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IPermission Interface

Defines methods implemented by permission types.

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

[ComVisibleAttribute(true)]
public interface class IPermission : ISecurityEncodable

Permissions in the common language runtime are objects that describe sets of operations that can be secured for specified resources. A permission object describes operations or access that is subject to security control; it does not represent access or a right to perform operations. Permissions are used by both application code and the .NET Framework security system in the following ways.

  • Code requests the permissions it needs in order to run.

  • The security system policy grants permissions to code in order for it to run.

  • Code demands that calling code has a permission.

  • Code overrides the security stack using assert/deny/permit-only.

NoteNote:

If you write a new permission, you must implement this interface in your class.

Important noteImportant Note:

A permission can be accessed by multiple threads. When implementing this interface, you must guarantee that the IsSubsetOf, Intersect, Union, and Copy method implementations are thread safe.

This example shows how to define a permission class for use with code access security. All of the necessary permission interfaces are implemented.

using namespace System;
using namespace System::Security;
using namespace System::Security::Permissions;
using namespace System::Reflection;

// Enumerated type for permission states.
[Serializable]
public enum class SoundPermissionState
{
    NoSound = 0,
    PlaySystemSounds = 1,
    PlayAnySound = 2
};

// Derive from CodeAccessPermission to gain implementations of the following 
// sealed IStackWalk methods: Assert, Demand, Deny, and PermitOnly. 
// Implement the following abstract IPermission methods:  
// Copy, Intersect, and IsSubSetOf. 
// Implementing the Union method of the IPermission class is optional. 
// Implement the following abstract ISecurityEncodable methods:  
// FromXml and ToXml. 
// Making the class 'sealed' is optional. 

public ref class SoundPermission sealed : public CodeAccessPermission, 
    public IPermission, public IUnrestrictedPermission, 
    public ISecurityEncodable, public ICloneable
{
private:
    bool specifiedAsUnrestricted;
private:
    SoundPermissionState stateFlags;

    // This constructor creates and initializes  
    // a permission with generic access. 
public:
    SoundPermission(PermissionState^ state)
    {
        specifiedAsUnrestricted = (state == PermissionState::Unrestricted);
    }

    // This constructor creates and initializes  
    // a permission with specific access. 
public:
    SoundPermission(SoundPermissionState flags)
    {
        if (flags < SoundPermissionState::NoSound ||
            flags > SoundPermissionState::PlayAnySound)
        {
            throw gcnew ArgumentException("The value of \"flags\" is not" +
                " valid for the SoundPermissionState enumerated type");
        }
        stateFlags = flags;
    }

    // For debugging, return the state of this object as XML. 
public:
    virtual String^ ToString() override
    {
        return ToXml()->ToString();
    }

    // Private method to cast (if possible) an IPermission to the type. 
private:
    SoundPermission^ VerifyTypeMatch(IPermission^ target)
    {
        if (GetType() != target->GetType())
        {
            throw gcnew ArgumentException(String::Format(
                "The variable \"target\" must be of the {0} type",
                GetType()->FullName));
        }
        return (SoundPermission^) target;
    }

    // This is the Private Clone helper method. 
private:
    SoundPermission^ Clone(bool specifiedAsUnrestricted, 
        SoundPermissionState flags)
    {
        SoundPermission^ soundPerm = (SoundPermission^) Clone();
        soundPerm->specifiedAsUnrestricted = specifiedAsUnrestricted;
        soundPerm->stateFlags = specifiedAsUnrestricted ? 
            SoundPermissionState::PlayAnySound : flags;
        return soundPerm;
    }

    #pragma region IPermission^ Members
    // Return a new object that contains the intersection  
    // of 'this' and 'target'. 
public:
    virtual IPermission^ Intersect(IPermission^ target) override
    {
        // If 'target' is null, return null. 
        if (target == nullptr)
        {
            return nullptr;
        }

        // Both objects must be the same type.
        SoundPermission^ soundPerm = VerifyTypeMatch(target);

        // If 'this' and 'target' are unrestricted,  
        // return a new unrestricted permission. 
        if (specifiedAsUnrestricted && soundPerm->specifiedAsUnrestricted)
        {
            return Clone(true, SoundPermissionState::PlayAnySound);
        }

        // Calculate the intersected permissions.  
        // If there are none, return null.
        SoundPermissionState minimumPermission = (SoundPermissionState)
            Math::Min((int) stateFlags, (int) soundPerm->stateFlags);
        if ((int)minimumPermission == 0)
        {
            return nullptr;
        }

        // Return a new object with the intersected permission value. 
        return Clone(false, minimumPermission);
    }

    // Called by the Demand method: returns true  
    // if 'this' is a subset of 'target'. 
public:
    virtual bool IsSubsetOf(IPermission^ target) override
    {
        // If 'target' is null and this permission allows nothing,  
        // return true. 
        if (target == nullptr)
        {
            return (int)stateFlags == 0;
        }

        // Both objects must be the same type.
        SoundPermission^ soundPerm = VerifyTypeMatch(target);

        // Return true if the permissions of 'this'  
        // is a subset of 'target'. 
        return stateFlags <= soundPerm->stateFlags;
    }

    // Return a new object that matches 'this' object's permissions. 
public:
    virtual IPermission^ Copy () override sealed
    {
        return (IPermission^) Clone();
    }

    // Return a new object that contains the union of 'this' and 'target'. 
    // Note: You do not have to implement this method.  
    // If you do not, the version 
    // in CodeAccessPermission does this: 
    //    1. If target is not null, a NotSupportedException is thrown. 
    //    2. If target is null, then Copy is called and  
    //       the new object is returned. 
public:
    virtual IPermission^ Union(IPermission^ target) override
    {
        // If 'target' is null, then return a copy of 'this'. 
        if (target == nullptr)
        {
            return Copy();
        }

        // Both objects must be the same type.
        SoundPermission^ soundPerm = VerifyTypeMatch(target);

        // If 'this' or 'target' are unrestricted,  
        // return a new unrestricted permission. 
        if (specifiedAsUnrestricted || soundPerm->specifiedAsUnrestricted)
        {
            return Clone(true, SoundPermissionState::PlayAnySound);
        }

        // Return a new object with the calculated, unioned permission value. 
        return Clone(false, (SoundPermissionState)
            Math::Max((int) stateFlags, (int) soundPerm->stateFlags));
    }
    #pragma endregion

    #pragma region ISecurityEncodable^ Members
    // Populate the permission's fields from XML. 
public:
    virtual void FromXml(SecurityElement^ element) override
    {
        specifiedAsUnrestricted = false;
        stateFlags = (SoundPermissionState)0;

        // If XML indicates an unrestricted permission,  
        // make this permission unrestricted.
        String^ attributeString = 
            (String^) element->Attributes["Unrestricted"];
        if (attributeString != nullptr)
        {
            specifiedAsUnrestricted = Convert::ToBoolean(attributeString);
            if (specifiedAsUnrestricted)
            {
                stateFlags = SoundPermissionState::PlayAnySound;
            }
        }

        // If XML indicates a restricted permission, parse the flags. 
        if (!specifiedAsUnrestricted)
        {
            attributeString = (String^) element->Attributes["Flags"];
            if (attributeString != nullptr)
            {
                stateFlags = (SoundPermissionState) Convert::ToInt32(
                    Enum::Parse(SoundPermissionState::typeid, 
                    attributeString, true));
            }
        }
    }

    // Produce XML from the permission's fields. 
public:
    virtual SecurityElement^ ToXml() override
    {
        // These first three lines create an element with the required format.
        SecurityElement^ element = gcnew SecurityElement("IPermission");
        // Replace the double quotation marks ()  
        // with single quotation marks () 
        // to remain XML compliant when the culture is not neutral.
        element->AddAttribute("class", 
            GetType()->AssemblyQualifiedName->Replace('\"', '\''));
        element->AddAttribute("version", "1");

        if (!specifiedAsUnrestricted)
        {
            element->AddAttribute("Flags", 
                Enum::Format(SoundPermissionState::typeid, stateFlags, "G"));
        }   
        else
        {
            element->AddAttribute("Unrestricted", "true");
        }
        return element;
    }
    #pragma endregion

    #pragma region IUnrestrictedPermission^ Members
    // Returns true if permission is effectively unrestricted. 
public:
    virtual bool IsUnrestricted()
    {
        // This means that the object is unrestricted at runtime. 
        return stateFlags == SoundPermissionState::PlayAnySound;
    }
    #pragma endregion

    #pragma region ICloneable^ Members

    // Return a copy of the permission. 
public:
    virtual Object^ Clone()
    {
        return MemberwiseClone();
    }

    #pragma endregion
};

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

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