WindowsPhone自定义控件详解（三） - 实战：自定义带水印的PasswordBox控件，Watermar
声明：这个控件是在WatermarkedTextBox的基础上改的。
从WP7-WatermarkedTextBox-custom-control">http://www.windowsphonegeek.com/articles/WP7-WatermarkedTextBox-custom-control上下载WatermarkedTextBox控件
原理分析：
在PasswordBox后面加水印和在TextBox后面加水印差不多，有以下要求：
PasswordBox里没内容时，显示水印
PasswordBox里有内容时，不显示水印，而显示内容
最简单的想法就是，在PasswordBox控件后面加上一个类似TextBlock的控件，然后重写焦点回调方法，当有焦点时，水印不显示，无焦点时，根据是否有内容而决定是否显示水印。
思路如上，下面开始分析WatermarkedTextBox的代码，看看它的作者是不是和我们想法一样。
一、 分析WatermarkedTextBox代码
themes/generic.xaml
自定义控件的样式文件必须要以generic.xaml命名，放到themes目录中。
[html] <ControlTemplate x:Key="PhoneDisabledTextBoxTemplate" TargetType="TextBox">
<ContentControl x:Name="ContentElement" BorderThickness="0" HorizontalContentAlignment="Stretch" Margin="{StaticResource PhoneTextBoxInnerMargin}" Padding="{TemplateBinding Padding}" VerticalContentAlignment="Stretch"/>
</ControlTemplate>
<Style TargetType="local:WatermarkedTextBox">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="local:WatermarkedTextBox">
<Grid Background="Transparent">
<Border x:Name="EnabledBorder">
<Grid>
<ContentControl x:Name="watermarkContent" Style="{TemplateBinding WatermarkStyle}" Content="{TemplateBinding Watermark}" Background="Transparent" Opacity="0.5"/>
<ContentControl x:Name="ContentElement" BorderThickness="0" VerticalContentAlignment="Stretch"/>
</Grid>
</Border>
<Border x:Name="DisabledOrReadonlyBorder" Background="Transparent" Visibility="Collapsed">
<TextBox x:Name="DisabledOrReadonlyContent" Background="Transparent" IsReadOnly="True" Text="{TemplateBinding Text}" Template="{StaticResource PhoneDisabledTextBoxTemplate}"/>
</Border>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<ControlTemplate x:Key="PhoneDisabledTextBoxTemplate" TargetType="TextBox">
<ContentControl x:Name="ContentElement" BorderThickness="0" HorizontalContentAlignment="Stretch" Margin="{StaticResource PhoneTextBoxInnerMargin}" Padding="{TemplateBinding Padding}" VerticalContentAlignment="Stretch"/>
</ControlTemplate>
<Style TargetType="local:WatermarkedTextBox">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="local:WatermarkedTextBox">
<Grid Background="Transparent">
<Border x:Name="EnabledBorder">
<Grid>
<ContentControl x:Name="watermarkContent" Style="{TemplateBinding WatermarkStyle}" Content="{TemplateBinding Watermark}" Background="Transparent" Opacity="0.5"/>
<ContentControl x:Name="ContentElement" BorderThickness="0" VerticalContentAlignment="Stretch"/>
</Grid>
</Border>
<Border x:Name="DisabledOrReadonlyBorder" Background="Transparent" Visibility="Collapsed">
<TextBox x:Name="DisabledOrReadonlyContent" Background="Transparent" IsReadOnly="True" Text="{TemplateBinding Text}" Template="{StaticResource PhoneDisabledTextBoxTemplate}"/>
</Border>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
注：上面省略了一部分无关紧要代码。
http://blog.csdn.net/mr_raptor/article/details/7251992
上面的XAML文件，定义了WatermarkedTextBox的样式：
文件开始，定义了一个ControlTemplate元素，由前两节知识可知，它是要对一个控件设置模板，从后面的TargetType="TextBox"可知，是针对TextBox类型控件，它里面自定义了一个ContentControl类名字为ContentElement。
通过TargetType="local:WatermarkedTextBox" 可知，它是针对WatermarkedTextBox的控件样式。
在EnabledBorder里定义了两个内容控件元素：watermarkContent和ContentElement，watermarkContent里，绑定了依赖属性Watermark（在WatermarkTextBox.cs里声明）。
在下面的DisabledOrReadonlyBorder里面是一个TextBox 控件，它绑定了WatermarkedTextBox里的Text属性，同时这个TextBox 控件，的模板设置为：PhoneDisabledTextBoxTemplate，它这么做的目的是，可以设置WatermarkedTextBox的属性为Disabled，这时，水印就消失了，而显示原先的TextBox控件。
2. WatermarkTextBox.cs
[csharp] namespace WatermarkedTextBoxControl
{
public class WatermarkedTextBox : TextBox
{
ContentControl WatermarkContent;
public static readonly DependencyProperty WatermarkProperty =
DependencyProperty.Register("Watermark", typeof(object), typeof(WatermarkedTextBox), new PropertyMetadata(OnWatermarkPropertyChanged));
public static readonly DependencyProperty WatermarkStyleProperty =
DependencyProperty.Register("WatermarkStyle", typeof(Style), typeof(WatermarkedTextBox), null);
public Style WatermarkStyle
{
get { return base.GetValue(WatermarkStyleProperty) as Style; }
set { base.SetValue(WatermarkStyleProperty, value); }
}
public object Watermark
{
get { return base.GetValue(WatermarkProperty) as object; }
set { base.SetValue(WatermarkProperty, value); }
}
public WatermarkedTextBox()
{
DefaultStyleKey = typeof(WatermarkedTextBox);
}
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
this.WatermarkContent = this.GetTemplateChild("watermarkContent") as ContentControl;
if(WatermarkContent != null)
{
DetermineWatermarkContentVisibility();
}
}
protected override void OnGotFocus(RoutedEventArgs e)
{
if (WatermarkContent != null && string.IsNullOrEmpty(this.Text))
{
this.WatermarkContent.Visibility = Visibility.Collapsed;
}
base.OnGotFocus(e);
}
protected override void OnLostFocus(RoutedEventArgs e)
{
if (WatermarkContent != null && string.IsNullOrEmpty(this.Text))
{
this.WatermarkContent.Visibility = Visibility.Visible;
}
base.OnLostFocus(e);
}
private static void OnWatermarkPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
{
WatermarkedTextBox watermarkTextBox = sender as WatermarkedTextBox;
if(watermarkTextBox != null && watermarkTextBox.WatermarkContent !=null)
{
watermarkTextBox.DetermineWatermarkContentVisibility();
}
}
private void DetermineWatermarkContentVisibility()
{
if (string.IsNullOrEmpty(this.Text))
{
this.WatermarkContent.Visibility = Visibility.Visible;
}
else
{
this.WatermarkContent.Visibility = Visibility.Collapsed;
}
}
}
}
}
namespace WatermarkedTextBoxControl
{
public class WatermarkedTextBox : TextBox
{
ContentControl WatermarkContent;
public static readonly DependencyProperty WatermarkProperty =
DependencyProperty.Register("Watermark", typeof(object), typeof(WatermarkedTextBox), new PropertyMetadata(OnWatermarkPropertyChanged));
public static readonly DependencyProperty WatermarkStyleProperty =
DependencyProperty.Register("WatermarkStyle", typeof(Style), typeof(WatermarkedTextBox), null);
public Style WatermarkStyle
{
get { return base.GetValue(WatermarkStyleProperty) as Style; }
set { base.SetValue(WatermarkStyleProperty, value); }
}
public object Watermark
{
get { return base.GetValue(WatermarkProperty) as object; }
set { base.SetValue(WatermarkProperty, value); }
}
public WatermarkedTextBox()
{
DefaultStyleKey = typeof(WatermarkedTextBox);
}
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
this.WatermarkContent = this.GetTemplateChild("watermarkContent") as ContentControl;
if(WatermarkContent != null)
{
DetermineWatermarkContentVisibility();
}
}
protected override void OnGotFocus(RoutedEventArgs e)
{
if (WatermarkContent != null && string.IsNullOrEmpty(this.Text))
{
this.WatermarkContent.Visibility = Visibility.Collapsed;
}
base.OnGotFocus(e);
}
protected override void OnLostFocus(RoutedEventArgs e)
{
if (WatermarkContent != null && string.IsNullOrEmpty(this.Text))
{
this.WatermarkContent.Visibility = Visibility.Visible;
}
base.OnLostFocus(e);
}
private static void OnWatermarkPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
{
WatermarkedTextBox watermarkTextBox = sender as WatermarkedTextBox;
if(watermarkTextBox != null && watermarkTextBox.WatermarkContent !=null)
{
watermarkTextBox.DetermineWatermarkContentVisibility();
}
}
private void DetermineWatermarkContentVisibility()
{
if (string.IsNullOrEmpty(this.Text))
{
this.WatermarkContent.Visibility = Visibility.Visible;
}
else
{
this.WatermarkContent.Visibility = Visibility.Collapsed;
}
}
}
}
}
原创地址：http://blog.csdn.net/mr_raptor/article/details/7251992
由这个WatermarkedTextBox类可知：
它继承了TextBox类
增加了Watermark和WatermarkStyle两个依赖属性，用于用户设置它的水印内容和样式，在Watermark属性里添加了属性改变事件：OnWatermarkPropertyChanged
重载了OnApplyTemplate方法来取得generic.xaml文件里声明的元素引用：watermarkContent，并且根据generic.xaml里的TextBox ：DisabledOrReadonlyContent，取得它里面是否有内容，如果有内容，则WatermarkContent不可见，否则WatermarkContent可见。
重载了OnGotFocus，OnLostFocus，当该自定义控件得到焦点时，设置WatermarkContent不可见，否则WatermarkContent可见。
由上面的分析可知，当用户设置了自定义控件的Watermark属性时，回调注册的OnWatermarkPropertyChanged方法，在该方法里，判断是否WatermarkContent里有内容，如果有，WatermarkContent不可见，否则WatermarkContent可见。两样，重载了OnGotFocus，OnLostFocus，在得到和失去焦点时也要判断是否将WatermarkContent设置为可见与否。
二、 自定义WatermarkedPasswordBox
根据前面的分析，我们可以试着做以下修改：
新建类WatermarkedPasswordBox
将WatermarkTextBox.cs拷贝到类WatermarkedPasswordBox里，改下类名，让WatermarkedPasswordBox继承了Password类
在themes/generic.xaml里，拷贝 <Style TargetType="local:WatermarkedPasswordBox">里的全部代码，改为WatermarkedPasswordBox的代码，中间细节自己改就行了，我们不打算支持Disabled属性，所以DisabledOrReadonlyBorder去掉就行了，将EnabledBorder里的ContentElement去掉，换成PasswordBox，名字还是ContentElement
编译时，错误出现了：WatermarkedPasswordBox里this.Text出错，这是因为Password没有Text属性，它有个Password属性，所以要做下面的修改：
让WatermarkedPasswordBox类继承TextBox，但是添加一个属性：PasswordBox类型的PasswordContent
在OnApplyTemplate方法里，获得自己加的PasswordBox控件的引用ContentElement，为PasswordBox控件添加PasswordChanged事件，当密码框里内容改变时，将TextBox的Text属性的值为PasswordBox.Password的值
同样，在XAML样式文件里，在PasswordBox控件里加上 Password="{TemplateBinding Text}"
修改后的代码如下：
XAML：
[html] <Style TargetType="local:WatermarkedPasswordBox">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="local:WatermarkedPasswordBox">
<Grid Background="Transparent">
<Border x:Name="EnabledBorder" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Margin="{StaticResource PhoneTouchTargetOverhang}">
<Grid>
<ContentControl x:Name="watermarkContent" Style="{TemplateBinding WatermarkStyle}" Content="{TemplateBinding Watermark}" Background="Transparent" Opacity="0.5"/>
<PasswordBox x:Name="ContentElement" Background="Transparent"
Password="{TemplateBinding Text}"
BorderThickness="0" HorizontalContentAlignment="Stretch"
Margin="-12,-12,-12,-12"
VerticalContentAlignment="Stretch"/>
</Grid>
</Border>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<Style TargetType="local:WatermarkedPasswordBox">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="local:WatermarkedPasswordBox">
<Grid Background="Transparent">
<Border x:Name="EnabledBorder" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Margin="{StaticResource PhoneTouchTargetOverhang}">
<Grid>
<ContentControl x:Name="watermarkContent" Style="{TemplateBinding WatermarkStyle}" Content="{TemplateBinding Watermark}" Background="Transparent" Opacity="0.5"/>
<PasswordBox x:Name="ContentElement" Background="Transparent"
Password="{TemplateBinding Text}"
BorderThickness="0" HorizontalContentAlignment="Stretch"
Margin="-12,-12,-12,-12"
VerticalContentAlignment="Stretch"/>
</Grid>
</Border>
</Grid>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
原创地址：http://blog.csdn.net/mr_raptor/article/details/7251992
C#：
[html] public class WatermarkedPasswordBox : TextBox
{
ContentControl WatermarkContent;
private PasswordBox PasswordContent;
public object Watermark
{
get { return base.GetValue(WatermarkProperty) as object; }
set { base.SetValue(WatermarkProperty, value); }
}
public static readonly DependencyProperty WatermarkProperty =
DependencyProperty.Register("Watermark", typeof(object), typeof(WatermarkedPasswordBox), new PropertyMetadata(OnWatermarkPropertyChanged));
private static void OnWatermarkPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
{
WatermarkedPasswordBox watermarkTextBox = sender as WatermarkedPasswordBox;
if (watermarkTextBox != null && watermarkTextBox.WatermarkContent != null)
{
watermarkTextBox.DetermineWatermarkContentVisibility();
}
Debug.WriteLine("OnWatermarkPropertyChanged");
}
public Style WatermarkStyle
{
get { return base.GetValue(WatermarkStyleProperty) as Style; }
set { base.SetValue(WatermarkStyleProperty, value); }
}
public static readonly DependencyProperty WatermarkStyleProperty =
DependencyProperty.Register("WatermarkStyle", typeof(Style), typeof(WatermarkedPasswordBox), null);
public WatermarkedPasswordBox()
{
DefaultStyleKey = typeof(WatermarkedPasswordBox);
}
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
thisthis.WatermarkContent = this.GetTemplateChild("watermarkContent") as ContentControl;
thisthis.PasswordContent = this.GetTemplateChild("ContentElement") as PasswordBox;
if (WatermarkContent != null && WatermarkContent != null)
{
PasswordContent.PasswordChanged += new RoutedEventHandler(PasswordContent_PasswordChanged);
DetermineWatermarkContentVisibility();
}
}
void PasswordContent_PasswordChanged(object sender, RoutedEventArgs e)
{
PasswordBox passwdBx = sender as PasswordBox;
this.Text = passwdBx.Password;
}
protected override void OnGotFocus(RoutedEventArgs e)
{
if (WatermarkContent != null && WatermarkContent != null && string.IsNullOrEmpty(this.PasswordContent.Password))
{
this.WatermarkContent.Visibility = Visibility.Collapsed;
}
base.OnGotFocus(e);
}
protected override void OnLostFocus(RoutedEventArgs e)
{
if (WatermarkContent != null && WatermarkContent != null && string.IsNullOrEmpty(this.PasswordContent.Password))
{
this.WatermarkContent.Visibility = Visibility.Visible;
}
base.OnLostFocus(e);
}
private void DetermineWatermarkContentVisibility()
{
if (string.IsNullOrEmpty(this.PasswordContent.Password))
{
this.WatermarkContent.Visibility = Visibility.Visible;
}
else
{
this.WatermarkContent.Visibility = Visibility.Collapsed;
}
}
}
public class WatermarkedPasswordBox : TextBox
{
ContentControl WatermarkContent;
private PasswordBox PasswordContent;
public object Watermark
{
get { return base.GetValue(WatermarkProperty) as object; }
set { base.SetValue(WatermarkProperty, value); }
}
public static readonly DependencyProperty WatermarkProperty =
DependencyProperty.Register("Watermark", typeof(object), typeof(WatermarkedPasswordBox), new PropertyMetadata(OnWatermarkPropertyChanged));
private static void OnWatermarkPropertyChanged(DependencyObject sender, DependencyPropertyChangedEventArgs args)
{
WatermarkedPasswordBox watermarkTextBox = sender as WatermarkedPasswordBox;
if (watermarkTextBox != null && watermarkTextBox.WatermarkContent != null)
{
watermarkTextBox.DetermineWatermarkContentVisibility();
}
Debug.WriteLine("OnWatermarkPropertyChanged");
}
public Style WatermarkStyle
{
get { return base.GetValue(WatermarkStyleProperty) as Style; }
set { base.SetValue(WatermarkStyleProperty, value); }
}
public static readonly DependencyProperty WatermarkStyleProperty =
DependencyProperty.Register("WatermarkStyle", typeof(Style), typeof(WatermarkedPasswordBox), null);
public WatermarkedPasswordBox()
{
DefaultStyleKey = typeof(WatermarkedPasswordBox);
}
public override void OnApplyTemplate()
{
base.OnApplyTemplate();
this.WatermarkContent = this.GetTemplateChild("watermarkContent") as ContentControl;
this.PasswordContent = this.GetTemplateChild("ContentElement") as PasswordBox;
if (WatermarkContent != null && WatermarkContent != null)
{
PasswordContent.PasswordChanged += new RoutedEventHandler(PasswordContent_PasswordChanged);
DetermineWatermarkContentVisibility();
}
}
void PasswordContent_PasswordChanged(object sender, RoutedEventArgs e)
{
PasswordBox passwdBx = sender as PasswordBox;
this.Text = passwdBx.Password;
}
protected override void OnGotFocus(RoutedEventArgs e)
{
if (WatermarkContent != null && WatermarkContent != null && string.IsNullOrEmpty(this.PasswordContent.Password))
{
this.WatermarkContent.Visibility = Visibility.Collapsed;
}
base.OnGotFocus(e);
}
protected override void OnLostFocus(RoutedEventArgs e)
{
if (WatermarkContent != null && WatermarkContent != null && string.IsNullOrEmpty(this.PasswordContent.Password))
{
this.WatermarkContent.Visibility = Visibility.Visible;
}
base.OnLostFocus(e);
}
private void DetermineWatermarkContentVisibility()
{
if (string.IsNullOrEmpty(this.PasswordContent.Password))
{
this.WatermarkContent.Visibility = Visibility.Visible;
}
else
{
this.WatermarkContent.Visibility = Visibility.Collapsed;
}
}
}
编译通过，将生成的库引入到Demo程序里，然后将控件加上，成功，效果如下。
左图，未输入内容，显示水印，右图，输入内容时显示效果。
摘自 mr_raptor的专栏