title: Property binding not updating
body: <p>I am continuously getting data for my application as it runs, but I am having a bit of trouble displaying the data once I have read it in and stored it in a map.</p>
  
  <p>When I try to display the data in the QML, it simply displays zero, despite the fact that I can see it updating in the application output.</p>
  
  <p>I access the value in QML using property bindings (I was under the impression that these led <code>headingSensor</code> to be updated whenever <code>carData.headingSensor</code> changed?):</p>
  
  <pre><code>property int headingSensor: carData.headingSensor
  Text {  text: "Heading: " + headingSensor }
  </code></pre>
  
  <hr>
  
  <p>In my data class I have:</p>
  
  <pre><code>Q_PROPERTY(int headingSensor READ getHeadingSensor NOTIFY headingSensorChanged)
          int headingSensor;
  </code></pre>
  
  <hr>
  
  <p>In the c++ implementation I originally had:</p>
  
  <pre><code>    int data::getHeadingSensor(){
          return data.value(heading)[headingSensorReading];
      }
  </code></pre>
  
  <hr>
  
  <p>Where it returns the value in the map which is being updated with the incoming information.</p>
  
  <p>This I realized, probably doesn’t work, because the property is dependent upon the headingSensor variable, which is itself not being updated despite the correct value being returned. So, I thought if I changed it to update the headingSensor value and return that it might work.</p>
  
  <p>So in my data aquisition logic I wrote a method to update the variables as well.</p>
  
  <pre><code>                data.insert(key, value);
                  updateVariables();
              }
          }
      }
      void data::updateVariables(){
          headingSensor = data.value(heading)[headingSensorReading];
      }
      int data::getHeadingSensor(){
          return headingSensor;
      }
  </code></pre>
  
  <p>While this led to the <code>headingSensor</code> variable being updated in addition to the value in the map, the correct value is still not displayed in the QML display. It simply displays <code>0</code> (its default value when it is initially displayed since it has not gotten a value from incoming data yet).</p>
  
  <p>So, I am wondering, how can I get the value of sensorHeading displayed in the QML to update as the value of it and/or the value in the map changes in C++? Do I need to do something like:</p>
  
  <pre><code>Connections {
      target: carData
      onSensorHeadingChanged: updateValues
  }
  </code></pre>
  
  <p>EDIT:
  Trying something like this, the onSensorHeadingChanged never fires. I am not sure why, since the value of sensorHeading clearly changes as I watch it in the application output</p>
  
  <hr>
  
  <pre><code>Connections{
       target: carData
       onHeadingSensorChanged: console.log("It's noting the change!")
  }
  </code></pre>