Can someone tell me what am I doing wrong? I have already tried everything, the pirmers that I downloaded from the Internet work, I made a minimal example, but it does not work.

I can't connect mine ViewModel in View

<Grid>
    <Grid.Resources>
        <DataTemplate DataType="{x:Type local:TestViewModel}">
            <Label Content="{Binding Wtf}"/>
        </DataTemplate>
    </Grid.Resources>
</Grid>

public class TestViewModel 
{
    public string Wtf => "wtf???";

    public TestViewModel() {}
}

I'm trying to connect the view model like this, so that I can use dependency injection later. But my Binding "wtf" does not display

CodePudding user response：

The two standard ways of assigning the ViewModel to the View are

1] In the Xaml - this only works if your ViewModel has a paramaterless constructor.

<Window ... >    
    <Window.DataContext>
        <local:MainViewModel />
   </Window.DataContext>

  ...

</Window>

2] In the code behind constructor of the View - you can use an IoC container for injected services to the ViewModel.

public MainView()
{
    DataContext = new MainViewModel();
    InitializeComponent();
}

or

public MainView()
{
    DataContext = IoCContainer.GetInstance<MainViewModel>();
    InitializeComponent();
}

For more details, including a more advanced way to assign the ViewModel that will provide data at design time, check out my blog post.

CodePudding user response：

The code provided is not showing the whole thing. There are 2 missing parts :

1. In the code behind instantiate the "TestViewModel" and put it in the DataContext.
2. Introduce a "ContentControl" that its DataContext was created as mentioned above.

The DataTemplate is just a declaration and not making the presentation. The technique you are attempting to use is somehow advanced. It tells WPF that when a given class is encountered by a ContentControl , the Data Template is being used.

    <Grid>
            <Grid.Resources>
                <DataTemplate DataType="{x:Type local:TestViewModel}">
                    <Label Content="{Binding Wtf}"/>
                </DataTemplate>
                
            </Grid.Resources>
            <ContentControl Content="{Binding }"/>
        </Grid>

    public partial class MainWindow : Window
        {
            public MainWindow()
            {
                InitializeComponent();
                DataContext = new TestViewModel();
            }
        }