Question

I implemented a textbox, and this binds to a viewmodel. I fill in the textbox default by ‘100’ for example, but if i change this to 10, the property always sets correctly. But when i delete all the numbers, i want that the property is set to null. But it just don’t set the value when nothing is filled in. He just keeps the last value..

this is my code , viewmodel + xaml:

public double MaxTime
{
    get
    {
        return maxTime;
    }
    set
    {
        maxTime = value;
        OnPropertyChanged("MaxTime");
        if (SelectedQuestionDropList != null)
        {
            foreach (QuestionCluster cluster in this.Examination.QuestionClusters)
            {
                if (cluster == SelectedQuestionDropList)
                {
                    cluster.MaxTime = value;
                }
            }
        }
    }
}


<TextBox Height="23" 
         Visibility="{Binding Path=VisibleClusterDetails, Converter={StaticResource boolToVis},UpdateSourceTrigger=PropertyChanged}"  
         Text="{Binding Path=MaxTime,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"
         HorizontalAlignment="Right" Margin="0,511,601,0" Name="textBox2" 
         VerticalAlignment="Top" Width="120" /> 

Answer 1

Your property is a double so it won’t support null or empty values.

Instead of using a double here I would expose the property as a string and convert between string and double in my property getter and setter. In the setter I could handle null or empty values as I wanted, and I could easily handle any special formatting that was needed.