Pass property itself to function as parameter in C#
C#PropertiesParameter PassingC# Problem Overview
I am looking for a method to pass property itself to a function. Not value of property. Function doesn't know in advance which property will be used for sorting. Simplest way in this example is: creating 4 overwrites with different parameter types. Other way is using of typeof()
inside function. Both these ways are unacceptable when Class1 has hundreds properties. So far I found following method:
class Class1
{
string vehName;
int maxSpeed;
int fuelCapacity;
bool isFlying;
}
class Processor
{
List<Class1> vehicles = null;
Processor(List<Class1> input)
{
vehicles = input;
}
List<Class1> sortBy(List<Class1> toSort, string propName)
{
if (toSort != null && toSort.Count > 0)
{
return toSort.OrderBy(x => typeof(Class1).GetProperty(propName).GetValue(x, null)).ToList();
}
else return null;
}
}
class OuterUser
{
List<Class1> vehicles = new List<Class1>();
// ... fill the list
Processor pr = new Processor(vehicles);
List<Class1> sorted = pr.sortBy("maxSpeed");
}
I don't like this method because of risk of "human error" when passing string to processing function. When the string is generated by other part of code this is going be even more ugly. Please, suggest more elegant way to implement passing of Class1 property to function for further processing. The best option for usage IMHO will be (or something like this):
vehicles = sortBy(vehicles, Class1.maxSpeed);
C# Solutions
Solution 1 - C#
You can pass a property accessor to the method.
List<Class1> SortBy(List<Class1> toSort, Func<Class1, IComparable> getProp)
{
if (toSort != null && toSort.Count > 0) {
return toSort
.OrderBy(x => getProp(x))
.ToList();
}
return null;
}
You would call it like this:
var result = SortBy(toSort, x => x.maxSpeed);
But you could go one step further and write your own extension method.
public static class CollectionExtensions
{
public static List<TSource> OrderByAsListOrNull<TSource, TKey>(
this ICollection<TSource> collection, Func<TSource,TKey> keySelector)
if (collection != null && collection.Count > 0) {
return collection
.OrderBy(x => keySelector(x))
.ToList();
}
return null;
}
}
Now you can sort like this
List<Class1> sorted = toSort.OrderByAsListOrNull(x => x.maxSpeed);
but also
Person[] people = ...;
List<Person> sortedPeople = people.OrderByAsListOrNull(p => p.LastName);
Note that I declared the first parameter as ICollection<T>
because it must fulfill two conditions:
- It must have a
Count
property - It must be an
IEnumerable<T>
in order to be able to apply the LINQ methodOrderBy
.
List<Class1>
is an ICollection<T>
but also an array Person[]
as many other collections.
So far, I have shown how you can read a property. If the method needs to set a property, you need to pass it a setter delegate as well
void ReadAndWriteProperty(Func<Class1, T> getProp, Action<Class1, T> setProp)
Where T
is the type of the property.
Solution 2 - C#
You can use an lambda expression to pass property information:
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");
}
}
Usage:
DoSomething(() => this.MyProperty);
Solution 3 - C#
What I found missing from @MatthiasG's answer is how to get property value not just its name.
public static string Meth<T>(Expression<Func<T>> expression)
{
var name = ((MemberExpression)expression.Body).Member.Name;
var value = expression.Compile()();
return string.Format("{0} - {1}", name, value);
}
use:
Meth(() => YourObject.Property);
Solution 4 - C#
Great solution over here...
https://stackoverflow.com/questions/1402803/passing-properties-by-reference-in-c-sharp
void GetString<T>(string input, T target, Expression<Func<T, string>> outExpr)
{
if (!string.IsNullOrEmpty(input))
{
var expr = (MemberExpression) outExpr.Body;
var prop = (PropertyInfo) expr.Member;
prop.SetValue(target, input, null);
}
}
void Main()
{
var person = new Person();
GetString("test", person, x => x.Name);
Debug.Assert(person.Name == "test");
}
Solution 5 - C#
Why don't you use Linq for this? Like:
vehicles.OrderBy(v => v.maxSpeed).ToList();
Solution 6 - C#
Just to add from the answers above. You can also do a simple flag for the order direction.
public class Processor
{
public List<SortableItem> SortableItems { get; set; }
public Processor()
{
SortableItems = new List<SortableItem>();
SortableItems.Add(new SortableItem { PropA = "b" });
SortableItems.Add(new SortableItem { PropA = "a" });
SortableItems.Add(new SortableItem { PropA = "c" });
}
public void SortItems(Func<SortableItem, IComparable> keySelector, bool isAscending)
{
if(isAscending)
SortableItems = SortableItems.OrderBy(keySelector).ToList();
else
SortableItems = SortableItems.OrderByDescending(keySelector).ToList();
}
}
Solution 7 - C#
I would like to give a simple, easy to understand answer.
Function's parameter is this: System.Func<class, type of the property>
And we pass the Property like this: Function(x => x.Property);
Here is the code:
class HDNData
{
private int m_myInt;
public int MyInt
{
get { return m_myInt; }
}
public void ChangeHDNData()
{
if (m_myInt == 0)
m_myInt = 69;
else
m_myInt = 0;
}
}
static class HDNTest
{
private static HDNData m_data = new HDNData();
public static void ChangeHDNData()
{
m_data.ChangeHDNData();
}
public static void HDNPrint(System.Func<HDNData, int> dataProperty)
{
Console.WriteLine(dataProperty(m_data));//Print to console the dataProperty (type int) of m_data
}
}
//******Usage******
HDNTest.ChangeHDNData();
//This is what you want: Pass property itself (which is MyInt) to function as parameter in C#
HDNTest.HDNPrint(x => x.MyInt);