Overwrite automatically calculated result

Question

I have 2 TextBoxes. The first one as input and the second one as output. In the output TextBox a result is displayed depending on the input TextBox. Is there a possibility to overwrite the calculated value (take the input value from the TextBox)?

XAML:

<Window.DataContext>
    <local:ViewModel/>
</Window.DataContext>
<Grid>
    <StackPanel VerticalAlignment="Center">
        <TextBox Width="200" Text="{Binding Int1, UpdateSourceTrigger=PropertyChanged}"/>
        <TextBox Width="200" Text="{Binding Out, UpdateSourceTrigger=LostFocus}"/>
    </StackPanel>
</Grid>

CS:

public class ViewModel : INotifyPropertyChanged
{
    private int _out;
    private int int1;

    public int Int1
    {
        get { return int1; }
        set
        {
            int1 = value;
            OnPropertyChanged();
            OnPropertyChanged("Out");
        }
    }
    public int Int2 { get; set; } = 50;
    public int Out
    {
        get
        {
            int res = 0;
            if (string.IsNullOrEmpty(Int1.ToString()) == false && Int1 > 0)
            {

                res = Int1 + Int2;
            }
            return res;
        }
        set
        {
            _out = value;
            OnPropertyChanged();
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
    internal void OnPropertyChanged([CallerMemberName] string propName = "") => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));
}

Answer 1

ViewModel:

public class ViewModel : INotifyPropertyChanged  
  {  
    private int _out;  
    private int int1;  
    public int Int1  
    {  
      get { return int1; }  
      set  
      {  
        int1 = value;  
        OnPropertyChanged("Int1");  
        OnPropertyChanged("Out");  
      }  
    }  
    private int int2= 50;  
    public int Int2  
    {  
      get { return int2; }  
      set { int2 = value; OnPropertyChanged("Out"); OnPropertyChanged("Int2"); }  
    }  
    public int Out  
    {  
      get { return Int1 + Int2; }  
    }  
    public event PropertyChangedEventHandler PropertyChanged;  
     
    internal void OnPropertyChanged([CallerMemberName] string propName = "") => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));  
  }  

The result:

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Answer 2

Hi Sarah,
I think your ViewModel must be like this:

  public class ViewModel : INotifyPropertyChanged
  {
    private int _out;
    private int _int1;
    private int _int2 = 50;

    public int Int1
    {
      get => _int1;
      set
      { _int1 = value; OnPropertyChanged(); SetValueOut(); }
    }
    public int Int2
    {
      get => _int2;
      set { _int2 = value; OnPropertyChanged(); SetValueOut(); }
    }

    public int Out
    {
      get => _out;
      set { _out = value; OnPropertyChanged(); }
    }

    private void SetValueOut()
    {
      _out = (_int1 == 0) ? 0 : _int1 + Int2;
      OnPropertyChanged(nameof(Out));
    }

    public event PropertyChangedEventHandler PropertyChanged;
    internal void OnPropertyChanged([CallerMemberName] string propName = "") => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));
  }