原文:數據綁定（十）Binding的數據轉換

當Source端Path所關聯的數據與Target端目標屬性數據類型不一致時，需要添加數據轉換器，數據轉換器是一個自定義的類，這個類需要實現IValueConverter接口，這個接口有兩個方法需要實現：Convert和ConvertBack，當數據從Source流向Target時，將調用Convert方法，反之，將調用ConvertBack方法

例子，首先定義飛機類型

public enum Category{Bomber,Fighter}public enum State{Available,Locked,Unknown}public class Plane{public Category Category { get; set; }public string Name { get; set; }public State State { get; set; }}
Plane類型的Category將在界面上轉換為圖片，而State類型將會轉換成界面上的CheckBox顯示，由于存在兩個轉換，因此需要提供兩個Converter，第一個轉換是做Category類型與字符類型的轉換，字符串是圖片的路徑

class CategoryToSourceConverter : IValueConverter{public object Convert(object value, Type targetType, object parameter, CultureInfo culture){Category c = (Category)value;switch (c){case Category.Bomber:{return @"\Icons\close.png";}case Category.Fighter:{return @"\Icons\closeing.png";}default:{return null;}}}public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture){return new NotImplementedException();}}
由于UI上不能修改圖片，所以只實現了從Source到Target的轉換

另一個轉換用于將State數據轉換為bool?

public class StateToNullableBoolConverter : IValueConverter{public object Convert(object value, Type targetType, object parameter, CultureInfo culture){State s = (State)value;switch (s){case State.Locked:{return false;}case State.Available:{return true;}case State.Unknown:default:{return null;}}}public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture){bool? nb = (bool?)value;switch (nb){case true:{return State.Available;}case false:{return State.Locked;}case null:default:{return State.Unknown;}}}}
界面代碼：

<Window x:Class="WpfApplication1.MainWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"xmlns:local="clr-namespace:WpfApplication1"Title="MainWindow" Height="275" Width="275"> <Window.Resources><local:CategoryToSourceConverter x:Key="cts" /><local:StateToNullableBoolConverter x:Key="stnb" /></Window.Resources><StackPanel Background="LightBlue"><ListBox x:Name="listBoxPlane" Height="160" Margin="5"><ListBox.ItemTemplate><DataTemplate><StackPanel Orientation="Horizontal"> <Image Width="20" Height="20" Source="{Binding Path=Category, Converter={StaticResource cts}}" /><TextBlock Text="{Binding Path=Name}" Width="60" Margin="80,0" /><CheckBox IsThreeState="True" IsChecked="{Binding Path=State, Converter={StaticResource stnb}}" /></StackPanel></DataTemplate></ListBox.ItemTemplate></ListBox><Button x:Name="buttonLoad" Content="Load" Height="25" Margin="5,0" Click="buttonLoad_Click" /><Button x:Name="buttonSave" Content="Save" Height="25" Margin="5,0" Click="buttonSave_Click" /></StackPanel> </Window>
加粗的部分是XAML中對轉換器的使用，后臺代碼中實現了Load和Save兩個按鈕的點擊事件

private void buttonLoad_Click(object sender, RoutedEventArgs e){List<Plane> planeList = new List<Plane>(){new Plane(){Category=Category.Bomber, Name="B-1", State=State.Unknown},new Plane(){Category=Category.Bomber, Name="B-2", State=State.Unknown},new Plane(){Category=Category.Fighter, Name="F-22", State=State.Unknown},new Plane(){Category=Category.Fighter, Name="Su-47", State=State.Unknown},new Plane(){Category=Category.Bomber, Name="B-52", State=State.Unknown},new Plane(){Category=Category.Fighter, Name="J-10", State=State.Unknown}};listBoxPlane.ItemsSource = planeList;}private void buttonSave_Click(object sender, RoutedEventArgs e){StringBuilder sb = new StringBuilder();foreach (Plane p in listBoxPlane.Items){sb.AppendLine(string.Format("Category={0}, Name={1}, State={2}", p.Category, p.Name, p.State));}File.WriteAllText(@"d:\PlaneList.txt", sb.ToString());}

界面效果如圖：

當改變checkbox的選中狀態時，Plane對象中的值會發生變化

總結

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