Question

Using WPF and Prism.

I have a view, containing 1 textblock

<UserControl x:Class="ArmoryModule.Views.ResultsView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:Views="clr-namespace:ArmoryModule.Views" xmlns:vmdc="clr-namespace:ArmoryModule.ViewModels"
             mc:Ignorable="d">

    <UserControl.DataContext>
        <vmdc:ResultsViewModel />
    </UserControl.DataContext>

    <Grid>
        <TextBlock Text="{Binding Name, UpdateSourceTrigger=PropertyChanged}" />
    </Grid>
</UserControl>

attempting to bind to the pertinent part of ResultsViewModel below

class ResultsViewModel : ViewModel
{
    private Character _character;

    public Character Character
    {
        get { return _character; }
        set
        {
            if (_character != value)
            {
                _character = value;
                RaisePropertyChanged(() => Name);
            }
        }
    }

    public string Name
    {
        get { return _character.Name; }
    }
}

Builds fine, breaks at startup. I get an object ref not sent to an instance of an object error on

get { return _character.Name; }

I know character isn’t populated at startup and thats the reason I’m getting the above error. I am kind of clueless as where to create Character so that the 2 viewmodels I have can use it.

Answer 1

Either add it to the constructor for the view model

public ResultsViewModel()
{
    _character = new Character();
}

or simply add a check in the getter, e.g.

get
{
    return _character != null ? _character.Name : string.empty;
}