("setAction",
>
> "(Ljava/lang/String;)Landroid/content/Intent;",
>                                     ACTION_CREATE_DOCUMENT.object<jstring>());
>             intent.callObjectMethod("setType",
>
> "(Ljava/lang/String;)Landroid/content/Intent;",
>
> QAndroidJniObject::fromString("text/html").object<jstring>());
>             intent.callObjectMethod("putExtra",
>
> "(Ljava/lang/String;Z)Landroid/content/Intent;",
>
> QAndroidJniObject::fromString("android.intent.extra.LOCAL_ONLY").object<jstring>(),
>                                     jboolean(true));
>             QtAndroid::startActivity(intent.object<jobject>(),
>
> AndroidOpenFileReceiver::NEW_FILE_NAME_REQUEST,
>                                      this->android_receiver_);
>         }
>
> 2. File could be selected and seen as immediately created in a
> derivative of a QAndroidActivityResultReceiver
>
> handleActivityResult
>
> const QString fileURI =
> data.callObjectMethod("getData","()Landroid/net/Uri;").toString();
>
> and that could be translated by calling Java to the absolute file path
> for the file selected, i.e. first.htm:
>
> /storage/emulated/0/Download/first.htm
>
> 3. The file content could be written or read in Java using Java I/O Streams.
> Further the stream and file are closed in Java.
>
> 4. Unfortunately, returning to C++ the file is found existing, but open fails.
> That happens in all cases consistently: whenever dealing with it in
> Java before or not.
>
> if (!QFile::exists(filename)) - it exists
>         return false;
>
> QFile file(filename);
> if (!file.open(QFile::ReadWrite)) - fails
> {
>      if (!file.open(QFile::ReadOnly)) - fails.
>             return false;
> }
>
> 5. The C++ code above works fine if the location of the files is in
> /data/data/<app-path>
>     or any writable standard path returned by Qt.
>
> 6. My conclusion is that on Nexus-7 the Intent returned path in
> /storage/emulated/0/Download/
>     is considered to be an External Storage.
>
>     But the manifest has appropriate Write and Read permissions for
> External Storage.
>
> The question is what I am missing like
> permission for that specific thread or running something on the GUI
> thread, or etc.
>
> Thanks in advance for any help or ideas.
>
> Kind regards,
> Robert