Question

I have the following xaml for changing the image for WPF button when mouse is on the button. It give below error. Any help is appreciated…

‘System.Windows.Media.Animation.DoubleAnimation’ animation object cannot be used to animate property ‘Source’ because it is of incompatible type ‘System.Windows.Media.ImageSource’.

<Style TargetType="{x:Type local:ButtonControl}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type local:ButtonControl}">
                    <Grid>
                        <VisualStateManager.VisualStateGroups>
                            <VisualStateGroup x:Name="CommonStates">
                                <VisualState x:Name="MouseOver">
                                    <Storyboard>
                                        <DoubleAnimation 
                                                Storyboard.TargetName="img"
                                                Storyboard.TargetProperty="Source"
                                                To="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=MouseOverImage}"
                                                />
                                    </Storyboard>
                            </VisualStateGroup>
                        </VisualStateManager.VisualStateGroups>
                            <Border>
                                <Image x:Name="img"
                                         Source="pack://application:,,,/Recipe_06_13;component/Resources/normal.bmp"
                                />
                            </Border>
                    </Grid>
                </ControlTemplate>
        </Setter.Value>
    </Setter>
    </Style>

Answer 1

The DoubleAnimation is used to animate a dependency property of type double. Therefore, it cannot be used to ‘animate’ an image source. To accomplish what you are doing, I would go about it a little differently. I’d bind the image source to a property of the code behind, and capture the MouseEnter and MouseLeave events to change this property.

XAML

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="336" Width="354">
    <Grid x:Name="myGrid">
        <Image 
            x:Name="myImage" 
            Stretch="UniformToFill"
            Source="{Binding MyImageSource}" 
            VerticalAlignment="Top" />
    </Grid>
</Window>

Code Behind:

namespace WpfApplication1
{
    using System.ComponentModel;
    using System.Windows;
    using System.Windows.Input;

    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window, INotifyPropertyChanged
    {
        public Window1()
        {
            this.MyImageSource = "/image_normal.png";
            InitializeComponent();

            this.DataContext = this;

            myImage.MouseEnter += new MouseEventHandler(myGrid_MouseEnter);
            myImage.MouseLeave += new MouseEventHandler(myGrid_MouseLeave);
        }

        private string _myImageSource;
        public string MyImageSource 
        {
            get
            {
                return _myImageSource;
            }
            set
            {
                if (_myImageSource != value)
                {
                    _myImageSource = value;
                    if (PropertyChanged != null)
                    {
                        PropertyChanged.Invoke(this, new PropertyChangedEventArgs("MyImageSource"));
                    }
                }
            }
        }

        void myGrid_MouseLeave(object sender, MouseEventArgs e)
        {
            this.MyImageSource = "/image_normal.png";
        }

        void myGrid_MouseEnter(object sender, MouseEventArgs e)
        {
            this.MyImageSource = "/image_hover.png";
        }

        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion
    }
}