Develop Reference

Is there a way to pass a class property as a parameter to a method?

I am trying to find a way to take a class's property and pass it to a method along with another variable to update the property based on conditions. For example
The class
public class MyClass{
public string? Prop1 { get; set; }
public string? Prop2 { get; set; }
public bool? Prop3 { get; set; }
public DateTime? Prop4 { get; set; }
... etc...
}
Test code I would like to get to work...:
var obj = new MyClass();
MyCheckMethod(ref obj.Prop1, someCollection[0,1]);
in the method:
private void MyCheckMethod(ref Object obj, string value)
{
if (!string.isnullorempty(value))
{
// data conversion may be needed here depending on data type of the property
obj = value;
}
}
I want to be able to pass any property of any class and update the property only after validating the value passed in the method. I was hoping I could do this with generics, but I haven't yet found a way to do so. Or if I am over complicating what I need to do.
The problem is that there may be a bit more to the validation of the passed in value than just a simple isnullorempy check.
I also thought about doing something like this:
private void MyCheckMethod(ref object obj, Action action)
Then I could do something like this:
...
MyCheckMethod(ref obj.Prop1, (somecollection[0,1]) => {
... etc....
})
So I am looking for some guidance on how to proceed.
updated info:
The incoming data is all in string format (this is how a 3rd party vendor supplies the data). The data is supplied via API call for the 3rd party product... part of their SDK. However in my class I need to have proper data types. Convert string values to datetime for dates, string values to int for int data types, etc... . The other caveat is that if there isnt a valid value for the data type then the default value of the property should be NULL.
Additional Information:
The incoming data is always in string format.
eg:
I have to update a boolean property.
The incoming value is "". I test to see if the string Value isNullOrEmpty. It is so I dont do anything to property.
The next property datatype is decimal.
The incoming value is "0.343".
I Test to see if the string value is NullorEmpty. It isnt so I can update the property once I do a convert etc.....
Hope this helps.
Thanks

Full solution after edits:
public static class Extensions
{
//create other overloads
public static void MyCheckMethodDate<TObj>(this TObj obj,Expression<Func<TObj,DateTime>> property, string value)
{
obj.MyCheckMethod(property, value, DateTime.Parse);
}
public static void MyCheckMethod<TObj,TProp>(this TObj obj,Expression<Func<TObj,TProp>> property, string value,Func<string, TProp> converter)
{
if(string.IsNullOrEmpty(value))
return;
var propertyInfo = ((MemberExpression)property.Body).Member as PropertyInfo;
if(null != propertyInfo && propertyInfo.CanWrite)
{
propertyInfo.SetValue(obj, converter(value));
}
}
}
public class Obj
{
public object Prop1{get;set;}
public string Prop2{get;set;}
public DateTime Prop3{get;set;}
}
public class Program
{
public static void Main()
{
var obj = new Obj();
obj.MyCheckMethodDate(x=>x.Prop3, "2018-1-1");
Console.WriteLine(obj.Prop3);
}
}

You can pass a lambda expression:
void DoSomething<T>(Expression<Func<T>> property)
{
var propertyInfo = ((MemberExpression)property.Body).Member as PropertyInfo;
if (propertyInfo == null)
{
throw new ArgumentException("The lambda expression 'property' should point to a valid Property");
}else{
var name = ((MemberExpression)property.Body).Member.Name;
var value = property.Compile();
//Do whatever you need to do
}
}
To use:
DoSomething(() => obj.Property1);

You can't pass a reference to an arbitrary property. A property is basically implemented as two methods, set_Property and get_Property, and there's no way to bundle these together.
One option is to have your checker function take delegates to access the property. For example:
private void MyCheckMethod(Func<string> getter, Action<string> setter)
{
var value = getter();
var newValue = value.ToUpper();
setter(value);
}
So now you would say something like this:
public class MyClass
{
public string Prop1 { get; set; }
public string Prop2 { get; set; }
}
var c = new MyClass();
MyCheckMethod(() => c.Prop1, value => c.Prop1 = value);

Use reflection with compiled expressions.
This performs better than reflection and a little bit slower than native code.
It's not type safe, but you can add runtime validation.

C# Attribute check is an value equals the constructor argument and get constructor values

How can i check that some string is equal to the "constructor" arguments of an attribute?
And how to get all constructor values (TestArg1, TestArg2)?
struct MyData
{
[MyAttr("TestArg1", "TestArg2")] //check that some string equals TestArg1/TestArg2
public string TestArg;
}

This primarily depends on what attribute you're looking at and how it's coded. See the code below as an example on how to do what you're asking.
//The attribute we're looking at
public class MyAtt : System.Attribute
{
public string name;
public string anotherstring;
public MyAtt(string name, string anotherstring)
{
this.name = name;
this.anotherstring = anotherstring;
}
}
public static class Usage
{
[MyAtt("String1", "String2")] //Using the attribute
public static string SomeProperty = "String1";
}
public static class Program
{
public static void Main()
{
Console.WriteLine(IsEqualToAttribute("String1"));
Console.WriteLine(IsEqualToAttribute("blah"));
Console.ReadKey();
}
public static bool IsEqualToAttribute(string mystring)
{
//Let's get all the properties from Usage
PropertyInfo[] props = typeof(Usage).GetProperties();
foreach (var prop in props)
{
//Let's make sure we have the right property
if (prop.Name == "SomeProperty")
{
//Get the attributes from the property
var attrs = prop.GetCustomAttributes();
//Select just the attribute named "MyAtt"
var attr = attrs.SingleOrDefault(x => x.GetType().Name == "MyAtt");
MyAtt myAttribute = attr as MyAtt; //Just casting to the correct type
if (myAttribute.name == mystring) //Compare the strings
return true;
if (myAttribute.anotherstring == mystring) //Compare the strings
return true;
}
}
return false;
}
}
As you can see we get the attribute off the property using reflection and then just compare the properties.
More info can be found here:
https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/attributes/accessing-attributes-by-using-reflection
As far as getting the constructor properties something along the lines of
typeof(MyAtt).GetConstructor().GetParameters()
Would retrieve the parameter details for the constructor.
There is also info on this in the Microsoft Docs: https://learn.microsoft.com/en-us/dotnet/api/system.reflection.customattributedata.constructor?view=netframework-4.7.2

Here is one way to do what you are asking for, but it's not particularly scaleable and requires a bunch of manual code to get working but may get you on the road to what you are trying to achieve. Assuming we have an attribute something like this that takes a string array in it's constructor:
public class MyAttrAttribute : Attribute
{
public string[] AllowedValues { get; }
public MyAttrAttribute(params string[] values)
{
AllowedValues = values;
}
}
You can change your field to be a property with a backing field. This allows you to override the set method and do your checking in there:
private string _testArg;
[MyAttr("TestArg1", "TestArg2")] //check that some string equals TestArg1/TestArg2
public string TestArg
{
get => _testArg;
set
{
var allowedValues = this.GetType() //Get the type of 'this'
.GetProperty(nameof(TestArg)) // Get this property
.GetCustomAttribute<MyAttrAttribute>() // Get the attribute
.AllowedValues; //Get the allowed values specified in the attribute
if(!allowedValues.Contains(value))
{
throw new ArgumentOutOfRangeException(nameof(value),
$"The value '{value}' is not allowed");
}
_testArg = value;
}
}
Having said all of this, I firmly believe that there is a better way to achieve what you are asking. For example, if you are restricted to a minimal set of values, then an enum would almost certainly be a better option than a string.

Looking for a more elegant way to perform custom get/set functionality on class properties

I'm trying to find a way to refine some code that I have. I work with a 3rd party API that has a REALLY complicated API request object (I'll call it ScrewyAPIObject) that has tons of repetition in it. Every time you want to set a particular property, it can take a page worth of code. So I built a library to provide a simplified wrapper around the setting/getting of its properties (and to handle some value preprocessing).
Here's a stripped-down view of how it works:
public abstract class LessScrewyWrapper
{
protected ScrewyAPIRequest _screwy = new ScrewyAPIRequest();
public void Set(string value)
{
Set(_getPropertyName(), value);
}
public void Set(string property, string value)
{
// Preprocess value and set the appropriate property on _screwy. This part
// has tons of code, but we'll just say it looks like this:
_screwy.Fields[property] = "[" + value + "]";
}
protected string _getPropertyName()
{
// This method looks at the Environment.StackTrace, finds the correct set_ or
// get_ method call and extracts the property name and returns it.
}
public string Get()
{
// Get the property name being access
string property = _getPropertyName();
// Search _screwy's structure for the value and return it. Again, tons of code,
// so let's just say it looks like this:
return _screwy.Fields[property];
}
public ScrewyAPIRequest GetRequest()
{
return _screwy;
}
}
Then I have a child class that represents one specific type of the screwy API request (there are multiple kinds that all have the same structure but different setups). Let's just say this one has two string properties, PropertyA and PropertyB:
public class SpecificScrewyAPIRequest : LessScrewyWrapper
{
public string PropertyA
{
get { return Get(); }
set { Set(value); }
}
public string PropertyB
{
get { return Get(); }
set { Set(value); }
}
}
Now when I want to go use this library, I can just do:
SpecificScrewyAPIRequest foo = new SpecificScrewyAPIRequest();
foo.PropertyA = "Hello";
foo.PropertyB = "World";
ScrewyAPIRequest request = foo.GetRequest();
This works fine and dandy, but there are different kinds of data types, which involves using generics in my Set/Get methods, and it just makes the child classes look a little kludgy when you're dealing with 50 properties and 50 copies of Get() and Set() calls.
What I'd LIKE to do is simply define fields, like this:
public class SpecificScrewyAPIRequest : LessScrewyWrapper
{
public string PropertyA;
public string PropertyB;
}
It would make the classes look a LOT cleaner. The problem is that I don't know of a way to have .NET make a callback to my custom handlers whenever the values of the fields are accessed and modified.
I've seen someone do something like this in PHP using the __set and __get magic methods (albeit in a way they were not intended to be used), but I haven't found anything similar in C#. Any ideas?
EDIT: I've considered using an indexed approach to my class with an object-type value that is cast to its appropriate type afterwards, but I'd prefer to retain the approach where the property is defined with a specific type.

Maybe in your case DynamicObject is a suitable choice:
public class ScrewyDynamicWrapper : DynamicObject
{
public override bool TryGetMember(GetMemberBinder binder, out object result)
{
// get your actual value based on the property name
Console.WriteLine("Get Property: {0}", binder.Name);
result = null;
return true;
}
public override bool TrySetMember(SetMemberBinder binder, object value)
{
// set your actual value based on the property name
Console.WriteLine("Set Property: {0} # Value: {2}", binder.Name, value);
return true;
}
}
And define your wrapper objects:
public class ScrewyWrapper
{
protected dynamic ActualWrapper = new ScrewyDynamicWrapper();
public int? PropertyA
{
get { return ActualWrapper.PropertyA; }
set { ActualWrapper.PropertyA = value; }
}
public string PropertyB
{
get { return ActualWrapper.PropertyB; }
set { ActualWrapper.PropertyB = value; }
}
}
However, you can't rely on the property type inside ScrewyDynamicWrapper with this approach, so it depends on your actual API requirements - maybe it won't work for you.

Instead of fields, If you define as property in class, It will be more easy.
public class SpecificScrewyAPIRequest
{
public string PropertyA { get; set; }
public string PropertyB { get; set; }
}
Then you can create extension generic method to return ScrewyAPIRequest object.
public static class Extensions
{
public static ScrewyAPIRequest GetRequest<T>(this T obj)
{
ScrewyAPIRequest _screwy = new ScrewyAPIRequest();
var test= obj.GetType().GetProperties();
foreach (var prop in obj.GetType().GetProperties())
{
_screwy.Fields[prop.Name] = prop.GetValue(obj, null);
}
return _screwy;
}
}
Now you can easily get ScrewyAPIRequest from any class object.
Your code will look like following.
SpecificScrewyAPIRequest foo = new SpecificScrewyAPIRequest();
foo.PropertyA = "Hello";
foo.PropertyB = "World";
ScrewyAPIRequest request = foo.GetRequest();

Capture Attribute's target

I have following attribute definition:
[System.AttributeUsage(System.AttributeTargets.Method)]
public class ClientFunction : System.Attribute {
public static List<???> Targets = new List<???>();
public string Display;
public string Tooltip;
public ClientFunction (string display, string tooltip = null) {
Display = display;
Tooltip = tooltip;
// Add target method of this specific attribute to Targets
Targets.Add(???);
}
}
I want to add to Targets the method the attribute is assigned to. How can I do this? Maybe with a third parameter that expects a delegate or something else?

You can't do that, attributes have no knowledge of the types/methods/etc they're assigned to.
Also, attributes constructors cannot have delegates as parameters. An attribute's parameters must be compile-time constants (e.g, strings, ints, enums). See available types: http://msdn.microsoft.com/en-us/library/aa664615%28v=vs.71%29.aspx
If you want to find all methods decorated with an attribute, you'll have to use reflection and inspect every method in every type in a given assembly, for example, and check whether those methods have the attribute defined.
Also note that, by convention, all attributes' names should be suffixed with the word "Attribute". In your case, ClientFunctionAttribute.

I think what you want to do here is this:
[System.AttributeUsage(System.AttributeTargets.Method)]
public class ClientFunctionAttribute : System.Attribute
{
private static List<MethodInfo> _targets;
public static List<MethodInfo> Targets
{
get
{
if (_targets == null)
{
_targets = Assembly.GetExecutingAssembly().GetTypes()
.SelectMany(t => t.GetMethods())
.Where(m => m.GetCustomAttributes(typeof(ClientFunctionAttribute), false).Length > 0)
.ToList();
}
return _targets;
}
}
public string Display;
public string Tooltip;
public ClientFunctionAttribute(string display, string tooltip = null)
{
Display = display;
Tooltip = tooltip;
}
}
And please add Attribute postfix after class name, you can still omit it in sqare brackets, like [ClientFunctionAttribute] and [ClientFunction] are the same.

Changing read only properties with reflection

Is it possible? With reflection or any other way?

As other stated, if you need to do that, you're facing a design issue to begin with. Now, if you want to know if it's possible just for the sake of knowing, or if there's no other way on earth to do it, it's indeed possible, with the help of a very small helper library and an extension method.
Consider the following code:
class Person {
int age;
string name;
public int Age { get { return age; } }
public string Name { get { return name; } }
}
// ...
using Mono.Reflection;
using System.Reflection;
// ...
Person person = new Person (27, "jb");
PropertyInfo nameProperty = typeof (Person).GetProperty ("Name");
FieldInfo nameField = nameProperty.GetBackingField ();
nameField.SetValue (person, "jbe");
Using this code, you can get the backing field of a property with just the property, and assign a new value to the backing field. You can read more details about the implementation.
Also note that it works only for simple properties, such as:
public int Age { get { return age; } }
public string Name {
get { return name; }
set { name = value; }
}
public double Velocity { get; private set; }
If you have complex properties with custom code (which includes expression-bodied member like int Answer=> 42;), the backing field resolver will fail as there is no backing field in such case.

An alternate to Simon Mattes answer would be
Assuming you have:
public class MyClass
{
public int MyNumber {get;}
}
You could do this if its for test purpose:
var field = typeof(MyClass).GetField("<MyNumber>k__BackingField", BindingFlags.Instance | BindingFlags.NonPublic);
field.SetValue(anIstanceOfMyClass, 3);

As a very dirty workaround for auto generated read only properties:
class MyTestClass
{
public string MyProperty { get; }
public MyTestClass( string MyProperty )
{
this.MyProperty = MyProperty;
}
}
You can modify the auto generated backing field in the following way:
MyTestClass MyClass = new MyTestClass( "Hello" );
FieldInfo MyWriteableField = MyClass.GetType().GetRuntimeFields().Where( a => Regex.IsMatch( a.Name, $"\\A<{nameof( MyClass.MyProperty )}>k__BackingField\\Z" ) ).FirstOrDefault();
MyWriteableField.SetValue( MyClass, "Another new value" );
PS: when you are using a .NET version < 4.6 you might have to change some of the code to work.
Enjoy!

it depends on the property. if it's a computed property - no, not unless you know what it's based on. if it's just an accessor to a private field, then you can try to modify the field.
in general, however, it's a very bad idea, as you likely have no knowledge of what side-effects this will cause.

PropertyInfo isReadOnly = typeof(System.Collections.Specialized.NameValueCollection).GetProperty("IsReadOnly", BindingFlags.Instance| BindingFlags.NonPublic);
//Remove the readonly property
isReadOnly.SetValue(param, false, null);
//.............put your code here.....
// Set readonly property
isReadOnly.SetValue(param, true, null);