Array.FindIndex(T) Method (T, Predicate(T))
Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the first occurrence within the entire Array.
Assembly: mscorlib (in mscorlib.dll)
The type of the elements of the array.
- Type: 
The one-dimensional, zero-based Array to search.
Return ValueType: System.Int32
The zero-based index of the first occurrence of an element that matches the conditions defined by match, if found; otherwise, –1.
array is a null reference (Nothing in Visual Basic).
match is a null reference (Nothing in Visual Basic).
The Array is searched forward starting at the first element and ending at the last element.
The Predicate(T) is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. The elements of array are individually passed to the Predicate(T).
This method is an O(n) operation, where n is the Length of array.
The following code example demonstrates all three overloads of the FindIndex generic method. An array of strings is created, containing 8 dinosaur names, two of which (at positions 1 and 5) end with "saurus". The code example also defines a search predicate method named EndsWithSaurus, which accepts a string parameter and returns a Boolean value indicating whether the input string ends in "saurus".
The method overload traverses the array from the beginning, passing each element in turn to the EndsWithSaurus method. The search stops when the EndsWithSaurus method returns true for the element at position 1.
In C# and Visual Basic, it is not necessary to create the Predicate<string> delegate (Predicate(Of String) in Visual Basic) explicitly. These languages infer the correct delegate from context and create it automatically.
The FindIndex(T)(T, Int32, Predicate(T)) method overload is used to search the array beginning at position 2 and continuing to the end of the array. It finds the element at position 5. Finally, the FindIndex(T)(T, Int32, Int32, Predicate(T)) method overload is used to search the range of three elements beginning at position 2. It returns –1 because there are no dinosaur names in that range that end with "saurus".