Is there a way to iterate (through foreach preferably) over a collection using reflection? I'm iterating over the properties in an object using reflection, and when the program gets to a type that is a collection, I'd like it to iterate over the contents of the collection and be able to access the objects in the collection.
At the moment I have an attribute set on all of my properties, with an IsCollection flag set to true on the properties that are collections. My code checks for this flag and if it's true, it gets the Type using reflection. Is there a way to invoke GetEnumerator or Items somehow on a collection to be able to iterate over the items?
I had this issue, but instead of using reflection, i ended up just checking if it was IEnumerable. All collections implement that.
if (item is IEnumerable)
{
foreach (object o in (item as IEnumerable))
{
}
} else {
// reflect over item
}
I've tried to use a similar technique as Darren suggested, however just beware that not just collections implement IEnumerable. string for instance is also IEnumerable and will iterate over the characters.
Here's a small function I'm using to determine if an object is a collection (which will be enumerable as well since ICollection is also IEnumerable).
public bool isCollection(object o)
{
return typeof(ICollection).IsAssignableFrom(o.GetType())
|| typeof(ICollection<>).IsAssignableFrom(o.GetType());
}
Just get the value of the property and then cast it into an IEnumerable. Here is some (untested) code to give you an idea:
ClassWithListProperty obj = new ClassWithListProperty();
obj.List.Add(1);
obj.List.Add(2);
obj.List.Add(3);
Type type = obj.GetType();
PropertyInfo listProperty = type.GetProperty("List", BindingFlags.Public);
IEnumerable listObject = (IEnumerable) listProperty.GetValue(obj, null);
foreach (int i in listObject)
Console.Write(i); // should print out 123
Just for information may be it will be of someone's help...
I had a class with nested classes and collection of some other classes. I wanted to save the property values of the class as well nested classes and collection of classes. My code is as follows:
public void LogObject(object obj, int indent)
{
if (obj == null) return;
string indentString = new string(' ', indent);
Type objType = obj.GetType();
PropertyInfo[] properties = objType.GetProperties();
foreach (PropertyInfo property in properties)
{
Type tColl = typeof(ICollection<>);
Type t = property.PropertyType;
string name = property.Name;
object propValue = property.GetValue(obj, null);
//check for nested classes as properties
if (property.PropertyType.Assembly == objType.Assembly)
{
string _result = string.Format("{0}{1}:", indentString, property.Name);
log.Info(_result);
LogObject(propValue, indent + 2);
}
else
{
string _result = string.Format("{0}{1}: {2}", indentString, property.Name, propValue);
log.Info(_result);
}
//check for collection
if (t.IsGenericType && tColl.IsAssignableFrom(t.GetGenericTypeDefinition()) ||
t.GetInterfaces().Any(x => x.IsGenericType && x.GetGenericTypeDefinition() == tColl))
{
//var get = property.GetGetMethod();
IEnumerable listObject = (IEnumerable)property.GetValue(obj, null);
if (listObject != null)
{
foreach (object o in listObject)
{
LogObject(o, indent + 2);
}
}
}
}
}
An called this function
LogObject(obj, 0);
However, I have some structs inside my classes and I need to figure out how to get their values. Moreoevr, I have some LIst. I need to get their value as well.... I will post if I update my code.
The best you could probably do would be to check if the object implements certain collection interfaces - probably IEnumerable would be all that you need. Then it's just a matter of calling GetEnumerator() off of the object, and using IEnumerator.MoveNext() and IEnumerator.Current to work your way through the collection.
This won't help you if the collection doesn't implement those interfaces, but if that's the case it's not really much of a collection, I suppose.
When your using reflection you aren't necessarily using an instance of that object. You would have to create an instance of that type of be able to iterate through the object's properties. So if you are using reflection use the ConstructorInfo.Invoke() (?) method to create a new instance or point to an instance of the type.
I would look at the Type.FindInterfaces method. This can filter out the interfaces implemented by a given type. As in PropertyInfo.PropertyType.FindInterfaces(filterMethod, filterObjects). You can filter by IEnumerable and see if any results are returned. MSDN has a great example in the method documentation.
If you're not using an instance of the object but rather a Type, you can use the following:
// type is IEnumerable
if (type.GetInterface("IEnumerable") != null)
{
}
A rather straightforward approach would be to type cast the object as the collection and directly use that.
Related
Using reflection I can obtain the object properties and values for all Data Types and the objects inside this object. But if the object contains a List of other objects I am having trouble in getting the objects in the list. The list can contain any type of object.
private static void SaveObj(object obj) {
foreach (var prop in obj.GetType().GetProperties()) {
if (prop.PropertyType.Namespace == "Entities") { //It is an object
object obL = prop.GetValue(obj, null);
SaveObj(obj);
}
else if (prop.PropertyType.Name == "List`1") { //This is a list of objects
object obP = prop.GetValue(obj);
//obP has the list of objects, I can see the list in debug mode.
List<object> obL = (List<object>)prop.GetValue(obj, null);
//This line returns an exception!!
}
else {
columns += prop.Name.ToLower() + ", ";
values[i] = prop.GetValue(obj, null).ToString();
}
... // the code continues ...
}
}
The exception message returned is:
"It is not possible to convert an object of type 'System.Collections.Generic.List1[Entities.OrderItem]' to type 'System.Collections.Generic.List1[System.Object]'."
Interesting is that I can see all the objects and its contents in degug mode. In Immediate Window I can print the content of the variable obP with all the objects in the list, but how to read them?
Any ideas on how to solve this?
You can try casting it to IEnumerable and then use .Cast<object>().ToList() Like this:
IEnumerable obL = prop.GetValue(obj, null) as IEnumerable;
List<object> list = obL.Cast<object>().ToList();
Sins a List implements the ICollection interface, you could, instead of attempting to cast the returned value to a List<object>, do something like:
ICollection collection = (prop.GetValue(obj, null) as ICollection);
if (collection != null)
{
object[] array = new object[collection.Count];
collection.CopyTo(array, 0);
//if you need a list just create a new one and pass in the array: new List<object>(array);
}
As a side note, wouldn't your:
if (prop.PropertyType.Namespace == "Entities")
{
object obL = prop.GetValue(obj, null);
SaveObj(obj);
}
just cause a infinite loop, which will lead to a StackOverflow/OutOfMemory exception, might want to change it to SaveObj(obL); if that was the intended behavior.
I'm recursively iterating through an object's properties using the following method:
void GetProps(object obj)
{
if (obj == null)
return;
var objType = obj.GetType();
var properties = objType.GetProperties();
foreach (var property in properties)
{
object value = property.GetValue(obj, null);
if (typeof(IEnumerable).IsAssignableFrom(property.PropertyType))
{
var enumerable = (IEnumerable)value;
foreach (object child in enumerable)
GetProps(child);
}
else
{
GetProps(value);
}
}
}
The object is very complex (over 30 classes). I'm getting a StackOverflowException when going deeper into the object at GetProps(value.
Is there a way to catch the exception and check why it's failing, and, solve the problem?
EDIT
I added a fail-safe at the top of the method:
if (visited.Contains(obj))
return;
visited.Add(obj);
The problem is not with circular references (which I don't have) but with property types such as DateTime, int and decimal. which was assuming they're primitive but the IsPrimitive property is false.
Can I differentiate between such types and my own classes?
A StackOverflowException can't be caught unless you threw it, because it indicates a fatal problem with your application.
Most likely this happens because you have a circular reference. I.e. an object that contains another object which contains a reference to the original object. There may be an arbitrary number of hierarchy levels between the two classes.
You need to implement some kind of mechanism to stop traversing an object that you already traversed, e.g. with the help of a hash set.
Here is an example not using recursion, which leverages Eric Lippert's explicit stack approach. I don't know if the behavior with strings is as you intended, but this may prevent your stack from blowing:
public static IEnumerable<object> GetPropertiesDepthFirst(object obj)
{
if (obj == null)
yield break;
var stack = new Stack<object>();
stack.Push(obj);
while (stack.Count > 0)
{
var current = stack.Pop();
yield return current;
var objType = current.GetType();
var properties = objType.GetProperties();
foreach (var property in properties)
{
object value = property.GetValue(current, null);
if (value == null)
continue;
if (typeof(IEnumerable).IsAssignableFrom(property.PropertyType))
{
var enumerable = (IEnumerable)value;
foreach (object child in enumerable)
stack.Push(child);
}
else
{
yield return value;
}
}
}
}
Also for IEnumerables with defined indexes, you may want to exclude Indexed Properties:
objType.GetProperties().Where(p => p.GetIndexParameters().Length == 0)
I'm using Value Injecters to map from 1 type to another using the LoopValueInjection and overriding the SetValue(object v) method with some custom logic. I am trying to detect when a HashSet is being passed in and go through the HashSet and apply a method to each item in it to do some clean up. The issues I'm having are because the parameter is just an object and I don't know what the type of item will be in the HashSet. For example, it could be HashSet or HashSet.
Here is the code I currently have but I'm getting an InvalidCastException.
protected override object SetValue(object v)
{
if (type.Name == "HashSet`1")
{
var genericType = type.GetGenericArguments()[0];
// this line throws the InvalidCastException
var cleanHashSet = (HashSet<object>)Activator.CreateInstance(type);
foreach (var item in (HashSet<object>)v) // I'm sure this cast will throw as well
{
cleanHashSet.Add(Clean(item));
}
return cleanHashSet;
}
return base.SetValue(v);
}
I guess the main question is how can I loop through the HashSet that is passed in as an object once I determine it is in fact a HashSet of some kind? I'm also thinking I will need to create a new empty HashSet of the specific type as well so I can put each item that gets cleaned up into it.
In .NET only interfaces and delegate types can be co- and contra-variant. So it is not possible to cast HashSet<SomeType> to HashSet<object>.
You want to cast your v to non-generic version of IEnumerable interface
dynamic cleanHashSet = Activator.CreateInstance(type);
foreach (object item in (IEnumerable)v)
{
cleanHashSet.Add(Clean(item));
}
If you don't want to use dynamic keyword then you need to call Add method with reflection
object cleanHashSet = Activator.CreateInstance(type);
var method = type.GetMethod("Add");
foreach (object item in (IEnumerable)v)
{
method.Invoke(cleanHashSet, new object[] { Clean(item) });
}
Use:
bool isHashSet = typeof(HashSet<object>).IsAssignableFrom(type);
or
object x = ...
HashSet<object> hs = x as HashSet<object>;
if (hs != null)
{
// use hs
}
If you really have <T> specified then use it instead of object.
HashSet<T> implements ICollection<T>, IEnumerabel<T>, IEnumerable. What means if you know T you can both enumerate and add. Otherwise enumerate only enumerate.
Using reflection I have an object which I need to cast into an iterable list of items (type unknown, will be object). Using the Watch window I can see my object is an array of some type as it tells me the number of elements and I can explode the tree view to see the elements themselves.
Firstly, I need to check that the object passed is some kind of array (might be List, might be object[], etc). Then I need to iterate through that array. However, I can't do the type conversion.
Here's how I'm using it (abbreviated):
private static void Example(object instance, PropertyInfo propInfo)
{
object anArray = propInfo.GetValue(instance, null);
ArrayList myList = anArray as ArrayList;
foreach (object element in myList)
{
// etc
}
}
I've tried various different casts. The above doesn't raise an exception but mylist is null when anArray actually exists and contains items. The actual instance being saved is a strongly-typed List<> but could take a limited subset of forms if necessary. But the point of the exercise is that this Example() method doesn't know the basic type of the property.
Casting it to an ArrayList is only going to work if the object actually is an ArrayList. It wont work with a System.Array, or a System.Collections.Generic.List`1 for example.
I think what you actually should do is cast it to IEnumerable, since that is your only requirement to loop over it...
object anArray = propInfo.GetValue(instance, null);
IEnumerable enumerable = anArray as IEnumerable;
if (enumerable != null)
{
foreach(object element in enumerable)
{
// etc...
}
}
Try to cast to IEnumerable. This is the most basic interface all enumerables, arrays, lists etc. implement.
IEnumerable myList = anArray as IEnumerable;
if (myList != null)
{
foreach (object element in myList)
{
// ... do something
}
}
else
{
// it's not an array, list, ...
}
Simply Try This
string[] arr = ((IEnumerable)yourOjbect).Cast<object>()
.Select(x => x.ToString())
.ToArray();
Try this:
var myList = anArray as IEnumerable;
if (mylist != null)
{
foreach (var element in myList)
{
// etc
}
}
You might also need to specify the generic type of the IEnumerable, depending on your situation.
You should be able to cast it to IEnumerable if it is a collection of any sorts (array, list, etc.). Also PropertyInfo contains a PropertyType property which you could use to find out the actual type if you wanted to.
Just in My case I need to define data type IEnumerable<string>
var myList = anArray as IEnumerable<string>;
How can i cast
from ObservableCollection<TabItem> into ObservableCollection<object>
this doesnt work for me
(ObservableCollection<object>)myTabItemObservableCollection
you should copy like this
return new ObservableCollection<object>(myTabItemObservableCollection);
Basically, you can't. Not now, and not in .NET 4.0.
What is the context here? What do you need? LINQ has Cast<T> which can get you the data as a sequence, or there are some tricks with generic methods (i.e. Foo<T>(ObservalbleCollection<T> col) etc).
Or you can just use the non-generic IList?
IList untyped = myTypedCollection;
untyped.Add(someRandomObject); // hope it works...
you could use IEnumerable.Cast<T>()
You can't. ObservableCollection<TabItem> does not derive from ObservableCollection<object>.
If you explain why you would want to perhaps we can point out an alternative interface you can use.
thanx for all answers, but I think I have solve this problem self with a "helpermethode".
Perhaps has any a better method or a linq statement for this.
private void ConvertTabItemObservableCollection()
{
Manager manager = this.container.Resolve<Manager>();
foreach (var tabItem in manager.ObjectCollection)
{
TabItemObservableCollection.Add((TabItem)tabItem);
}
}
None of the examples I have found have worked for me, I have cobbled together the below code and it seems to work. I have a hierarchy that is created by deserializing an XML file and I am able to loop through all the objects in the hierarchy, but you can adapt this to just loop through one ObservableCollection and get the objects as objects and not strongly typed.
I want to add a PropertyChangingEventHandler to every property in the hierarchy so that I can implement undo/redo functionality.
public static class TraversalHelper
{
public static void TraverseAndExecute(object node)
{
TraverseAndExecute(node, 0);
}
public static void TraverseAndExecute(object node, int level)
{
foreach (var property in node.GetType().GetProperties())
{
var propertyValue = node.GetType().GetProperty(property.Name).GetGetMethod().Invoke(node, null); // Get the value of the property
if (null != propertyValue)
{
Console.WriteLine("Level=" + level + " : " + property.Name + " :: " + propertyValue.GetType().Name); // For debugging
if (property.PropertyType.IsGenericType && property.PropertyType.GetGenericTypeDefinition() == typeof(ObservableCollection<>)) // Check if we are dealing with an observable collection
{
//var dummyvar = propertyValue.GetType().GetMethods(); // This was just used to see which methods I could find on the Collection
Int32 propertyValueCount = (Int32)propertyValue.GetType().GetMethod("get_Count").Invoke(propertyValue, null); // How many objects in the collection
level++;
for (int i = 0; i < propertyValueCount; i++) // Loop over all objects in the Collection
{
object properyValueObject = (object)propertyValue.GetType().GetMethod("get_Item").Invoke(propertyValue, new object[] { i }); // Get the specified object out of the Collection
TraverseAndExecute(properyValueObject, level); // Recursive call in case this object is a Collection too
}
}
}
}
}
}
The method is just called like this
TraversalHelper.TraverseAndExecute(object);
If you just want to create a collection of objects you just need this bit of code
ObservableCollection<Field> typedField = migration.FileDescriptions[0].Inbound[0].Tables[0].Table[0].Fields[0].Field; // This is the strongly typed decalaration, a collection of Field objects
object myObject = typedField; // Declare as object
Int32 propertyValueCount = (Int32)myObject.GetType().GetMethod("get_Count").Invoke(myObject, null); // How many objects in this Collection
for (int i = 0; i < propertyValueCount; i++) // Loop over all objects in the Collection
{
object properyValueObject = (object)myObject.GetType().GetMethod("get_Item").Invoke(myObject, new object[] { i }); // Get the specified object out of the Collection, in this case a Field object
// Add the object to a collection of objects, or whatever you want to do with object
}
You can Cast it as INotifyCollectionChanged;
Like:
if (myTabItemObservableCollection is INotifyCollectionChanged collection)
{
Do Stuff
}