Set property value with reflection

Question

I have class Settings

public class Settings
{
  public string A{get;set;}
  public bool B {get;set;}
  public int C {get;set;}
}

I another class I have property type of Settings

public class VM
{
   public class Settings Settings{get;set;}
}

I want setup values of property Settings with reflection.

I need pass argument type of object to InitializeSettings method.

 public void Init(object viewModel)
    {
        try
        {
            PropertyInfo settings = viewModel.GetType().GetProperty("Settings");

            PropertyInfo[] settingsProperties = settings.PropertyType.GetProperties();

            foreach (PropertyInfo settingsProperty in settingsProperties)
            {
                object value = //load from app.config

                var convertedValue = Convert.ChangeType(value, settingsProperty.PropertyType);

                //how set  value ???
                settingsProperty.SetValue(settings, convertedValue, null);

            }
        }
        catch (Exception exception)
        {
            throw;
        }
    }

This sample code finish with exception

base = {"Object does not match target type."}

I don’t know how can I set values on viewModel.Settings properties in Init method?

You never instantiate your class either. I have a feeling you're over complicating things a bit. Exactly what are you trying to accomplish with this code? — Hein Andre Grønnestad
– Hein Andre Grønnestad, Commented Mar 8, 2014 at 19:40
I have several module, each module is class library. Each module has has own app.config and own definition of Setting class (with different properties). Also in each module can be several ViewModels. I would like have one service class in Service module which will be setup Settings for modules from thier app.config. — imodin
– imodin, Commented Mar 8, 2014 at 20:10

poke · Accepted Answer · 2014-03-08 20:15:08Z

You don’t need to do it that complicated. Once you have extracted the settings object, you can just update that:

PropertyInfo settingsProperty = viewModel.GetType().GetProperty("Settings");
Settings settings = (Settings) settingsProperty.GetValue(viewModel);

settings.A = "Foo";
settings.B = true;
settings.C = 123;

This is already enough to change the settings stored in the view model. If Settings is a value type, you will have to write the changed settings object back to the object, like this:

settingsProperty.SetValue(viewModel, settings);

But that’s really all you will have to do. Of course, if you know that viewModel is of type VM, you can just type-cast it, and access the property directly:

Settings settings = ((VM)viewModel).Settings;

So instead of using reflection, a much better way would be to define some base type, or an interface, that has the Settings property and make your view models implement that:

public interface HasSettings
{
    Settings Settings { get; set; }
}

public class VM : HasSettings
{ … }

That way, your method can accept a HasSettings object instead of a plain object, and you can just access the settings object directly:

public void Init (HasSettings viewModel)
{
    viewModel.Settings.A = "Foo bar";
}

If you have different Settings types with different properties, and you want to run reflection on those too, then you can do that as well:

PropertyInfo settingsProperty = viewModel.GetType().GetProperty("Settings");
object settings = settingsProperty.GetValue(viewModel);

for (PropertyInfo prop in settings.GetType().GetProperties())
{
    object value = GetValueForPropertyName(prop.Name); // magic
    prop.SetValue(settings, value);
}

Again, no need to write the settings object back unless it’s a value type.

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