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Type.ContainsGenericParameters-Eigenschaft

 

Veröffentlicht: Oktober 2016

Ruft einen Wert ab, der angibt, ob das aktuelle Type-Objekt über Typparameter verfügt, die nicht durch bestimmte Typen ersetzt wurden.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

public virtual bool ContainsGenericParameters { get; }

Eigenschaftswert

Type: System.Boolean

true, wenn das Type-Objekt selbst ein generischer Parametertyp ist oder über Typparameter verfügt, für die keine bestimmten Typen angegeben wurden, andernfalls false.

In order to create an instance of a type, there must be no generic type definitions or open constructed types in the type arguments of the type itself, in any enclosing generic types, or in any elements of the type. Another way of saying this is that when examined recursively, the type must contain no generic type parameters.

Since types can be arbitrarily complex, making this determination is difficult. For convenience and to reduce the chance of error, the P:System.Type.ContainsGenericParameters property provides a standard way to distinguish between closed constructed types, which can be instantiated, and open constructed types, which cannot. If the P:System.Type.ContainsGenericParameters property returns true, the type cannot be instantiated.

The P:System.Type.ContainsGenericParameters property searches recursively for type parameters. For example, it returns true for an array whose elements are type A<T> (A(Of T) in Visual Basic), even though the array is not itself generic. Contrast this with the behavior of the P:System.Type.IsGenericType property, which returns false for arrays.

For a set of example classes and a table showing the values of the P:System.Type.ContainsGenericParameters property, see P:System.Type.IsGenericType.

The following example defines a generic class with two type parameters and then defines a second generic class that derives from the first class. The derived class's base class has two type arguments: the first is T:System.Int32 and the second is a type parameter of the derived type. The example displays information about these generic classes, including the positions reported by the P:System.Type.GenericParameterPosition property.

using System;
using System.Reflection;
using System.Collections.Generic;

// Define a base class with two type parameters.
public class Base<T, U> { }

// Define a derived class. The derived class inherits from a constructed
// class that meets the following criteria:
//   (1) Its generic type definition is Base<T, U>.
//   (2) It specifies int for the first type parameter.
//   (3) For the second type parameter, it uses the same type that is used
//       for the type parameter of the derived class.
// Thus, the derived class is a generic type with one type parameter, but
// its base class is an open constructed type with one type argument and
// one type parameter.
public class Derived<V> : Base<int, V> { }

public class Test
{
    public static void Main()
    {
        Console.WriteLine(
            "\r\n--- Display a generic type and the open constructed");
        Console.WriteLine("    type from which it is derived.");

        // Create a Type object representing the generic type definition 
        // for the Derived type, by omitting the type argument. (For
        // types with multiple type parameters, supply the commas but
        // omit the type arguments.) 
        //
        Type derivedType = typeof(Derived<>);
        DisplayGenericTypeInfo(derivedType);

        // Display its open constructed base type.
        DisplayGenericTypeInfo(derivedType.BaseType);
    }

    private static void DisplayGenericTypeInfo(Type t)
    {
        Console.WriteLine("\r\n{0}", t);

        Console.WriteLine("\tIs this a generic type definition? {0}", 
            t.IsGenericTypeDefinition);

        Console.WriteLine("\tIs it a generic type? {0}", 
            t.IsGenericType);

        Console.WriteLine("\tDoes it have unassigned generic parameters? {0}", 
            t.ContainsGenericParameters);

        if (t.IsGenericType)
        {
            // If this is a generic type, display the type arguments.
            //
            Type[] typeArguments = t.GetGenericArguments();

            Console.WriteLine("\tList type arguments ({0}):", 
                typeArguments.Length);

            foreach (Type tParam in typeArguments)
            {
                // IsGenericParameter is true only for generic type
                // parameters.
                //
                if (tParam.IsGenericParameter)
                {
                    Console.WriteLine(
                        "\t\t{0}  (unassigned - parameter position {1})",
                        tParam,
                        tParam.GenericParameterPosition);
                }
                else
                {
                    Console.WriteLine("\t\t{0}", tParam);
                }
            }
        }
    }
}

/* This example produces the following output:

--- Display a generic type and the open constructed
    type from which it is derived.

Derived`1[V]
        Is this a generic type definition? True
        Is it a generic type? True
        Does it have unassigned generic parameters? True
        List type arguments (1):
                V  (unassigned - parameter position 0)

Base`2[System.Int32,V]
        Is this a generic type definition? False
        Is it a generic type? True
        Does it have unassigned generic parameters? True
        List type arguments (2):
                System.Int32
                V  (unassigned - parameter position 0)
 */

.NET Framework
Verfügbar seit 2.0
Portierbare Klassenbibliothek
Unterstützt in: portierbare .NET-Plattformen
Silverlight
Verfügbar seit 2.0
Windows Phone Silverlight
Verfügbar seit 7.0
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