数值更改时，NumericUpDown DataBinding属性不会更新

Question

I am attempting to perform a DataBinding on a NumericUpDown WinForm control. Performing the binding works as designed, but I am having an issue with the value not being pushed to the binded property until the element goes out of focus. Is there something I am missing to get the property to update when the value changes in the control without requiring the focus to be lost?

If this is working as designed, is there a way to force the property update without losing focus?

Logic:

using System;
using System.Windows.Forms;

public partial class Form1 : Form
{
    private NumericUpDown numericUpDown1 = new NumericUpDown();
    private ExampleData _ed = new ExampleData();

    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        // Define the UI Control
        numericUpDown1.DecimalPlaces = 7;
        numericUpDown1.Location = new System.Drawing.Point(31, 33);
        numericUpDown1.Name = "numericUpDown1";
        numericUpDown1.Size = new System.Drawing.Size(120, 20);
        numericUpDown1.TabIndex = 0;

        // Add the UI Control
        Controls.Add(numericUpDown1);

        // Bind the property to the UI Control
        numericUpDown1.DataBindings.Add("Value", _ed, nameof(_ed.SampleDecimal));

        numericUpDown1.ValueChanged += NumericUpDown1_ValueChanged;
    }

    private void NumericUpDown1_ValueChanged(object sender, EventArgs e)
    {
        // This will fire as you change the control without losing focus.
        System.Diagnostics.Debugger.Break();
    }
}

public class ExampleData
{
    public decimal SampleDecimal
    {
        get { return _sampleDecimal; }
        set
        {
            // This set isn't called until after you lose focus of the control.
            System.Diagnostics.Debugger.Break();
            _sampleDecimal = value;
        }
    }

    private decimal _sampleDecimal = 1.0m;
}

Answer 1

Change your binding to this:

numericUpDown1.DataBindings.Add(nameof(NumericUpDown.Value), _ed, nameof(ExampleData.SampleDecimal), false, DataSourceUpdateMode.OnPropertyChanged);

This will ensure that the binding fires when the value changes rather than when you move focus away from the control.

If you then want to be able to update the SampleDecimal from code and have it update on your numericupdown you'd need to implement the INotifyPropertyChanged interface on your SampleData class, like this:

public class ExampleData : INotifyPropertyChanged
{

    protected void OnPropertyChanged([CallerMemberName] string propertyName = "")
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public decimal SampleDecimal
    {
        get { return _sampleDecimal; }
        set
        {
            _sampleDecimal = value;
            OnPropertyChanged();
        }
    }

    private decimal _sampleDecimal = 1.0m;
}