WPF/XAML/C# Setting a Boolean variable on MouseOver

Question

If I have a boolean variable in a ViewModel Class, lets say

public bool test = true; (This is in C#)

Is there ANYWAY in XAML/Expression Blend to take this variable and change it to false USING PURELY XAML, no code behind or anything?

I want to do this for a mouse over event. If the mouse is over a certain object the boolean variable should become false, otherwise it should remain true.

Normally you handle this in your ViewModel to make data binding easier. If you don't want to flip the bool in your ViewModel you can write a custom control that has a MouseOver property that works the way you like it. Clients using this control will not require any code behind then since handled in control. Another alternative is to use a ValueConverter in your binding that flips a bool value. — Wallstreet Programmer, Sep 16 '09 at 19:48
Why does your ViewModel want to know if the mouse is over a control used to display a part of it? — Simon Fox, Sep 17 '09 at 00:49

Carlo · Answer 1 · 2009-09-17T03:37:13.223

Answer 1 (easiest):

Why not do this?

public bool Test
{
    get { return myControl.IsMouseOver; }
}

I know you want to do it in all XAML, but since you're already declaring the property, you might as well do this instead of saying.

public bool Test = false;

Answer 2 (more code, MVVM approach which is better in the long run):

Here basically, you create a Dependency Property (called Test) on Window1, and on the XAML side, you create a style for Window1 that says that its Test property will be the same as the button IsMouseOver property (I left the myButton_MouseEnter event so you can check the state of the variable when the mouse is over the button, I checked myself and it does change to true, you can remove the MouseEnter handler, and it'll still work)

XAML:

<Window x:Class="StackOverflowTests.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" x:Name="window1" Height="300" Width="300"
    xmlns:local="clr-namespace:StackOverflowTests">
    <Window.Resources>
        <Style TargetType="{x:Type local:Window1}">
            <Setter Property="Test" Value="{Binding ElementName=myButton, Path=IsMouseOver}">
            </Setter>
        </Style>
    </Window.Resources>
    <Grid>
        <Button x:Name="myButton" Height="100" Width="100" MouseEnter="myButton_MouseEnter">
            Hover over me
        </Button>
    </Grid>
</Window>

C#:

public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();
        }

        public bool Test
        {
            get { return (bool)GetValue(TestProperty); }
            set { SetValue(TestProperty, value); }
        }

        // Using a DependencyProperty as the backing store for Test.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty TestProperty =
            DependencyProperty.Register("Test", typeof(bool), typeof(Window1), new UIPropertyMetadata(false));

        private void myButton_MouseEnter(object sender, MouseEventArgs e)
        {
            bool check = this.Test;
        }
    }

WPF/XAML/C# Setting a Boolean variable on MouseOver

1 Answers1