SetValue在c＃中的反射

Question

Consider this code:

var future = new Future();
future.GetType().GetProperty(info.Name).SetValue(future, converted);

In the code above we should pass two arguments for SetValue . First,The object that we want to set its property. Second,the new value. But we select the specific property.

Why we should pass the first parameter to set the value as we have set the future object before!?

Answer 1

Because the future object is an instance. The PropertyInfo is retrieved from the type ( Type type = future.GetType(); ) and isn't bound to any instance. That's why you have to pass the instance in the SetValue() .

So:

var future = new Future();

var propertyName = "...";
Type type = future.GetType();
PropertyInfo propertyInfo = type.GetProperty(propertyName);

propertyInfo.SetValue(future, value);

You can reuse the propertyInfo to set properties of other instances.

Answer 2

Here

future.GetType()

future was used only to obtain its type. Effectively it is the same as

Type t = future.GetType();
t.GetProperty(info.Name).SetValue(future, converted);

On the second line of the code above all the knowledge about what object was used to get the type is lost, and we are dealing with the type itself. Later, when we have information about the property of the type, we need to know what object it should be used with, so we are providing future yet again.

Answer 3

You haven't set the future object before - you've simply extracted its type, and then operated on that. What you end up with is a PropertyInfo object that refers to that property on any instance of type Future .

Answer 4

You could easily do following:

typeof(Future).GetProperty(info.Name).SetValue(future, converted);

How could the instance be taken without future parameter?

Answer 5

Consider these 2 classes:

class Future
{
    public int MyProperty { get; set; }
}
class FarFuture : Future { }

Take a look at this code:

var future = new Future();
var farFuture = new FarFuture();
future.GetType().GetProperty(info.Name).SetValue(farFuture, converted);

The PropertyInfo is not bound to an instance, but to a type.