Develop Reference

Get the field name from the parameter [duplicate]

I want to get the value of a field of an object by using a string as variable name.
I tried to do this with reflection:
myobject.GetType().GetProperty("Propertyname").GetValue(myobject, null);
This works perfectly but now I want to get the value of "sub-properties":
public class TestClass1
{
public string Name { get; set; }
public TestClass2 SubProperty = new TestClass2();
}
public class TestClass2
{
public string Address { get; set; }
}
Here I want to get the value Address from a object of TestClass1.

You already did everything you need to do, you just have to do it twice:
TestClass1 myobject = ...;
// get SubProperty from TestClass1
TestClass2 subproperty = (TestClass2) myobject.GetType()
.GetProperty("SubProperty")
.GetValue(myobject, null);
// get Address from TestClass2
string address = (string) subproperty.GetType()
.GetProperty("Address")
.GetValue(subproperty, null);

Your SubProperty member is actually a Field and not a Property, that is why you can not access it by using the GetProperty(string) method. In your current scenario, you should use the following class to first get the SubProperty field, and then the Address property.
This class will allow you to specify the return type of your property by closing the type T with the appropriate type. Then you will simply need to add to the first parameter the object whose members you are extracting. The second parameter is the name of the field you are extracting while the third parameter is the name of the property whose value you are trying to get.
class SubMember<T>
{
public T Value { get; set; }
public SubMember(object source, string field, string property)
{
var fieldValue = source.GetType()
.GetField(field)
.GetValue(source);
Value = (T)fieldValue.GetType()
.GetProperty(property)
.GetValue(fieldValue, null);
}
}
In order to get the desired value in your context, simply execute the following lines of code.
class Program
{
static void Main()
{
var t1 = new TestClass1();
Console.WriteLine(new SubMember<string>(t1, "SubProperty", "Address").Value);
}
}
This will give you the value contained in the Address property. Just make sure you first add a value to the said property.
But should you actually want to change the field of your class into a property, then you should make the following change to the original SubMember class.
class SubMemberModified<T>
{
public T Value { get; set; }
public SubMemberModified(object source, string property1, string property2)
{
var propertyValue = source.GetType()
.GetProperty(property1)
.GetValue(source, null);
Value = (T)propertyValue.GetType()
.GetProperty(property2)
.GetValue(propertyValue, null);
}
}
This class will now allow you to extract the property from your initial class, and get the value from the second property, which is extracted from the first property.

try
myobject.GetType().GetProperty("SubProperty").GetValue(myobject, null)
.GetType().GetProperty("Address")
.GetValue(myobject.GetType().GetProperty("SubProperty").GetValue(myobject, null), null);

Why I can't assign dynamic data in constructor C#?

I'm a PHP Developer...
I need to do a class that can be created and fill of dynamic way, similar to this in PHP.
class Person{
private $name;
private $age;
function __construct($params = array()){
foreach ($this as $key => $val) {
$this -> $key = (isset($params[$key])) ? $params[$key] : "";
}
}
function getName(){
return $this->name;
}
function getAge(){
return $this->age;
}
function setName($value){
$this->name = $value;
}
function setAge($value){
$this->age = $value;
}
}
I read about the reflection in C#, but I don't find the correct way to do.
This is my C# code
public class Person
{
private String _name { get { return _name; } set { _name = value; } }
private int _age { get { return _age; } set { _age = value; } }
public Person()
{
}
public Person(Hashtable _data)
{
PropertyInfo[] propertyInfos;
propertyInfos = typeof(Person).GetProperties(BindingFlags.NonPublic | BindingFlags.Instance);
foreach (var propInfo in propertyInfos)
{
typeof(Person).GetProperty(propInfo.Name).SetValue(this, _data[propInfo.Name]);
}
}
}
In runtime I get an Exception
Object reference not set to an instance of an object.
The typeof(Person) I try to change it to this.getType() and I get the same.
I hope that can help me.

You are grabbing all properties on the object and then looking them up in the hashtable. You likely want the reverse--all objects in the hashtable set to properties on the object. Otherwise you'll get an exception when you don't specify every single member.
As Alexei points out, the NullReferenceException is due to the second call to GetProperties only returning public properties when no BindingFlags are supplied. Since there are no public properties, you get an exception.
Because C# is strongly typed, you run into a number of issues you don't have in PHP. These include setting a value with an object of a type that doesn't match or convert to the property type, entries in your data parameter that don't exist as properties, etc. I've done my best to document the gotchas I see below.
Here is what the Person class would look like (I've cleaned up some of the style and used classes to make it feel more like a C# class):
public class Person
{
private string name { get; set; }
private int age { get; set; }
public Person()
{
}
public Person(IDictionary<string,object> data)
{
foreach (var value in data)
{
// The following line will be case sensitive. Do you need to standardize the case of the input dictionary before getting the property?
PropertyInfo property = typeof(Person).GetProperty(value.Key, BindingFlags.Instance | BindingFlags.NonPublic);
if (property != null)
{
property.SetValue(this, value.Value); // You are allowing any old object to be set here, so be prepared for conversion and casting exceptions
}
else
{
// How do you want to handle entries that don't map to properties? Ignore?
}
}
}
}
And here is an example of usage:
static void Main(string[] args)
{
var person = new Person(new Dictionary<string,object>() {{"name" ,"Mike"}, {"age", 32}});
}

You should stay away from using var if you're new to the language, it only complicates things.
The propInfo in your foreach-loop already is a PropertyInfo, so you don't need to find it again:
BindingFlags flags = BindingFlags.NonPublic | BindingFlags.Instance;
PropertyInfo[] propertyInfos = typeof(Person).GetProperties(flags);
foreach (PropertyInfo propInfo in propertyInfos)
{
propInfo.SetValue(this, _data[propInfo.Name]);
}
The NullReferenceException is probably caused by the following part of your original code:
typeof(Person).GetProperty(propInfo.Name)...
Since no BindingFlags are provided to the GetProperty() this time, it looks for public instance properties, and when no such property is found, it returns null (that, or _data is null to begin with).
As others have pointed out, your properties currently will cause StackOverflowExceptions. Try changing them to:
private String _name { get; set; }
private int _age { get; set; }

I am wondering why you would want to do this. There may be better, more idiomatic C#, designs to achieve the behavior you want. But we can't know that because there is no additional contextual information mentioned in the question.
So I will simply try to answer your question. The version below takes your code, using auto properties, and a simple dictionary lookup for the initialization of its members from the supplied dictionary. Also note that this does not require any reflection, because there is nothing dynamic about the members of this class.
public class Person
{
public string Name { get; set; }
public int Age { get; set; }
public Person(IDictionary<string, object> data)
{
// What to do if the map does not contain "Name" or "Age" ?
// Right now: initialize to default value.
Name = TryLookup<string>(data, "Name", null);
Age = TryLookup<int>(data, "Age", default(int));
// What to do if the map contains other items that do not
// map to a member variable?
}
private static T TryLookup<T>(IDictionary<string, object> data, string key, T defaultValue)
{
return data.ContainsKey(key) ? (T)data[key] : defaultValue;
}
}
In case you actually really really badly need a dynamic type as opposed to a statically defined type with fixed member properties, you could use an ExpandoObject or alternatively (but this is far from trivial) build a dynamic type using an AssemblyBuilder with a TypeBuilder

C# - Set Property of a Property with Reflection

SO Community,
So I'm learning C# and am still trying to wrap my head around reflection. In particular trying to use it to access a property of a property on a class.
I've boiled down the basic task that I'm trying to accomplish below:
public enum SIGNAL_STATE { NOT_RETRIEVED = 0, RETRIEVING = 1, RETRIEVED = 2, FAILED = 3 }
public class MyObjectClass
{
public string MyString;
private SIGNAL_STATE _state = SIGNAL_STATE.NOT_RETRIEVED;
public SIGNAL_STATE State { get { return _state; } set { _state = value;} }
}
public class NeedToReflect
{
private MyObjectClass _myObject1 = new MyObjectClass();
private MyObjectClass _myObject2 = new MyObjectClass();
private MyObjectClass _myObject3 = new MyObjectClass();
public MyObjectClass MyObject1
{
get{return _myObject1;}
set{_myObject1 = value;}
}
public MyObjectClass MyObject2
{
get{return _myObject2;}
set{_myObject2 = value;}
}
public MyObjectClass MyObject3
{
get{return _myObject3;}
set{_myObject3 = value;}
}
public static void Main(string [] args){
NeedToReflect needToReflect = new NeedToReflect();
string fieldName;
for(int idx = 1; idx<=3; ++idx)
{
fieldName = String.Format("MyObject{0}",idx);
//TODO: set state of 'MyObject' values to SIGNAL_STATE.RETRIEVING
}
}
}
edit 1:
At Yair Nevet's suggestion I'm grabbing the FieldInfo from the applicable object like,
FieldInfo fieldInfo = needToReflect.GetType().GetField(fieldName, BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.Instance);
But from there I get hung up on accessing and setting the right 'State' Field/Property on that member field
Solution (ie. here's what I plugged in on that TODO comment):
// Determine what binding flags will give us proper access to our member field
BindingFlags bindFlags = BindingFlags.NonPublic | BindingFlags.GetField | BindingFlags.Instance;
// Get the field for that field
FieldInfo fieldInfo = needToReflect.GetType().GetField(fieldName, bindFlags);
// Pass in the containing object that we're reflecting on to get an instance of the member field
MyObjectClass myField = (MyObjectClass) fieldInfo.GetValue(needToReflect);
// We can now directly access and edit the value in question
myField.State = SIGNAL_STATE.RETRIEVING;
That does it. Thanks to Shlomi Borovitz for pointing me in the right direction.
Thanks!

The FieldInfo object which returned by GetField has property which called FieldInfo, which returns the type of that field.
And you can query it for that type's (the type of the field) properties/fields (and whatever you want) - and get/set them.
Remember that both GetType method (of any object), and the FieldInfo.FieldType property return Type object, that you can query in reflection.
object obj =...
var field = obj.GetType().GetField(fieldName,...);
field.FieldType.GetField(...
//etc... etc...
For each field, you can query the type and for each type, you can query the fields, and get/set them.
BTW, in C# 4.0 you can use the dynamic pseudo type (it used as a type when declaring dynamic variable, but it's not a real type), and then using that variable, while assuming which properties/fields/methods that variable would have in runtime (ie, using them like they are known in compile time although they don't).
This will not work for private members (and I can't warn you enough against calling private members in reflection), but for public members, this would make your code simple and readable, like you never used reflection (although, behind the scenes [in this case] reflection would be used).

You are trying to access a Property while the member is actually a private Field:
propertyName = String.Format("MyObject{0}",idx);
Use GetField method instead for that:
needToReflect.GetType().GetField(propertyName, BindingFlags.NonPublic |BindingFlags.GetField | BindingFlags.Instance);

Go through these steps...
1) Get the Type.
2) Have an instance of that type.
3) Get the PropertyInfo for the property.
4) Call "GetSetMethod" on the PropertyInfo object. It will return a MethodInfo object.
5) Invoke the MethodInfo object using the instance of the type and a value.

Given:
class ClassyMcClass
{
public int PropertyB { get; set; }
}
class MyClass
{
public ClassyMcClass PropertyA { get; set; }
}
The following code uses reflection on a MyClass object to set the int value of PropertyB in PropertyA to NewValue:
PropertyInfo propA = typeof(MyClass).GetProperty("PropertyA");
PropertyInfo probBofA = propA.PropertyType.GetProperty("PropertyB");
// Set property B of property A, where obj is of type MyClass
probBofA.SetValue(propA.GetValue(obj), NewValue, null);

How to check if property setter is public

Given a PropertyInfo object, how can I check that the setter of the property is public?

Check what you get back from GetSetMethod:
MethodInfo setMethod = propInfo.GetSetMethod();
if (setMethod == null)
{
// The setter doesn't exist or isn't public.
}
Or, to put a different spin on Richard's answer:
if (propInfo.CanWrite && propInfo.GetSetMethod(/*nonPublic*/ true).IsPublic)
{
// The setter exists and is public.
}
Note that if all you want to do is set a property as long as it has a setter, you don't actually have to care whether the setter is public. You can just use it, public or private:
// This will give you the setter, whatever its accessibility,
// assuming it exists.
MethodInfo setter = propInfo.GetSetMethod(/*nonPublic*/ true);
if (setter != null)
{
// Just be aware that you're kind of being sneaky here.
setter.Invoke(target, new object[] { value });
}

.NET properties are really a wrapping shell around a get and set method.
You can use the GetSetMethod method on the PropertyInfo, returning the MethodInfo referring to the setter. You can do the same thing with GetGetMethod.
These methods will return null if the getter/setter is non-public.
The correct code here is:
bool IsPublic = propertyInfo.GetSetMethod() != null;

public class Program
{
class Foo
{
public string Bar { get; private set; }
}
static void Main(string[] args)
{
var prop = typeof(Foo).GetProperty("Bar");
if (prop != null)
{
// The property exists
var setter = prop.GetSetMethod(true);
if (setter != null)
{
// There's a setter
Console.WriteLine(setter.IsPublic);
}
}
}
}

You need to use the underling method to determine accessibility, using PropertyInfo.GetGetMethod() or PropertyInfo.GetSetMethod().
// Get a PropertyInfo instance...
var info = typeof(string).GetProperty ("Length");
// Then use the get method or the set method to determine accessibility
var isPublic = (info.GetGetMethod(true) ?? info.GetSetMethod(true)).IsPublic;
Note, however, that the getter & setter may have different accessibilities, e.g.:
class Demo {
public string Foo {/* public/* get; protected set; }
}
So you can't assume that the getter and the setter will have the same visibility.

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);