why would GetPropertyValue return null when I just ran ApplyPropertyValue

Question

I use ApplyPropertyValue to apply a property to a TextRange. Then the next statement is GetPropertyValue of that TextRange. Why would I get back null for that property value? The property value is being successfully applied.

    public List<TextRange> Lines
    {
      get;
      set;
    }

    public void HighlightLines()
    {
      WasBackProp = new object[this.Lines.Count];

      int ix = 0;
      foreach (var tr in this.Lines)
      {
        var wasProp = tr.GetPropertyValue(TextElement.BackgroundProperty);
        WasBackProp[ix] = wasProp;

        tr.ApplyPropertyValue(TextElement.BackgroundProperty, "Yellow");


// threw this in the code. xx is coming back as null????
        var xx = tr.GetPropertyValue(TextElement.BackgroundProperty);
      }
    }

Answer 1

If you are reading data from stream then call TextRange.Save to make it persistent  checkout MSDN documentation  

Answer 2

If you are reading data from stream then call TextRange.Save to make it persistent  checkout MSDN documentation  

not a stream. The TextRanges apply to the FlowDocument of a RichTextBox.

Answer 3

The property you are attempting to set is a Brush not a string.

http://msdn.microsoft.com/en-us/library/system.windows.documents.textelement.background.aspx

Surprised that you don't get an error when attempting to set it, but as you can see it doesn't set the property to a type that is not.

Hope this helps

LS

---

Lloyd Sheen

Answer 4

what i see there is you are making that code complex, use the following code instead:

tr.Background = new SolidBrush("color to be set");

This one line of code will do instead of that lengthy code

___________________________________________________________

Do vote the answer and propose the answer

Answer 5

Hi kishhr

We Appreciate your effort and contribution but we should not propose our own reply as proposed answer.

Thanks 

Ashwini

Answer 6

what i see there is you are making that code complex, use the following code instead:

tr.Background = new SolidBrush("color to be set");

This one line of code will do instead of that lengthy code

but TextRange does not have a Background property.

Answer 7

The property you are attempting to set is a Brush not a string.

Hi Lloyd,

Thanks for the correction. But I changed the ApplyPropertyValue statement and GetPropertyValue still returns null.

    
publicList<TextRange> Lines
    {
      
get;
      
set;
    }
    public void HighlightLines()
    {
      ResetBackProp();

      WasBackProp = new object[this.Lines.Count];

      int ix = 0;
      foreach (var tr in this.Lines)
      {
        // get and save the background property before the range is highlighted.
        var wasProp = tr.GetPropertyValue(TextElement.BackgroundProperty);

        WasBackProp[ix] = wasProp;
        tr.ApplyPropertyValue(TextElement.BackgroundProperty, Brushes.DarkRed);

        var xx = tr.GetPropertyValue(TextElement.BackgroundProperty);
      }
    }

Answer 8

I created simple RichTextBox and used the following code (sorry VB) to test.

    Private Sub Button_Click(sender As System.Object, e As System.Windows.RoutedEventArgs)
        Dim tr As TextRange = New TextRange(theRTB.Document.ContentStart, theRTB.Document.ContentEnd)
        tr.ApplyPropertyValue(TextBlock.BackgroundProperty, Brushes.Red)

        Dim t = tr.GetPropertyValue(TextBlock.BackgroundProperty)
    End Sub

What I found is that if there is text in the RTB then I get a value from the GetPropertyValue, but if there is no text I still get a TextRange but the GetPropertyValue now returns NULL/Nothing.

LS

---

Lloyd Sheen

Answer 9

I created simple RichTextBox and used the following code (sorry VB) to test.

    Private Sub Button_Click(sender As System.Object, e As System.Windows.RoutedEventArgs)
        Dim tr As TextRange = New TextRange(theRTB.Document.ContentStart, theRTB.Document.ContentEnd)
        tr.ApplyPropertyValue(TextBlock.BackgroundProperty, Brushes.Red)

        Dim t = tr.GetPropertyValue(TextBlock.BackgroundProperty)
    End Sub

What I found is that if there is text in the RTB then I get a value from the GetPropertyValue, but if there is no text I still get a TextRange but the GetPropertyValue now returns NULL/Nothing.

LS

---

Lloyd Sheen

I would add that null is a valid value when ApplyPropertyValue. Setting to null effectively clears the property value back to its default setting.