Tomorrow Karl Shifflett is giving a Code Camp session in Charlotte. Unfortunately it’s too far away for me to participate. 
Today Karl has posted a really great WPF Multi-Layer Business Application that can be downloaded from his blog. Check it out here and learn from it. Thx to Karl for posting and sharing that great sample app.
If you bind the Text-Property of a TextBox to something, the "something" is updated when the TextBox loses focus. This is the Default-UpdateSourceTrigger defined in the Metadata for the TextBox.TextProperty. In a Data Binding you can specify another UpdateSourceTrigger, like e.g. PropertyChanged.
If a TextBox has LostFocus as UpdateSourceTrigger, which is the default, you can get problems if the TextBox is inside of a Dialog that contains a OK-Button with the IsDefault-Property set to true. When the TextBox has the Focus, the user can press Enter and the Button is clicked, but the TextBox still keeps the Focus. The LostFocus-Event doesn’t occur, so the Source of a Data Binding isn’t updated with the value of the TextBoxs Text-Property. You need to update the source explicit. Let’s take an example and use the Person-class of my previous post:
public class Person : INotifyPropertyChanged { private string _name; public string Name { get { return _name; } set { _name = value; if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs("Name")); } } public event PropertyChangedEventHandler PropertyChanged; }
The Window below just contains a TextBox and a Button. The Text-Property of the TextBox is bound to the Name of the data in the DataContext. This would be a Person-instance, as you’ll see below in the codebehind-file. The Button has it’s IsDefault-Property set to true and defines an eventhandler for the Click-Event.
<Window x:Class="LostFocusTest.Window1" ... xmlns:local="clr-namespace:LostFocusTest" Title="Focus/IsDefault" Width="200" SizeToContent="Height"> <StackPanel> <TextBox Margin="5" Text="{Binding Name}"/> <Button Content="OK" IsDefault="True" Click="Button_Click"/> </StackPanel> </Window>
In the Constructor in the Codebehind-file a Person-instance is created. It’s assigned to the Windows DataContext-Property, so the TextBox above will display the Persons name, which is set to "Thomas". The Click-Eventhandler for the Button simply displays the name of the Person in a MessageBox.
public partial class Window1 : Window { private Person _pers; public Window1() { InitializeComponent(); _pers = new Person(); _pers.Name = "Thomas"; this.DataContext = _pers; } private void Button_Click(object sender, RoutedEventArgs e) { MessageBox.Show(_pers.Name); } }
If I start the application and type "Urs" into the TextBox and press Enter, the Button is clicked but the TextBox keeps the focus. So the Source, which is the Person-Instance, isn’t updated and the MessageBox still displays the old value (“Thomas”), as you can see in the Image below:
For such a scenario, you have to update the source explicit. You could do this in the Click-Eventhandler. To update the source, you have to get the BindingExpression for the TextProperty. You get the BindingExpression by calling the GetBindingExpression-Method on the TextBox. Pass in the Text-Property as parameter. On the BindingExpression call the UpdateSource-Method to update the Person-instance explicitly with the value defined in the Text-Property of the TextBox. With the Eventhandler below the Person-Instance would always be actualized when the Button is clicked. The MessageBox would display the right value:
private void Button_Click(object sender, RoutedEventArgs e) { TextBox textBox = Keyboard.FocusedElement as TextBox; if (textBox != null) { BindingExpression be = textBox.GetBindingExpression(TextBox.TextProperty); if (be != null) be.UpdateSource(); } MessageBox.Show(_pers.Name); }
Just kick it for me:
Windows Vista contains new Win32-Dialogs to save and open a file. There are also the old dialogs from XP available.
Windows Presentation Foundation has two wrapper-classes for Win32-Dialogs. The Microsoft.Win32-Namespace contains a SaveFileDialog- and an OpenFileDialog-class. The classes are located in the PresentationFramework-Assembly, one of the central assemblies of WPF.
When you use the classes from Microsoft.Win32-Namespace, you get the old dialogs from XP. In the snippet below the OpenFileDialog is opened.
Microsoft.Win32.OpenFileDialog dlg = new Microsoft.Win32.OpenFileDialog(); dlg.ShowDialog()
With the two lines above the dialog below is shown, and that’s the old-style Windows XP OpenFileDialog:
Windows Forms also wraps the two Dialogs SaveFileDialog and OpenFileDialog with classes in the namespace System.Windows.Forms. Add a reference to the assembly System.Windows.Forms.dll to your WPF-Project, and you can use these wrapper-classes. The interesting part is that they show per default the new Vista Dialog.
System.Windows.Forms.OpenFileDialog dlg = new System.Windows.Forms.OpenFileDialog(); dlg.ShowDialog();
With the lines above the new Vista Dialog is displayed:
Both WinForms-Dialog-Classes contain a property called AutoUpgradeEnabled (inherited from FileDialog, property is supported in .NET Versions 3.5, 3.0 SP1 and 2.0 SP1). This property is per default true, so the FileDialog-Instance will automatically upgrade appearance and behavior when running on Windows Vista. Set it to false, to get the old dialog-style:
System.Windows.Forms.OpenFileDialog dlg = new System.Windows.Forms.OpenFileDialog(); dlg.AutoUpgradeEnabled = false; dlg.ShowDialog();
On XP, the AutoUpgradeEnabled-property doesn’t have any effect, of course, there’s only the old dialog available.
Fazit: The cool thing about Microsoft.Win32 is that you can add a using-directive to your WPF-Project and use the classes inside that namespace without a full qualified name. Adding a using-directive for System.Windows.Forms isn’t a good thing in a WPF-Project. There are many double-matches in System.Windows.Forms and e.g. WPF’s System.Windows.Controls-Namespace, like e.g. the Button-class. So the compiler needs full qualified names. But if you wan’t to use the new Dialogs, you have to use the Wrappers from Windows Forms, but don’t add a using-directive for System.Windows.Forms, use full qualified names instead.
There are also other possibilities to get the new vista dialogs. E.g. you could make a Win32-call into comdlg32.dll, but the already available wrappers from Windows Forms are the easiest and fastest way to do it. And you won’t program something, if it’s already there, right? But you have to know that it is there. 
I think Microsoft will update the classes in Microsoft.Win32 in the near future, maybe in the upcoming servicing release for .NET 3.5 planned for Summer 2008? It’s really a little bit strange, WPF is the technology to create first class Vista apps, and its wrappers show still old dialogs, while Windows Forms wrappers don’t…
I was asked, if it would be possible to save the snapshots created in my last post as an animated gif. With a DispatcherTimer and the GifBitmapEncoder-class you’re not far away from it. Just create a MediaElement in your Window:
<MediaElement Source="thomasOnBoard.wmv" x:Name="media" MediaOpened="media_MediaOpened" MediaEnded="media_MediaEnded" Width="300" Height="200" Stretch="Fill"/>
In the Codebehind-File, implement Eventhandlers for MediaOpened and MediaEnded-Events. In MediaOpened you start the DispatcherTimer. I’ve just used an interval of 100 milliseconds. In the Tick-Eventhandler, which is called each 100 milliseconds, a BitmapFrame is added to the GifBitmapEncoders Frames-Property. When the video ends, the MediaEnded-Eventhandler writes the GIF to your disk and opens the file. That’s it.
public partial class Window1 : Window { ... GifBitmapEncoder _encoder; DispatcherTimer _timer; private void media_MediaOpened(object sender, ...) { _timer = new DispatcherTimer(); _timer.Interval = TimeSpan.FromMilliseconds(100); _timer.Tick += OnTick; _timer.Start(); } void OnTick(object sender, EventArgs e) { Size dpi = new Size(96, 96); RenderTargetBitmap bmp = new RenderTargetBitmap(300, 200, dpi.Width, dpi.Height, PixelFormats.Pbgra32); bmp.Render(media); if (_encoder == null) _encoder = new GifBitmapEncoder(); _encoder.Frames.Add(BitmapFrame.Create(bmp)); } private void media_MediaEnded(object sender, ...) { _timer.Tick -= OnTick; _timer = null; string filename = Guid.NewGuid().ToString() + ".gif"; FileStream fs = new FileStream(filename, FileMode.Create); _encoder.Save(fs); fs.Close(); _encoder = null; Process.Start(filename); } }
Here’s the gif saved from my video. Just click on it to see it animated:
With WPF’s Imaging-Classes you can take snapshots of any Visual. The snapshot can be saved in any common Image-Format, like e.g. JPG. Let’s take a look at a pretty short example, that shows how easy this can be done. The example takes snapshots of a Video.
The following Window contains a MediaElement and a Button. The MediaElement plays the Video thomasOnBoard.wmv. The Button defines an Eventhandler for the Click-Event. It takes a snapshot of the video, when you click it.
<Window x:Class="SnapShots.Window1" xmlns=http://schemas.microsoft.com/winfx/2006/xaml/... xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Window1" Height="300" Width="300" ResizeMode="NoResize"> <StackPanel> <MediaElement x:Name="media" Height="200" Stretch="Fill"> <MediaElement.Triggers> <EventTrigger RoutedEvent="MediaElement.Loaded"> <BeginStoryboard> <Storyboard> <MediaTimelineSource="thomasOnBoard.wmv" RepeatBehavior="Forever"/> </Storyboard> </BeginStoryboard> </EventTrigger> </MediaElement.Triggers> </MediaElement> <Button Click="Button_Click" Content="Snapshot"/> </StackPanel> </Window>
Let’s look at the Eventhandler of the Button. An instance of the RenderTargetBitmap-class is created with some parameters about image-size, dots per inch (dpi) and Pixelformat. The Render-Method gets the MediaElement as a parameter, so MediaElements visual appearance is stored in the RenderTargetBitmap in memory. With a JpegBitmapEncoder and a FileStream the Image is written as a JPG to disk. That’s it.
void Button_Click(object sender, RoutedEventArgs e) { Size dpi = new Size(96,96); RenderTargetBitmap bmp = new RenderTargetBitmap(300, 200, dpi.Width, dpi.Height, PixelFormats.Pbgra32); bmp.Render(media); JpegBitmapEncoder encoder = new JpegBitmapEncoder(); encoder.Frames.Add(BitmapFrame.Create(bmp)); string filename = Guid.NewGuid().ToString()+".jpg"; FileStream fs = new FileStream(filename,FileMode.Create); encoder.Save(fs); fs.Close(); Process.Start(filename); }
Instead of taking the picture in the Button_Click eventhandler, you could create a Timer and take an Image every 0.1s. That allows you to extract an image-sequence of your videos. As it works for any Visual, and everything that’s on the screen in a WPF-Application is a visual, there are many things you can do with it. You could create a snapshot of an Image drawn to an inkCanvas, upload it to a webserver to display it on a webpage etc.
The value of a Dependency Properties in WPF can be set from many sources: Templates, Styles, Data Binding, Animation, Local, Inherited from Element Tree,… That’s the reason why they are called "Dependency" Properties. Their values depend on many sources.
To get not a total chaos, there’s a precedence list in WPF that rules which value finally will be set. Here’s the list beginning with the source with lowest precedence (1.) up to the Source with highest precedence (10.):
WPF or better say its Property Engine calculates the value of a Dependency Property out of these sources. Finally the ValidateValueCallback checks if the value is valid (If a ValidateValueCallback was registered with the Dependency Property). If the value is not valid, the calculated-value wouldn’t be used (of course).
You have always to be aware of this precedence list, even in simple scenarios. Let’s take a short example. The Attached Property TextElement.Foreground has the Inherits-Flag set to true, so the value of this property is inherited through the element tree and you can set it on any element by using the attached property syntax, e.g. on a StackPanel like below:
<StackPanel TextElement.Foreground="Green"> <TextBox>Should be green</TextBox> <TextBlock>Should also be green</TextBlock> </StackPanel>
What do you think is the result of the codesnippet above? Do both, TextBox and TextBlock, display green text? I wouldn’t ask if they would do so.
No, not both Elements display green text. The text inside the TextBox is still in the standard black or darkGray. The TextBlock displays its text in green.
Mhm… why doesn’t the TextBox inherit the Foreground-Value from the StackPanel? If you set the TextElement.Foreground-Property locally, it works, and the text inside the TextBox gets green:
<TextBox TextElement.Foreground="Green"> Should be green </TextBox>
So lets find out why the TextBox doesn’t get the inherited Value and displays its text still in standard color. Let’s take a look at the TextBox’s ControlTemplate defined in the Theme-Style for Vista’s Aero-Theme (the theme my PC is running on). In the Triggers-Section of the ControlTemplate a Trigger is defined that is actived when the IsEnabled-Property of the TextBox is true. You can see the Templates Trigger-Section below. And as you can see there, the Trigger sets the TextElement.Foreground-Property to the Brush stored in the Field SystemColors.GrayTextBrush (by using the GrayTextBrushKey-ResourceKey).
<ControlTemplate.Triggers> <Trigger Property="UIElement.IsEnabled"> <Setter Property="Panel.Background" TargetName="Bd"> <Setter.Value> <DynamicResource ResourceKey="{x:Static SystemColors.ControlBrushKey}"/> </Setter.Value> </Setter> <Setter Property="TextElement.Foreground"> <Setter.Value> <DynamicResource ResourceKey="{x:Static SystemColors.GrayTextBrushKey}"/> </Setter.Value> </Setter> <Trigger.Value> <s:Boolean>False</s:Boolean> </Trigger.Value> </Trigger> </ControlTemplate.Triggers>
If you look to the precedence-list at the beginning of this post, you see that the Inherited Value is on position 2., and the Template Trigger is on Position 6. So the Template Trigger has higher precedence. In the StackPanel with a TextBox and a TextBlock, the Template Trigger of the TextBox will set the foreground, and not the inherited value. When we set the local value, this local value is used, cause local value is on a higher position than the Template Trigger in the precedence list.
To go one step further, let’s override the Template of the TextBox and don’t set the TextElement.Foreground-Property in the Trigger-Section. As a result of the following code with the new TextBox-Template you’ll see that both, TextBox and TextBlock will display green text.
<Window.Resources> <Style TargetType="TextBox"> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="TextBoxBase" ...> <ScrollViewer Name="PART_ContentHost" .../> <ControlTemplate.Triggers> <Trigger Property="UIElement.IsEnabled"> <Setter Property="TextElement.Foreground"> <Setter.Value> <DynamicResource ResourceKey="{x:Static SystemColors.GrayTextBrushKey}" /> </Setter.Value> </Setter> <Trigger.Value> <s:Boolean>False</s:Boolean> </Trigger.Value> </Trigger> </ControlTemplate.Triggers> </ControlTemplate> </Setter.Value> </Setter> </Style> </Window.Resources> <StackPanel TextElement.Foreground="Green"> <TextBox>Should be green</TextBox> <TextBlock>Should also be green</TextBlock> </StackPanel>
I’m just finishing the Animation-Chapter of my German-speaking WPF book (WPF-Buch erscheint im Juni 2008). I had a hard time to find a good idea how to show the reader animations in a really "non-boring", but easy way. And I think I’ve found one.
Animations in WPF are really powerful. You can create them completely in XAML. Even if the example of this post doesn’t make sense for a business application, think of the things you can do with animations:
Of course, Animations in business applications must be placed in the right way. It’s not recommended to animate everything you can. If you do so, your application won’t be serious anymore.
The application we are looking at here isn’t a business application. It’s just a small Loose XAML-File that allows you to become a soccer profi. It show’s how animations are completely created in XAML and how they can be controlled.
Animations in XAML are placed inside Triggers. Either in an EventTriggers Action-Property or in another Triggers EnterAction or ExitAction-Property. These Properties are all of type TriggerAction. The BeginStoryboard-class and some other classes derive from TriggerAction. BeginStoryboard contains a Storyboard. The Storyboard itself contains the Animations.
Below a loose XAML. The Animation (bold) changes the Canvas.Top-Property of an image that contains a ball (the teamgeist-ball of worldcup 2006 Germany). The Animation starts, when a button with the Name btnStart is clicked. Between the ball-image the Canvas contains an image of me. And the clou is, it looks like I kick the ball for thousand times like a real profi.
<Grid Height="260" Width="300"> <Grid.RowDefinitions> <RowDefinition/> <RowDefinition Height="Auto"/> </Grid.RowDefinitions> <Grid.Triggers> <EventTrigger RoutedEvent="Button.Click" SourceName="btnStart"> <BeginStoryboard Name="beginStoryboard"> <Storyboard TargetProperty="(Canvas.Top)" TargetName="imgBall"> <DoubleAnimation AutoReverse="True" To="110" RepeatBehavior="Forever" Duration="0:0:0.25" AccelerationRatio="1"/> </Storyboard> </BeginStoryboard> </EventTrigger> <EventTrigger RoutedEvent="Button.Click" SourceName="btnStop"> <StopStoryboard BeginStoryboardName="beginStoryboard"/> </EventTrigger> <EventTrigger RoutedEvent="Button.Click" SourceName="btnPause"> <PauseStoryboard BeginStoryboardName="beginStoryboard"/> </EventTrigger> <EventTrigger RoutedEvent="Button.Click" SourceName="btnResume"> <ResumeStoryboard BeginStoryboardName="beginStoryboard"/> </EventTrigger> <EventTrigger RoutedEvent="Button.Click" SourceName="btnSpeed2x"> <SetStoryboardSpeedRatio SpeedRatio="2" BeginStoryboardName="beginStoryboard"/> </EventTrigger> <EventTrigger RoutedEvent="Button.Click" SourceName="btnSpeed1x"> <SetStoryboardSpeedRatio SpeedRatio="1" BeginStoryboardName="beginStoryboard"/> </EventTrigger> </Grid.Triggers> <Canvas Width="250" Height="185"> <Image Height="185" Source="fussballthomi.png" Canvas.Left="40"/> <Image x:Name="imgBall" Width="25" Canvas.Top="10" Canvas.Left="140" Source="teamgeist.png"/> </Canvas> <DockPanel Grid.Row="1" LastChildFill="False"> <Button Margin="5" x:Name="btnStart" Content="Start"/> <Button Margin="5" x:Name="btnStop" Content="Stop"/> <Button Margin="5" x:Name="btnPause" Content="Pause"/> <Button Margin="5" x:Name="btnResume" Content="Weiter"/> <Button Margin="5" x:Name="btnSpeed1x" Content="1x"/> <Button Margin="5" x:Name="btnSpeed2x" Content="2x"/> </DockPanel> </Grid>
Thomas kicks it like beckham.
More informations about my book, that contains the sample above and hundreds more (also more real world applications), you’ll find by march on www.thomasclaudiushuber.com
Two classes inherit from DataSourceProvider. XmlDataProvider and ObjectDataProvider. ObjectDataProvider wraps an object and allows you to bind to the wrapped object in XAML. The ObjectDataProvider has a ConstructorParameters-Property for creating an object by using a constructor with parameters.
The cool thing is that a Data Binding to the wrapped object of the ObjectDataProvider is not all. With ObjectDataProvider you can even bind to a static method or to an instance method of the wrapped object. I’ll show you an example.
Just think about a really simple ComboBox that allows the user to chose some colors. Between the name of the color a rectangle filled with the color should be displayed (In WPF this is quite easy. You haven’t to create eventhandlers like you would do in Windows Forms. There you consumed the DrawItem-event of the ComboBox and used the Graphics-object to do a little bit of GDI+. In WPF GDI+ is gone). WPF’s Color class doesn’t have a name property. So just create a static class ColorHelper with one static method GetColorNames that returns an IEnumerable<string> and uses reflection to iterate over all public static properties of the Colors class that all contain Color-objects.
public static class ColorHelper { public static IEnumerable<string> GetColorNames() { foreach (PropertyInfo p in typeof(Colors).GetProperties( BindingFlags.Public | BindingFlags.Static)) { yield return p.Name; } } }
The Window in the following XAML contains an ObjectDataProvider that uses the Static GetColorNames-Method of the ColorHelper class. The ItemsSource-Property (Typ: IEnumerable) of the ComboBox is bound to the ObjectDataProvider. The ItemTemplate-Property contains a DataTemplate that specifies the Visual Tree (the "look") of an item. Thanks to TypeConverters, a SolidColorBrush-Object is created for the Fill-Property of each Rectangle specified in the DataTemplate.
<Window ... xmlns:local="clr-namespace:SimpleObjectDataProvider"> <Window.Resources> <ObjectDataProvider x:Key="colors" ObjectType="{x:Type local:ColorHelper}" MethodName="GetColorNames"/> </Window.Resources> <StackPanel> <ComboBox ItemsSource="{Binding Source={StaticResource colors}}"> <ComboBox.ItemTemplate> <DataTemplate> <StackPanel Margin="1" Orientation="Horizontal"> <Rectangle Fill="{Binding}" Height="10" Width="10" Margin="2"/> <TextBlock Text="{Binding}" Margin="2 0 0 0"/> </StackPanel> </DataTemplate> </ComboBox.ItemTemplate> </ComboBox> </StackPanel> </Window>
The displayed, open ComboBox looks like this:
The XmlDataProvider class enables Binding to XML inside XAML. This will allow you to bind e.g. to the rss feed of a blog like http://www.thomasclaudiushuber.com/blog/feed/, cause rss is simple XML.
A XmlDataProvider-Element is declared as a logic resource. You simply set the Source-Property to a XML-Document and optionally set the XPath-Property. The default value of the IsAsynchronous-Property of the XmlDataProvider is true, so your client won’t freeze if you specify a url as the source.
The following XAML creates a simple rss-reader. The root is a Window object that contains a XmlDataProvider inside its Resources-Property. The XmlDataProvider loads the feed of this blog and its XPath-Property points to the blogs items. The elements inside the Window are indirectly bound to the XmlDataProvider. They use the DataContext specified on the DockPanel. The special thing of the Bindings on this elements is that they do not directly point to the XmlDataProvider. Instead the Bindings start at the /rss/channel/item like specified in the XPath-Property of the XmlDataProvider. If you want to point directly to the XmlDataProvider-object, you’ve to set the BindsDirectlyToSource-Property of the Binding to true. This is used by the first TextBox. It allows the user to change the Source-Property of the XmlDataProvider to navigate to another feed like http://blog.trivadis.com/blogs/MainFeed.aspx. The Binding for this TextBox also specifies that the UpdateSourceTrigger is PropertyChanged. Without this, the Source would be updated on LostFocus, cause the TextBox.TextProperty has specified this behaviour in its metadata.
<Window x:Class="SimpleRssReader.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/..." xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="RSS Reader" Height="600" Width="800"> <Window.Resources> <XmlDataProvider x:Key="blog" Source="http://www.thomasclaudiushuber.com/blog/feed/" XPath="/rss/channel/item"/> </Window.Resources> <DockPanel DataContext="{Binding Source={StaticResource blog}}"> <StackPanel DockPanel.Dock="Top" TextElement.FontWeight="Bold" Background="LightGray"> <TextBlock Text="{Binding XPath=./../title}" FontSize="20" Margin="10 10 10 0"/> <TextBlock Text="{Binding XPath=./../description}" FontSize="10" FontWeight="Normal" Margin="10 0"/> <TextBox Margin="5" Text="{Binding Source={StaticResource blog}, BindsDirectlyToSource=True, Path=Source, UpdateSourceTrigger=PropertyChanged}"/> </StackPanel> <StatusBar DockPanel.Dock="Bottom"> <StatusBarItem Content="{Binding XPath=title}"/> <Separator/> <StatusBarItem Content="{Binding XPath=pubDate}"/> </StatusBar> <Grid> <Grid.ColumnDefinitions> <ColumnDefinition Width="308"/> <ColumnDefinition Width="Auto"/> <ColumnDefinition/> </Grid.ColumnDefinitions> <GroupBox Header="Blog-Eintr?ge"> <ListBox IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding}" DisplayMemberPath="title"/> </GroupBox> <GridSplitter Grid.Column="1" HorizontalAlignment="Center" Width="10"/> <Frame Grid.Column="2" Source="{Binding XPath=link}"/> </Grid> </DockPanel> </Window>
To test the rss reader yourself, simply create a new WPF-Application Project and paste the XAML above into the Window1.xaml. You have just to set the value of the x:Class-Attribut on the Window-Element so that it matches your class in the Codebehind-File. The Codebehind-File itself doesn’t need any logic. The reader looks like this:
In many applications you want to fill up a ListView or a GridView with some data. In WPF applications you set the View-Property of the ListView to a GridView to show the data nicely in columns. In most cases you have an entity class (think of it as a "real" entity class or a DataRow as part of a DataTable), and objects of this class should be represented in a row of the GridView. In WPF the DisplayMemberBinding-Property of each GridViewColumn is bound to a property of the entity class, so objects of the entity class can be easily added to the ListView and are displayed correctly in the GridViewColumns. But…
The problem (… the problem is more code as you want to have) begins, when you have no entity class and your data is stored in objects of different classes, maybe only in some variables, and you just want to display the data in one row of the ListView. If your variables have a relation to each other, it’s semantically correct to put them into one row of the ListView, displayed in different GridViewColumns. But to display the data in the ListView, you have to create a dummy entity class that contains your data. There’s no other way!
… no other way with C# 2.0. But now we have C# 3.0, and things can get much easier, cause the compiler can create nearly everything for you. To show you how some C# 3.0 features can help you for the problem above with the dummy entity class, I have to step some months back in time and pick out a small sample that exactly shows the necessity of creating a dummy entity class.
Some months ago I created a small WPF application (.NET 3.0 and C# 2.0) to show developers how Routed Events are routed through the Element Tree. The application contains a Button and a ListView. The Button contains a StackPanel and inside this StackPanel is a Rectangle. Below the Window1.xaml:
<Window x:Class="RoutedEventsBeispiel.Window1" xmlns=="http://schemas.microsoft.com/winfx/2006/xaml/.." xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="RoutedEventsBeispiel" Height="450" Width="500"> <Grid> <Grid.RowDefinitions> <RowDefinition Height="Auto"/> <RowDefinition/> </Grid.RowDefinitions> <Button x:Name="button1" Width="100" Height="100" Margin="5"> <StackPanel x:Name="stackPanel1" Background="Black"> <Rectangle x:Name="rectangle1" Margin="10" Fill="Red" Width="50" Height="50"/> </StackPanel> </Button> <ListView x:Name="listView" Grid.Row="1"> <ListView.View> <GridView> <GridViewColumn Header="RoutedEvent" DisplayMemberBinding="{Binding RoutedEventName}"/> <GridViewColumn Header="Sender" DisplayMemberBinding="{Binding Sender}"/> </GridView> </ListView.View> </ListView> </Grid> </Window>
Especially take a look at the DisplayMemberBinding-Property of the two GridViewColumns in the Window1.xaml above. To represent some data in this ListView, the Data must be represented by an object that has a Property RoutedEventName and a Property Sender. Therefore the Dummy class joins the game. Of course the class could be named in a better way like "RoutedEventInfo", but I decided to name it Dummy, because later with C# 3.0 this class won’t be necessary anymore:
public class Dummy { private string _sender; private string _routedEventName; public string Sender { get { return _sender; } set { _sender = value; } } public string RoutedEventName { get { return _routedEventName; } set { _routedEventName = value; } } }
In the constructor of Window1 in the codebehind Window1.xaml.cs a general Eventhandler for the Events UIElement.PreviewMouseLeftButtonDown and UIElement.MouseLeftButtonDown is added to the Window, the Button, the StackPanel and the Rectangle. The third parameter of the AddHandler-Method is always set to true. This true stands for "handledEventsToo", so the GeneralOnMouseDown-Eventhandler is called even if any EventHandler has set the Handled-Property of the RoutedEventArgs to true (That’s exactly what the ButtonBase class does internally with the MouseLeftButtonDown-Event, when the ButtonBase class raises its own Click-Event. So the third parameter is necessary here to get the application show the tunneling and bubbling of the events like expected)
public partial class Window1 : System.Windows.Window { public Window1() { InitializeComponent(); this.AddHandler(UIElement.PreviewMouseLeftButtonDown..., new RoutedEventHandler(GeneralOnMouseDown), true); this.AddHandler(UIElement.MouseLeftButtonDownEvent, new RoutedEventHandler(GeneralOnMouseDown), true); button1.AddHandler(UIElement.PreviewMouseLeftButtonDown..., new RoutedEventHandler(GeneralOnMouseDown), true); button1.AddHandler(UIElement.MouseLeftButtonDown..., new RoutedEventHandler(GeneralOnMouseDown), true); stackPanel1.AddHandler(UIElement.PreviewMouseLe..., new RoutedEventHandler(GeneralOnMouseDown), true); stackPanel1.AddHandler(UIElement.MouseLeftButton..., new RoutedEventHandler(GeneralOnMouseDown), true); rectangle1.AddHandler(UIElement.PreviewMouseLeft..., new RoutedEventHandler(GeneralOnMouseDown), true); rectangle1.AddHandler(UIElement.MouseLeftButton..., new RoutedEventHandler(GeneralOnMouseDown), true); } void GeneralOnMouseDown(object sender,RoutedEventArgs e) { if (sender is Window1 && e.RoutedEvent==UIElement.PreviewMouseLeftButton...) { listView.Items.Clear(); } Dummy d = new Dummy(); d.Sender = sender.GetType().Name; d.RoutedEventName = e.RoutedEvent.Name; listView.Items.Add(d); } }
The general Eventhandler GeneralOnMouseDown clears the Items of the ListView if the sender is a Window1 instance and the routed event is the tunneling event PreviewMouseLeftButtonDown. After that, it creates an instance of type Dummy, sets its Sender- and RoutedEventName-Property, and adds the Dummy instance to the ListView.
When you click on the red Rectangle located inside of the black StackPanel that is located inside of the Button, the ListView is filled up with Dummy objects, and it shows us, in which order the routed events are raised. The PreviewMouseLeftButtonDown-Events tunnels down from the Window1 to the Rectangle, then the MouseLeftButtonDown-Event bubbles up to the Window1.
That’s the application like I developed it with C# 2.0 and .NET 3.0. The need of the Dummy class is only necessary, because I got two string variables (the name of the routed event and the type name of the sender) that I have to put into one object, and this one object is put into the ListView. The GridViewColumns are bound to the Properties Sender and RoutedEventName of the object inside the ListView, so the Dummy objects are displayed like expected in the correct GridViewColumns.
Now how can I shorten my code with C# 3.0? We just focus on the GeneralOnMouseDown-Eventhandler and the Dummy-class. To add a Dummy object to the ListView, you can just use the Object Initializer to get it done in one instead of four statements:
listView.Items.Add(new Dummy() { Sender = sender.GetType().Name, RoutedEventName = e.RoutedEvent.Name });
Of course you could alternatively add a constructor to the Dummy-class instead of using an object initializer and you would reach a similar effect. But not always you’re the owner of such a Dummy-class and so you won’t be able to add a constructor. Even if you’re the owner of the Dummy-class, I think you like it to write less code (if you’re not paid per lines of code ). With object initializers you won’t have to create many different constructors.
Now take a look at the Dummy class itself. It could be much shorter, if you use the Automation Properties of C# 3.0 (the IL-Code will still look the similar like before). With automation properties, the compiler creates the backing private fields for the specified properties:
public class Dummy { public string Sender { get; set; } public string RoutedEventName{get;set;} }
We can go even further.
If you’ve read the C# 3.0 specification, you’ve also read about Anonymous Types. So let’s go ahead one more step. Anonymous types are not only a feature that is good to use in LINQ-statements. In this small application here we could throw the Dummy class away and instead of Dummy objects we can add anonymous type objects to the ListView. The anonymous type must contain the properties Sender and RoutedEventName. So without the Dummy class you could fill up the ListView in the GeneralOnMouseDown-Eventhandler just with anonymous types like below, and the application still works the same way:
void GeneralOnMouseDown(object sender,RoutedEventArgs e) { if (sender is Window1 && e.RoutedEvent==...) listView.Items.Clear(); listView.Items.Add(new { Sender = sender.GetType().Name, RoutedEventName = e.RoutedEvent.Name }); }
In the background, the compiler creates an Anonymous class, that contains two properties Sender and RoutedEventName. So in IL you’ll find a class created from the anonymous type used above. But that’s not your problem, your C# Code itself gets much shorter.
The cool thing about C# 3.0 and Visual Studio 2008 is that you can use these C# 3.0 features to build .NET 2.0 applications (Of course for WPF applications you need at least version 3.0 of .NET). But be careful when using C# 3.0 features for .NET 2.0 apps. E.g. language enhancement features like LINQ are based on Extension Methods located in assemblies introduced with .NET 3.5.
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