为什么依赖属性在五秒钟内起作用。
出现的问题：在五秒钟内改变textbox的值，lable 和textblock都可以改变，过了五种就不行了。

namespace WpfApplication1
{

public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
Student stu = new Student();
stu.SetBinding(Student.NameProperty, new Binding("Text") { Source = tx1 });//数据源为 textbox
l1.SetBinding(Label.ContentProperty, new Binding("Name") { Source = stu }); //l1为lable
txb1.SetBinding(TextBlock.TextProperty, new Binding("Name") { Source = stu });//txb1为TextBlock



}
}

public class Student:DependencyObject
{


public string Name
{
get { return (string)GetValue(NameProperty); }
set { SetValue(NameProperty, value); }
}


public static readonly DependencyProperty NameProperty =
DependencyProperty.Register("Name", typeof(string), typeof(Student));

public BindingExpressionBase SetBinding(DependencyProperty dp,BindingBase binding)
{
return BindingOperations.SetBinding(this,dp,binding);
}



}
}
[解决办法]
把 Student stu = new Student(); 放到外面（MainWindow的全局变量）。