学步园

这一节是对.NET2.0事件绑定技术的总结。
    .NET事件绑定是基于Observer模式的，关于这部分见我的《CLR笔记10.事件》。在.NET2.0中，对Observer进行了一次包装，可以引用System.Component命名空间，实现INotifyPropertyChanged接口，可以获得事件PropertyChanged，以及PropertyChangedEventArgs。于是在这套体系下，事件机制事先搭建好了。

namespace System.ComponentModel
{
    public delegate void PropertyChangedEventHandler(object sender, PropertyChangedEventArgs e);

    public interface INotifyPropertyChanged
    {
        event PropertyChangedEventHandler PropertyChanged;
    }

    public class PropertyChangedEventArgs : EventArgs
    {
        public PropertyChangedEventArgs(string propertyName);

        public virtual string PropertyName { get; }
    }
}

下面看一个例子，这个例子将贯穿本章。

XAML部分：

<Window >
  <Grid>
    
    <TextBlock >Name:</TextBlock>
    <TextBox x:Name="nameTextBox"  />
    <TextBlock >Age:</TextBlock>
    <TextBox x:Name="ageTextBox"  />
    <Button x:Name="birthdayButton" >Birthday</Button>
  </Grid>
</Window>

后台代码部分：

    public partial class Window1 : System.Windows.Window
    {
        Person person = new Person("Tom", 9);

        public Window1()
        {
            InitializeComponent();

            this.nameTextBox.Text = person.Name;
            this.ageTextBox.Text = person.Age.ToString();

            // Watch for changes in the controls
            this.nameTextBox.TextChanged += nameTextBox_TextChanged;
            this.ageTextBox.TextChanged += ageTextBox_TextChanged;

            person.PropertyChanged += person_PropertyChanged;

            this.birthdayButton.Click += birthdayButton_Click;
        }

        void person_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            switch (e.PropertyName)
            {
                case "Name":
                    this.nameTextBox.Text = person.Name;
                    break;

                case "Age":
                    this.ageTextBox.Text = person.Age.ToString();
                    break;
            }
        }

        void nameTextBox_TextChanged(object sender, TextChangedEventArgs e)
        {
            person.Name = nameTextBox.Text;
        }

        void ageTextBox_TextChanged(object sender, TextChangedEventArgs e)
        {
            int age = 0;
            if (int.TryParse(ageTextBox.Text, out age))
            {
                person.Age = age;
            }
        }

        private void birthdayButton_Click(Object sender, RoutedEventArgs e)
        {
            ++person.Age;

            MessageBox.Show(
              string.Format(
                "Happy Birthday, {0}, age {1}!",
                person.Name,
                person.Age),
              "Birthday");
        }
    }

辅助类：

    public class Person : INotifyPropertyChanged
    {
        public Person() { }
        public Person(string name, int age)
        {
            this.name = name;
            this.age = age;
        }

        string name;
        public string Name
        {
            get { return this.name; }
            set
            {
                this.name = value;
                OnPropertyChanged("Name");
            }
        }

        int age;
        public int Age
        {
            get { return this.age; }
            set
            {
                this.age = value;
                OnPropertyChanged("Age");
            }
        }


        INotifyPropertyChanged Members#region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion

        protected void OnPropertyChanged(string propName)
        {
            if (this.PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propName));
            }
        }

    }

显示效果：