Friday, 9 October 2015

Switchbased delay with Dispatcher in WPF

Extended my DispatcherUtil class today, with SwitchBasedDelay! Example of calling the new method, note we use a fixed Guid in this case to "group" calls into a logical switch:

 DispatcherUtil.SwitchbasedDelayedInvokeAction(Guid.Parse(@"{4E101F98-31F3-4E19-B18B-2820AEA60A1B}"), () =>
     {
      PublishEvent<ProcedureFreeTypeTextChangedEvent, ProcedureFreeTypeTextChangedEventArg>(
       new ProcedureFreeTypeTextChangedEventArg
        {
          FreshId = Context.CurrentOperationalUnit.FreshId,
          ProcedureCode = Model.ProcedureTypeFreeText,
          OperationId = Model.OperationId
        });
      }, 2000);


using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Windows.Threading;

namespace SomeAcme.SomePackage
{

    /// <summary>
    /// Contains helper methods for dispatcher operations 
    /// </summary>
    public static class DispatcherUtil
    {

        private static readonly List<DelayedAction> ActionsRegistered = new List<DelayedAction>();

        private static readonly Dictionary<Guid?, bool> SwitchDelays = new Dictionary<Guid?, bool>();

        /// <summary>
        /// Executes an action passed into this method by a timeout measured in millisecond in a switch-based manner. 
        /// </summary>
        /// <param name="keyToken">A key token (Guid) to identity the switch (basic grouping)</param>
        /// <param name="executeAction">Action to execute</param>
        /// <param name="timeOut">The timeout to wait before executing (in milliseconds)</param>
        /// <param name="priority">Priority of the dispatcher operation</param>
        /// <returns></returns>
        public static bool SwitchbasedDelayedInvokeAction(Guid keyToken, Action executeAction, int timeOut,
            DispatcherPriority priority = DispatcherPriority.Background)
        {
            if (SwitchDelays.ContainsKey(keyToken) && SwitchDelays[keyToken])
                return false; //do not execute, already in progress 

            SwitchDelays[keyToken] = true;

            DelayedInvokeAction(executeAction, timeOut, priority, keyToken);
            return true; //delayed action sent off
        }

        /// <summary>
        /// Executes an action passed into this method by a timeout measured in milliseconds
        /// </summary>
        /// <param name="executeAction">Action to execute</param>
        /// <param name="timeOut">The timeout to wait before executing (in milliseconds)</param>
        /// <param name="priority"></param>
        ///    /// <param name="keyToken">A key token to identity the switch (basic grouing). Will be used as a tag on the DispatcherTimer</param>
        public static bool DelayedInvokeAction(Action executeAction, int timeOut, DispatcherPriority priority = DispatcherPriority.Background, Guid? keyToken = null)
        {
            var delayedAction = new DelayedAction(executeAction, timeOut, keyToken);
            ActionsRegistered.Add(delayedAction);
            DispatcherTimer dtimer = new DispatcherTimer(priority);

            dtimer.Interval += new TimeSpan(0, 0, 0, 0, timeOut);
            dtimer.Tag = delayedAction.ExecuteGuid;
            dtimer.Tick += DelayedInvokeTimerTick;
            dtimer.IsEnabled = true;
            dtimer.Start();

            return true;
        }

        private static void DelayedInvokeTimerTick(object sender, EventArgs e)
        {
            var dtimer = sender as DispatcherTimer;
            if (dtimer != null)
            {
                dtimer.IsEnabled = false;
                dtimer.Stop();
                dtimer.Tick -= DelayedInvokeTimerTick; //unsubscribe
                Guid targetActionGuid = (Guid)dtimer.Tag;

                DelayedAction delayedAction = ActionsRegistered.Single(a => a.ExecuteGuid == targetActionGuid);
                delayedAction.ActionToExecute(); //now execute the action 
                ActionsRegistered.Remove(delayedAction);

                if (dtimer.Tag != null)
                {
                    Guid? keyToken = dtimer.Tag as Guid?; 
                    if (SwitchDelays.ContainsKey(keyToken))
                    {
                        SwitchDelays.Remove(keyToken); //remove the switch 
                    } //if 
                } //if 

                // ReSharper disable once RedundantAssignment
                dtimer = null; //ensure free up dispatcher timer - do not starve threading resources 
            } //if 
        }

        /// <summary>
        /// Invokes an action on the current dispatcher, used to execute operations on the GUI thread
        /// </summary>
        /// <param name="executeAction">The action to execute, pass in e.g. delegate { --code lines goes here } </param>
        /// <param name="dispatcherPriority">The priority to give the action on the thread (signal to the WPF messaging queue). Default is background.</param>
        /// <returns>Returns true when the action was dispatched</returns>
        /// <remarks>Default priority is DispatcherPriority.Background</remarks>
        public static bool InvokeAction(Action executeAction, DispatcherPriority dispatcherPriority = DispatcherPriority.Background)
        {
            Dispatcher.CurrentDispatcher.Invoke(new Action(() =>
            {
                executeAction();
            }), dispatcherPriority);
            return true;
        }

        /// <summary>
        /// Asynchronously invokes an action on the current dispatcher, used to execute operations on the GUI thread
        /// </summary>
        /// <param name="executeAction">The action to execute, pass in e.g. delegate { --code lines goes here } </param>
        /// <param name="dispatcherPriority">The priority to give the action on the thread (signal to the WPF messaging queue). Default is background.</param>
        /// <returns>Returns true when the action was dispatched</returns>
        /// <remarks>Default priority is DispatcherPriority.Background</remarks>
        public static bool BeginInvokeAction(Action executeAction, DispatcherPriority dispatcherPriority = DispatcherPriority.Background)
        {
            Dispatcher.CurrentDispatcher.BeginInvoke(new Action(() =>
            {
                executeAction();
            }), dispatcherPriority);
            return true;
        }

        public static void AsyncWorkAndUiThreadUpdate<T>(Dispatcher currentDispatcher, Func<T> threadWork, Action<T> guiUpdate)
        {
            // ReSharper disable once UnusedAnonymousMethodSignature
            ThreadPool.QueueUserWorkItem(delegate(object state)
            {
                T resultAfterThreadWork = threadWork();
                // ReSharper disable once UnusedAnonymousMethodSignature
                // ReSharper disable once UnusedAnonymousMethodSignature
                currentDispatcher.BeginInvoke(DispatcherPriority.Normal, new Action<T>(delegate {
                    guiUpdate(resultAfterThreadWork);
                }), resultAfterThreadWork);

            });
        }

    }
}



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