WPF and Silverlight 学习笔记（二十一）：数据绑定值的自定义转换

对于数据绑定，绑定的数据源的值类型和绑定目标的依赖属性的值类型可能会不同，系统提供了一些默认的绑定类型转换，另外也可以由用户自定义这种绑定转换：

一、定义CLR类型

定义一个CLR类型，内部存在两个属性字符串类型的ColorString和Color对象类型的ColorObject，供应用程序界面调用：

1: using System.ComponentModel;

2: using System.Windows.Media;

3: 

4: namespace BasicWPFDataBinding

5: {

6:     public class MyBindingColor : INotifyPropertyChanged

7:     {

8:         public event PropertyChangedEventHandler PropertyChanged;

9: 

10:         public MyBindingColor()

11:         {

12:             _ColorString = "Red";

13:             _ColorObject = Colors.Red;

14:         }

15: 

16:         // 字符串类型的ColorString

17:         private string _ColorString;

18:         public string ColorString

19:         {

20:             set

21:             {

22:                 _ColorString = value;

23:                 if (PropertyChanged != null)

24:                 {

25:                     PropertyChanged(this,new PropertyChangedEventArgs("ColorString"));

26:                 }

27:             }

28:             get

29:             {

30:                 return _ColorString;

31:             }

32:         }

33: 

34:         // Color对象类型的ColorObject

35:         private Color _ColorObject;

36:         public Color ColorObject

37:         {

38:             set

39:             {

40:                 _ColorObject = value;

41:                 if (PropertyChanged != null)

42:                 {

43:                     PropertyChanged(this, new PropertyChangedEventArgs("ColorObject"));

44:                 }

45:             }

46:             get

47:             {

48:                 return _ColorObject;

49:             }

50:         }

51:     }

52: }

二、系统自带的类型转换

系统定义了一系列的常用的绑定的数据类型转换，例如可以由字符串（String）型和SolidColorBrush对象间相互转换。字符串与SolidColorBrush的转换规则有两种，一种是对应命名的颜色，如Red、Green、Blue等，另一种是#AARRGGBB或#RRGGBB组成的RGB颜色或ARGB颜色。

例如，下面的示例将字符串类型的ColorString属性绑定到Rectangle的Brush类型的Fill属性上（SolidColorBrush是Brush的子类，可以自动转换）。

XAML代码如下：

1: <StackPanel Grid.Row="0" Grid.Column="0" x:Name="panelBindingColorString">

2:     <StackPanel.Resources>

3:         <c:MyBindingColor x:Key="myDataSourceA" />

4:     </StackPanel.Resources>

5:     <StackPanel.DataContext>

6:         <Binding Source="{StaticResource myDataSourceA}" />

7:     </StackPanel.DataContext>

8:     <TextBlock Margin="5" Text="Binding Fill To String" />

9:     <Rectangle Margin="5" Height="30"

10:                Fill="{Binding Path=ColorString}" />

11:     <TextBox Margin="5" x:Name="txtValueA" />

12:     <Button Margin="5" Content="Change Fill"

13:             x:Name="btn_ChangeColorString" Click="btn_ChangeColorString_Click" />

14:     <Button Margin="5" Content="Get Fill"

15:             x:Name="btn_GetColorString" Click="btn_GetColorString_Click" />

16: </StackPanel>

CS代码如下：

1: #region 利用系统自带的字符串向SolidColorBrush对象的转换实现绑定

2: private void btn_ChangeColorString_Click(object sender, RoutedEventArgs e)

3: {

4:     try

5:     {

6:         MyBindingColor source = (MyBindingColor)(panelBindingColorString.DataContext);

7:         source.ColorString = txtValueA.Text;

8:     }

9:     catch (Exception ex)

10:     {

11:         MessageBox.Show(

12:             ex.Message,

13:             "System Information",

14:             MessageBoxButton.OK,

15:             MessageBoxImage.Error);

16:     }

17:

18: }

19: 

20: private void btn_GetColorString_Click(object sender, RoutedEventArgs e)

21: {

22:     MyBindingColor source = (MyBindingColor)(panelBindingColorString.DataContext);

23: 

24:     MessageBox.Show(

25:         string.Format("The Binding ColorString to {0}.", source.ColorString),

26:         "System Information",

27:         MessageBoxButton.OK,

28:         MessageBoxImage.Information);

29: }

30: #endregion

三、自定义的绑定类型转换

如定义自定义的绑定类型转换，需要定义一个类，对于这个类要求：

实现System.Windows.Data命名空间的IValueConverter接口，这个接口有两个抽象方法，对应两个方向的转换

为此类添加System.Windows.Data命名空间的ValueConversion这个Attribute，指定转换的源类型和目标类型

代码如下：

1: using System;

2: using System.Windows.Data;

3: using System.Windows.Media;

4: 

5: namespace BasicWPFDataBinding

6: {

7:     /// <summary>

8:     /// 自定义的由Color对象向SolidColorBrush对象进行转换

9:     /// </summary>

10:     [ValueConversion(typeof(Color),typeof(SolidColorBrush))]

11:     public class MyColorConverter : IValueConverter

12:     {

13:         #region IValueConverter Members

14: 

15:         // 由Color对象向SolidColorBrush对象转换

16:         public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)

17:    {

18:             Color val = (Color) (value);

19:             return new SolidColorBrush(val);

20:         }

21: 

22:         // 由SolidColorBrush对象向Color对象转换

23:         public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)

24:         {

25:             SolidColorBrush brush = (SolidColorBrush) value;

26:             return brush.Color;

27:         }

28: 

29:         #endregion

30:     }

31: }

在绑定时，需要在绑定中指明转换的类型Converter

示例代码如下：

XAML代码：

1: <StackPanel Grid.Row="1" Grid.Column="0" x:Name="panelBindingColorObject">

2:     <StackPanel.Resources>

3:         <c:MyBindingColor x:Key="myDataSourceB" />

4:         <c:MyColorConverter x:Key="myConverter" />

5:     </StackPanel.Resources>

6:     <StackPanel.DataContext>

7:         <Binding Source="{StaticResource myDataSourceB}" />

8:     </StackPanel.DataContext>

9:     <TextBlock Margin="5" Text="Binding Fill To Color" />

10:     <Rectangle Margin="5" Height="30"

11:                Fill="{Binding Path=ColorObject, Converter={StaticResource myConverter}}" />

12:     <TextBox Margin="5" x:Name="txtValueB" />

13:     <Button Margin="5" Content="Change Fill"

14:             x:Name="btn_ChangeColorObject" Click="btn_ChangeColorObject_Click" />

15:     <Button Margin="5" Content="Get Fill"

16:             x:Name="btn_GetColorObject" Click="btn_GetColorObject_Click" />

17: </StackPanel>

CS代码：

1: #region 使用自定义的由Color对象向SolidColorBrush对象进行转换

2: private void btn_ChangeColorObject_Click(object sender, RoutedEventArgs e)

3: {

4:     try

5:     {

6:         MyBindingColor source = (MyBindingColor)(panelBindingColorObject.DataContext);

7: 

8:         string txt = txtValueB.Text;

9:         string[] items = txt.Split(',');

10: 

11:         Color clr = Colors.Black;

12:         if (items.Length == 3)

13:         {

14:             byte r = byte.Parse(items[0], NumberStyles.HexNumber);

15:             byte g = byte.Parse(items[1], NumberStyles.HexNumber);

16:             byte b = byte.Parse(items[2], NumberStyles.HexNumber);

17: 

18:             clr = Color.FromRgb(r, g, b);

19:         }

20:         else if (items.Length == 4)

21:         {

22:             byte a = byte.Parse(items[0], NumberStyles.HexNumber);

23:             byte r = byte.Parse(items[1], NumberStyles.HexNumber);

24:             byte g = byte.Parse(items[2], NumberStyles.HexNumber);

25:             byte b = byte.Parse(items[3], NumberStyles.HexNumber);

26: 

27:             clr = Color.FromArgb(a, r, g, b);

28:         }

29: 

30:         source.ColorObject = clr;

31:     }

32:     catch (Exception ex)

33:     {

34:         MessageBox.Show(

35:             ex.Message,

36:             "System Information",

37:             MessageBoxButton.OK,

38:             MessageBoxImage.Error);

39:     }

40: }

41: 

42: private void btn_GetColorObject_Click(object sender, RoutedEventArgs e)

43: {

44:     MyBindingColor source = (MyBindingColor)(panelBindingColorObject.DataContext);

45:     Color clr = source.ColorObject;

46: 

47:     string txt = string.Format(

48:         "Color ARGB Value is ({0:X},{1:X},{2:X},{3:X}).",

49:         clr.A, clr.R, clr.G, clr.B);

50: 

51:     MessageBox.Show(

52:         txt,

53:         "System Information",

54:         MessageBoxButton.OK,

55:         MessageBoxImage.Information);

56: }

57: #endregion

本系列博客索引页