DataGrid Calculated column does not show any data

Question

Let's have an example to understand my problem clearly :

I have three TextBox Controls as below :

So, I want to calculate Amount when Quantity or Rate Changes. Amount = Quantity * Rate

Similarly I want to change Rate if user intends to change Amount. So, formula for Rate will be Rate = Amount / Quantity

Actual Problem:

I have a DataGrid with the three Columns :

Property declaration in ViewModel :

public MainWindowViewModel()
{
    OpeningBalances = new ObservableCollection();
}

private ObservableCollection _openingBalances;
public ObservableCollection OpeningBalances
{
    get
    {
        return _openingBalances;
    }
    set
    {
        _openingBalances = value;
        OnPropertyChanged("OpeningBalances");
    }
}

ItemOpeningBalnceRow.cs :

public class ItemOpeningBalanceRow 
{
    public double Quantity { get; set; }
    public double Rate { get; set; }
    public double Amount { get; set; }
}

Converter - AmountFromQuantityAndRateConverter.cs

public class AmountFromQuantityAndRateConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        int _quantity = 0;
        int _rate = 0;

        if (int.TryParse(values[0].ToString(), out _quantity) && int.TryParse(values[1].ToString(), out _rate))
        {
            return _quantity * _rate;
        }

        return 0;
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

I have used above mentioned Multi Value converter but still Amount column always remains null. I mean it does not display any data.

Update:

The answer given by @sky-dev is the best possible answer and is working fine. But I would like to get the same approach using converters.

What I have tried?:

I have created two converters as follows:

RateFromAmountAndQuantityConverter.cs

public class RateFromAmountAndQuantityConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        int _quantity = 0;
        int _amount = 0;
        int _rate = 0;

        if (int.TryParse(values[0].ToString(), out _quantity) && int.TryParse(values[1].ToString(), out _amount) && int.TryParse(values[2].ToString(), out _rate))
        {
            if (_quantity != 0 && _amount != 0)
            {
                if (_rate == _amount / _quantity)
                    return _rate.ToString();
                else
                    return (_amount / _quantity).ToString();
            }
        }

        return "0";
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

And other is AmountFromQuantityAndRateConverter.cs

public class AmountFromQuantityAndRateConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        int _quantity = 0;
        int _rate = 0;
        int _amount = 0;

        if (int.TryParse(values[0].ToString(), out _quantity) && int.TryParse(values[1].ToString(), out _rate) && int.TryParse(values[2].ToString(), out _amount))
        {
            if (_rate != 0)
            {
                if (_amount == _quantity * _rate)
                    return _amount.ToString();
                else
                    return (_quantity * _rate).ToString();
            }
        }

        return "0";
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

I call them as follows:

Problems using above two converters :

They refer to each-other, like cyclic reference but I don't get stackOverflow exeption. Infact I don't get any errors but no matter whatever I set the value of rate or amount both remains 0. I also know why they remains 0. But don't know the solution.

Lee O. · Accepted Answer

In order to use a converter, you will only use 1 converter. You will need to make the scope of the quantity field in your converter be at class level so that it can retain the value of quantity to calculate the new rate on the ConvertBack call. My model doesn't have an Amount property now but if you need it for any business logic, you would just have a getter that returns Quantity * Rate since Amount will always equal that result.

AmountConverter - I used decimals but you can change to int and handle rounding however you decide.

public class AmountConverter : IMultiValueConverter
{
    decimal quantity = 0m;
    decimal rate = 0m;

    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (decimal.TryParse(values[0].ToString(), out quantity) && decimal.TryParse(values[1].ToString(), out rate))
        {
            return (quantity * rate).ToString();
        }

        return "0";
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        decimal amount = 0m;
        object[] values = new object[2];
        values[0] = quantity;
        values[1] = rate;

        if (decimal.TryParse(value.ToString(), out amount))
        {
            if (quantity != 0m)
                values[1] = amount / quantity;
        }

        return values;
    }
}

XAML - I simplified to use a few TextBlocks just to demo the functionality. If Quantity is 0 then entering a new Amount will reset the Amount to 0 since you can't divide by 0.

DataGrid Calculated column does not show any data

Answers (2)

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