CodeAccessPermission.IsSubsetOf(IPermission) Method

Definition

Namespace:

System.Security

Assembly:

System.Security.Permissions.dll

Source:

CodeAccessPermission.cs

When implemented by a derived class, determines whether the current permission is a subset of the specified permission.

C#

public abstract bool IsSubsetOf(System.Security.IPermission target);

Parameters

target

IPermission

A permission that is to be tested for the subset relationship. This permission must be of the same type as the current permission.

Returns

Boolean

true if the current permission is a subset of the specified permission; otherwise, false.

Implements

IsSubsetOf(IPermission)

Exceptions

ArgumentException

The target parameter is not null and is not of the same type as the current permission.

Examples

The following code example shows an override of the IsSubsetOf method. This code example is part of a larger example provided for the CodeAccessPermission class.

C#

        public override bool IsSubsetOf(IPermission target)
        {
#if(debug)
            Console.WriteLine ("************* Entering IsSubsetOf *********************");
#endif
            if (target == null)
            {
                Console.WriteLine ("IsSubsetOf: target == null");
                return false;
            }
#if(debug)

            Console.WriteLine ("This is = " + (( NameIdPermission)this).Name);
            Console.WriteLine ("Target is " + (( NameIdPermission)target).m_Name);
#endif
            try
            {
                 NameIdPermission operand = ( NameIdPermission)target;

                // The following check for unrestricted permission is only included as an example for
                // permissions that allow the unrestricted state. It is of no value for this permission.
                if (true == operand.m_Unrestricted)
                {
                    return true;
                }
                else if (true == this.m_Unrestricted)
                {
                    return false;
                }

                if (this.m_Name != null)
                {
                    if (operand.m_Name == null) return false;

                    if (this.m_Name == "") return true;
                }

                if (this.m_Name.Equals (operand.m_Name))
                {
                    return true;
                }
                else
                {
                    // Check for wild card character '*'.
                    int i = operand.m_Name.LastIndexOf ("*");

                    if (i > 0)
                    {
                        string prefix = operand.m_Name.Substring (0, i);

                        if (this.m_Name.StartsWith (prefix))
                        {
                            return true;
                        }
                    }
                }

                return false;
            }
            catch (InvalidCastException)
            {
                throw new ArgumentException (String.Format ("Argument_WrongType", this.GetType ().FullName));
            }
        }

Remarks

The current permission is a subset of the specified permission if the current permission specifies a set of operations that is wholly contained by the specified permission. For example, a permission that represents access to C:\example.txt is a subset of a permission that represents access to C:\. If this method returns true, the current permission represents no more access to the protected resource than does the specified permission.

The following statements are required to be true for all overrides of the IsSubsetOf method. X, Y, and Z represent custom code access permission objects that are not null references, U represents an unrestricted code access permission, and N represents an empty permission with a PermissionState of None.

• X.IsSubsetOf(X) returns true.

• X.IsSubsetOf(Y) returns the same value as Y.IsSubsetOf(X) if and only if X and Y represent the same set of permissions.

• If X.IsSubsetOf(Y) and Y.IsSubsetOf(Z) both return true, X.IsSubsetOf(Z) returns true.

• X.IsSubsetOf(U) returns true.

• X.IsSubsetOf(N) returns false.

• N.IsSubsetOf(X) returns true.

If X and Y represent custom code access permission objects that are null references, X.IsSubsetOf(Y) returns true. If Z is also null, the compound set operation X.Union(Y).IsSubsetOf(Z) also returns true because the union of two null permissions is a null permission.

Notes to Implementers

You must override this method in a derived class.

Applies to