public partial class Form1 : Form
    {
        MyData _myData = null;
        public Form1()
        {
            InitializeComponent();


        }

        private void Form1_Load(object sender, EventArgs e)
        {
            _myData = new MyData();
            textBox1.DataBindings.Add(
 
"Text", _myData, "TheValue", false, DataSourceUpdateMode.OnPropertyChanged);
            textBox2.DataBindings.Add("Text", _myData, "TheValue", false, DataSourceUpdateMode.Never);
        }

        private void textBox3_TextChanged(object sender, EventArgs e)
        {
            _myData.TheValue 
 
= textBox3.Text;
        }




    }

    public class MyData:INotifyPropertyChanged
    {
        private string _theValue = string.Empty;
        public string TheValue
        {
            get { return _theValue; }
            set {
                if (string.IsNullOrEmpty(value) || value == _theValue)
                    
 
return;
                _theValue = value;
                NotifyPropertyChanged(() => TheValue);
            }

        }

        public event PropertyChangedEventHandler PropertyChanged;

        public void NotifyPropertyChanged<T>(Expression<Func<T>> property)
        {
            if (PropertyChanged == null)
                return;

            var memberExpression = property.Body as MemberExpression;
            if (memberExpression == null)
                return;

            PropertyChanged.Invoke(this, new PropertyChangedEventArgs(memberExpression.Member.Name));
        }


    }

觀察者模式

https://www.cnblogs.com/xmfdsh/p/4047114.html