Represents the method that defines a set of criteria and determines whether the specified object meets those criteria.
Assembly: mscorlib (in mscorlib.dll)
- in T
The type of the object to compare.
This type parameter is contravariant. That is, you can use either the type you specified or any type that is less derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.
The object to compare against the criteria defined within the method represented by this delegate.
Return ValueType: System.Boolean
true if obj meets the criteria defined within the method represented by this delegate; otherwise, false.
Typically, the delegate is represented by a lambda expression. Because locally scoped variables are available to the lambda expression, it is easy to test for a condition that is not precisely known at compile time. This is simulated in the following example, which defines a HockeyTeam class that contains information about a National Hockey League team and the year in which it was founded. The example defines an array of integer values that represent years, and randomly assigns one element of the array to foundedBeforeYear, which is a variable that is locally scoped to the example's Main method. Because locally scoped variables are available to a lambda expression, the lambda expression passed to the List(T).FindAll method is able to return a HockeyTeam object for each team founded on or before that year.
The following code example uses a delegate with the Array.Find(T) method to search an array of Point structures. The example explicitly defines a delegate named predicate and assigns it a method named FindPoints that returns true if the product of the Point.X and Point.Y fields is greater than 100,000. Note that it is customary to use a lambda expression rather than to explicitly define a delegate of type , as the second example illustrates.
The following example is identical to the previous example, except that it uses a lambda expression to represent the delegate. Each element of the points array is passed to the lambda expression until the expression finds an element that meets the search criteria. In this case, the lambda expression returns true if the product of the X and Y fields is greater than 100,000.