深入探索Silverlight数据绑定与模板技术

### 深入探索Silverlight数据绑定与模板技术 #### 一、Silverlight数据绑定基础 Silverlight的数据绑定系统为开发者提供了强大的功能，但与WPF不同，它缺少`IMultiValueConverter`接口，这意味着开发者只能进行单个值的转换，无法进行值的组合或计算。 #### 二、使用值转换器创建对象 值转换器在弥合数据存储方式和显示方式之间的差距时非常重要。例如，当数据库中的图片数据以字节数组形式存储时，可以使用值转换器将其转换为`BitmapImage`对象。 以下是一个`ImagePathConverter`的示例： ```vb Public Class ImagePathConverter Implements IValueConverter Private _rootUri As String Public Property RootUri() As String Get Return _rootUri End Get Set(ByVal value As String) _rootUri = value End Set End Property Public Sub New() Dim uri As String = HtmlPage.Document.DocumentUri.ToString() ' Remove the web page from the current URI to get the root URI. RootUri = uri.Remove(uri.LastIndexOf("/"c), _ uri.Length - uri.LastIndexOf("/"c)) End Sub Public Function Convert(ByVal value As Object, ByVal targetType As Type, _ ByVal parameter As Object, ByVal culture As CultureInfo) As Object _ Implements IValueConverter.Convert Dim imagePath As String = RootUri & "/" & CStr(value) Return New BitmapImage(New Uri(imagePath)) End Function Public Function ConvertBack(ByVal value As Object, ByVal targetType As Type, _ ByVal parameter As Object, ByVal culture As CultureInfo) As Object _ Implements IValueConverter.ConvertBack ' Images aren't editable, so there's no need to support ConvertBack. Throw New NotSupportedException() End Function End Class ``` 使用步骤如下： 1. 将转换器添加到资源中： ```xml <UserControl.Resources> <local:ImagePathConverter x:Key="ImagePathConverter"></local:ImagePathConverter> </UserControl.Resources> ``` 2. 创建绑定表达式： ```xml <Image Margin="5" Grid.Row="2" Grid.Column="1" Stretch="None" HorizontalAlignment="Left" Source= "{Binding ProductImagePath, Converter={StaticResource ImagePathConverter}}"> </Image> ``` 为了提高这个示例的健壮性，可以添加一些属性来处理异常情况，例如添加`SuppressExceptions`属性或`DefaultImage`属性。 #### 三、应用条件格式 有些值转换器用于根据数据规则格式化元素的外观。例如，`PriceToBackgroundConverter`可以根据产品价格设置不同的背景颜色。 以下是`PriceToBackgroundConverter`的示例： ```vb Public Class PriceToBackgroundConverter Implements IValueConverter Private _minimumPriceToHighlight As Double Public Property MinimumPriceToHighlight() As Double Get Return _minimumPriceToHighlight End Get Set(ByVal value As Double) _minimumPriceToHighlight = value End Set End Property Private _highlightBrush As Brush Public Property HighlightBrush() As Brush Get Return _highlightBrush End Get Set(ByVal value As Brush) _highlightBrush = value End Set End Property Private _defaultBrush As Brush Public Property DefaultBrush() As Brush Get Return _defaultBrush End Get Set(ByVal value As Brush) _defaultBrush = value End Set End Property Public Function Convert(ByVal value As Object, ByVal targetType As ```