Skip to main content

Bindable RichTextBox with HTML conversion in WPF

In WPF, the RichTextBox control is not really like other controls. Due to its flexible nature, there is no built in way of binding a property to the content. In this case, I wanted a simple RichTextBox control with a binding to an HTML formatted string to be able to use the built-in formatting features of the RichTextBox and allow users to create simple HTML formatted content.

First, doing the conversion on-the-fly proved to have major performance issues, so I ended up binding the content to a XAML string. The XAML to HTML conversion can be performed at any time.

I created a UserControl with a bindable Text-property. The view contains a RichTextBox control.

<RichTextBox x:Name="richTextBox" TextChanged="OnRichTextBoxChanged">

The source code for the user control contains the Text property and the methods to handle the binding.

public static readonly DependencyProperty TextProperty = DependencyProperty.Register(
    "Text", typeof(string), typeof(TextEditor),
    new FrameworkPropertyMetadata(string.Empty, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnTextPropertyChanged));

private static void OnTextPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    textEditor.richTextBox.Document = GetDocumentFromXaml((string) e.NewValue);
}

private void OnRichTextBoxChanged(object sender, TextChangedEventArgs e)
{
    Text = GetXamlFromDocument(richTextBox.Document);
}

private static string GetXamlFromDocument(FlowDocument document)
{
    return XamlWriter.Save(document);
}

private static FlowDocument GetDocumentFromXaml(string xaml)
{
    if (string.IsNullOrEmpty(xaml))
        return new FlowDocument();

    return (FlowDocument)XamlReader.Parse(xaml);
}

Putting this together as a custom control either derived from RichTextBox or just as a simple UserControl as above both works fine. I choose this method since I have exended the control to be more than just a bindable RichTextBox, so this made more sense. When it comes to comverting the XAML to HTML, Microsoft have put together a sample library which does a great job. I haven't had to do any changes to their original code for my scenarios to work, but there might be scenarios where modification is necessary.

Comments

Popular posts from this blog

Binding Enum with DescriptionAttribute in WPF

Binding an enumeration to a ComboBox can be done in several ways. In most cases you don't want to display the value itself, but a more user friendly description. One common approach is to use the DescriptionAttribute on the Enum values to supply a description for each value.  This is all possible in a very MVVM friendly way. First step is to add the  DescriptionAttribute  to the values of the enumeration. public enum MyValues { [Description("First value")] First, [Description("Second value")] Second } To retrieve the description from the enum we use a simple extension method. This method returns the value of the DescriptionAttribute if it exists, otherwise the string representation of the enum value is returned. public static string GetDescription(this Enum value) { var fieldInfo = value.GetType().GetField(value.ToString()); var attribute = fieldInfo.GetCustomAttributes(typeof(DescriptionAttribute), false).FirstOrDefault() as

User.Identity returns old login name after name change

When a person gets married or makes a name change for some other reason this usually means that the login name for the Active Directory-account changes as well. This is rarely a problem, but it turned out to cause some issues on our web server, where the  User.Identity  property was still returning the old login name. The user logged on with the new login name, but was identified by the web application as the old login name. The reason this occurs is because the  User.Identity  property relies on the  LsaLookupSids  method to convert the user SID to a login name. The method first calls the local  LSA-cache , which is not synchronized with the Active Directory. For this purpose a simple reboot of the web server to clear the  LSA-cache  propably would have sufficed. But since we didn't want to take the application offline rebooting was not an option. Instead, it is possible to set the registry value  LsaLookupCacheMaxSize in HKLM\SYSTEM\CurrentControlSet\Control\Lsa. If this val

Binding a HTML-formatted string to a WPF WebBrowser control

Sometimes there is a need to display a HTML formatted string in a WPF application. There are a couple of ways to do this, but the most stright forward is to use a WebBrowser control and the NavigateToString method. This approach has one big flaw, you cannot use binding to a string out of the box, but I found a great solution through Stack Overflow which adds a bindable property to the  WebBrowser  control using  NavigateToString . The following class is all that is needed to add that behavior. A new depencency property named Html is introduced to the  WebBrowser  and the proper change action is performed in the OnHtmlChanged method. public class BrowserBehavior { public static readonly DependencyProperty HtmlProperty = DependencyProperty.RegisterAttached( "Html", typeof(string), typeof(BrowserBehavior), new FrameworkPropertyMetadata(OnHtmlChanged)); [AttachedPropertyBrowsableForType(typeof(WebBrowser))] public static string GetHtml(WebBrowser bro