Question

I am trying to construct a Control template from code behind. Things were working fine till recently I found that the code was throwing an exception because of escape characters in string. The error message is dynamically constructed by retrieving from resource file.

The exception is

A first chance exception of type ‘System.Windows.Markup.XamlParseException’ occurred in PresentationFramework.dll
Additional information: Name cannot begin with the ‘@’ character, hexadecimal value 0x40. Line 1, position 537.

 //In this case when exception is thrown, 
 //string errorMessage = "Name cannot contain any of the following characters  $ \" @ ; ^ |   "


    public static ControlTemplate GetErrorTemplate(string errorMessage)
    {
        string xamlString = "<ControlTemplate xmlns=\"http://schemas.microsoft.com/winfx/2006/xaml/presentation\" " +
                                  "xmlns:x=\"http://schemas.microsoft.com/winfx/2006/xaml\" " +
                                  "xmlns:nicefx=\"clr-namespace:NiceFx.Interop.UIComponents;assembly=NiceFx\" " +
                                  "xmlns:wpfkit=\"http://schemas.microsoft.com/wpf/2008/toolkit\" >" +
                                  " <DockPanel  LastChildFill=\"True\">" +
                                  "<TextBlock Foreground=\"White\" Background=\"Red\" FontSize=\"12\" Padding=\"2\" FontFamily=\"Trebuchet MS\"  Margin=\"5,5,0,0\" TextWrapping=\"Wrap\" DockPanel.Dock=\"Bottom\" Text=\"" + errorMessage + "\"></TextBlock>" +
                                  "<AdornedElementPlaceholder />" +
                                  " </DockPanel>" +
                                  " </ControlTemplate>";

        //EXCEPTION OCCURS IN THIS LINE
        ControlTemplate ct = (ControlTemplate)XamlReader.Load(XmlReader.Create(
            new StringReader(xamlString)));

        return ct;
    }

How do I escape this string? I tried all possible ways but I am unable to do so.

Answer 1

According to the comment in your code, errorMessage contains a ", which will be inserted (without escaping it) into the XAML you are constructing. This " will then act as the closing quote of the Text attribute. At this point, the next non-whitespace character the parser encounters will be @, which is not an allowed character for the name of a XAML attribute, so it stops and reports the error.

That covers the why. As for how to escape it, you can use the XML entity for double quote: " Note that you may need to apply this escaping to multiple characters in your parameter.