Many different items to show in QML GridView.

GoRo3

Hi!

I'm programming in Qt and QML about 2 years from now. It's great framework. Until now all I dealt with solving problems using Qt documentation (one of the best I know). But now I have problem and could find any good answer for it.

I'm writing my own IoT Hub for home, using Raspberry Pi and nrf24L01 radio transceiver. All logic is written in C++ and presentation in Qml. So I have Qlist with pointers to abstract class named "BaseDevice" and from this base class I have inherited new classes like TemperatureDevice, HumidityDevice, etc..
In Qml I used StackView with Page for every device category like "Temperature Devices" With GridView taking the model from C++ logic (standard model View with C++ and QML pattern).

Now I seeking the solution to put all devices form C++ list and present them in one gridVeiw. I would like to have a main page with a view of all devices and sensors. But as far i know GridView or other "views" in QML could have only one model. I read about "Loader" as component creator in View's but with this object i don't know how to pass a device type to QML?

Has someone have similar problems?? Some good pattern to solving my problem would be great!

Best Regards!

J.Hilk

hi @goro3 and welcome,

If I understand you correctly, you would like to assign different models to your gridview depending on specific cases ?

The easiest solution would be by using a JS-expression for your model property

GridView {
   width: 300; height: 200

   model: {
       if(condition1)
           return model1
       else
           return model2
  }
}

Gojir4

Hi @goro3,

As you already have a BaseDevice class inherited by all your device classes, you can probably use a single model of BaseDevice objects and then display them on QML according to their types using a Loader.

GoRo3

@j-hilk Jest, but in this case can i use two or three models at one time?

@Gojir4 It will be the best solution. But how could I check wat type this item is? In C++ i can use std::dynamic_cast to check inherited type, but how to do this in QML??

J.Hilk

@goro3 said in Many different items to show in QML GridView.:

@j-hilk Jest, but in this case can i use two or three models at one time?

only one model will be active at only given time, but there's no limit on how many if/else (or a switch statement) you can have.

Gojir4

@goro3 said in Many different items to show in QML GridView.:

@Gojir4 It will be the best solution. But how could I check wat type this item is? In C++ i can use std::dynamic_cast to check inherited type, but how to do this in QML??

By adding a property in the base class which indicate the type ?

class BaseDevice: public QObject
{
    Q_OBJECT
    Q_PROPERTY(int type READ type) 
    //...
};

//qml
Repeater{
    model: myModel
    Loader{
     sourceComponent: {
            switch(type){ //Type provided by model data
                default: return unimplementedComponent
                case TempSensor: return tempSensorComponent
                case HumiditySensor: return humiditySensorComponent
                
            }
        }
    }
}

IntruderExcluder

Also you can set property as enum and decalre it as Q_ENUM(enum_name); Then, register yor base type like:

qmlRegisterUncreatableType<Base>("Test", 1, 0, "Base", "Base cannot be created at QML");

After this you can use your enum at QML like Base.EnumValue, instead of integer comparison.

GoRo3

@Gojir4 , @IntruderExcluder Thank you for help. I will try this solution!