Accessing subclass properties in a List

Question

I have written a C# program that controls a robot. I have a Sensor class that defines common properties among different types of sensors, but then I have individual sub-classes for sensors with specific properties. My problem is that I want to define my robot as having a list of sensors (List<Sensor>) but I want to be able to access the special properties of sub-classed sensors if they are in the list. Here is some specific code. First, the Sensor class:

public abstract class Sensor : Node
    {
        private PropertyClass _Properties;

        public new class PropertyClass : Node.PropertyClass
        {
            public int Value;
            public int UpdateInterval;
            public SensorType Type;
            public SensorModel Model;
        }

        public new PropertyClass Properties
        {
            get { return _Properties; }
            set { _Properties = value; }
        }

        public enum SensorType
        {
            IR,
            Sonar,
            Touch,
            Light,
            PIR
        }

        public enum SensorModel
        {
            Sharp_GP2D12,
            Ping_Sonar
        }

        public Sensor(string Name) : base(Name)
        {
            _Properties = new PropertyClass();
        }
    }

Now a subclass for an IR Sensor:

public class IR : Sensor
    {
        private PropertyClass _Properties;

        public new class PropertyClass : Sensor.PropertyClass
        {
            public int MinRange;
            public int MaxRange;
        }

        public new PropertyClass Properties
        {
            get { return _Properties; }
            set { _Properties = value; }
        }

        public IR(string Name)
            : base(Name)
        {
            _Properties = new PropertyClass();
            this.Properties.Type = Sensor.SensorType.IR;
        }

If I define a list of sensors like this:

List<Sensor> mySensors = new List<Sensor>();

And then I add an IR sensor:

mySensors.Add(new IR("My IR Sensor"));

Then I cannot get access to the MinRange and MaxRange properties of the sensor. For example, mySensors[0].MinRange is not defined because the compiler thinks mySensors[0] is just a generic Sensor type and doesn't know that it is the IR sub-type.

Is there a way I can make this work?

Thanks!

Jaish Mathews · Answer

Yes. So you made that Properties for Sharp_GP2D12 and IR always Ref. to Properties of RangeSensor . So you are handling common entity in alll case and value not losing. Please close this thread if it's fine.

Pi Robot · Answer

Thanks again! Your reply gave me an idea that now works perfectly. It turns out that if I leave out the _Properties = new PropertClass() statement from the constructors in the abstract IR class and the Sharp_GP2D12 class then everything works great--and I don't have to specify which kind of Range Sensor (IR Sonar Sharp etc) to get back the MinRange and MaxRange values. In other words I can now do this: this.Properties. MySensors.Add(new Sharp_GP2D12(My Sharp IR Sensor); foreach (RangeSensor sensor in this.Properties.MySensors) { Console.WriteLine(sensor.Properties.MaxRange.ToString()); } And I get the correct value without having to specify that it is a Sharp_GP2D12 sensor in the foreach loop. So the final RangeSensor IR and Sharp_GP2D12 classes look like this: public abstract class RangeSensor : Sensor { private PropertyClass _Properties; public new class PropertyClass : Sensor.PropertyClass { public int MinRange; public int MaxRange; public int FieldOfView; } public new PropertyClass Properties { get { return _Properties; } set { _Properties = value; } } public RangeSensor(string Name) : base(Name) { _Properties = new PropertyClass(); } public abstract class IR : RangeSensor { public new class PropertyClass : RangeSensor.PropertyClass { } public IR(string Name) : base(Name) { this.Properties.Type = Sensor.SensorType.IR; } } public class Sharp_GP2D12 : IR { public new class PropertyClass : IR.PropertyClass { } public Sharp_GP2D12(string Name) : base(Name) { this.Properties.Model = SensorModel.Sharp_GP2D12; this.Properties.MinRange = 4; this.Properties.MaxRange = 31; this.Properties.FieldOfView = 2; } }

Jaish Mathews · Answer

Hi ONly need to adjust the foreach like below. No casting needed. foreach ( Sharp_GP2D12 sensor in MySensors) { Console.WriteLine(sensor.Properties.MaxRange.ToString()); } NB:Look at the bolded red part. Based on storing type in side List  you need to change there too. That's it.

Pi Robot · Answer

Hey thanks! This is really close to what I need. I have added one modification which introduces a catch. Just to back up for a moment what I am trying to do is produce a hierarchy of sensor property classes from the more general to the more specific like this: Node->Sensor->RangeSensor->IR->Sharp_GP2D12 I'll list the Node and Sensor classes at the end of this message but the new RangeSensor class looks like this: public abstract class RangeSensor : Sensor { private PropertyClass _Properties; public new class PropertyClass : Sensor.PropertyClass { public int MinRange; public int MaxRange; public int FieldOfView; } public new PropertyClass Properties { get { return _Properties; } set { _Properties = value; } } public RangeSensor(string Name) : base(Name) { _Properties = new PropertyClass(); } And so my IR sensor class now looks like this: public abstract class IR : RangeSensor { private PropertyClass _Properties; public new class PropertyClass : RangeSensor.PropertyClass { } public new PropertyClass Properties { get { return _Properties; } set { _Properties = value; } } public IR(string Name) : base(Name) { _Properties = new PropertyClass(); Properties.Type = Sensor.SensorType.IR; } And my class for the Sharp IR sensor is: public class Sharp_GP2D12 : IR { private PropertyClass _Properties; public new class PropertyClass : IR.PropertyClass { } public new PropertyClass Properties { get { return _Properties; } set { _Properties = value; } } public Sharp_GP2D12(string Name) : base(Name) { _Properties = new PropertyClass(); this.Properties.Model = SensorModel.Sharp_GP2D12; this.Properties.MinRange = 4; this.Properties.MaxRange = 31; this.Properties.FieldOfView = 2; } So now using your idea I want to be able to do something like this: List MySensors = new List (); MySensors.Add(new Sharp_GP2D12(My Sharp IR Sensor); foreach (Sensor sensor in this.Properties.MySensors) { if (sensor is RangeSensor) { Console.WriteLine(((RangeSensor)sensor).Properties.MaxRange.ToString()); } } However when I do this I get back 0 instead of 31. It seems that the value is coming from the default value of the RangeSensor class rather than being propagated down to the Sharp_GP2D12 class. Is there a way to make this happen without having to specifically down-cast to the Sharp_GP2D12 class? Here now are the Node and Sensor classes: public abstract class Node { private string _name; private PropertyClass _Properties; public Node(string Name) { _name = Name; } public Node() { } public class PropertyClass { public Message.Status Status; } public PropertyClass Properties { get { return _Properties; } set { _Properties = value; } } public string Name { get { return _name; } set { _name = value; } } } public abstract class Sensor : Node { private PropertyClass _Properties; public new class PropertyClass : Node.PropertyClass { public int Value; public int UpdateInterval; public bool Active; public SensorType Type; public SensorModel Model; } public new PropertyClass Properties { get { return _Properties; } set { _Properties = value; } } public enum SensorType { IR Sonar Laser Touch Light PIR Temperature } public enum SensorModel { Sharp_GP2D12 Rovio } public Sensor(string Name) : base(Name) { _Properties = new PropertyClass(); } }

Jaish Mathews · Answer

Hi I got access to you properties using below foreach foreach ( IR irObj in mySensors) { Console .WriteLine( irObj.Properties.MaxRange.ToString()); } NB:But You never given your Node class definition. So doubting about the same solution in your code.

Pi Robot · Answer

Thanks for your reply. However the idea is that I do not want to put the MinRange and MaxRange properties in the parent class since not all sensor types have these properties (e.g. Light sensor). Instead I want them only in the IR child class where they are applicable. (I should have made clear that MinRange and MaxRange refer to distances which are only applicable to range sensors like infrared and sonar.) I found in another post that I can down-cast a child list member to get the range properties: (Sensors.IR)this.Properties.MySensors[0]).Properties.MinRange However this requires that I have the child's class type hard coded on the line above which I'd rather not do.

Amit Choudhary · Answer

hi friend make your MinRange and MaxRange property of sensor class protected or public.. and Implement the indexer inside your Sensor class to access the properties and method using Collection index instance e.g. MySeson[0].MinRange Please mark as Do you like this post if it helps you.