WPF Edit Resource

Question

Hi is there any way to change a Resource brush from code or via some binding? what I want to do is change the color of my "main" brush when a button is clicked.

Thanks a lot!

Edit:

Its a GradientBrush how do i change the colors on that?

myBrush.GradientStops[0].Color = Colors.Red;

just gives me a exception... and is there any way to animate the color change, like a story board?

Answer 1

Edit: Changed to LinearGradientBrush.

Not sure why you are getting an exception. This particular syntax works fine for me: XAML:

<LinearGradientBrush x:Key="MainBrush" StartPoint="0, 0.5" EndPoint="1, 0.5" >
    <GradientBrush.GradientStops>
        <GradientStop Color="Blue" Offset="0" />
        <GradientStop Color="Black" Offset="1" />
    </GradientBrush.GradientStops>
</LinearGradientBrush>

Code:

LinearGradientBrush myBrush = FindResource("MainBrush") as LinearGradientBrush;
myBrush.GradientStops[0].Color = Colors.Red;

If you would like to "animate" the color of a GradientStop, I recommend the MSDN article on the subject.

Answer 2

If you're using the Model-View-ViewModel (MVVM) pattern or something similar, you could make the brush colour (or the entire brush) a property of your viewmodel and bind directly to it.

In my (inexperienced) opinion, resources shouldnt change at runtime. If it's going to be changing, bind it.

(edit2: Changed from Silverlight-style top-level UserControl to WPF Window. As Ray Booysen noted in the comments, a UserControl in WPF would expose the colour via a DependencyProperty, not have it bound to a ViewModel.)

XAML:

<Grid x:Name="LayoutRoot">
    <Grid.Background>
        <SolidColorBrush Color="{Binding BackgroundColor}" />
    </Grid.Background>
    ...

Viewmodel class:

public class MyViewModel : INotifyPropertyChanged
{
    public Color BackgroundColor
    {
        get { ... }
        set { ... } // fire PropertyChanged event
    }
    ...

XAML.cs:

public partial class MyWindow : Window
{
     private MyViewModel m_viewmodel;

     public MyWindow()
     {
          InitializeComponent();
          viewmodel = new MyViewModel();
          this.LayoutRoot.DataContext = viewmodel;
     }

     private void ButtonClick(object sender, RoutedEventArgs e)
     {
         this.viewmodel.BackgroundColor = Color.Red;
     }
     ...

Answer 3

For animating the change, try creating a Storyboard and calling Begin on it.

(I'll go throw together an example)

edit: Looks like it's another Silverlight != WPF fail on my part. I cant seem to get it going in WPF.