Update UI With WPF Dispatcher And TPL

13 Comments

Join the conversation! Your thoughts help the community grow.

manish singh6y ago
You can use CheckAccess before calling the disptacher.
- manish singh6y ago
  Public MainWindow() { InitializeComponent(); Task.Factory.StartNew(() => { var lb = label1 as Label; if (lb.Dispatcher.CheckAccess()) { label1.Content = "Updating by main thread"; } else { Dispatcher.BeginInvoke(new Action(() => { label1.Content = "Updating by worker thread"; })); } } ); }
Johnny Ancich7y ago
Such a shame this does not worth with winforms.
Helvetier1 Helvetier18y ago
Thanks man! This was a really good one.
vivek sharma8y ago
Thanks a lot... brother, u really saved me.. this works like a charm..
- Former member8y ago
  Great to hear... always.
ashok rathod10y ago
Good one
Former member10y ago
Thanks
Sibeesh Venu10y ago
Nice Share
Raja T10y ago
Good.Thanks for sharing
Mohammed Ibrahim10y ago
nice
Former member10y ago
Thanks
Santhakumar Munuswamy10y ago
Thanks for nice article

Introduction

WPF application works on the principle of Thread affinity which means other threads can't interact with each other. This is called Single threaded apartment model. Sometimes developers need to manage the thread or update WPF UI. But, WPF objects run on the principle of thread affinity that derives from the Dispatcher object.

So, if developers create their own thread and try to update WPF UI then thread affinity principles stops them by using the method "VerifyAccess()" of DispatcherObject class. It will throw an exception “InvalidOperationException”.

So, I will explain one code example by using "Dispatcher" and "TPL" by which you can update WPF UI. Below is the WPF code example

.XAML File:

<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<StackPanel>
<Label Name="myLabel"></Label>
</StackPanel>
</Window>

Here, I took one label - <Label Name="myLabel"></Label>

Go to code behind or .XAML.cs file:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Threading;
namespace WpfApplication1
{
/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
var mySource = Enumerable.Range(1, 1000).ToList();
Task.Factory.StartNew(() => CalculateMyOperation(mySource));
}
private void CalculateMyOperation(List<int> values)
{
foreach (var i in values)
{
var currentProgress = i;
Dispatcher.BeginInvoke(new Action(() =>
{
myLabel.Content = "Updating..." + currentProgress;
}), DispatcherPriority.Background);
}
}
}
}

Output:

Updating... 1

Updating ...2

Updating....3

...................

Updating...100

Here, I have used method "BeginInvoke" with Dispatcher because "Dispatcher.BeginInvoke" schedules the given action for execution in the UI thread and then returns control to allow the current thread to continue executing.

But, Invoke method blocks the caller until the scheduled action is completed.

The priority of dispatcher describes the priority at which the operation can be invoked. Here, I used DispatcherPriority.Background as a dispatccher priorty. The Priority "Background" explains that I will start my operation after all other non-idle operations are complete.

I defined UI updating operations inside action delegate "new Action(() =>".

Note: Please find attached code for reference.

Related Link: Threads in WPF

Conclusion

Dispatcher is an important technique or concept to run an operation that will be executed on the UI thread. It updates the UI.

Introduction

Note: Please find attached code for reference. Related Link: Threads in WPF

Conclusion

Note: Please find attached code for reference.

Related Link: Threads in WPF