例如：我们把一个 Slider 的Value 属性和 TextBox 的 Text 属性双向绑定在一起， Slider 的Value 的有效值是 0~100。当我们使用 Binding 绑定数值时，需要对该 Binding 的 ValidationRules 添加校验规则。具体实现如下所示：
第一步：我们声明一个 RangeValidationRule 类编写校验规则，该类需要继承 ValidationRule 类（该类为抽象类），ValidationRule类的作用是提供创建自定义规则的一个方式，旨在检查用户输入的有效性。具体代码如下：
public class RangeValidationRule : ValidationRule
{
public override ValidationResult Validate(object value, CultureInfo cultureInfo)
{
if (double.TryParse(value.ToString(), out var d))
{
if (d >= 0 && d <= 100)
{
return new ValidationResult(true, null);
}
}
return new ValidationResult(false, "Validation value");
}
}
第二步：对 TextBox 的 Text 属性进行 Binding 绑定，并对该 Binding 的 ValidationRules 添加一个校验规则 RangeValidationRule 类，具体实现如下：
<StackPanel Grid.Row="0">
<TextBox x:Name="TextBox0" Margin="5" Height="50" VerticalContentAlignment="Center" ToolTip="{Binding ElementName=TextBox0,Path=e}">
<TextBox.Text>
<Binding ElementName="Slider0" Path="Value" UpdateSourceTrigger="PropertyChanged">
<Binding.ValidationRules>
<local:RangeValidationRule ></local:RangeValidationRule>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
<Slider x:Name="Slider0" Margin="5" Minimum="0" Maximum="100"></Slider>
</StackPanel>
然后，我们在文本框中，输入200，发现 TextBox 会显示红色边框，这表示数值是错误的，具体显示如下图：
image-20210205151612353
三、Binding 的数据转换#
例如：我们实现如下一个程序，程序的用途是在列表里向玩家显示一些军用飞机的状态。数据类型如下：
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; }
}
在UI中，Plane 的 Category 属性被映射为图片，State 被映射为 CheckBox 的 IsChecked 属性。具体转换规则如下：
public class CategoryToSourceConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var c = (Category)value;
switch (c)
{
case Category.Bomber:
return "image/bomber.png";
case Category.Fighter:
return "image/fighter.png";
}
return new ValidationResult(false, "Validation Value");
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
public class StateToBoolConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var s = (State) value;
switch (s)
{
case State.Available:
return true;
case State.Locked:
return false;
default:
return null;
}
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
var b = (bool?) value;
switch (b)
{
case true:
return State.Available;
case false:
return State.Locked;
default:
return State.Unknown;
}
}
}
我们添加一个 ViewModel 绑定到 UI 上，ViewModel 代码如下（属性变更可以阅读 WPF 之 INotifyPropertyChanged 接口的使用 （一））：
public class Window3VM : NotifyProperty
{
private ObservableCollection<Plane> _planes;
private string _output;
public ObservableCollection<Plane> Planes
{
get => _planes;
set => SetProperty(ref _planes, value);
}
public string Output
{
get => _output;
set => SetProperty(ref _output, value);
}
}
我们把 ViewModel 绑定到 UI 界面上，并把转换规则添加到对应的 Binding 上，具体实现如下：
<Window x:Class="UI.Window3"
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:UI"
mc:Ignorable="d"
d:DataContext="{d:DesignInstance local:Window3VM}"
Title="Window3" Height="500" Width="600">
<Window.Resources>
<local:CategoryToSourceConverter x:Key="CTS"></local:CategoryToSourceConverter>
<local:StateToBoolConverter x:Key="STB"></local:StateToBoolConverter>
</Window.Resources>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="100"></RowDefinition>
<RowDefinition Height="*"></RowDefinition>
</Grid.RowDefinitions>
<StackPanel Grid.Row="0">
<TextBox x:Name="TextBox0" Margin="5" Height="50" VerticalContentAlignment="Center" ToolTip="{Binding ElementName=TextBox0,Path=e}">
<TextBox.Text>
<Binding ElementName="Slider0" Path="Value" UpdateSourceTrigger="PropertyChanged">
<Binding.ValidationRules>
<local:RangeValidationRule ></local:RangeValidationRule>
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
<Slider x:Name="Slider0" Margin="5" Minimum="0" Maximum="100"></Slider>
</StackPanel>
<Grid Grid.Row="1">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"></ColumnDefinition>
<ColumnDefinition Width="200"></ColumnDefinition>
</Grid.ColumnDefinitions>
<StackPanel Grid.Column="0" Margin="10">
<ListBox Margin="5" Height="200" ItemsSource="{Binding Path=Planes}">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<Image Margin="0,2,0,2" Width="50" Source="{Binding Path=Category,Converter={StaticResource CTS}}"></Image>
<TextBlock Margin="0,2,0,2" Width="200" TextAlignment="Center" VerticalAlignment="Center" Text="{Binding Path=Name}"></TextBlock>
<CheckBox Margin="0,2,0,2" Width="20" IsChecked="{Binding Path=State,Converter={StaticResource STB}}"></CheckBox>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<Button Margin="5" Height="50" Content="Load" Click="ButtonLoad_OnClick"></Button>
<Button Margin="5" Height="50" Content="Save" Click="ButtonSave_OnClick"></Button>
</StackPanel>
<StackPanel Grid.Column="1">
<TextBlock Margin="5,5,5,0" Text="Output Data："></TextBlock>
<TextBox x:Name="TextBox" Margin="5" Height="310" BorderBrush="Black" Text="{Binding Path=Output}"></TextBox>
</StackPanel>
</Grid>
</Grid>
</Window>
如下所示，当我们点击Load 按钮后，加载出来列表，点击 Save 按钮后，把整个列表输出到右边的文本框：
/// <summary>
/// Window3.xaml 的交互逻辑
/// </summary>
public partial class Window3 : Window
{
private readonly Window3VM vm;
public Window3()
{
InitializeComponent();
this.DataContext= vm =new Window3VM();
}
private void ButtonLoad_OnClick(object sender, RoutedEventArgs e)
{
vm.Planes=new ObservableCollection<Plane>()
{
new Plane(){Name = "B-1", Category = Category.Bomber, State = State.Unknown,},
new Plane(){Name = "F-35",Category = Category.Fighter,State = State.Unknown,},
new Plane(){Name = "B-6", Category = Category.Bomber, State = State.Unknown,},
new Plane(){Name = "F-22",Category = Category.Fighter,State = State.Unknown,},
new Plane(){Name = "J-20",Category = Category.Fighter,State = State.Unknown,},
};
}
private void ButtonSave_OnClick(object sender, RoutedEventArgs e)
{
StringBuilder sb = new StringBuilder();
foreach (var plane in vm.Planes)
{
sb.Append($"{plane.Category},{plane.Name},{plane.State}\r\n");
}
vm.Output = sb.ToString();
}
}
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