[Interest] Android-6 File Opening Permissions

[Robert Iakobashvili]

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
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