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Object does not match target type PropertyInfo SetValue - one class to another

So I have 2 classes, both have identical Property names. One class contains different variables: int, strings, bool and DateTime The second class contains only 1 int and the rest are all strings.
Now I want to loop through all the properties, get the value from class1, encrypt that data and save it as a string in obj2, then return it to the main form (to save it in a database later).
public PersoonEncrypted EncryptPersonClass(Class1 object1)
{
PersoonEncrypted persEncrypt = new PersoonEncrypted(); //second class obj
Type type = object1.GetType();
PropertyInfo[] properties = type.GetProperties();
Type type2 = persEncrypt.GetType();
PropertyInfo[] properties2 = type.GetProperties();
foreach (var bothProperties in properties.Zip(properties2, (obj1, obj2) => new { Obj1 = obj1, Obj2 = obj2 }))
{
string value = "";
value = bothProperties.Obj1.GetValue(object1) as string;
if (!string.IsNullOrWhiteSpace(value))
{
string encryptValue = Encrypt(value);
if ((bothProperties.Obj2 != null) && (bothProperties.Obj2.PropertyType == typeof(string)))
{ //!= null check has no effect at all
bothProperties.Obj2.SetValue(persEncrypt, encryptValue, null); //errorLine
}
}
}
return persEncrypt;
}
That is what I came up with until now.
I have, of course, searched for other solutions like this one. This, after applying some own changes, didn't return any errors, but it didn't save any encrypted strings into the class persEncrypt. What I concluded was, from that test, is that it was testing if the value in the second class(persEncrypt in my example) from the particular property was null, while it shouldn't do that, it should make a new instance of that variable and save it in the object class, but removing that check gave me the same error.

you're just .Zip-ing the two lists of PropertyInfo objects, which simply iterates through both lists and doesn't check or sort for any sort of matching. This could result in erroneous behavior depending on the order in which properties appear - consider using a .Join instead to match property names.
This code doesn't check for an indexer on the property before attempting to assign to it without one - any indexed property which is of type string will make it to this point and then throw an exception when you try to set it.
Because this code is calling into Properties, there's the possibility an exception is being thrown by the code of the Property itself. This is where a StackTrace from your exception could reveal much more about what's happening.
Your code also checks for a property of type string directly - when using reflection you should use IsAssignableFrom instead in order to allow for inherited types, though that is unlikely the issue in this one case.

Optional Design Pattern, Advantages [closed]

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So, it's pretty well known that the infamous NullReferenceException is the most common exception in software products. I've been reading some articles, and found myself with the Optional approach.
Its aim is to create some kind of encapsulation around a nullable value
public sealed class Optional<T> where T : class {
private T value;
private Optional(T value) {
this.value = value;
}
//Used to create an empty container
public static Optional<T> Empty() {
return new Optional(null);
}
//Used to create a container with a non-null value
public static Optional<T> For(T value) {
return new Optional(value);
}
//Used to check if the container holds a non-null value
public bool IsPresent {
get { return value != null; }
}
//Retrieves the non-null value
public T Value {
get { return value; }
}
}
Afterwards, the now optional value can be returned like this:
public Optional<ICustomer> FindCustomerByName(string name)
{
ICustomer customer = null;
// Code to find the customer in database
if(customer != null) {
return Optional.Of(customer);
} else {
return Optional.Empty();
}
}
And handled like this:
Optional<ICustomer> optionalCustomer = repository.FindCustomerByName("Matt");
if(optionalCustomer.IsPresent) {
ICustomer foundCustomer = optionalCustomer.Value;
Console.WriteLine("Customer found: " + customer.ToString());
} else {
Console.WriteLine("Customer not found");
}
I don't see any improvement, just shifted complexity.
The programmer must remember to check if a value IsPresent, in the same way he must remember to check if a value != null.
And if he forgets, he would get a NullReferenceException on both approaches.
What am I missing? What advantages (if any) does the Optional pattern provide over something like Nullable<T> and the null coalescing operator?

Free your mind
If you think of Option as Nullable by a different name then you are absolutely correct - Option is simply Nullable for reference types.
The Option pattern makes more sense if you view it as a monad or as a specialized collection that contain either one or zero values.
Option as a collection
Consider a simple foreach loop with a list that cannot be null:
public void DoWork<T>(List<T> someList) {
foreach (var el in someList) {
Console.WriteLine(el);
}
}
If you pass an empty list to DoWork, nothing happens:
DoWork(new List<int>());
If you pass a list with one or more elements in it, work happens:
DoWork(new List<int>(1));
// 1
Let's alias the empty list to None and the list with one entry in it to Some:
var None = new List<int>();
var Some = new List(1);
We can pass these variables to DoWork and we get the same behavior as before:
DoWork(None);
DoWork(Some);
// 1
Of course, we can also use LINQ extension methods:
Some.Where(x => x > 0).Select(x => x * 2);
// List(2)
// Some -> Transform Function(s) -> another Some
None.Where(x => x > 0).Select(x => x * 2);
// List()
// None -> None
Some.Where(x => x > 100).Select(x => x * 2);
// List() aka None
// Some -> A Transform that eliminates the element -> None
Interesting side note: LINQ is monadic.
Wait, what just happened?
By wrapping the value that we want inside a list we were suddenly able to only apply an operation to the value if we actually had a value in the first place!
Extending Optional
With that consideration in mind, let's add a few methods to Optional to let us work with it as if it were a collection (alternately, we could make it a specialized version of IEnumerable that only allows one entry):
// map makes it easy to work with pure functions
public Optional<TOut> Map<TIn, TOut>(Func<TIn, TOut> f) where TIn : T {
return IsPresent ? Optional.For(f(value)) : Empty();
}
// foreach is for side-effects
public Optional<T> Foreach(Action<T> f) {
if (IsPresent) f(value);
return this;
}
// getOrElse for defaults
public T GetOrElse(Func<T> f) {
return IsPresent ? value : f();
}
public T GetOrElse(T defaultValue) { return IsPresent ? value: defaultValue; }
// orElse for taking actions when dealing with `None`
public void OrElse(Action<T> f) { if (!IsPresent) f(); }
Then your code becomes:
Optional<ICustomer> optionalCustomer = repository.FindCustomerByName("Matt");
optionalCustomer
.Foreach(customer =>
Console.WriteLine("Customer found: " + customer.ToString()))
.OrElse(() => Console.WriteLine("Customer not found"));
Not much savings there, right? And two more anonymous functions - so why would we do this? Because, just like LINQ, it enables us to set up a chain of behavior that only executes as long as we have the input that we need. For example:
optionalCustomer
.Map(predictCustomerBehavior)
.Map(chooseIncentiveBasedOnPredictedBehavior)
.Foreach(scheduleIncentiveMessage);
Each of these actions (predictCustomerBehavior, chooseIncentiveBasedOnPredictedBehavior, scheduleIncentiveMessage) is expensive - but they will only happen if we have a customer to begin with!
It gets better though - after some study we realize that we cannot always predict customer behavior. So we change the signature of predictCustomerBehavior to return an Optional<CustomerBehaviorPrediction> and change our second Map call in the chain to FlatMap:
optionalCustomer
.FlatMap(predictCustomerBehavior)
.Map(chooseIncentiveBasedOnPredictedBehavior)
.Foreach(scheduleIncentiveMessage);
which is defined as:
public Optional<TOut> FlatMap<TIn, TOut>(Func<TIn, Optional<TOut>> f) where TIn : T {
var Optional<Optional<TOut>> result = Map(f)
return result.IsPresent ? result.value : Empty();
}
This starts to look a lot like LINQ (FlatMap -> Flatten, for example).
Further possible refinements
In order to get more utility out of Optional we should really make it implement IEnumerable. Additionally, we can take advantage of polymorphism and create two sub-types of Optional, Some and None to represent the full list and the empty list case. Then our methods can drop the IsPresent checks, making them easier to read.
TL;DR
The advantages of LINQ for expensive operations are obvious:
someList
.Where(cheapOp1)
.SkipWhile(cheapOp2)
.GroupBy(expensiveOp)
.Select(expensiveProjection);
Optional, when viewed as a collection of one or zero values provides a similar benefit (and there's no reason it couldn't implement IEnumerable so that LINQ methods would work on it as well):
someOptional
.FlatMap(expensiveOp1)
.Filter(expensiveOp2)
.GetOrElse(generateDefaultValue);
Further suggested reading
Option (F#)
When null is not enough (C#)
The neophytes guide to Scala Part 5: The Option type
The Marvel of Monads (C#)
Eric Lippert's series on LINQ and monads

it would probally make more sense if you used something like this
interface ICustomer {
String name { get; }
}
public class OptionalCustomer : ICustomer {
public OptionalCustomer (ICustomer value) {
this.value = value;
}
public static OptionalCustomer Empty() {
return new OptionalCustomer(null);
}
ICustomer value;
public String name { get {
if (value == null ) {
return "No customer found";
}
return value.Name;
}
}
}
now if your pass an "empty" optional customer object you can still call the .Name property (without getting nullpointers)

The advantage of Optional is you know if something may not exist.
The problem with many types of queries that return a null is that that could mean 2 things:
The query didn't return a result
The query returned a result whose value was null.
I know you're asking specifically about C# but Java just introduced Optionals in Java 8 so there are a lot of articles about it so I'll use Java as an example. but it's completely the same idea as in C#:
Consider the Java Map.get(key) method
Object value = map.get(key);
if(value ==null){
//is there an entry in the map key =>null or does key not exist?
}
to get around that you have to have an additional method containsKey( k)
With optional, you only need one method
Optional<Object> result = map.get(key);
if(result.isPresent()){
Object value = result.get();
//if value is null, then we know that key =>null
}
More info see this Java article : http://www.oracle.com/technetwork/articles/java/java8-optional-2175753.html

Did you mean: Null Object pattern
The article linked to me in the comments contains a conclusion section explained this programming tool.
... The purpose of Optional is not to replace every single null reference in your codebase but rather to help design better APIs in which—just by reading the signature of a method—users can tell whether to expect an optional value. .... deal with the absence of a value; as a result, you protect your code against unintended null pointer exceptions.
Anyway, let it crash and find the reason. If you do not want endlessly embedded if statements than use an implementation pattern Guard Clause pattern, which says the following:
While programs have a main flow, some situations require deviations from the
main flow. The guard clause is a way to express simple and local exceptional
situations with purely local consequences.

Passing properties as parameters to be Got and Set

Well, I need to repeat same code for many properties.
I've seen examples taking Action delegates, but they don't fit quite well here.
I want something like this: (see explanation below)
Dictionary<Property, object> PropertyCorrectValues;
public bool CheckValue(Property P) { return P.Value == PropertyCorrectValues[P]; }
public void DoCorrection(Property P) { P.Value = PropertyCorrectValues[P]; }
.
I want to have a dictionary containing many properties and their respective "correct" values. (I know it's not well declared, but that's the idea). Properties are not necessarely inside my class, some of them are in objects of different assemblies.
A method bool CheckValue(Property). This method must access the actual value of the property and compare to the correct value.
And a method a void DoCorrection(Property). This one sets the property value to the correct value.
Remember I have many of those properties, I wouldn't like to call the methods by hand for each property. I'd rather iterate through the dicionary in a foreach statement.
So, the main question is in the title.
I've tried the by ref, but properties don't accept that.
Am I obligated to use reflection??? Or is there another option (if I need, reflection answer will be accepted as well).
Is there anyway I can make a dictionary with pointers in C#? Or some kind of assignment that changes the value of variable's target instead of changing the target to another value?
Thanks for the help.

You can do this using reflection. Get a list of the properties on the object of interest with typeof(Foo).GetProperties(). Your PropertyCorrectValues property can have type IDictionary<PropertyInfo, object>. Then use the GetValue and SetValue methods on PropertyInfo to perform the desired operations:
public bool CheckProperty(object myObjectToBeChecked, PropertyInfo p)
{
return p.GetValue(myObjectToBeChecked, null).Equals(PropertyCorrectValues[p]);
}
public void DoCorrection(object myObjectToBeCorrected, PropertyInfo p)
{
p.SetValue(myObjectToBeCorrected, PropertyCorrectValues[p]);
}

In addition to Ben's code I'd like to contribute the following code fragment:
Dictionary<string,object> PropertyCorrectValues = new Dictionary<string,object>();
PropertyCorrectValues["UserName"] = "Pete"; // propertyName
PropertyCorrectValues["SomeClass.AccountData"] = "XYZ"; // className.propertyName
public void CheckAndCorrectProperties(object obj) {
if (obj == null) { return; }
// find all properties for given object that need to be checked
var checkableProps = from props
in obj.GetType().GetProperties()
from corr in PropertyCorrectValues
where (corr.Key.Contains(".") == false && props.Name == corr.Key) // propertyName
|| (corr.Key.Contains(".") == true && corr.Key.StartsWith(props.DeclaringType.Name + ".") && corr.Key.EndsWith("." + props.Name)) // className.propertyName
select new { Property = props, Key = corr.Key };
foreach (var pInfo in checkableProps) {
object propValue = pInfo.Property.GetValue(obj, null);
object expectedValue = PropertyCorrectValues[pInfo.Key];
// checking for equal value
if (((propValue == null) && (expectedValue != null)) || (propValue.Equals(expectedValue) == false)) {
// setting value
pInfo.Property.SetValue(obj, expectedValue, null);
}
}
}
When using this "automatic" value correction you might also consider:
You cannot create a PropertyInfo object just by knowing the property name and independently of the declaring class; that's why I chose string for the key.
When using the same property name in different classes then you might need to change the code that is doing the actual assignment because the type between the correct value and the property type might differ.
Using the same property name in different classes will always perform the same check (see point above), so you might need a syntax for property names to restrict it to a specific class (simple dot notation, doesn't work for namespaces or inner classes, but might be extended to do so)
If needed you can replace the "check" and "assign" part with separate method calls, but it might be done inside the code block as stated in my example code.

Efficient way of initializing a generic class' fields and/or properties

I am writing a ConfigParser class, which reads from a config file structured like this:
[Section]
option1 = foo
option2 = 12
option3 = ;
...
The information read is actually stored in a Dictionary<string, string>. What i'd like to achieve is the following:
struct ConfigStruct
{
public string option1;
public int option2;
public char option3 { get; set; }
// Any other _public_ fields or properties
}
ConfigParser Cp = new ConfigParser("path/to/config/file"); // Loads content
ConfigStruct Cs = Cp.CreateInstance<ConfigStruct>("Section");
Console.WriteLine(Cs.option1); // foo
Console.WriteLine(Cs.option2.ToString()); // 12
Console.WriteLine(Cs.option3.ToString()); // ;
The struct (or class, it doesn't matter) ConfigStruct, is application-specific, and the ConfigParser class should know nothing about it. Basically, I want to parse the value from a specific option, and store it into the field/property with the same name. Parsing should be done according to the field/property type.
I've developed a stub method for it:
public T CreateInstance<T>(string Section) where T : new()
{
// Gets options dictionary from loaded data
Dictionary<string, string> Options = this.Data[Section];
T Result = new T();
Type StructType = Result.GetType();
foreach (var Field in StructType.GetFields())
{
if (!Options.ContainsKey(Field.Name))
continue;
Object Value;
if (Field.FieldType == typeof(bool))
Value = Boolean.Parse(Options[Field.Name]);
else if (Field.FieldType == typeof(int))
Value = Int32.Parse(Options[Field.Name]);
else if (Field.FieldType == typeof(double))
Value = Double.Parse(Options[Field.Name]);
else if (Field.FieldType == typeof(string))
Value = Options[Field.Name];
else if (Field.FieldType == typeof(char))
Value = Options[Field.Name][0];
// Add any ifs if needed
else { /* Handle unsupported types */ }
Field.SetValue(Result, Value);
}
foreach (var Property in StructType.GetProperties())
{
// Do the same thing with public properties
}
return Result;
}
Do you think this is the right approach to the problem? Or should I move the responsability of initializing the struct to the application logic instead of the ConfigParser class? I know it's more efficient, but using reflection I write this method only once, and works for every struct.
Should I use reflection to invoke Parse() so that I can avoid all those ifs? Or you'd rather make those conversions type by type, to prevent unexpected behaviour?
Thanks for your time.

Assuming there is a specific reason why you are not using app.config/web.config or other built-in configuration files.
I think this comes down to what the rest of the application is doing, but personally I would do it this way. It allows you to get the return type cleanly and you are not passing an extra stuct down the stack that you don't need to be.
Reflection is a fantastic tool but has some overhead so if the list of types is finite then specifying them manually is more efficient, or alternately only reflecting the unknown types. Also I would change your if blocks to a switch statement, you will gain efficiencies if the IL complier can fully optimise the condition block.

I think there is a simpler solution. You could use a custom section handler to store your settings, custom section handlers are well described here: http://devlicio.us/blogs/derik_whittaker/archive/2006/11/13/app-config-and-custom-configuration-sections.aspx).

Testing if an Object is a Dictionary in C#

Is there a way to test if an object is a dictionary?
In a method I'm trying to get a value from a selected item in a list box. In some circumstances, the list box might be bound to a dictionary, but this isn't known at compile time.
I would like to do something similar to this:
if (listBox.ItemsSource is Dictionary<??>)
{
KeyValuePair<??> pair = (KeyValuePair<??>)listBox.SelectedItem;
object value = pair.Value;
}
Is there a way to do this dynamically at runtime using reflection? I know it's possible to use reflection with generic types and determine the key/value parameters, but I'm not sure if there's a way to do the rest after those values are retrieved.

Check to see if it implements IDictionary.
See the definition of System.Collections.IDictionary to see what that gives you.
if (listBox.ItemsSource is IDictionary)
{
DictionaryEntry pair = (DictionaryEntry)listBox.SelectedItem;
object value = pair.Value;
}
EDIT:
Alternative when I realized KeyValuePair's aren't castable to DictionaryEntry
if (listBox.DataSource is IDictionary)
{
listBox.ValueMember = "Value";
object value = listBox.SelectedValue;
listBox.ValueMember = ""; //If you need it to generally be empty.
}
This solution uses reflection, but in this case you don't have to do the grunt work, ListBox does it for you. Also if you generally have dictionaries as data sources you may be able to avoid reseting ValueMember all of the time.

It should be something like the following. I wrote this in the answer box so the syntax may not be exactly right, but I've made it Wiki editable so anybody can fix up.
if (listBox.ItemsSource.IsGenericType &&
typeof(IDictionary<,>).IsAssignableFrom(listBox.ItemsSource.GetGenericTypeDefinition()))
{
var method = typeof(KeyValuePair<,>).GetProperty("Value").GetGetMethod();
var item = method.Invoke(listBox.SelectedItem, null);
}

I know this question was asked many years ago, but it is still visible publicly.
There were few examples proposed here in this topic and in this one:
Determine if type is dictionary [duplicate]
but there are few mismatches, so I want to share my solution
Short answer:
var dictionaryInterfaces = new[]
{
typeof(IDictionary<,>),
typeof(IDictionary),
typeof(IReadOnlyDictionary<,>),
};
var dictionaries = collectionOfAnyTypeObjects
.Where(d => d.GetType().GetInterfaces()
.Any(t=> dictionaryInterfaces
.Any(i=> i == t || t.IsGenericType && i == t.GetGenericTypeDefinition())))
Longer answer:
I believe this is the reason why people make mistakes:
//notice the difference between IDictionary (interface) and Dictionary (class)
typeof(IDictionary<,>).IsAssignableFrom(typeof(IDictionary<,>)) // true
typeof(IDictionary<int, int>).IsAssignableFrom(typeof(IDictionary<int, int>)); // true
typeof(IDictionary<int, int>).IsAssignableFrom(typeof(Dictionary<int, int>)); // true
typeof(IDictionary<,>).IsAssignableFrom(typeof(Dictionary<,>)); // false!! in contrast with above line this is little bit unintuitive
so let say we have these types:
public class CustomReadOnlyDictionary : IReadOnlyDictionary<string, MyClass>
public class CustomGenericDictionary : IDictionary<string, MyClass>
public class CustomDictionary : IDictionary
and these instances:
var dictionaries = new object[]
{
new Dictionary<string, MyClass>(),
new ReadOnlyDictionary<string, MyClass>(new Dictionary<string, MyClass>()),
new CustomReadOnlyDictionary(),
new CustomDictionary(),
new CustomGenericDictionary()
};
so if we will use .IsAssignableFrom() method:
var dictionaries2 = dictionaries.Where(d =>
{
var type = d.GetType();
return type.IsGenericType && typeof(IDictionary<,>).IsAssignableFrom(type.GetGenericTypeDefinition());
}); // count == 0!!
we will not get any instance
so best way is to get all interfaces and check if any of them is dictionary interface:
var dictionaryInterfaces = new[]
{
typeof(IDictionary<,>),
typeof(IDictionary),
typeof(IReadOnlyDictionary<,>),
};
var dictionaries2 = dictionaries
.Where(d => d.GetType().GetInterfaces()
.Any(t=> dictionaryInterfaces
.Any(i=> i == t || t.IsGenericType && i == t.GetGenericTypeDefinition()))) // count == 5

you can check to see if it implements IDictionary. You'll just have to enumerate over using the DictionaryEntry class.

I'm coming from Determine if type is dictionary, where none of the answers there adequately solve my issue.
The closest answer here comes from Lukas Klusis, but falls short of giving a IsDictionary(Type type) method. Here's that method, taking inspiration from his answer:
private static Type[] dictionaryInterfaces =
{
typeof(IDictionary<,>),
typeof(System.Collections.IDictionary),
typeof(IReadOnlyDictionary<,>),
};
public static bool IsDictionary(Type type)
{
return dictionaryInterfaces
.Any(dictInterface =>
dictInterface == type || // 1
(type.IsGenericType && dictInterface == type.GetGenericTypeDefinition()) || // 2
type.GetInterfaces().Any(typeInterface => // 3
typeInterface == dictInterface ||
(typeInterface.IsGenericType && dictInterface == typeInterface.GetGenericTypeDefinition())));
}
// 1 addresses public System.Collections.IDictionary MyProperty {get; set;}
// 2 addresses public IDictionary<SomeObj, SomeObj> MyProperty {get; set;}
// 3 (ie the second .Any) addresses any scenario in which the type implements any one of the dictionaryInterfaces Types.
The issues with the other answers - assuming they address #3 - is that they don't address #1 and #2. Which is understandable, since getting and checking a Property's Type probably isn't a common scenario. But in case you're like me, and that scenario is part of your use-case, there you go!

You could be a little more generic and ask instead if it implements IDictionary. Then the KeyValue collection will contina plain Objects.

I believe a warning is at place.
When you're testing if an object 'is a' something this or that, you're reimplementing (part of) the type system. The first 'is a' is often swiftly followed by a second one, and soon your code is full of type checks, which ought to be very well handled by the type system - at least in an object oriented design.
Of course, I know nothing of the context of the question. I do know a 2000 line file in our own codebase that handles 50 different object to String conversions... :(

if(typeof(IDictionary).IsAssignableFrom(listBox.ItemsSource.GetType()))
{
}