How do I reinitialize or reset the properties of a class?

Question

I've created a class with properties that have default values. At some point in the object's lifetime, I'd like to "reset" the object's properties back to what they were when the object was instantiated. For example, let's say this was the class:

public class Truck {
   public string Name = "Super Truck";
   public int Tires = 4;

   public Truck() { }

   public void ResetTruck() {
      // Do something here to "reset" the object
   }
}

Then at some point, after the Name and Tires properties have been changed, the ResetTruck() method could be called and the properties would be reset back to "Super Truck" and 4, respectively.

What's the best way to reset the properties back to their initial hard-coded defaults?

Answer 1

You can have the initialization in a method instead of inlining with the declaration. Then have the constructor and reset method call the initialization method:

public class Truck {
   public string Name;
   public int Tires;

   public Truck() {
      Init();
   }

   public void ResetTruck() {
      Init();
   }

   private void Init() {
      Name = "Super Truck";
      Tires = 4;
   }
}

Another way is not to have a reset method at all. Just create a new instance.

Answer 2

Reflection is your friend. You could create a helper method to use Activator.CreateInstance() to set the default value of Value types and 'null' for reference types, but why bother when setting null on a PropertyInfo's SetValue will do the same.

    Type type = this.GetType();
    PropertyInfo[] properties = type.GetProperties();
    for (int i = 0; i < properties.Length; ++i)
      properties[i].SetValue(this, null); //trick that actually defaults value types too.

To extend this for your purpose, have private members:

//key - property name, value - what you want to assign
Dictionary<string, object> _propertyValues= new Dictionary<string, object>();
List<string> _ignorePropertiesToReset = new List<string>(){"foo", "bar"};

Set the values in your constructor:

 public Truck() {
    PropertyInfo[] properties = type.GetProperties();

    //exclude properties you don't want to reset, put the rest in the dictionary
    for (int i = 0; i < properties.Length; ++i){
        if (!_ignorePropertiesToReset.Contains(properties[i].Name))  
            _propertyValues.Add(properties[i].Name, properties[i].GetValue(this));
    }
}

Reset them later:

public void Reset() {
    PropertyInfo[] properties = type.GetProperties();
    for (int i = 0; i < properties.Length; ++i){
        //if dictionary has property name, use it to set the property
        properties[i].SetValue(this, _propertyValues.ContainsKey(properties[i].Name) ? _propertyValues[properties[i].Name] : null);     
    }
}