Bound Hint text not updating

[GeoffEngelstein]

I have hint text in a textbox (using HintAssist) that I would like to change based on the contents of the textbox. I'm using the floating hint that tucks up into the upper left when there is something in the box.

The xaml is:
materialDesign:HintAssist.Hint="{Binding ElementName=Root, Path=HintTo, Mode=OneWay}"

In the code behind I am doing:
OnPropertyChanged(nameof(HintTo));

which is being executed. However the hint text doesn't change. I put a breakpoint on the HintTo property and it doesn't get hit.

Suggestions?

[nicolaihenriksen]

@GeoffEngelstein Could you please share a bit more context? I just tested out binding the HintAssist.Hint to a view model property and changing it from the view model (with INotifyPropertyChanged) works just fine.

Please paste a bit more XAML, and also a bit more of the view model / code-behind you're using.

[GeoffEngelstein]

Thanks. Here is some more info.

This is for a To/From user control that gets placed into a search form, made from two text boxes.

<TextBox Grid.Column="0" 
            Foreground="Black"
            Margin="0,3,3,0"
            Text="{Binding ElementName=Root, Path=FromInternal, UpdateSourceTrigger=PropertyChanged}"
            Width="150"
            Style="{StaticResource MaterialDesignFilledTextBox}"
            materialDesign:HintAssist.Hint="{Binding ElementName=Root, Path=HintFrom}"
         />

<TextBox Grid.Column="1" 
         Foreground="Black"
         Text="{Binding ElementName=Root, Path=ToInternal, UpdateSourceTrigger=PropertyChanged, Mode=OneWay}"
         Margin="0,3,3,0"
         Width="150"
         Style="{StaticResource MaterialDesignFilledTextBox}"
         materialDesign:HintAssist.Hint="{Binding ElementName=Root, Path=HintTo, Mode=OneWay}"
/>

When one of the textboxes changes, it updates the backing field, which also checks to see if the Hint should be updated:

public string FromInternal
{
    get => _fromInternal;
    set { _fromInternal = value;
        UpdateValues();
        ChangeHintPrompts();
        OnPropertyChanged(); }
}

ChangeHintPrompts looks like this:

private void ChangeHintPrompts()
{
    HintTo = $"To{AnyString(ToInternal)}";
    HintFrom = $"From{AnyString(FromInternal)}";
}

and HintTo and HintFrom are (now) just standard backing properties.

public string HintFrom
{
    get => _hintFrom;
    set { _hintFrom = value; OnPropertyChanged(); }
}

I've put a breakpoint on OnPropertyChanged and it is definitely firing with the "HintFrom" and "HintTo" parameters. But the Hint text in the control never changes. After "OnPropertyChanged" the getters for HintFrom and HintTo are not called. There are no issues noted in the XAML Binding Failures window.

Apologies for the lack of line breaks in the code. Not sure how to add that in there.

[nicolaihenriksen]

I've put a breakpoint on OnPropertyChanged and it is definitely firing with the "HintFrom" and "HintTo" parameters

I took the liberty to change your code blocks into something slightly more readable.

I am not really sure what could go wrong. The View Model (or code-behind) containing the HintFrom and HintTo properties does implement INotifyPropertyChanged right? And the OnPropertyChanged() method does indeed raise the PropertyChanged event right? Those are the only things that come to mind.

I am also noticing the bindings for the 2 TextBoxes are different: one is a 2-way binding (default for TextBox.Text) and the other is an explicit OneWay binding. Intentional?