# Examples

## Receive and send signals from a QML application

This example shows how to create a QML applications and update it using LinX Manager Data Engine to send and receive
values from Data Engine.

### Prerequisites

* A running instance of Data Engine on target device.

Data Engine is pre-installed on UX Designer VM 4.0. A shortcut is located on the Desktop to start Data Engine with debug
flags active.

### Create a QML project

1. Open Qt Creator.
2. `File` > `New file or Project...`.
3. Select `CrossControl Project` and pick `Qt Quick 2 Application`.
4. Follow the on-screen instructions to finalize the project creation:
   1. Display resolution: 800x480
   2. Kit: Desktop

### Create signals for the application

1. Open LinX Manager Data Engine from the mode selector (left side).
2. Select the created project from the project selector drop-down menu.
3. Create three signals by pressing the add button ![Add signal](../../source/assets/add_mask.png).
4. Update the signals with the following information:

| Name        | Data Type | Signal Type | RX Filter | TX Filter |
|-------------|-----------|-------------|-----------|-----------|
| engineRPM   | INT       | CONSUMER    | GLOBAL    | GLOBAL    |
| oilPressure | FLOAT     | CONSUMER    | GLOBAL    | GLOBAL    |
| stopEngine  | BOOL      | PRODUCER    | GLOBAL    | GLOBAL    |

### Update the project

1. From the projector selector, press "Save" for the changes to take effect.
2. Verify that the project was updated by opening the General Messages tab (`Alt+6`):
    > LinX Manager Data Engine: Project updated successfully.
3. Selected project is now updated with new code and files. See [How-tos](usage) for a complete list of generated files.

Snippet from `dataengine.h` and `dataengine.cpp`:

```cpp
class DataEngine : public DataEngineBase
{
    Q_OBJECT
    // Generated Signal MetaProperties
    Q_PROPERTY (IntConsumerSignal* engineRPM READ engineRPM CONSTANT)
    Q_PROPERTY (FloatConsumerSignal* oilPressure READ oilPressure CONSTANT)
    Q_PROPERTY (BoolProducerSignal* stopEngine READ stopEngine CONSTANT)
```

```cpp
DataEngine::DataEngine() {
    // Define necessary signal properties for dataengine link initiation
    m_engineRPM = new IntConsumerSignal(false, false, 0);
    SIGNALTYPEDEF engineRPMDef;
    engineRPMDef.dataType = DATATYPE_INT;
    engineRPMDef.qtTypeName = "int";
    engineRPMDef.signalType = kSignalTypeConsumer;
    engineRPMDef.persistent = false;
    engineRPMDef.signal = m_engineRPM;
    m_signalTypeDefs["engineRPM"] = engineRPMDef;
```

### Display signal value in QML

1. Open `main.qml` with the editor
2. Locate `// add your GUI code below this line`
3. Add the following to display engineRPM and oilPressure signals in a Text component:

    ``` qml
    Text {
        id: engineRPM
        color: "white"
        text: dataEngine.engineRPM.value
    }

    Text {
        id: oilPressure
        color: "white"
        anchors.top: engineRPM.bottom
        text: dataEngine.oilPressure.value
    }
    ```

4. Compile and run the application.
5. Two text elements are shown and display "0" (no value is received yet).
6. Stop the application.

### Set a signal value from QML

1. Add the following snippet beneath the code added in the previous section:

    ``` qml
    Rectangle {
        id: stopEngine
        width: 220;  height: 60
        anchors.top: oilPressure.bottom
        color: buttonMouseArea.pressed ? Qt.darker("grey", 1.5) : "grey"
        Text {
            anchors.centerIn: parent
            text: "Stop engine request"
        }
        MouseArea {
            id: buttonMouseArea
            anchors.fill: parent
            onPressed: dataEngine.stopEngine.value = true
            onReleased: dataEngine.stopEngine.value = false
        }
    }
    ```

2. Compile and run the application again.
3. The signal stopEngine is set to `true` when the button is pressed and `false` when released. Assigned value is then sent to Data Engine to be consumed by another client.
4. Stop the application