WindowsPhone自定义控件详解（三） 实战：自定义带水印的PasswordBox控件，WatermarkedPasswordBox

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本文系本站原创,欢迎转载! 转载请注明出处:

http://blog.csdn.net/mr_raptor/article/details/7251992

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声明：这个控件是在WatermarkedTextBox的基础上改的。

• 从http://www.windowsphonegeek.com/articles/WP7-WatermarkedTextBox-custom-control上下载WatermarkedTextBox控件

原创地址：http://blog.csdn.net/mr_raptor/article/details/7251992

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：

1. PasswordBox里没内容时，显示水印
2. 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

 

1. 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。

<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

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：

<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#：

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。

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本文系本站原创,欢迎转载! 转载请注明出处:

http://blog.csdn.net/mr_raptor/article/details/7251992

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