What is the use of Dispatcher Priority, DispatcherTimer, DispatcherFrame

Question

I have an Async DataGrid loading feature. Hence, i need to call WaitFor(). Here's that code:

WaitFor(TimeSpan.Zero, DispatcherPriority.SystemIdle);

And following are the 2 methods. Can someone explain what this methods are exactly doing?

public static void WaitFor(TimeSpan time, DispatcherPriority priority)
{
    DispatcherTimer timer = new DispatcherTimer(priority);
    timer.Tick += new EventHandler(OnDispatched);
    timer.Interval = time;
    DispatcherFrame dispatcherFrame = new DispatcherFrame(false);
    timer.Tag = dispatcherFrame;
    timer.Start();
    Dispatcher.PushFrame(dispatcherFrame);
}

public static void OnDispatched(object sender, EventArgs args)
{
    DispatcherTimer timer = (DispatcherTimer)sender;
    timer.Tick -= new EventHandler(OnDispatched);
    timer.Stop();
    DispatcherFrame frame = (DispatcherFrame)timer.Tag;
    frame.Continue = false;
}

dev hedgehog · Accepted Answer · 2014-02-04T09:32:39.260

1

You do not need any WaitFor(). Why waiting for something anyways? Just let the UI thread unfrozen and once data loaded the DataGrid will display them.

The methods you posted are doing the.... WaitFor mechanism. The method name explains it all :)

Here are few more details:

DispatcherTimer is a simple dumb Timer you might already know from basic C# just once tick method invoked it will be executed directly on UI thread, hence you do not need to care whether you are on UI thread or not. You always are :)

DispatcherTimer has a prority means if proprity set to high the tick invocation method will be called immediately after interval. If proprity is set to Background the tick method will be invoked when UI thread is not busy.

DispatcherFrame is the current scope you are in. Every displatcher operation has sort of scope. Each scope processes pending work items

Dispatcher.PushFrame is same as DoEvent() back when people used WinForms alot. To keep it simple with DoEvent you are forcing UI thread to do something.

To sum up you wait for things to get done in UI thread.

I hope this helps you any futher.

edited Feb 04 '14 at 09:32

answered Feb 04 '14 at 07:58

dev hedgehog

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Thanks a lot for ur suggestion. Just as of curiosity, I would like to know what is "timer.Tick += new EventHandler(OnDispatched) and timer.Tick -= new EventHandler(OnDispatched)" doing ? – surajitk Feb 04 '14 at 09:22
Are you new to C#? Those two commands subscribe and unsubscribe to a event called Tick? – dev hedgehog Feb 04 '14 at 09:25
Yaa Iam a newbie to C# . .I knew += subscribes to a event but was not sure about -= . Thanks a lot man!! – surajitk Feb 04 '14 at 09:29
You release unused resources when unsubscribing. That will allow garbage collector to collect the objects which are no more in use – dev hedgehog Feb 04 '14 at 09:31
C# is easy, just follow this rule. Everytime you forgot to unsubscribe handler you are one step closer to judgement day :) – dev hedgehog Feb 04 '14 at 09:35

What is the use of Dispatcher Priority, DispatcherTimer, DispatcherFrame

1 Answers1