13、依赖属性

例子一：简单的依赖属性

<StackPanel>
        <TextBox Name="txtBox1"></TextBox>
        <TextBox Name="txtBox2"></TextBox>
        <Button Name="btnTest" Width="120" Height="36" Click="BtnTest_OnClick">OK</Button>
</StackPanel>

    class Student:DependencyObject
    {
        //最简单的依赖属性
        public static readonly DependencyProperty NameProperty = DependencyProperty.Register("Name", typeof (string),
                                                                                             typeof (Student));
    }

        private void BtnTest_OnClick(object sender, RoutedEventArgs e)
        {
            Student stu=new Student();
            stu.SetValue(Student.NameProperty,this.txtBox1.Text);
            this.txtBox2.Text = (string)stu.GetValue(Student.NameProperty);
        }

程序的效果是：在txtBox1中输入内容，点击btnTest按钮，textBox2中Text获得属性值。实质上首先定义了个依赖属性，然后通过txtBox1修改属性值，最后txtBox2获取属性值。这里暂时看不出来依赖属性有啥奇特之处。

例子二：将UI作为数据源，属性作为依赖目标

    <StackPanel>
        <TextBox Name="txtBox1"></TextBox>
        <Button Name="btnTest" Width="120" Height="36" Margin="5" Click="BtnTest_OnClick">Test</Button>
    </StackPanel>

        private Student stu;
        public MainWindow ( )
        {
            InitializeComponent ( );
            stu=new Student();
            Binding binding=new Binding("Text"){Source = txtBox1};
            BindingOperations.SetBinding(stu, Student.NameProperty, binding);
        }

        private void BtnTest_OnClick(object sender, RoutedEventArgs e)
        {
            MessageBox.Show(stu.GetValue(Student.NameProperty).ToString());
        }

        private Student stu;
        private Binding binding;
        public MainWindow ( )
        {
            InitializeComponent ( );
            stu=new Student();
            binding=new Binding("Text"){Source = txtBox1};
            BindingOperations.SetBinding(stu, Student.NameProperty, binding);
        }

        private void BtnTest_OnClick(object sender, RoutedEventArgs e)
        {
            MessageBox.Show(stu.GetValue(Student.NameProperty).ToString());
        }

        private void BtnTest1_OnClick(object sender, RoutedEventArgs e)
        {
            txtBox2.SetBinding ( TextBox.TextProperty,binding );
        }

现在我们使用的依赖属性依靠GetValue和SetValue两个方法进行对外界的暴露，而且在使用GetValue的时候还需要进行一次数据类型的转换。

例子三：为依赖属性添加一个CLR属性外包装

    class Student:DependencyObject
    {
        //依赖属性
        public static readonly DependencyProperty NameProperty = DependencyProperty.Register("Name", typeof (string),
                                                                                             typeof (Student));
        //CLR属性包装器
        public string Name
        {
            get { return (string) GetValue(NameProperty); }
            set{SetValue(NameProperty,value);}
        }
        
        //SetBinding包装
        public BindingExpressionBase SetBinding(DependencyProperty dp, BindingBase binding)
        {
            return BindingOperations.SetBinding(this, dp, binding);
        }

    }

        <TextBox Name="txtBox1" Text="你是谁" ></TextBox>
        <TextBox Name="txtBox2"></TextBox>

        private Student stu;
        public MainWindow ( )
        {
            InitializeComponent ( );
            stu=new Student();
            stu.SetBinding(Student.NameProperty, new Binding("Text") {Source = txtBox1});
            txtBox2.SetBinding(TextBox.TextProperty, new Binding("Name") {Source = stu});
        }

运行程序，当在txtBox1中输入字符的时候，txtBox2就会同步显示，此时Student对象的Name属性值也同步变化了。

了解依赖属性存取值得秘密

 依赖属性多用在自定义控件和扩展已有空间的某些功能-小灰猫说的