无法将用户控制（视图）分配给我的 ContentControl，始终为空

Question

I have a WPF application and I'm trying to display a dynamic user control in my main window. For this I have a ContentControl and I am binding it to a property called MyFooView which is of type FooView .

When the constructor of my main window gets called I am assigning FooView to my UserControl as such:

//using statements above...
//public class MainWindowViewModel, implements INotifyPropertyChanged

public FooView MyFooView
{
    get
    {
        return _myfooView;
    }
    set
    {
        if (_myfooView!= null)
        {
            _myfooView= value;
            RaisePropertyChanged(nameof(MyFooView));
        }
    }
}
private FooView _myfooView;

public MainWindowViewModel()
{
   MyFooView = new FooView(...); //takes in parameters
   //at this point MyFooView is (null)
}

My Xaml:

   <Grid Grid.Row="1" Margin="30,0" Width="880">
        <ContentControl Content="{Binding MyFooView}"/>
        <Rectangle Stroke="Black" StrokeThickness="2"/>
    </Grid>

No matter what MyFooView is always null. Thus, the space where I'm expecting to see my view is empty. Can anyone help me understand what am I doing wrong? Many thanks in advance!

Answer 1

It is always null because you have a null check inside the setter. You can not assign a value to the property when the field is null, but the field starts off null.

Change from:

public FooView MyFooView
{
    get
    {
        return _myfooView;
    }
    set
    {
        if (_myfooView!= null)
        {
            _myfooView= value;
            RaisePropertyChanged(nameof(MyFooView));
        }
    }
}

to:

public FooView MyFooView
{
    get
    {
        return _myfooView;
    }
    set
    {
        _myfooView= value;
        RaisePropertyChanged(nameof(MyFooView));
    }
}

Alternatively, you could perform a null check on the value , which is perhaps what you intended to do to begin with, as such:

public FooView MyFooView
{
    get
    {
        return _myfooView;
    }
    set
    {
        if (value!= null)
        {
            _myfooView= value;
            RaisePropertyChanged(nameof(MyFooView));
        }
    }
}