List<object>.RemoveAll - How to create an appropriate Predicate
The RemoveAll()
methods accept a Predicate<T>
delegate (until here nothing new). A predicate points to a method that simply returns true or false. Of course, the RemoveAll
will remove from the collection all the T
instances that return True with the predicate applied.
C# 3.0 lets the developer use several methods to pass a predicate to the RemoveAll
method (and not only this one…). You can use:
Lambda expressions
vehicles.RemoveAll(vehicle => vehicle.EnquiryID == 123);
Anonymous methods
vehicles.RemoveAll(delegate(Vehicle v) {
return v.EnquiryID == 123;
});
Normal methods
vehicles.RemoveAll(VehicleCustomPredicate);
private static bool
VehicleCustomPredicate (Vehicle v) {
return v.EnquiryID == 123;
}
A predicate in T is a delegate that takes in a T and returns a bool. List<T>.RemoveAll will remove all elements in a list where calling the predicate returns true. The easiest way to supply a simple predicate is usually a lambda expression, but you can also use anonymous methods or actual methods.
{
List<Vehicle> vehicles;
// Using a lambda
vehicles.RemoveAll(vehicle => vehicle.EnquiryID == 123);
// Using an equivalent anonymous method
vehicles.RemoveAll(delegate(Vehicle vehicle)
{
return vehicle.EnquiryID == 123;
});
// Using an equivalent actual method
vehicles.RemoveAll(VehiclePredicate);
}
private static bool VehiclePredicate(Vehicle vehicle)
{
return vehicle.EnquiryID == 123;
}
This should work (where enquiryId
is the id you need to match against):
vehicles.RemoveAll(vehicle => vehicle.EnquiryID == enquiryId);
What this does is passes each vehicle in the list into the lambda predicate, evaluating the predicate. If the predicate returns true (ie. vehicle.EnquiryID == enquiryId
), then the current vehicle will be removed from the list.
If you know the types of the objects in your collections, then using the generic collections is a better approach. It avoids casting when retrieving objects from the collections, but can also avoid boxing if the items in the collection are value types (which can cause performance issues).