Xamarin.Forms DataTrigger不起作用

Question

I'm trying to set DataTrigger on my control in Xamarin.Forms, but I cannot get it working.

I have Property in ViewModel with OnPropertyChange execution for bool IsValid

I have tried:

DataTrigger in Xaml:

<customControls:NumericTextBox
    Grid.Row="0" Grid.Column="2"
    Text="{Binding StringValue, Mode=TwoWay}"
    IsEnabled="{Binding IsEditable}"
    XAlign="End">
  <customControls:NumericTextBox.Style>
    <Style TargetType="customControls:NumericTextBox">
      <Style.Triggers>
        <DataTrigger TargetType="customControls:NumericTextBox" Binding="{Binding IsValid}" Value="true">
          <Setter Property="TextColor" Value="Red"/>
        </DataTrigger>
      </Style.Triggers>
    </Style>
  </customControls:NumericTextBox.Style>
</customControls:NumericTextBox>

Getting exception: The Property TargetType is required to create a Xamarin.Forms.DataTrigger object.

DataTrigger in Control:

_item = new DataTrigger(typeof(NumericTextBox));
_item.Binding = new Binding("IsValid",BindingMode.Default,new NegativeBooleanConverter());
_item.Value = true;
Setter s = new Setter();
s.Property = TextColorProperty;
s.Value = Color.Red;
_item.Setters.Add(s);
this.Style.Triggers.Add(_item);

Exception: Exception has been thrown by the target of an invocation.

I have tried also changing line : this.Style.Triggers.Add(_item); to this.Triggers.Add(_item); . This wasn't raising exception, but it just didn't worked.

In this last try, it even hits converter, but does not change TextColor of Control.

Am I doing something wrong? How to handle that?

Answer 1

I ran into this same issue. As a workaround, instead of using a DataTrigger you could bind the TextColor property to a Color property in your ViewModel. In the IsValid setter you could then set the color based on the value.

public bool IsValid
{
    get { return _isValid; }
    set
    {
        _isValid = value;
        MyNewTextColorProperty = _isValid ? Color.Blue : Color.Red;

        OnPropertyChanged();
    }
}