Android: Fix local ref handling.

We where allowing conversion from jobject to QJNIObject without taking
ownership of the jobject. Since we are managing the JNI environment we
should not allow conversions without having the option of taking
ownership of the local ref. This is now done by making the conversions
explicit, i.e., local refs are converted through
QJNIObjectPrivate::fromLocalRef() and global refs through the
QJNIObjectPrivate's jobject constructor.

This change breaks SC, but the API is private and no usage have been
found outside QtBase.

Change-Id: I3175f171699ec3f8e65144aaebc6246bc6e5bb4d
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>

src/corelib/io/qstandardpaths_android.cpp

@@ -57,7 +57,7 @@ static QJNIObjectPrivate applicationContext()
     if (appCtx.isValid())
         return appCtx;
 
-    QJNIObjectPrivate activity = QtAndroidPrivate::activity();
+    QJNIObjectPrivate activity(QtAndroidPrivate::activity());
     if (!activity.isValid())
         return appCtx;
 
@@ -131,7 +131,7 @@ static QString getExternalFilesDir(const char *directoryField = 0)
     if (!path.isEmpty())
         return path;
 
-    QJNIObjectPrivate activity = QtAndroidPrivate::activity();
+    QJNIObjectPrivate activity(QtAndroidPrivate::activity());
     if (!activity.isValid())
         return QString();
 

src/corelib/kernel/qjni.cpp

@@ -96,7 +96,7 @@ static jclass loadClassDotEnc(const QString &classDotEnc, JNIEnv *env)
     if (clazz != 0 || isCached)
         return clazz;
 
-    QJNIObjectPrivate classLoader = QtAndroidPrivate::classLoader();
+    QJNIObjectPrivate classLoader(QtAndroidPrivate::classLoader());
     if (!classLoader.isValid())
         return 0;
 
@@ -2239,6 +2239,13 @@ bool QJNIObjectPrivate::isValid() const
     return d->m_jobject;
 }
 
+QJNIObjectPrivate QJNIObjectPrivate::fromLocalRef(jobject lref)
+{
+    QJNIObjectPrivate o(lref);
+    QJNIEnvironmentPrivate()->DeleteLocalRef(lref);
+    return o;
+}
+
 bool QJNIObjectPrivate::isSameObject(jobject obj) const
 {
     QJNIEnvironmentPrivate env;

src/corelib/kernel/qjni_p.h

@@ -84,7 +84,10 @@ public:
     QJNIObjectPrivate(const char *className, const char *sig, ...);
     explicit QJNIObjectPrivate(jclass clazz);
     QJNIObjectPrivate(jclass clazz, const char *sig, ...);
-    QJNIObjectPrivate(jobject obj);
+    // In most cases you should never call this function with a local ref. unless you intend
+    // to manage the local ref. yourself.
+    // NOTE: see fromLocalRef() for converting a local ref. to QJNIObjectPrivate.
+    explicit QJNIObjectPrivate(jobject globalRef);
 
     template <typename T>
     T callMethod(const char *methodName,
@@ -183,6 +186,9 @@ public:
         return *this;
     }
 
+    // This function takes ownership of the jobject and releases the local ref. before returning.
+    static QJNIObjectPrivate fromLocalRef(jobject lref);
+
 private:
     friend class QAndroidJniObject;
 

src/plugins/bearer/android/src/wrappers/androidconnectivitymanager.cpp

@@ -295,8 +295,7 @@ QList<AndroidNetworkInfo> AndroidConnectivityManager::getAllNetworkInfo() const
         if (exceptionCheckAndClear(env))
             break;
 
-        list << AndroidNetworkInfo(lref);
+        list << AndroidNetworkInfo(QJNIObjectPrivate::fromLocalRef(lref));
-        env->DeleteLocalRef(lref);
     }
 
     return list;