如何从共享相同接口的对象列表中访问对象的特定属性

Question

I have an application where i have say 10 objects of different types. I wish to have them in same list and iterate through them on many occasions. I cant push them into one list because they are of different types. So i created an interface and created a property that all objects share. Now i have the list of objects and type of the list is the "interface". When i iterate through the object, i can't access the specific properties of the object because the compiler will only know at runtime what object it is. So if i try to code Object_A.Name, visual studio will show error because it doesn't know they type of object. I can obviously do an if else or something similar to find the type of object and cast it, but i want to know of there is a better way, or if this whole approach of having an interface is wrong and if i should have begun in a different direction.

In the code below, i want to get the Devname, which i can't because its not part of the interface, but belongs to every object. I could make it part of the interface, but every now and then i may need to get a specific property. hence wanting to know if there is a way to do it.

foreach (ICommonDeviceInterface device in Form1.deviceList)
{
if (device.DevName.Equals(partnername))
{
return device.Port[portNo].PortRef;
}
}

Answer 1

One way you could do this is by using reflection to try to get the property value of a named property from an object, using a helper method like:

public static object GetPropValue(object src, string propName)
{
    return src?.GetType().GetProperty(propName)?.GetValue(src, null);
}

Credit for above code goes to: Get property value from string using reflection in C#

This requires no checking types or casting, it just returns the value of the property, or null if it doesn't contain the property.

In use it might look like:

private static void Main()
{
    // Add three different types, which all implement the same interface, to our list
    var devices = new List<ICommonDeviceInterface>
    {
        new DeviceA {DevName = "CompanyA", Id = 1},
        new DeviceB {DevName = "CompanyB", Id = 2},
        new DeviceC {Id = 3},
    };

    var partnerName = "CompanyB";

    foreach (var device in devices)
    {
        // Try to get the "DevName" property for this object
        var devName = GetPropValue(device, "DevName");

        // See if the devName matches the partner name
        if (partnerName.Equals(devName))
        {
            Console.WriteLine($"Found a match with Id: {device.Id}");
        }
    }
}

Classes used for the sample above:

interface ICommonDeviceInterface
{
    int Id { get; set; }
}

class DeviceA : ICommonDeviceInterface
{
    public int Id { get; set; }
    public string DevName { get; set; }
}

class DeviceB : ICommonDeviceInterface
{
    public int Id { get; set; }
    public string DevName { get; set; }
}

class DeviceC : ICommonDeviceInterface
{
    public int Id { get; set; }
}

Answer 2

Use "as" and "is" to know what type of interface

public class A : ICommonDeviceInterface 
{
  public int AMember;
}
public class B :ICommonDeviceInterface 
{
  public int BMember;
}

foreach (ICommonDeviceInterface device in Form1.deviceList)
{

    if(device is A)
    {
       A a = device as A;
       a.AMember = 100;
    }
    else if(device is B)
    {
       B b = device as B;
       b.BMember = 123;
    }
}