WPF make combobox binding twoways - wpf

Question

I have a combo box that is editable, and i have a button that is enable when SelectedReplacement that binds to the combobox is not null and disable when it is. When it's null, i would input some random text to make the button enable, the problem is it wouldn't become enable when there I input text. making the Mode TwoWay doesn't help. i assumed setting the propertychangedevent would bind the new text to SelectedReplacement, but Im wrong, so any help is appreciated.
<ComboBox ItemsSource="{Binding SelectedError.Suggestions}"
Text="{m:Binding Path=SelectedError.SelectedReplacement, Mode=TwoWay}"
IsEditable="True"
HorizontalAlignment="Stretch"/>
i also tried to get the propertychanged
private void ViewModelPropertyChanged(SpellcheckViewModel sender, PropertyChangedEventArgs e)
{
if (e.PropertyName == nameof(sender.SelectedError.SelectedReplacement))
{
_correctCommand?.Refresh();
}
}

Answer 1

I try to write a demo project to meet your requirement.
Mainly, the enable state is controlled by another boolean property IsButtonEnabled in the view model, the value for that property is controlled by InputText property which is controlled by the text you input in the ComboBox control.
Here is the UI:
<StackPanel Margin="10">
<ComboBox
x:Name="cmb"
IsEditable="True"
ItemsSource="{Binding AllItems}"
TextBoxBase.TextChanged="cmb_TextChanged"
TextSearch.TextPath="Name">
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Name}" />
</DataTemplate>
</ComboBox.ItemTemplate>
</ComboBox>
<TextBox
x:Name="hiddenTextBox"
Text="{Binding InputText, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
Visibility="Collapsed" />
<Button
x:Name="btn"
Margin="0,10,0,0"
Content="Show message"
IsEnabled="{Binding IsButtonEnabled}" />
</StackPanel>
And here is the main logic in the view model:
public ObservableCollection<Item> AllItems
{
get { return _allItems; }
set { _allItems = value; this.RaisePropertyChanged("AllItems"); }
}
public bool IsButtonEnabled
{
get { return _isButtonEnabled; }
set { _isButtonEnabled = value; this.RaisePropertyChanged("IsButtonEnabled"); }
}
/// <summary>
/// When InputValue changed, change the enable state of the button based on the current conditions
/// </summary>
public string InputText
{
get { return _inputText; }
set
{
_inputText = value;
this.RaisePropertyChanged("InputText");
// You can control the enable state of the button easily
if (AllItems.Any(item => item.Name == value))
{
// SelectedItem is not null
IsButtonEnabled = true;
}
else if (!string.IsNullOrEmpty(value))
{
// SelectedItem is null
IsButtonEnabled = true;
}
else
{
IsButtonEnabled = false;
}
}
}
Finally, here is the project: ComboBoxDemo