Running an animation when text is changed of TextBlock in ViewModel - wpf

Question

I am making an WPF application following MVVM pattern. I have one button and textblock. TextBlock is only shown when its text is not empty. On start of application text is empty to textblock is not shown. When i click button sample text is set and textblock is shown. And when i click again button text is set to empty and textblock hides.
Now what I want is that when text is set there start animation (fading) opacity changes from 0 to 1 in 5 seconds.
Here is my XAML
<TextBlock Text="{Binding StatusMessage}" Visibility="{Binding IsStatusMessageVisible}" />
<Button Content="UpdateText" Command="{Binding UpdateTextCommand}" />
And here is my ViewModel.
private string _statusMessage;
public string StatusMessage
{
get { return _statusMessage ?? (_statusMessage = string.Empty); }
set
{
_statusMessage = value;
NotifyOfPropertyChange(() => IsStatusMessageVisible);
NotifyOfPropertyChange(() => StatusMessage);
}
}
public System.Windows.Visibility IsStatusMessageVisible
{
get
{
return (string.IsNullOrEmpty(StatusMessage))
? System.Windows.Visibility.Collapsed
: System.Windows.Visibility.Visible;
}
}
public void UpdateText()
{
if (string.IsNullOrEmpty(StatusMessage))
StatusMessage = Properties.Resources.WaitMessageStatus;
else
StatusMessage = string.empty;
}
I just want that when StatusMessage text is set animation runs.

Answer 1

Follow these steps:
declare a TextChanged event in your ViewModel
in the set method of your StatusMessage property, before the line "_statusMessage = value;" raise your TextChanged event if (_statusMessage != value && !string.IsNulOrEmpty(value));
in your XAML, create a StoryBoard to change the opacity of the TextBlock
in you XAML, add a ControlStoryBoardBehavior to the TextBlock, and select your TextChanged event and your StoryBoard

Answer 2

First, get rid of the "Visibility" property on your viewmodel, that doesn't belong there...it should be a boolean. Then, create a style for your TextBlock. In that style, add DataTrigger to bind to the boolean "IsVisible" property. Insdide of the DataTrigger, create a storyboard:
<DataTrigger.EnterActions>
<BeginStoryboard>
<Storyboard>
<!--Animation code in here />
</Storyboard>
</BeginStoryboard>
</DataTrigger.EnterActions>
For an example of how to do opacity animation, just Google it...but here's one way

Answer 3

One way to run an animation on a TextChanged in a TextBlock is the following:
<TextBlock
Text="{Binding MyText, NotifyOnTargetUpdated=True}">
<TextBlock.Triggers>
<EventTrigger RoutedEvent="Binding.TargetUpdated">
<BeginStoryboard>
<Storyboard>
<DoubleAnimation
Storyboard.TargetProperty="(TextBlock.Opacity)"
From="0.0"
To="1.0"
Duration="0:0:0.300" />
</Storyboard>
</BeginStoryboard>
</EventTrigger>
</TextBlock.Triggers>
</TextBlock>
NB: This code is only for learning purposes: the animation itself is not very useful or nice.