原文:

                                                 [WPF]实现密码框的密码绑定

                                                           周银辉

正如绑定TextBox控件的Text属性一样, 我们希望能够将PasswordBox空间的Password属性进行绑定, 比如在MVVM模式中,这似乎是必须的, 但可惜的是, Password属性是不支持绑定的(不是依赖属性, 也没有实现INotifyPropertyChanged).

这可能是出于安全性的考虑. 但在我们的系统为了实现View层密码框中的密码与后台其它层之间的密码属性之间的绑定, 可以采取如下思路: 将密码框的密码和某一个缓冲区进行同步, 缓冲区在和后台进行绑定. 其中密码框与缓冲区之间的同步可采用事件进行通知, 并将缓冲区打造成依赖属性, 然后缓冲区就支持绑定了, 并给后台提供正确的密码.

缓冲区可以是哈希表或其他字典结构, 以便将密码框和缓冲区中的密码一 一对应起来, 也可以使AttachProperty(附加属性), 其实附加属性的机制也就是对缓存了的一个大字典进行操作

    

public

 

static

 

class

 PasswordBoxBindingHelper

    {

        

public

 

static

 

bool

 GetIsPasswordBindingEnabled(DependencyObject obj)

        {

            

return

 (

bool

)obj.GetValue(IsPasswordBindingEnabledProperty);

        }

        

public

 

static

 

void

 SetIsPasswordBindingEnabled(DependencyObject obj, 

bool

 value)

        {

            obj.SetValue(IsPasswordBindingEnabledProperty, value);

        }

        

public

 

static

 

readonly

 DependencyProperty IsPasswordBindingEnabledProperty 

=

            DependencyProperty.RegisterAttached(

"

IsPasswordBindingEnabled

"

, 

typeof

(

bool

), 

            

typeof

(PasswordBoxBindingHelper), 

            

new

 UIPropertyMetadata(

false

, OnIsPasswordBindingEnabledChanged));

        

private

 

static

 

void

 OnIsPasswordBindingEnabledChanged(DependencyObject obj, 

                                                              DependencyPropertyChangedEventArgs e)

        {

            var passwordBox 

=

 obj 

as

 PasswordBox;

            

if

(passwordBox 

!=

 

null

)

            {

                passwordBox.PasswordChanged 

-=

 PasswordBoxPasswordChanged;

                

if

 ((

bool

)e.NewValue)

                {

                    passwordBox.PasswordChanged 

+=

 PasswordBoxPasswordChanged;

                }

               

            }

        }

        

//

when the passwordBox's password changed, update the buffer

        

static

 

void

 PasswordBoxPasswordChanged(

object

 sender, RoutedEventArgs e)

        {

            var passwordBox 

=

 (PasswordBox) sender;

            

if

 (

!

String.Equals(GetBindedPassword(passwordBox),passwordBox.Password))

            {

                SetBindedPassword(passwordBox, passwordBox.Password);

            }

        }

        

public

 

static

 

string

 GetBindedPassword(DependencyObject obj)

        {

            

return

 (

string

)obj.GetValue(BindedPasswordProperty);

        }

        

public

 

static

 

void

 SetBindedPassword(DependencyObject obj, 

string

 value)

        {

            obj.SetValue(BindedPasswordProperty, value);

        }

        

public

 

static

 

readonly

 DependencyProperty BindedPasswordProperty 

=

            DependencyProperty.RegisterAttached(

"

BindedPassword

"

, 

typeof

(

string

), 

            

typeof

(PasswordBoxBindingHelper), 

            

new

 UIPropertyMetadata(

string

.Empty, OnBindedPasswordChanged));

        

//

when the buffer changed, upate the passwordBox's password

        

private

 

static

 

void

 OnBindedPasswordChanged(DependencyObject obj, 

                                                    DependencyPropertyChangedEventArgs e)

        {

            var passwordBox 

=

 obj 

as

 PasswordBox;

            

if

 (passwordBox 

!=

 

null

)

            {

                passwordBox.Password 

=

 e.NewValue 

==

 

null

 

?

 

string

.Empty : e.NewValue.ToString();

            }

        }       

    }

在View层, 如下使用便可以了:

<

PasswordBox  

Helpers:PasswordBoxBindingHelper.IsPasswordBindingEnabled

="True"

 

                     Helpers:PasswordBoxBindingHelper.BindedPassword

=

                     "

{Binding Path=Password, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}

"

 

/>

另外, 在更改了密码框的密码后, 需要手动更新密码框插入符(CaretIndex)的位置, 可惜的是, 密码框并没有给我们提供这样的属性或方法(TextBox有, PasswordBox没有), 可以采用下面的方法来设置:

        

private

 

static

 

void

 SetPasswordBoxSelection(PasswordBox passwordBox, 

int

 start, 

int

 length)

        {

            var select 

=

 passwordBox.GetType().GetMethod(

"

Select

"

, 

                            BindingFlags.Instance 

|

 BindingFlags.NonPublic);

            select.Invoke(passwordBox, 

new

 

object

[] { start, length });

        }