WPF-19 IValueConverter接口

我们先来看看微软官方给出的定语：提供将自定义逻辑应用于绑定的方法，我们来看一下该接口的定义，Convert提供了将数据源到UI的格式化，ConvertBack表示反向

namespace System.Windows.Data
{//// Summary://     Provides a way to apply custom logic to a binding.public interface IValueConverter{object Convert(object value, Type targetType, object parameter, CultureInfo culture);object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture);}
}

我们做一个简单的例子实现商品列表的绑定，定义一个DecimalConverter数据转化接口来实现一个价格的格式化，我们将价格格式化成两位小数：

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using System;
using System.Collections.Generic;
using System.Globalization;
using System.Windows;
using System.Windows.Data;
using System.Windows.Media;
namespace Example_17
{/// <summary>/// Interaction logic for MainWindow.xaml/// </summary>public partial class MainWindow : Window{public MainWindow(){InitializeComponent();this.Loaded += MainWindow_Loaded;}private void MainWindow_Loaded(object sender, RoutedEventArgs e){List<Order> orders = new List<Order>();Order order = new Order();order.Merchindise = "IPhone 14";order.Quantity = 1;order.Price = 8000;orders.Add(order);order = new Order();order.Merchindise = "卫生纸";order.Quantity = 10;order.Price = 28.7895M;orders.Add(order);order = new Order();order.Merchindise = "笔记本";order.Quantity = 10;order.Price = 87.7895M;orders.Add(order);this.lstOrder.ItemsSource = orders;}}[ValueConversion(typeof(decimal), typeof(string))]public class DecimalConverter : IValueConverter{public object? Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture){if (value != null)return ((decimal)value).ToString("f2");elsereturn null;}public object? ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture){return null;}}public class Order{public string Merchindise { get; set; } = null!;public int Quantity { get; set; }public decimal Price { get; set; }}
}

<Window x:Class="Example_17.MainWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"xmlns:d="http://schemas.microsoft.com/expression/blend/2008"xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"xmlns:local="clr-namespace:Example_17"mc:Ignorable="d" Title="MainWindow" Height="450" Width="800"><Window.Resources><local:DecimalConverter x:Key="myDecimalConverter"></local:DecimalConverter></Window.Resources><StackPanel x:Uid="staOrder"><ListView x:Uid="lstOrder" IsSynchronizedWithCurrentItem="True" ScrollViewer.CanContentScroll="True" x:Name="lstOrder" AllowDrop="True" BorderThickness="0,0,0,1" Focusable="False"><ListView.View><GridView x:Uid="GridView_1"><GridViewColumn x:Name="colMerchindise" x:Uid="GridViewColumn_1" Header="商品名称" Width="250"><GridViewColumn.CellTemplate><DataTemplate><Border Width="138" Height="Auto"><Grid x:Uid="Grid_2" Height="Auto" Width="Auto"><TextBlock x:Uid="TextBlock_2" Margin="0,0,0,0" HorizontalAlignment="Left"  VerticalAlignment="Stretch" Text="{Binding Path=Merchindise}" FontFamily="Arial" FontWeight="Bold" FontSize="15" TextWrapping="NoWrap" TextTrimming="WordEllipsis" /></Grid></Border></DataTemplate></GridViewColumn.CellTemplate></GridViewColumn><GridViewColumn x:Name="colQuantity" x:Uid="GridViewColumn_2" Header="数量" Width="170" ><GridViewColumn.CellTemplate><DataTemplate><Border Width="56" Height="Auto"><Grid x:Uid="Grid_3" Height="Auto" Width="Auto"><TextBlock x:Uid="TextBlock_3" Margin="0,0,0,0" Text="{Binding Path=Quantity}" HorizontalAlignment="Right" VerticalAlignment="Center"  FontFamily="Arial" FontWeight="Bold" FontSize="15" Background="{x:Null}" TextTrimming="WordEllipsis" /></Grid></Border></DataTemplate></GridViewColumn.CellTemplate></GridViewColumn><GridViewColumn x:Name="colPrice" x:Uid="GridViewColumn_3" Header="价格" Width="170"><GridViewColumn.CellTemplate><DataTemplate><Grid x:Uid="Grid_4" Height="Auto" Width="Auto"><TextBlock x:Uid="TextBlock_4" HorizontalAlignment="Right" VerticalAlignment="Center"  Margin="0,0,0,0" FontFamily="Arial" FontWeight="Bold" FontSize="15" TextTrimming="WordEllipsis" FontStretch="Normal" ><TextBlock.Text><Binding Path="Price" Converter="{StaticResource myDecimalConverter}"/></TextBlock.Text></TextBlock></Grid></DataTemplate></GridViewColumn.CellTemplate></GridViewColumn></GridView></ListView.View></ListView></StackPanel>
</Window>

运行效果如下，我们可以看到我们的价格已经被格式化：

我们如果想将数量等于10的背景颜色设置为绿色，又该怎么做的，同样的我们定义一个ColorConverter转换器：

[ValueConversion(typeof(int), typeof(SolidColorBrush))]public class ColorConverter : IValueConverter{public object? Convert(object value, Type targetType, object parameter, CultureInfo culture){if ((int)value == 10)return new SolidColorBrush(Colors.Green); ;return null;}public object? ConvertBack(object value, Type targetType, object parameter, CultureInfo culture){return null;}}

同样我们在XAML中引用一下该对象：

<local:ColorConverter x:Key="myColorConverter"></local:ColorConverter>

在ListView中添加如下样式：

<ListView.ItemContainerStyle><Style x:Uid="Style_2" TargetType="{x:Type ListViewItem}"><Setter Property="Background" Value="{Binding Path=Quantity, Converter={StaticResource myColorConverter}}"></Setter></Style>
</ListView.ItemContainerStyle>

运行效果如下：