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How to Individuate an element of a list using reflection?

I have a List<T> of element and a PropertyInfo with a list of the property of T.
How can I identify a single property of an element in a loop ?
Ideally :
List<T>[i].PropertyInfo[y].Name

If i understood the question currently and you're looking to match the two collections, then you could use the type of the property info(Has a property type Property) and the typeof(T).
For efficiency i would recommend creating a dynamic method that would be cached for future usage.

If you are looking for the type of the properties, you must use the property:
PropertyInfo.PropertyType

I solved the problem using a solution like the one in the post "Get property value from string using reflection in C#".

Get Leaf Property Value Out Of Object's Tree Graph

I am stuck with PropertyInfo, big time. Basically it a tiny issue though idk where to start solving it. I dont usually use reflection but I need it now.
I have an object which has a property of type MyClass and MyClass futhermore holds another property. I want that last one. How do I get it?
Take a look at this:
obj.myClass.Attribute
How do I get that Attribute property by using PropertyInfo?

Use PropertyInfo.GetValue(Object):
Type type = obj.myClass.GetType();
PropertyInfo prop = type.GetProperty("Attribute");
object value = prop.GetValue(obj.myClass);

Access all properties of an unknown type

On my WinForm, I want to show each Property (as a label) and its value at run time depending on the type of the object. Something like this:
public void ShowDetails(object anyType)
{
// Generate label per property and show value of the property against a label.
}
How can I achieve this? There are more than 100 classes having different properties.
I am using C# 4.0.

You use reflection.
PropertyInfo[] properties = obj.GetType().GetProperties();
foreach (PropertyInfo property in properties)
{
object propertyValue = property.GetValue(obj, null);
}
That should be enough to get you started.
You can also get lots of other information out of the PropertyInfo such as the name of the property, the type, the accessibility, and so on. Note that it's possible (but very uncommon) to have a property without a getter, so you may want to check for that first. You also may want to only get public properties, rather than all properties. You also may want to check if the property is an indexer, as it will need a non-null value for the second parameter of GetValue. Oh, and you will also get static properties returned; you may or may not want those as well.

Use System.Reflection.PropertyInfo . You can loop through all properties (and sub-properties)
MSDN link

You can easily store the properties and their values in a dictionary
Dictionary<string,object> properties = anyType.GetType()
.GetProperties()
.ToDictionary(p=>p.Name,p=>p.GetValue(anyType,null));

I'd read up on Reflection. It will allow you to access the property names and values of class member at runtime.

How to set a value when the name of the value isn't known until runtime?

I am trying to set the properties of one object to be the same as the properties of another object. Here the code so far:
private T SetObjectAttributes<T> (dynamic fromO, T toO)
{
foreach (var prop in fromO.GetType().GetProperties())
{
toO[prop] = fromO[prop];
}
return toO;
}
The syntax here is incorrect:
toDbObject[prop] = fromObject[prop];
Basically, I am trying to set a property but the property name isn't known until run time. So my question is how to assign the value of the property at runtime.

You have to use the methods GetValue( object sourceObject) respectively SetValue( object target, object value ) of the PropertyInfo instance of the property.

You want to use PropertyInfo.SetValue to actually set the value. Also I hope you're caching those PropertyInfo instances - because it's going to really slow otherwise.
You should also look at ExpandoObject or some other options.
What exactly are you trying to do? Perhaps there's an altogether better way.

How to Loop through all the properties of a Class?

Is there a way to loop through all the properties from within a class's constructor so I can set all their default values instead of having to list each one like
this.prop1 = "?";
//repeat for each prop
For example:
public class thisClass()
{
library()
{
foreach (property as p in thisClass)
{
p.value = "?";
}
}
public string prop1 {get; set;}
public string prop2 {get; set;}
etc.
}

You could do this with Reflection (via Type.GetProperties and PropertyInfo.SetValue), but I wouldn't recommend it. It will reduce the readability and maintainability, as well as have a negative performance impact.
The advantage of listing out the properties and defining their initial values is that you see it, right up front, in your constructor. You can, alternatively, provide the backing field for your properties, and define them inline on the fields.

I wouldn't do it, really. Properties should be explicitly initialized by constructors, that's why they exist. Don't forget to initialize fields as well.
But I don't know why you need it, so here is some code.
It is not so easy to reliably set any property, including private properties. Usually I do this like this (out of my head, I will check with my real code tomorrow):
var properties = this.GetType().Properties(
BindingFlags.Instance
| BidningFlags.NonPublic
| BindingFlags.Public);
foreach(PropertyInfo property in properties)
{
// if a property is declared on a base type with a private setter,
// get the definition again from the declaring type,
// unless you can't call the setter.
// Probably it is even more reliable to get the properties setter
// from the declaring type.
if (property.DeclaringType != this)
{
property = property.DeclaringType.GetProperty(
property.PropertyName,
BindingFlags.Instance
| BidningFlags.NonPublic
| BindingFlags.Public);
}
if (property.CanWrite)
{
// assumed that you define a dictionary having the default values.
property.SetValue(this, defaultValues[property.PropertyType];
}
}

I would not recommend it, but since you are asking:
var props = GetType().GetProperties().Where(prop => prop.CanWrite && prop.PropertyType == typeof(string))
foreach(var prop in props)
prop.SetValue(this, "?", null);

Do something like this. Works great. Only problem you can't rely on order.
var properties = typeof(T).GetProperties();
foreach(var prop in properties ){
}
From the horses mouth: The GetProperties method does not return properties in a particular order, such as alphabetical or declaration order. Your code must not depend on the order in which properties are returned, because that order varies.
That said, your problem is better (as in software design better) addressed by just assigning all properties manually. If you find yourself in a situation with too many properties, you should use a container instead. A List<>, for example.

I probably wouldn't recommend setting all properties to a fixed value other than null... Particularly as it may be naive to assume that all of your properties are happy with that default state and even more so, that users of your class would most likely be expecting null (or more precisely default(T)) in place of an unknown value.
Just as a suggestion, if this is for the sakes of displaying the "?" in a UI when the specific values are not yet known then perhaps you could make use of the appropriate binding classes within the framework.
For example, winforms Binding class has "NullValue" property that will be passed to the bound control's property when the datasource has null or DbNull.Value in it.
But if you really want to go down the path that you've asked for then, as suggested above, the Type.GetProperties() should do the trick. Make sure you consider cases of inherited, abstract, overridden or virtual properties and whether setting the default value is appropriate - particularly in light of the fact that the norm is set/leave a value to null/default(T) when you don't actually have a known value.