在Silverlight 2中创建密码输入框

Silverlight Beta2中，没有提供密码输入框控件，估计在正式版里应该提供吧。Chris Pietschmann自己写了一个，原文地址是：

http://pietschsoft.com/post/2008/03/PasswordTextBox-for-Silverlight-2-Beta-1.aspx

创建一个PasswordTextBox.cs类，代码如下：

/// Copyright2008ChrisPietschmann( http://pietschsoft.com )
/// ThisworkislicensedunderaCreativeCommonsAttribution3.0UnitedStatesLicense
/// http://creativecommons.org/licenses/by/3.0/us/
///
/// ThisisaPasswordTextBoxbuiltforusewithSilverlight2Beta1
/// Thereasonthiswasbuilt,isbecausethestandardTextBoxin
/// Silverlight2Beta1doesnothavePasswordsupport.
/// OriginalLink: http://pietschsoft.com/post/2008/03/PasswordTextBox-for-Silverlight-2-Beta-1.aspx
///

using System.Windows.Controls;

namespace SilverlightPasswordTextBox
{
public partial class PasswordTextBox:TextBox
{
public PasswordTextBox()
{
this .TextChanged += new TextChangedEventHandler(PasswordTextBox_TextChanged);
this .KeyDown += new System.Windows.Input.KeyEventHandler(PasswordTextBox_KeyDown);
}

#region EventHandlers

public void PasswordTextBox_TextChanged( object sender,TextChangedEventArgse)
{
if ( base .Text.Length >= _Text.Length)
_Text += base .Text.Substring(_Text.Length);
DisplayMaskedCharacters();
}

public void PasswordTextBox_KeyDown( object sender,System.Windows.Input.KeyEventArgse)
{
int cursorPosition = this .SelectionStart;
int selectionLength = this .SelectionLength;

// HandleDeleteandBackspaceKeysAppropriately
if (e.Key == System.Windows.Input.Key.Back
|| e.Key == System.Windows.Input.Key.Delete)
{
if (cursorPosition < _Text.Length)
_Text = _Text.Remove(cursorPosition,(selectionLength > 0 ? selectionLength: 1 ));
}

base .Text = _Text;
this .Select((cursorPosition > _Text.Length ? _Text.Length:cursorPosition), 0 );
DisplayMaskedCharacters();
}

#endregion

#region PrivateMethods

private void DisplayMaskedCharacters()
{
int cursorPosition = this .SelectionStart;

// ThischangestheTextpropertyofthebaseTextBoxclasstodisplayallAsterisksinthecontrol
base .Text = new string (_PasswordChar,_Text.Length);

this .Select((cursorPosition > _Text.Length ? _Text.Length:cursorPosition), 0 );
}

#endregion

#region Properties

private string _Text = string .Empty;
/// <summary>
/// Thetextassociatedwiththecontrol.
/// </summary>
public new string Text
{
get { return _Text;}
set
{
_Text = value;
DisplayMaskedCharacters();
}
}

private char _PasswordChar = ' * ' ;
/// <summary>
/// Indicatesthecharactertodisplayforpasswordinput.
/// </summary>
public char PasswordChar
{
get { return _PasswordChar;}
set {_PasswordChar = value;}
}

#endregion
}
}

使用方法：

< UserControl x:Class ="SilverlightApplication1.Page"
xmlns ="http://schemas.microsoft.com/client/2007"
xmlns:x ="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:myctl ="clr-namespace:SilverlightApplication1;assembly=SilverlightApplication1" Width ="600" Height ="480" >
< Grid x:Name ="LayoutRoot" Background ="White" >
< Canvas Canvas.Top ="20" >
< myctl:PasswordTextBox x:Name ="UserPassword" Width ="200" Height ="30" Canvas.Top ="40" Canvas.Left ="20" ></ myctl:PasswordTextBox >
</ Canvas >
</ Grid >
</ UserControl >

注意：要先加入名称空间，具体的值是：

clr-namespace:名称空间全名;assembly=程序集名称

通过使用，发现两个问题：

1，<myctl:PasswordTextBoxPasswordChar="" />设置会报错

2，Text="初始值"仍旧是明文