AsyncDataRequest.cs source code in C# .NET

                        Code:
                         / 4.0 / 4.0 / untmp / DEVDIV_TFS / Dev10 / Releases / RTMRel / wpf / src / Framework / MS / Internal / Data / AsyncDataRequest.cs / 1305600 / AsyncDataRequest.cs
                        
                        
                            //---------------------------------------------------------------------------- 
//
// 
//    Copyright (C) Microsoft Corporation.  All rights reserved.
//  
//
// Description: Defines a request to the async data system. 
// 
// Specs:       http://avalon/connecteddata/M5%20Specs/Asynchronous%20Data%20Model.mht
// 
//---------------------------------------------------------------------------

using System;
 
namespace MS.Internal.Data
{ 
    ///  Type for the work and completion delegates of an AsyncDataRequest  
    internal delegate object AsyncRequestCallback(AsyncDataRequest request);
 
    ///  Status of an async data request. 
    internal enum AsyncRequestStatus
    {
        ///  Request has not been started  
        Waiting,
        ///  Request is in progress  
        Working, 
        ///  Request has been completed 
        Completed, 
        ///  Request was cancelled 
        Cancelled,
        ///  Request failed 
        Failed 
    }
 
    ///  A request to the async data system.  
    internal class AsyncDataRequest
    { 
        //-----------------------------------------------------
        //
        //  Constructors
        // 
        //-----------------------------------------------------
 
        ///  Constructor  
        internal AsyncDataRequest(  object bindingState,
                                    AsyncRequestCallback workCallback, 
                                    AsyncRequestCallback completedCallback,
                                    params object[] args
                                    )
        { 
            _bindingState = bindingState;
            _workCallback = workCallback; 
            _completedCallback = completedCallback; 
            _args = args;
        } 

        //------------------------------------------------------
        //
        //  Public Properties 
        //
        //----------------------------------------------------- 
 
        /* unused by default scheduler.  Restore for custom schedulers.
        ///  The "user data" from the binding that issued the request.  
        public object BindingState { get { return _bindingState; } }
        */

        ///  The result of the request (valid when request is completed).  
        public object Result { get { return _result; } }
 
        ///  The status of the request.  
        public AsyncRequestStatus Status { get { return _status; } }
 
        ///  The exception (for a failed request). 
        public Exception Exception { get { return _exception; } }

 
        //------------------------------------------------------
        // 
        //  Public Methods 
        //
        //------------------------------------------------------ 

        ///  Run the request's work delegate and return the result. 
        /// 
        /// This method should be called synchronously on a worker thread, as it 
        /// calls the work delegate, which potentially takes a long time.  The
        /// method sets the status to "Working".  It is normally followed by a 
        /// call to Complete. 
        ///
        /// If the request has already been run or has been abandoned, this method 
        /// returns null.
        /// 
        public object DoWork()
        { 
            if (DoBeginWork() && _workCallback != null)
                return _workCallback(this); 
            else 
                return null;
        } 


        /// If the request is in the "Waiting" state, return true and
        /// set its status to "Working".  Otherwise return false. 
        /// 
        ///  
        /// This method is thread-safe and works atomically.  Therefore only 
        /// one thread will be permitted to run the request.
        ///  
        public bool DoBeginWork()
        {
            return ChangeStatus(AsyncRequestStatus.Working);
        } 

 
        ///  Set the request's status to "Completed", save the result, 
        /// and call the completed delegate. 
        ///  
        /// This method should be called on any thread, after
        /// either calling DoWork or performing the work for a request in some
        /// other way.
        /// 
        /// If the request has already been run or has been abandoned, this method
        /// does nothing. 
        ///  
        public void Complete(object result)
        { 
            if (ChangeStatus(AsyncRequestStatus.Completed))
            {
                _result = result;
                if (_completedCallback != null) 
                    _completedCallback(this);
            } 
        } 

 
        ///  Cancel the request.
        ///  This method can be called from any thread.
        /// Calling Cancel does not actually terminate the work being
        /// done on behalf of the request, but merely causes the result 
        /// of that work to be ignored.
        ///  
        public void Cancel() 
        {
            ChangeStatus(AsyncRequestStatus.Cancelled); 
        }


        ///  Fail the request because of an exception. 
        ///  This method can be called from any thread. 
        public void Fail(Exception exception) 
        { 
            if (ChangeStatus(AsyncRequestStatus.Failed))
            { 
                _exception = exception;
                if (_completedCallback != null)
                    _completedCallback(this);
            } 
        }
 
 
        //-----------------------------------------------------
        // 
        //  Internal properties
        //
        //------------------------------------------------------
 
        ///  The caller-defined arguments. 
        internal object[] Args { get { return _args; } } 
 
        //-----------------------------------------------------
        // 
        //  Private methods
        //
        //-----------------------------------------------------
 
        // Change the status to the new status.  Return true if this is allowed.
        // Do it all atomically. 
        bool ChangeStatus(AsyncRequestStatus newStatus) 
        {
            bool allowChange = false; 

            lock(SyncRoot)
            {
                switch (newStatus) 
                {
                    case AsyncRequestStatus.Working: 
                        allowChange = (_status == AsyncRequestStatus.Waiting); 
                        break;
                    case AsyncRequestStatus.Completed: 
                        allowChange = (_status == AsyncRequestStatus.Working);
                        break;
                    case AsyncRequestStatus.Cancelled:
                        allowChange = (_status == AsyncRequestStatus.Waiting) || 
                                        (_status == AsyncRequestStatus.Working);
                        break; 
                    case AsyncRequestStatus.Failed: 
                        allowChange = (_status == AsyncRequestStatus.Working);
                        break; 
                }

                if (allowChange)
                    _status = newStatus;; 
            }
 
            return allowChange; 
        }
 
        //-----------------------------------------------------
        //
        //  Private data
        // 
        //------------------------------------------------------
 
        AsyncRequestStatus _status; 
        object _result;
        object _bindingState; 
        object[] _args;
        Exception _exception;

        AsyncRequestCallback _workCallback; 
        AsyncRequestCallback _completedCallback;
 
        object SyncRoot = new object();     // for synchronization 
    }
 

    ///  Async request to get the value of a property on an item. 
    internal class AsyncGetValueRequest : AsyncDataRequest
    { 
        //-----------------------------------------------------
        // 
        //  Constructors 
        //
        //------------------------------------------------------ 

        ///  Constructor. 
        internal AsyncGetValueRequest( object item,
                            string propertyName, 
                            object bindingState,
                            AsyncRequestCallback workCallback, 
                            AsyncRequestCallback completedCallback, 
                            params object[] args
                            ) 
            : base(bindingState, workCallback, completedCallback, args)
        {
            _item = item;
            _propertyName = propertyName; 
        }
 
        //------------------------------------------------------ 
        //
        //  Public Properties 
        //
        //-----------------------------------------------------

        ///  The item whose property is being requested  
        public object SourceItem { get { return _item; } }
 
        /* unused by default scheduler.  Restore for custom schedulers. 
        ///  The name of the property being requested 
        public string PropertyName { get { return _propertyName; } } 
        */

        //------------------------------------------------------
        // 
        //  Private data
        // 
        //----------------------------------------------------- 

        object _item; 
        string _propertyName;
    }

 
    ///  Async request to set the value of a property on an item. 
    internal class AsyncSetValueRequest : AsyncDataRequest 
    { 
        //-----------------------------------------------------
        // 
        //  Constructors
        //
        //-----------------------------------------------------
 
        ///  Constructor. 
        internal AsyncSetValueRequest( object item, 
                            string propertyName, 
                            object value,
                            object bindingState, 
                            AsyncRequestCallback workCallback,
                            AsyncRequestCallback completedCallback,
                            params object[] args
                            ) 
            : base(bindingState, workCallback, completedCallback, args)
        { 
            _item = item; 
            _propertyName = propertyName;
            _value = value; 
        }

        //------------------------------------------------------
        // 
        //  Public Properties
        // 
        //----------------------------------------------------- 

        ///  The item whose property is being set  
        public object TargetItem { get { return _item; } }

        /* unused by default scheduler.  Restore for custom schedulers.
        ///  The name of the property being set  
        public string PropertyName { get { return _propertyName; } }
        */ 
 
        ///  The new value for the property 
        public object Value { get { return _value; } } 

        //------------------------------------------------------
        //
        //  Private data 
        //
        //------------------------------------------------------ 
 
        object _item;
        string _propertyName; 
        object _value;
    }

} 


// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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AsyncDataRequest.cs source code in C# .NET

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