Question

I have a slider and a label control. The text is displayed in the label (few paragraphs).

1. I need to show only 3 words at a time.Every 1 second, move to the next set of 3 words.
2. The slider is used to select the number of words that can be seen at once. So a user can increase it to say 10 and now every 1 second, a set of 10 words need to be displayed.

How would I achieve this behavior in WPF? I know I need to do some kind of databinding between the slider and a label, but not sure how to get the effect of (1) or (2).

Any help is appreciated!

Answer 1

Here is how I would solve it without using my {edf:ExpressionBinding} feature (which, alas, is not yet publically available):

Step 1: Create three DependencyProperties (not traditional NET properties) in your class:

 Text
 WordsPerGroup
 GroupToShow

Step 2: Bind the Slider to the “WordsPerGroup” property:

 <Slider ... Value="{Binding WordsPerGroups}" />

Step 3: Create an animation using a LinearInt32KeyFrame to animate the “GroupToShow” property that counts once per second and lasts as long as you like, for example this lasts 1 hour and counts to 3600:

 <Int32AnimationUsingKeyFrames Storyboard.TargetProperty="GroupToShow" ...>
   <LinearInt32KeyFrame KeyTime="01:00:00" Value="3600" />
 <Int32AnimationUsingKeyFrames>

Step 4: Create a Converter that takes “Text”, “GroupToShow” and “WordsPerGroup” and returns the text to display:

public SelectWordsConverter : IMultiValueConverter
{
  public object ConvertTo(object [] values, ...)
  {
    string text = values[0] as string;
    int groupToShow = values[1] as int;
    int wordsPerGroup = values[2] as int;  // maybe double, depending on slider binding

    return
      string.Join(" ",
        text
         .Split(" ", StringSplitOptions.RemoveEmptyEntries)
         .Skip(groupToShow * wordsPerGroup)
         .Take(wordsPerGroup)
      );
   }
   ...

Step 5: Use a MultiBinding to bind the TextBlock’s Text property using your converter:

<TextBlock ...>
  <TextBlock.Text>
    <MultiBinding Converter="{x:Static local:SelectWordsConverter.Instance}">
      <Binding Path="Text" />
      <Binding Path="GroupToShow" />
      <Binding Path="WordsPerGroup" />
    </MultiBinding>
  </TextBlock.Text>
</TextBlock>

Step 6: Make sure you start your animation on load, or whenever you want the animation to start moving.

Step 7: (optional) Add a PropertyChangedCallback to “GroupToShow” to detect when the words have all been shown and do something appropriate (like start over, or stop the animation).