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c#wpfxamlmvvmeventtrigger
Ben Russell
Ben Russell

Reputation: 127

WPF Interaction.Triggers MouseDown EventTrigger Not Working with Canvas Element

I'm attempting to create an MVVM WPF application that allows me to draw a rectangle in the window. Right now, I've created a canvas element that covers the entire screen. Following other questions and guides, it looks like the only way to use command bindings on mouse events (such as MouseDown, MouseUp, etc) is to use the System.Windows.Interactivity assembly and add EventTriggers for the mouse events. However, this doesn't seem to be working with the canvas element. Clicking, click/hold, click/drag, right clicking, none of them trigger the Execute method of my command.

What are the supported events for a canvas element? Why would MouseDown or PreviewMouseDown not be working?

XAML for the window:

<Window x:Class="RutheniumReader.SnippingWindow.SnippingShade"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity"
    xmlns:snippingWindow="clr-namespace:MyApp.SnippingWindow"
    mc:Ignorable="d"
    Title="Snipping Window"
    WindowState="Maximized"
    Background="Black"
    >
    <Window.DataContext>
        <snippingWindow:SnippingWindowViewModel />
    </Window.DataContext>
    <Canvas x:Name="Canvas">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="MouseDown">
                <i:InvokeCommandAction Command="{Binding Path=MouseDownCommand}" />
            </i:EventTrigger>
        </i:Interaction.Triggers>
    </Canvas>
</Window>

For testing purposes, I've tried the following events with no luck:

Upvotes: 3

Views: 8554

Answers (1)

snickro
snickro

Reputation: 481

The mouse events aren't working because the canvas's background isn't set. If a control (in this case your Canvas) has no background color set, the background color will default to null, and that makes the control non hit-testable.

The background can be set either explicitly or through styles, and as long as it has a value different from null (even 'Transparent') it should pickup mouse events.

Upvotes: 7

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