Command-Binding is not correctly executed in WPF application

Question

I want to implement my navigation in my WPF application. Currently the StartScreen.xaml is shown on startup, but when I click on the button the DeviceManagement.xaml is not shown. Not even the ShowDeviceManagement command is called.

This let me assume that the Command of the Button is not correct? How can I fix it?

App.xaml

<Application.Resources>
    <DataTemplate DataType="{x:Type vm:DeviceManagementViewModel}">
        <view:DeviceManagement />
    </DataTemplate>

    <DataTemplate DataType="{x:Type vm:MainWindowViewModel}">
        <view:StartScreen />
    </DataTemplate>
</Application.Resources>

MainWindow.xaml

<Window ...>
    <Window.DataContext>
        <vm:MainWindowViewModel/>
    </Window.DataContext>
    <ContentControl
        Content="{Binding ViewModel}">
    </ContentControl>
</Window>

StartScreen.xaml

<UserControl ...>
     <Button
         Content="Click Me"
         Command="{Binding DataContext.ShowDeviceManagement, RelativeSource={RelativeSource AncestorType={x:Type vm:MainWindowViewModel}}, Mode=OneWay}"/>
</UserControl>

MainWindoViewModel.cs

class MainWindowViewModel : ViewModelBase
{
    public ViewModelBase ViewModel { get; set; }

    public MainWindowViewModel()
    {
        ViewModel = this;
    }

    public ICommand ShowDeviceManagement
    {
        get
        {
            return new RelayCommand(action => ViewModel = new DeviceManagementViewModel());
        }
    }
}

Anton Danylov · Accepted Answer · 2016-02-03 09:38:38Z

1

"DataContext" is obsolete in your command binding. RelativeSource is used to find ancestor in visual tree, and your MainWindowViewModel is not Visual. Should be like this:

Command="{Binding ShowDeviceManagement, Mode=OneWay}"

answered Feb 3, 2016 at 9:38

Anton Danylov

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1 Comment

Anton Danylov Over a year ago

Try to initialize your RelayCommand and set it to private field in the constructor and in ShowDeviceManagement property just return this field, instead of creating command instance each time the property accessed.

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