Don't update cached char value when property is not readable

In addition we update the documentation to reflect the slightly changed
API behavior.

Change-Id: Ieddee750aa35a32d3c01213dfbf678ee2a1d88d7
Reviewed-by: Timur Pocheptsov <Timur.Pocheptsov@digia.com>
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>

4 files changed, 23 insertions, 6 deletions

diff --git a/src/android/bluetooth/src/org/qtproject/qt5/android/bluetooth/QtBluetoothLE.java b/src/android/bluetooth/src/org/qtproject/qt5/android/bluetooth/QtBluetoothLE.java
index 748d709e..b9f7e184 100644
--- a/src/android/bluetooth/src/org/qtproject/qt5/android/bluetooth/QtBluetoothLE.java
+++ b/src/android/bluetooth/src/org/qtproject/qt5/android/bluetooth/QtBluetoothLE.java
@@ -919,7 +919,7 @@ public class QtBluetoothLE {
                             into two operations. BluetoothGatt.enableCharacteristicNotification
                             ensures the local Blueooth stack forwards the notifications. In addition,
                             BluetoothGattDescriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE)
-                            must be written to the peripheral
+                            must be written to the peripheral.
                          */
 
 
diff --git a/src/bluetooth/qlowenergycharacteristic.cpp b/src/bluetooth/qlowenergycharacteristic.cpp
index 2f8bd6fa..91e9d94d 100644
--- a/src/bluetooth/qlowenergycharacteristic.cpp
+++ b/src/bluetooth/qlowenergycharacteristic.cpp
@@ -195,9 +195,11 @@ QLowEnergyCharacteristic::PropertyTypes QLowEnergyCharacteristic::properties() c
     \l {QLowEnergyService::writeCharacteristic()}{write operation} or when an update
     notification is received.
 
-    The returned \l QByteArray is empty if the characteristic does not have the
-    \l {QLowEnergyCharacteristic::Read}{read permission}. However, a non-readable
-    characteristic may obtain a non-empty value via a related notification or write operation.
+    The returned \l QByteArray always remains empty if the characteristic does not
+    have the \l {QLowEnergyCharacteristic::Read}{read permission}. In such cases only
+    the \l QLowEnergyService::characteristicChanged() or
+    \l QLowEnergyService::characteristicWritten() may provice information about the
+    value of this characteristic.
 */
 QByteArray QLowEnergyCharacteristic::value() const
 {
diff --git a/src/bluetooth/qlowenergycontroller_android.cpp b/src/bluetooth/qlowenergycontroller_android.cpp
index 9be5cff0..e1b668ca 100644
--- a/src/bluetooth/qlowenergycontroller_android.cpp
+++ b/src/bluetooth/qlowenergycontroller_android.cpp
@@ -431,7 +431,10 @@ void QLowEnergyControllerPrivate::characteristicWritten(
         return;
     }
 
-    updateValueOfCharacteristic(charHandle, data, false);
+    // only update cache when property is readable. Otherwise it remains
+    // empty.
+    if (characteristic.properties() & QLowEnergyCharacteristic::Read)
+        updateValueOfCharacteristic(charHandle, data, false);
     emit service->characteristicWritten(characteristic, data);
 }
 
@@ -479,7 +482,10 @@ void QLowEnergyControllerPrivate::characteristicChanged(
         return;
     }
 
-    updateValueOfCharacteristic(characteristic.attributeHandle(),
+    // only update cache when property is readable. Otherwise it remains
+    // empty.
+    if (characteristic.properties() & QLowEnergyCharacteristic::Read)
+        updateValueOfCharacteristic(characteristic.attributeHandle(),
                                 data, false);
     emit service->characteristicChanged(characteristic, data);
 }
diff --git a/src/bluetooth/qlowenergyservice.cpp b/src/bluetooth/qlowenergyservice.cpp
index 10307332..96c3bbeb 100644
--- a/src/bluetooth/qlowenergyservice.cpp
+++ b/src/bluetooth/qlowenergyservice.cpp
@@ -242,6 +242,15 @@ QT_BEGIN_NAMESPACE
     by calling \l writeCharacteristic(). If the write operation is not successful,
     the \l error() signal is emitted using the \l CharacteristicWriteError flag.
 
+    Since this signal is an indication of a successful write operation \a newValue
+    generally matches the value that was passed to the associated
+    \l writeCharacteristic() call. However, it may happen that the two values differ
+    from each other. This can occur in cases when the written value is
+    used by the remote device to trigger an operation and it returns some other value via
+    the written and/or change notification. Such cases are very specific to the
+    target device. In any case, the reception of the written signal can still be considered
+    as a sign that the target device received the to-be-written value.
+
     \note If \l writeCharacteristic() is called using the \l WriteWithoutResponse mode,
     this signal and the \l error() are never emitted.