如何取消数据绑定更改?

我有一个包含对象的列表视图。当用户选择要编辑的项目时,将打开一个表单,用户可以在其中进行更改。当前,当用户在进行更改后关闭表单时,列表视图中的原始对象将被更新,即使他在不单击“保存”的情况下关闭了表单。当用户要取消更改时,如何阻止数据绑定?

<!--xaml-->
<TextBox x:Name="tbFirstName" Text="{Binding Path=MyObject.first_name}" />
<TextBox x:Name="tbLastName" Text="{Binding Path=MyObject.last_name}"  />

public class MyObject {
     public string FirstName {get; set;}
     public string LastName {get; set;}
}

List<MyObject> listOfObjects = new List<MyObject>(); 

//user selects what he wants to edit from a ListView and clicks the Edit button
//the object is passed to a new form where he can make the desired changes.
//the editing form is automatically populated with the object thanks to data binding! this is good! :)

//Edit Button Clicked:
EditorForm ef = new EditorForm(listOfObjects[listview.SelectedIndex]);
ef.ShowDialog();

private MyObject myObject;

public EditorForm(MyObject obj) {
    InitializeComponent();
    myObject = obj;
    DataContext = this;
}        

//user makes changes to FirstName
//user decides to cancel changes by closing form.
//>>> the object is still updated thanks to data-binding. this is bad. :(