Gotcha: System.IO.GetInvalidPathChars result not guaranteed

at System.IO.Path.GetInvalidPathChars one reads:

The array returned from this method is not guaranteed to contain the complete set of characters that are invalid in file and directory names

note: can also call this method from non-trusted Silverlight app – not as Intellisense tooltip wrongly says in Visual Studio 2013 with Silverlight 5.1

I just found out about this the hard way (since DotNetZip library was failing at SelectFiles to open .zip files that it had before successfully saved with item filenames containing colons). So I had to update my ReplaceInvalidFileNameChars string extension method to also replace/remove invalid characters such as the colon, wildcard characters (* and ?) and double quote.

    public static string ReplaceInvalidFileNameChars(
this string s,
string replacement = "") { return Regex.Replace(s, "[" + Regex.Escape( Path.VolumeSeparatorChar + Path.DirectorySeparatorChar + Path.AltDirectorySeparatorChar + ":" + //added to cover Windows & Mac in case code is run on UNIX "\\" + //added for future platforms "/" + //same as previous one "<" + ">" + "|" + "\b" + "" + "\t" + //based on characters not allowed on Windows new string(Path.GetInvalidPathChars()) + //seems to miss *, ? and " "*" + "?" + "\"" ) + "]", replacement, //can even use a replacement string of any length RegexOptions.IgnoreCase); //not using System.IO.Path.InvalidPathChars (deprecated insecure API) }

Useful to know:


slash ("/") on UNIX, and a backslash ("\") on the Windows and Macintosh operating systems



slash ("/") on UNIX, and a backslash ("\") on the Windows and Macintosh operating systems



backslash (‘\’) on UNIX, and a slash (‘/’) on Windows and Macintosh operating systems

More info on illegal characters at various operating systems can be found at:

HowTo: Drop files onto Silverlight controls

I was recently adding drop-files support to ClipFlair Studio, so I had to do some research on the related API that is available to Silverlight apps.

Silverlight supports a limited set of Drag-and-Drop interaction with the operating system (supposedly for security reasons, but most probably because of the classic cross-platform implementation pains).

For example it allows you to drop a collections of file objects from the operating system’s file explorer (or other similar application) onto a Silverlight drop target, but not the other way around.

Also, it doesn’t allow dropping other flavors of content, like text, images etc., only collections of file objects.

To allow dropping files onto a Silverlight control you set AllowDrop property to true and handle the Drop and optionally the DragEnter/DragOver/DragLeave events to provide visual feedback during the drop operation (mostly when over the drop target, unless you do Mouse Capturing).




  #region DragAndDrop

    private void rtb_Drop(object sender, System.Windows.DragEventArgs e)
      VisualStateManager.GoToState(this, "Normal", true);

      //the Drop event passes in an array of FileInfo objects for the list of files that were selected and drag-dropped onto the RichTextBox.
      if (e.Data == null)

     IDataObject f = e.Data as IDataObject;
      if (f != null) //checks if the dropped objects are files

        object data = f.GetData(DataFormats.FileDrop); //Silverlight only supports FileDrop
        FileInfo[] files = data as FileInfo[]; //…GetData returns null if format is not supported

        e.Handled = true;

        if (files != null)

          //Walk through the list of FileInfo objects of the selected and drag-dropped files and parse the .txt and .docx files
          //and insert their content in the RichTextBox.
          foreach (FileInfo file in files)
            Load(file, false);


    private void rtb_DragEnter(object sender, System.Windows.DragEventArgs e)
      VisualStateManager.GoToState(this, "DragOver", true);
      e.Handled = true;
    private void rtb_DragOver(object sender, System.Windows.DragEventArgs e)
      e.Handled = true;

    private void rtb_DragLeave(object sender, System.Windows.DragEventArgs e)
      VisualStateManager.GoToState(this, "Normal", true);
      e.Handled = true;



For the visual feedback you can use VisualStateManager and respective VisualStates at say a Grid that wraps the drop target in the XAML layout.

<Grid x:Name="LayoutRoot">
     <VisualStateGroup x:Name="DragStates">
         <VisualTransition GeneratedDuration="0:0:0.3">
             <CircleEase EasingMode="EaseIn"/>
       <VisualState x:Name="Normal"/>
       <VisualState x:Name="DragOver">
           <ColorAnimationUsingKeyFrames Storyboard.TargetProperty="(Control.Background).(SolidColorBrush.Color)" Storyboard.TargetName="rtb">
             <EasingColorKeyFrame KeyTime="0" Value="#FFFFF7D1"/>


Note that on MacOS-X Safari doesn’t pass drop events automatically to plugins and you have to catch them via Javascript and pass them to Silverlight, plus I’ve read that in MacOS-X Firefox doesn’t support this at all.

Even worse, Microsoft’s workaround article has a typo in the Javascript (should call dragDrop instead of drop) and there is a chance it doesn’t work in latest version of Safari. For more see: (this says one can use HTML5 events and the Silverlight HTML/Javascript Bridge to notify Silverlight)

Gotcha: OnLostMouseCapture always called by CaptureMouse at WPF

It seems that CaptureMouse is behaving differently in WPF and Silverlight, in that in the former one it immediately calls OnLostMouseCapture at a Visual, whereas in Silverlight it doesn’t get called if the element didn’t have the mouse capture already (btw, in Silverlight that method is at a UIElement – there is no Visual ancestor as in WPF).

    #region --- Events ---

    private void OnMouseLeftButtonDown(object source, MouseButtonEventArgs e)
      if (IsMoveToPointEnabled)
        CaptureMouse(); //must do before setting dragging=true, since WPF seems
//to be always calling OnLostMouseCapture on all
//controls, even if they didn't have the mouse capture
dragging = true; //always set, we might not make it to capture the mouse } } private void OnMouseLeftButtonUp(object source, MouseButtonEventArgs e) { ReleaseMouseCapture(); dragging = false; //always clear, in case we never had the mouse capture } protected override void OnMouseMove(MouseEventArgs e) { base.OnMouseMove(e); if (dragging && IsMoveToPointEnabled) MoveThumbToPoint(e.GetPosition(this)); } protected override void OnLostMouseCapture(MouseEventArgs e) { base.OnLostMouseCapture(e); dragging = false; //set dragging to false whatever the value of
//IsMoveToPointEnabled (may have changed while dragging)
} #endregion


The rest of the code of the SliderExt class that I’ve just added to ClipFlair codebase is below, where … is where the code region that was quoted above goes. This class is a descendent of Slider and implements IsMoveToPointEnabled property for Silverlight (in WPF that property exists), plus in WPF it fixes the behavior of the control so that when that property is set, it not only supports moving the slider thumb to the point on its track where mouse button was held down (instead of stepping up/down as is usually done in scrollbars), but also supports dragging from any point in the slider track which WPF’s implementation of IsMouseToPointEnabled didn’t do (it only allowed to drag from the thumb).

//Project: ClipFlair (
//Filename: SliderExt.cs
//Version: 20140313

using System.Windows;
using System.Windows.Controls;
using System.Windows.Controls.Primitives;
using System.Windows.Input;

namespace SliderExtLib
  public class SliderExt : Slider

    public SliderExt()

      //peek into mouse button events (even handled ones)
new MouseButtonEventHandler(OnMouseLeftButtonDown), true); AddHandler(MouseLeftButtonUpEvent,
new MouseButtonEventHandler(OnMouseLeftButtonUp), true); } #region --- Fields --- protected bool dragging; #endregion #region --- Properties --- public bool IsMoveToPointEnabled //WPF has this prop (hiding it), doesn't
//implement move to point if you click and drag on the track instead of thumb
{ get { return (bool)GetValue(IsMoveToPointEnabledProperty); } set { SetValue(IsMoveToPointEnabledProperty, value); } } public static readonly DependencyProperty IsMoveToPointEnabledProperty = DependencyProperty.RegisterAttached("IsMoveToPointEnabled", typeof(bool), typeof(SliderExt),
new PropertyMetadata(false)); #endregion #region --- Methods --- private void MoveThumbToPoint(Point p) { if (Orientation == Orientation.Horizontal) Value = p.X / ActualWidth * Maximum; else //if (Orientation == Orientation.Vertical) Value = p.Y / ActualHeight * Maximum; } #endregion



The incentive of making such a slider was for using it at the ColorPicker control I’ve just added to the ClipFlair codebase.

HowTo: Take screenshot on Windows desktop, Windows 8 and MacOS-X

copying from an e-mail I received from Skype support:

Taking a screenshot on Windows desktop

1. On your keyboard, press the Print Screen (Prt Scr) key to take a screenshot of your entire desktop. To take a screenshot of an active window, press the Alt+Print Screen (Prt Scr) key combination.

2. Save a copy of the image in Microsoft Paint. To do so, simply click Start > All Programs/Programs > Accessories > Paint.

3. Press the Ctrl+V key combination to paste your screenshot into Paint.

4. Go to the menu and click File > Save. Make sure you can remember where you save the image to, as you’ll need to find the file to attach the image in an email.

5. Enter a file name.

6. In the Save as type: drop-down menu, select JPEG.

7. Click Save.

Taking a screenshot on Windows 8

On your keyboard, press the Windows + Print Screen (Prt Scr) key combination. A screenshot of the entire screen is taken. To take a screenshot of an active window, press the Alt + Print Screen (Prt Scr) key combination. The screenshots are automatically saved in your Screenshots folder.

To find the folder:

1. In the Start screen, press the Windows key. Windows 8 switches to classic view.

2. Open the File Explorer from the task bar.

3. Under the Libraries folder on the left side, select Pictures. Your Screenshots folder is located here.

Taking a screenshot on Mac

On your keyboard, press the Command+Shift+4+Spacebar key combination and click the window you want to take a screenshot of.

To take a screenshot of your entire desktop, press the Command+Shift+3 key combination. To capture a portion of the desktop, press the Command+Shift+4 key combination. A cross-hair cursor will appear. Simply click and drag the cursor to select the area you’d like to capture. To save the screenshot, just release the mouse button.

The screenshots will be saved on your desktop in .png format.

Should you have further concerns or clarifications, please do not hesitate to contact us again.

It’s nice that Windows 8 now has a Screenshots folder under a user’s account folder, this is similar behaviour to the facility that Dropbox includes for taking screenshots directly to a Screenshots subfolder under your Dropbox folder. Wonder though why Windows key is needed to be pressed and what will happen if you just press PrintScreen on the Windows 8 home screen (Metro/Modern UI).

Also, wonder why Apple keeps on using those cryptic key combinations for doing things (sticking to MacOS legacy I guess).

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Fix: XAML – The member Content is not recognized or is not accessible

I was looking into some third-party code, upgrading it from Silverlight 4.x and was getting error ‘The member "Content" is not recognized or is not accessible’ at the following code part:


Looking it up, found that you don’t need to bind the Content property of a ContentPresenter at all if you put it inside the ControlTemplate of a ContentControl (a Button is such too).

Quoting from:


When you put a ContentPresenter in the ControlTemplate of a ContentControl, it automatically displays the Content of the templated control. For example, if you put a ContentPresenter in a ControlTemplate of a Button, the Content property of the ContentPresenter is implicitly bound to the Content of the Button that uses the ControlTemplate.

It is introduced in this MSDN article and have a sample in it,

Nice DeepZoom image samples via ClipFlair Studio’s Image component

Here are some DeepZoom image samples to enjoy via ClipFlair‘s Image component, in our ClipFlair Studio app (Silverlight-based):

Another impressive one is this Mandelbrot fractal, a dynamically generated DeepZoom image from Google AppEngine SDK demos:

You can point the mouse and scroll the mouse wheel or double click to zoom in where you want.

One can make DeepZoom tiled images and DeepZoom image collections (can read more at with various authoring tools, including DeepZoom Composer (can read more about that tool at

However, the easiest way is to use ZoomIt service ( to make a DeepZoom image wrapper (hosted at that site) for any big image on the web (giving it the original image URL). e.g. is a ClipFlair Poster (the respective DZI image is at – internally ClipFlair’s image component converts URLs to get the real .DZI image and show it)

2013 in review

The stats helper monkeys prepared a 2013 annual report for this blog.

Here’s an excerpt:

The concert hall at the Sydney Opera House holds 2,700 people. This blog was viewed about 48,000 times in 2013. If it were a concert at Sydney Opera House, it would take about 18 sold-out performances for that many people to see it.

Click here to see the complete report.

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