具有数据绑定为null属性值的NumericUpDown控件不起作用

Question

I have a method that sets up a numeric up down to display the value of a property in an object. That property value could be null . I want the numeric up down to display zero if that's the case. This is the code I'm using:

    private void NudNullBindingSetup(NumericUpDown nud, MyObject obj, string propertyName)
    {
        var b = new Binding("Value", obj, propertyName, true,
                            DataSourceUpdateMode.OnPropertyChanged)
        {
            NullValue = 0,
            DataSourceNullValue = null
        };
        nud.DataBindings.Add(b);
    }

If I put a value in the NumericUpDown, then call this binding with an object that has a null for the property, the control is still displaying the original value.

BTW, this method works perfectly if the object actually has a value in the property.

What have I missed?

Edit: I should note this is a null and not DBNull.Value in the object property.

Answer 1

EDIT

You can simply set:

NullValue = (decimal)0,
DataSourceNullValue = null

And it works as expected.

Original

You can use Format event to solve the problem.

The Format event is raised when data is pushed from the data source into the control. You can handle the Format event to convert unformatted data from the data source into formatted data for display.

For example, here is what I wrote and works as expected in the question:

private void NudNullBindingSetup(NumericUpDown nud, MyObject obj, string propertyName)
{
    var b = new Binding("Value", obj, propertyName, true, DataSourceUpdateMode.OnPropertyChanged);
    b.NullValue = 0;                /*Only used in Format event*/
    b.DataSourceNullValue = null;   /*Only used in Format event*/
    b.Format += (s, e) =>
    {
        var binding = (Binding)s;
        var control = (NumericUpDown)binding.Control;

        control.Value =
            e.Value == binding.DataSourceNullValue ?
                (int)binding.NullValue : ((int?)e.Value).Value;
    };
    nud.DataBindings.Add(b);
}

And here is MyObject

public class MyObject
{
    public int? Value { get; set; }
}