WPF XAML demo

This page gives a Dyalog APL demonstratration of WPF XAMPL with some utility functions, delivered in the form of a namespace.

Please read the Dyalog tutorials for a more detailed explanation. Part of the code was taken from CodeProject: A Beginner's Guide.

What is XAML?

XAML stands for Extensible Application Markup Language (and pronounced "Zammel"). It's a simple language based on wikipedia:XML to create and initialize .NET objects with hierarchical relations.

All you can do in XAML can also be done in code. XAML is just another way to create and initialize objects.

You can use WPF without using XAML. It's up to you whether you want to declare it in XAML or write it as code. There is a XAML Overview from Microsoft.

Here is an example of XAML found in the attached namespace called sample1:

<Window
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   Height="200"
   Width="250"
   Title="MainWindow"
   WindowStartupLocation="CenterScreen">
   <Grid>
      <Grid.RowDefinitions>
         <RowDefinition Height="0.5*"/>
         <RowDefinition Height="0.5*"/>
      </Grid.RowDefinitions>
      <TextBox
         x:Name="textBox1"
         Width="130"
         HorizontalAlignment="Center"
         VerticalAlignment="Center"
         Text="TextBox"
         TextAlignment="Center"/>
      <Button
         x:Name="button1"
         Height="40"
         Width="120"
         Grid.Row="1"
         HorizontalAlignment="Center"
         VerticalAlignment="Center"
         Content="Click Me !"/>
   </Grid>
</Window>

FixSimpleXaml

If you install the attached namespace and execute the following 2 lines in your workspace:

      win ← FixSimpleXaml sample1
      win.Show

The following window is displayed:

FixSimpleXaml is a function used to execute the XAML and return the root element as a .Net object. All the other elements that are named in the XAML will be attached to their names to the root object automatically.

For example, the element !TextBox that is named textBox1 (line 15) and the element Button that is named button1 (line 22) are attached automatically to the root element by the function FixSimpleXaml:

      win.textBox1.Text
Textbox
      win.button1
System.Windows.Controls.Button: Click Me !

That way you don't need to define a separate variable for each named element. If you install the user command called sfPropGrid you can see all the properties, methods and events of all the named objects by doing (click the combo of NOE to access all the named objects):

      ]noe win       ⍝ noe = .Net Object Explorer

In conclusion FixSimpleXaml is a simple function to use on simple XAML that does not have events and is properly formed. In production code you may want to do something like this:

 :If ⎕NULL≡myObject ← FixSimpleXaml myXaml
    ⍝ Fixing the XAML did not work. Show an error and exit.
     ⎕ ← 'Error Fixing XAML'
     →0
 :Else
    ⍝ There is no error.
 :EndIf

FixXaml

For cases where there are events that need to be fixed and have better error handling the function FixXaml is available. It is useful when using XAML taken directly from Visual Studio. For example, with the XAML code in sample2 that has an event on the button (Click="__Button_Click") at line 24, if you do the following:

<Window
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   x:Class="WpfApplication3.MainWindow"
   Height="200"
   Width="250"
   Title="MainWindow"
   WindowStartupLocation="CenterScreen">
   <Grid>
      <Grid.RowDefinitions>
         <RowDefinition Height="0.5*"/>
         <RowDefinition Height="0.5*"/>
      </Grid.RowDefinitions>
      <TextBox
         x:Name="textBox1"
         Width="130"
         HorizontalAlignment="Center"
         VerticalAlignment="Center"
         Text="TextBox"
         TextAlignment="Center"/>
      <Button
         x:Name="button1"
         Click="__Button_Click"
         Height="40"
         Width="120"
         Grid.Row="1"
         HorizontalAlignment="Center"
         VerticalAlignment="Center"
         Content="Click Me !"/>
   </Grid>
</Window>

      win ← FixXaml sample2
      win.Show

and then if you click on the button, the value of the !TextBox will change. The value of the !TextBox can be retrieved simply by doing:

      win.textBox1.Text
I Was Clicked !

The function __Button_Click is handling the event. The author has taken the convention of naming the callback functions with a double underscore prefix.

The goal is to be able to take the XAML directly from Visual Studio to APL. The single underscore '_' is a valid first character in Visual Studio and APL but is in conflict with the menu object that will accept an underscore as the first character to define a keyboard shortcut.

The line 5 of sample2 (x:Class="!WpfApplication3.!MainWindow") that is required by Visual Studio is removed by FixXaml. See the comments in the function for more information.

In production code you may want to trap any error by using code like this:

 :If ⎕NULL≡↑myObject ← FixXaml myXaml
    ⍝ Fixing the XAML did not work. Show an error and exit.
     ⎕ ← 2⊃myObject
     →0
 :Else
    ⍝ There is no error.
 :EndIf

About ⎕USING

In general, when using XAML there is no need to define a ⎕USING before fixing it except when there is a 3rd party dll involved. For example, the variable NewWindow is defined as:

<Window
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
</Window>

and if you do:

      win ← FixSimpleXaml NewWindow
      win.Show

a Window will appear. In procedural code, the following is required for the same result:

      ⎕USING←'System.Windows,WPF/PresentationFramework.dll'
      win ← ⎕NEW Window
      win.Show

The first element of XAML must contain the xmlns= and the xmlns:x= declarations. This is instructing the parser (in our case System.Windows.Markup.!XamlReader in the function FixSimpleXaml and FixXaml) to load a series of .NET namespaces required to parse the XAML. This is just a convention, there is actually no such web site.

3rd Party Dll

When using 3rd party dll, they must be added to the declaration in the first element of XAML. There are 2 choices on how to do it:

   xmlns:myname="clr‑namespace:MyNamespace;assembly=MyDllName"  ⍝ Notice that there is no '.dll' after MyDllName
or
   xmlns:myname="http://schemas.somewebsite.com/xaml"           ⍝ A website name given by the 3rd party dll (may not exists)

The method on the first line is recommended. Here is an example with the Syncfusion !PropertyGrid:

   xmlns:sf="clr-namespace:Syncfusion.Windows.PropertyGrid;assembly=Syncfusion.PropertyGrid.Wpf"  ⍝ Notice no .dll at the end

and the XAML will look like this:

   <sf:PropertyGrid x:Name="PGrid"/>  ⍝ Notice the prefix 'sf' is the same on both lines (you choose the prefix).

but this is not enough, ⎕USING must be set up correctly before fixing the XAML for 3rd party dlls in order for the parser to find the assembly. Here is an example for the Syncfusion !PropertyGrid (Syncfusion/4.5/ is the Dyalog sub-directory where the assemblies live):

     ⎕USING ← 'Syncfusion.Windows.PropertyGrid,Syncfusion/4.5/Syncfusion.PropertyGrid.Wpf.dll'    ⍝ The .dll is required

or more general

     ⎕USING ← 'MyNamespace,FullPathOfAssembly/MyDllName.dll'          ⍝ If the dll is outside of the dyalog.exe folder
     ⎕USING ← 'MyNamespace,SubDirectoryOfDyalogFolder/MyDllName.dll'  ⍝ If the dll is in a sub-directory of dyalog.exe
     ⎕USING ← 'MyNamespace,MyDllName.dll'                             ⍝ If the dll is in the same directory as dyalog.exe

Another thing with the value of ⎕USING for 3rd party dll is that it must be set in the __same namespace__ as where FixXaml or FixSimpleXaml is located (because ⎕USING is Namespace scope). Alternatively, if you setup your dyalog.exe.config file that is in the same directory as the dyalog.exe file with a directive to look in the Syncfusion/4.5 directory you will not need to set up ⎕USING and you don't need to worry about loading it into memory.

Typically the file will look like this:

    <configuration>
       <startup useLegacyV2RuntimeActivationPolicy="true">
          <supportedRuntime version="v4.0">
          </supportedRuntime>
       </startup>
       <runtime>
          <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
             <probing privatePath="MJHSoftware;Syncfusion/4.5">
             </probing>
          </assemblyBinding>
          <!-- <NetFx40_LegacySecurityPolicy enabled="true"/> -->
          <loadFromRemoteSources enabled="true"/>
       </runtime>
    </configuration>

When using procedural code instead of XAML you may want to define a one time ⎕USING like this:

      ⎕USING←Using

A typical definition of the function Using is like this (contributed by Dyalog and Michael J. Hughes):

 use←Using
 ⍝ Full ⎕Using used by system.

 use←'' 'System,System.dll'
 use,←⊂'System.Windows,WPF/PresentationFramework.dll'
 use,←⊂'System.Windows,WPF/PresentationCore.dll'
 use,←⊂'System.Windows.Input,WPF/PresentationCore.dll'
 use,←⊂'System.Windows.Shapes'
 use,←⊂'System.Windows.MessageBox'
 use,←⊂'Microsoft.Win32,WPF/PresentationFramework.dll'
 use,←⊂'System.Windows.Controls'
 use,←⊂'System.Windows.Markup'
 use,←⊂'System.Windows.Navigation'
 use,←⊂'System.Windows.Media'
 use,←⊂'System.Windows.Media.Imaging'
 use,←⊂'System.Windows.Documents'
 use,←⊂'System.Drawing.Bitmap'
 use,←⊂'System.Windows.Controls.Primitives'
 use,←⊂'System.Windows.Data'
 use,←⊂'System.Data,system.data.dll'
 use,←⊂'System.Xml,system.xml.dll'
 use,←⊂'System.Windows.Automation.Peers'
 use,←⊂'System.Windows.Automation.Provider,WPF/UIAutomationProvider.dll'
 use,←⊂'System.Windows,WPF/WindowsBase.dll'
 use,←⊂'System.ComponentModel,System.dll'
 use,←⊂'System.Windows.Media.Animation,WPF/PresentationFramework.dll'
 use,←⊂'System.Windows.Media.Animation,WPF/PresentationCore.dll'
 use,←⊂'System.Printing,WPF/ReachFramework.dll'
 use,←⊂'System.Windows.Threading'
 use,←⊂'System.Threading'
 use,←⊂'System.IO'
 use,←⊂'System.Windows.SystemParameters'
 use,←⊂'System.Collections'
 use,←⊂'System.Collections.Generic'
 use,←⊂'System.Collections.ObjectModel'
 use,←⊂'System.Objects'
 use,←⊂'System.Globalization'

To add a new definition to an existing ⎕USING and to prevent duplicate entries the 'Union' operator is used like this:

      ⎕USING∪←⊂'System.Windows.Controls,PresentationFramework.dll'

Fixing Images

In XAML you declare an Image object that is on disk the following way:

<Image x:Name="MyImageName"
       Source="PathOfMyImage\MyImage.png"   ⍝ PathOfMyImage can be tricky to declare sometimes and is not discussed here.
       Width="24"
       Height="24"/>

When you want to keep the Image definition in the APL workspace (because it is easier that way to distribute the workspace or the namespace) one way of doing it is by keeping a Base64 definition of the Image. Base64 encoding is using a set of 64 visible characters to encode binary data.

It is widely used on the internet, for example in emails for images and binary attachments.

Here are the steps to use this technique with APL:

Step 1: Save all the images in the workspace with the function FileToBase64String

At design time, save the images in the workspace. The APL variable name of any image must be the original name of the image name in the XAML with the added suffix _b64 (naming convention only).

      Paste_b64 ← FileToBase64String 'D:\Paste.png'
      Copy_b64  ← FileToBase64String 'D:\Copy.png'
      Cut_b64   ← FileToBase64String 'D:\Cut.png'

The variable Copy_b64 in the attached namespace looks like this:

      Copy_b64
iVBORw0KGgoAAAANSUhEUgAAABgAAAAYCAMAAADXqc3KAAAAaVBMVEX///8AAAC2tra2tra2tra2trb////+/v62trb9/f309PT7+/vExMSurq6Hh4f4+Pj8/Pz5+fnMzMyenp6/zduoqKilpaXNzc2xsbHu7u6Li4vk5OTa2tro6Oj6+vrm5uaMjIympqby8vJPA9lJAAAABnRSTlMAAM8Q7zCjkYU+AAAAiklEQVR4XoXM2Q7CMAxE0bqAk+7s+/7/H4mJMGNXQdzXo5mCiKK2X01nlCpSkbXdspxk4VCLOHBvDvwbYPSWgxu/JQMn5rotMzA8L+d24wAFB+tvzEeFIGDr/0LlrjwEE2D+CxoZ4aoCLASQgau8mQAsb7hqFLp7L28mBSKKPJgS0AdcgO6xtQm8AN3LEZUq6MiXAAAAAElFTkSuQmCC

This format is perfect for scripted namespaces; compare this to storing the image with the original file values that would have some non-visual characters.

Step 2: Set the .Source of each Image with the function ImageFromBase64String

At run time, after obtaining the root object set the .Source of each Image from the previously saved APL variable.

      win ← FixSimpleXaml sample3

      win.Paste_b64.Source ← ImageFromBase64String Paste_b64
      win.Copy_b64.Source  ← ImageFromBase64String Copy_b64
      win.Cut_b64.Source   ← ImageFromBase64String Cut_b64

If there are many images in the XAML, the following lines of code can automate the process at run time:

    ⍝ Get the names of all the 'Image' object that has been fixed in the root object
      imgNames ← {((⊂'Image')≡¨(⍵.⍎¨(⍵.⎕NL-9)).GetType.Name)/(⍵.⎕NL-9)} win

    ⍝ Set the Source of all the 'Image'. Each 'Image' names must have an equivalent
    ⍝ Base64 variable ending with '_b64' in the APL workspace.
      win {(⍺.⍎⍵).Source←ImageFromBase64String⍎⍵}¨ imgNames

The icon and the cursor of the main window can be fixed manually by doing the following:

    ⍝ Fix manually the Icon of the main window.
     win.Icon ← ImageFromBase64String Settings_b64

    ⍝ Fix manually the Cursor of the main window.
     win.Cursor ← CursorFromBase64String HandCursor_b64

Routed Events

In WPF it is possible to set a single function that will receive all the Click events on the window (in this example it is __EventHandler) by doing:

  ⍝ Set Routed Events on the whole Window for ClickEvent when a MenuItem or a Button are clicked.
    ⎕USING←'System.Windows,WPF/PresentationCore.dll' 'System.Windows.Controls.Primitives,WPF/PresentationFramework.dll'
    win.AddHandler(Controls.MenuItem.ClickEvent)(⎕NEW RoutedEventHandler(⎕OR'__EventHandler'))
    win.AddHandler(ButtonBase.ClickEvent)(⎕NEW RoutedEventHandler(⎕OR'__EventHandler'))

This is useful because that way you don't need to define individual click events for each control.

The function __EventHandler will handle all the click events on the window code (the double underscore prefix is not necessary but is kept for naming consistency)

 __EventHandler(sender event);name
⍝ Single Event Handler for the Window

⍝ Get name of the control that was clicked
 name←event.Source.Name

⍝ sender is the Root Object in this case because
⍝ the routed event was attached to it.
 sender.lStatusBar.Content←'I Was Clicked: ',name

⍝ Select the code to be executed:
 :Select name
 :Case 'mnuCut'

 :Case 'mnuCopy'

 :Case 'mnuPaste'

 :Case 'mnuPrint'

 :Case 'mnuQuit'

 :Case 'mnuAbout'

 :Case 'btnButton1'

 :Case 'btnButton2'

 :Case 'btnButton3'

 :Else
     'Error: Unknow Name'
 :EndSelect

When all this is done the window can be shown:

      win.Show

The function DemoSample3 contains all the code related to sample3

    ∇ DemoSample3;imgNames

     ⍝ Parse the xaml of the variable sample3
      win←FixSimpleXaml sample3

      ⍝ Get the names of all the 'Image' object that has been fixed in rootObj
      imgNames←{((⊂'Image')≡¨(⍵.⍎¨(⍵.⎕NL-9)).GetType.Name)/(⍵.⎕NL-9)}win

     ⍝ Set the Source of all the 'Image'. Each 'Image' must have a Base64 variable of the same name.
      win{(⍺.⍎⍵).Source←ImageFromBase64String⍎⍵}¨imgNames

     ⍝ Fix manually the Icon of the main window.
      win.Icon←ImageFromBase64String Settings_b64

     ⍝ Fix manually the Cursor of the main window.
      win.Cursor←CursorFromBase64String HandCursor_b64

     ⍝ Set Routed Events on the whole Window for ClickEvent when a MenuItem or a Button are clicked.
      ⎕USING←'System.Windows,WPF/PresentationCore.dll' 'System.Windows.Controls.Primitives,WPF/PresentationFramework.dll'
      win.AddHandler(Controls.MenuItem.ClickEvent)(⎕NEW RoutedEventHandler(⎕OR'__EventHandler'))
      win.AddHandler(ButtonBase.ClickEvent)(⎕NEW RoutedEventHandler(⎕OR'__EventHandler'))

     ⍝ Show the window.
      win.Show
    ∇

The function ScrubAndFix will remove all the events from the XAML by looping on a XamlXmlReader object. It is slower than FixXaml but the events don't need to have a specific prefix. Perfect for experimenting with the XAML taken directly from the Web. All the named objects are attached to the root object

    ∇ rootObj←ScrubAndFix xamlString;err;names;nodeNumber;reader;stringReader;writer;⎕USING
    ⍝ Function to remove the Class and Events elements of XAML and fix the resulting XAML.
    ⍝ Each named element(s) object will be attached to rootObject.
    ⍝ Root element name is removed in all cases. Use the rootObj directly to access its properties/methods.
    ⍝ This function is most usefull when experimenting with XAML taken directly from the Web but is slower than FixXaml.
    ⍝ Inspired from the code of XAMLPAD2009.
    ⍝
    ⍝ XamlString = Vector of Characters representing a XAML string
    ⍝ rootObj    = WPF Root Element Object if no error
    ⍝            = ⎕NULL (explanation of error) if error

      :Trap 0

          ⎕USING,←'System.IO' 'System.Windows.Markup,WPF/PresentationFramework.dll' 'System.XAML,System.XAML.dll'
          stringReader←⎕NEW StringReader(⊂xamlString)
          reader←⎕NEW XamlXmlReader(stringReader XamlReader.GetWpfSchemaContext)
          writer←⎕NEW XamlObjectWriter(reader.SchemaContext)

          ⎕USING←0⍴⊂''
          names←''         ⍝ Initial value of the names to fix.
          nodeNumber←0     ⍝ Initial value of the node number.

          :While reader.Read

              :If 'StartObject'≡⍕reader.NodeType
                ⍝ Will increment of 1 each time a new node (with a new object) begins.
                  nodeNumber+←1
              :End

              :If 'StartMember'≡⍕reader.NodeType
              :AndIf reader.Member.Name≡'Class'
                  {}reader.Read
                  {}reader.Read

              :ElseIf 'StartMember'≡⍕reader.NodeType
              :AndIf reader.Member.IsEvent
                  {}reader.Read
                  {}reader.Read

              :ElseIf 'StartMember'≡⍕reader.NodeType
              :AndIf reader.Member.Name≡'Name'
                  writer.WriteNode(reader)
                  {}reader.Read
                  writer.WriteNode(reader)

                ⍝ Check if reader is on first node
                  :If 1≠nodeNumber
                    ⍝ reader is not on first node. Keep the name.
                      names,←⊂reader.Value
                  :Else
                    ⍝ reader is on first node. Don't keep the name.
                  :End

                  {}reader.Read
                  writer.WriteNode(reader)

              :Else
                  writer.WriteNode(reader)

              :End

          :EndWhile

          rootObj←writer.Result

         ⍝ Assign the value of each names found to the root object:
          :If 0≠⍴names
              rootObj{⍎'⍺.',⍵,'←⍺.FindName(⊂,⍵)'}¨names
          :Else
             ⍝ Do nothing, there is no names.
          :End

      :Else
        ⍝ Build the Error Message
          :If 90≠⎕EN
            ⍝ APL Error
              err←(1⊃⎕DM),': ',{(' '=1↑⍵)↓((1↓a,0)∨a←' '≠⍵)/⍵}(2⊃⎕DM),(⎕UCS 13)

          :Else
             ⍝ .Net Error
              :Trap 0
                ⍝ Show the value of ⎕EXCEPTION.Message if not ⎕NULL.
                  err←('EXCEPTION: ',⎕EXCEPTION.Message),(⎕UCS 13)
              :Else
                ⍝ Sometimes ⎕EXCEPTION is (NULL) and will bug here.
                  err←'Exception (NULL): Unknown error',(⎕UCS 13)

              :EndTrap

          :End

          rootObj←⎕NULL err

      :EndTrap
    ∇

The User Command | is designed to edit the XAML saved in the workspace and on disk.

Inserting WPF Controls into Traditional Dyalog Windows

You can insert a WPF control into an already existing application developed with ⎕WC by using an ElementHost and a Dyalog's NetControl. Here is an example of how to insert a WPF Button:

      ⎕USING∪←⊂'System.Windows.Forms.Integration,WPF/WindowsFormsIntegration.dll'  ⍝ Location of 'ElementHost'
      ⎕USING∪←⊂'System.Windows.Controls,WPF/PresentationFramework.dll'             ⍝ Location of WPF Button

      'F' ⎕WC 'Form' ('Caption' 'My WPF Button')('Posn' (10 10))('Size'(10 20))    ⍝ Create a Form
      'F.eh' ⎕WC 'NetControl' 'ElementHost' ('Posn'(10 10))('Size'(15 20))         ⍝ Add 'ElementHost'

     ⍝ Prepare the WPF Button, and make it the 'child' property of the 'ElementHost' control
      bn ← ⎕NEW Button
      bn.Content ← 'Click Me'
      bn.onClick ← '__Button_Click'
      F.eh.Child ← bn

Instead of a Button, you could use some complex XAML developed with Visual Studio. You just need to fix the XAML with FixXaml and make it the child of the ElementHost element.

How to Access the UI Thread from Another Thread

Since Net 2.0 Microsoft does not allow writing on the UI thread from another thread for security and stability reasons. Consequently, if you are executing a long calculation on another thread and you want to show the results by accessing directly the UI thread it is not possible.

With a Delegate

You need to use a little function with the code to be executed that will be put in queue to be executed on the UI thread. This is called a 'Delegate' by Microsoft. The function DispatchDelegate is an example of how to do this

 obj DispatchDelegate action;delegate;⎕USING
⍝ Function to write asynchronously to the UI thread from another thread.
⍝ The calling thread does not wait for the operation to finish.

⍝ obj    = UI Object that you want to write to from another thread
⍝ action = Line to execute in the UI thread. Use '⋄' to write multiple lines.

 :Trap 0
     ⎕USING←'System,System.dll' 'System.Windows.Threading,WPF/WindowsBase.dll'

    ⍝ Create a function (⍙Delegate) with the 'action' to execute in the UI thread.
    ⍝ The function will be executed where 'DispatchDelegate' is called and not where
    ⍝ 'DispatchDelegate' is located.
     delegate←(⎕IO⊃⎕RSI).⎕OR(⎕IO⊃⎕RSI).⎕FX'⍙Delegate'action'⎕EX ''⍙Delegate'''

    ⍝ Get a 'Dispatcher' from the UI object. That way we are sure to have the right UI thread.
    ⍝ Use the method '.Invoke' instead of '.BeginInvoke' for synchronous call.
     {}obj.Dispatcher.BeginInvoke(DispatcherPriority.Normal(⎕NEW Action delegate))

 :Else
     ⎕←'Error DispatchDelegate: ',action

   ⍝ Returns the Last Error
     :If 90=⎕EN
         ⎕←'EXCEPTION: ',⎕EXCEPTION.Message
     :Else
         ⎕←(1⊃⎕DM),': ',(2⊃⎕DM)
     :EndIf
 :End

Here is an example of how to use that function:

      ⎕USING←'System.Windows,WPF/PresentationFramework.dll'
      win ← ⎕NEW Window
      win.Show
      win.Title ← 'MyTitle'

      win DispatchDelegate& 'win.Title←''MyDelegateTitle'''  ⍝ The .Title property is changed from another thread

If you have many lines that need to be executed in the UI thread the function ScriptFollowsDispatchDelegate can be used like this

 ScriptFollowsDispatchDelegate obj;actions;delegate;dtlb;⎕IO;⎕ML;⎕USING
⍝ Function to write asynchronously to the UI thread from another thread.
⍝ The calling thread does not wait for the operation to finish.
⍝ Treat following commented lines in caller as a script.
⍝ Lines beginning with ⍝∇ are kept
⍝ Lines beginning with ⍝∇⍝ are stripped out (comments)

⍝ obj     = UI Object that you want to write to from another thread
⍝ actions = Lines to execute in the UI thread.

 (⎕IO ⎕ML)←1 3

 :Trap 0
     ⎕USING←'System,System.dll' 'System.Windows.Threading,WPF/WindowsBase.dll'

    ⍝ Create a function (⍙Delegate) with the 'action' to execute in the UI thread.
    ⍝ The function will be executed where 'DispatchDelegate' is called and not where
    ⍝ 'DispatchDelegate' is located.
     dtlb←{⍵{((∨\⍵)∧⌽∨\⌽⍵)/⍺}' '≠⍵}
     actions←{{'⍝'=↑⍵:'' ⋄ ' ',dtlb ⍵}¨2↓¨⍵/⍨∧\(⊂'⍝∇')≡¨2↑¨⍵}dtlb¨(1+2⊃⎕LC)↓⎕NR 2⊃⎕XSI
     delegate←(⎕IO⊃⎕RSI).⎕OR(⎕IO⊃⎕RSI).⎕FX(⊂'⍙Delegate'),actions,(⊂'⎕EX ''⍙Delegate''')

    ⍝ Get a 'Dispatcher' from the UI object. That way we are sure to have the right UI thread.
    ⍝ Use the method '.Invoke' instead of '.BeginInvoke' for synchronous call.
     {}obj.Dispatcher.BeginInvoke(DispatcherPriority.Normal(⎕NEW Action delegate))

 :Else
     ⎕←'Error ScriptFollowsDispatchDelegate: ',actions

    ⍝ Returns the Last Error
     :If 90=⎕EN
         ⎕←'EXCEPTION: ',⎕EXCEPTION.Message
     :Else
         ⎕←(1⊃⎕DM),': ',(2⊃⎕DM)
     :EndIf
 :End

[3]
[4]  ⍝ ... long running process on another thread ...
[5]
[6]    ScriptFollowsDispatchDelegate myObj
[7]  ⍝∇ line 1 to by executed in the UI thread
[8]  ⍝∇ line 2 to by executed in the UI thread
[9]  ⍝∇ line 3 to by executed in the UI thread
[10] ⍝∇ line 4 to by executed in the UI thread

The author has taken the prefix '⍝∇' instead of '⍝' because in production code you will probably want to erase all the comments in your runtime WS because they are useless and it is helping to obfuscate the code while taking less space.

With a DispatcherTimer

If you have a repetitive task to be executed on the UI thread then you can use a DispatcherTimer like this:

     ⎕USING∪←'System.Windows,WPF/WindowsBase.dll' 'System,mscorlib.dll'
     tm1_obj ← ⎕NEW Threading.DispatcherTimer(Threading.DispatcherPriority.Normal myObj.Dispatcher)
     tm1_obj.Interval ← TimeSpan.FromSeconds 1
     tm1_obj.onTick   ← '#.MyFunction'       ⍝ Function to be executed every 1 second on the Dispatcher of the object 'myObj'
     tm1_obj.Start

Note that since the DispatcherTimer is executed on the UI thread you cannot have a long callback because it will freeze the UI during its execution.

With a BackgroundWorker

The .NET framework provides a simple way to get started in threading with the BackgroundWorker component. This wraps much of the complexity and makes spawning a background thread relatively safe. It offers several features which include spawning a background thread, the ability to cancel the background process before it has completed, and the chance to report the progress back to your UI. The BackgroundWorker is an excellent tool when you want multithreading in your application with access to the UI thread, mainly because it's so easy to use.

An example is included in this namespace. It is inspired by this article. You start the example by doing:

      BackgroundWorkerSample& 1000

A window will appear and if you click on the 'Start' button, the UI will be refreshed with the multiple of 42 between 1 and 1000 while simulating a long calculation. Check the comments of this function with the links for more details.

How to install wpfXamlDemo in your workspace

1. Download attachment:wpfXamlDemo.v1.6.txt
2. Do a Select all (Ctrl+A) and a copy (Ctrl+C).
3. In your workspace execute )ed ⍟ wpfXamlDemo
4. Paste (Ctrl+V) the text into the Dyalog editor
5. Press Escape and ')save' your workspace

Optionally to de-script the namespace you can do:

    #.wpfXamlDemo←{('n' ⎕NS ⍵)⊢n←⎕NS ''}#.wpfXamlDemo