从不同的 ViewModel 调用 WPF mvvm 视图不会更新

Question

I've been trying to update a property inside a usercontrol with it's own VM.

<Label Content="{Binding Path =LabelText,UpdateSourceTrigger=PropertyChanged }" Grid.Column="0"/>

The Label itself works when I set it's text in the VM's constructor, and also updates if I use a command within the VM.

But changing it from outside won't do anything:

        private LabelTextBoxVM _testThing;
        public LabelTextBoxVM TestThing
        {
            get => _testThing;
            set
            {
                _testThing = value;
                NotifyPropertyChanged("TestThing");
            }
        }

           private void Update()
        {
            TestThing.LabelText = "Eureka";
            TestThing.TextBoxText = "Wooosh";
            NotifyPropertyChanged("TestThing");
        }

From all I've read, calling NotifyPropertyChanged for TestThing should update the content of both Label and Textbox, but nothing happens.

Answer 1

@Clemens

I found the answer, provided by you actually, in another question:

wpf-mvvm-usercontrol-binding

I have to set my DataContext in the parent view, binding to a property in the parent, and delete the Datacontext inside the childVM

So:

<myViewes:UserControlName DataContext="{Binding VMProperty}/>"

And this part cannot be in my UserControls:

<UserControl.DataContext>
        <viewModels:UserControlVM/>
</UserControl.DataContext>

I am guessing this was what you meant by "inheriting" the VM

Thank you!