WPF Converter（转）

WPF Binding 用于数据有效性校验的关卡是它的 ValidationRules 属性，用于数据类型转换的关卡是它的 Converter 属性。下面是实例：

1. Binding 的数据校验

<Window x:Class="WpfStudy.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:WpfStudy"
        Title="MainWindow"
        Height="266" Width="300">
    <StackPanel>
        <TextBox x:Name="textBox1" Margin="5"/>
        <Slider x:Name="slider1" Minimum="0" Maximum="100" Margin="5"/>
    </StackPanel>
</Window>

　　 public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            Binding binding = new Binding("Value") { Source = this.slider1 };
            binding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
            binding.NotifyOnValidationError = true;
            RangeValidationRule rvr = new RangeValidationRule();
            rvr.ValidatesOnTargetUpdated = true;
            binding.ValidationRules.Add(rvr);
            this.textBox1.SetBinding(TextBox.TextProperty, binding);

            this.textBox1.AddHandler(Validation.ErrorEvent, new RoutedEventHandler(this.ValidationError));
        }

        public void ValidationError(object sender, RoutedEventArgs e)
        {
            if (Validation.GetErrors(this.textBox1).Count > 0)
            {
                this.textBox1.ToolTip = Validation.GetErrors(this.textBox1)[0].ErrorContent.ToString();
            }
        }
    }

　　 public class RangeValidationRule : ValidationRule
    {
        //需要实现 Validate 方法
        public override ValidationResult Validate(object value, CultureInfo cultureInfo)
        {
            double d = 0;
            if(double.TryParse(value.ToString(),out d))
            {
                if (d >= 0 && d <= 100)
                {
                    return new ValidationResult(true, null);
                }
            }

            return new ValidationResult(false, "Validation Failed");
        }
    }

2. Binding 的数据转换

<Window x:Class="WpfStudy.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:WpfStudy"
        Title="MainWindow"
        Height="266" Width="300">
    <Window.Resources>
        <local:CategoryToSourceConverter x:Key="cts"/>
        <local:StateToNullableBoolConverter x:Key="stnb"/>
    </Window.Resources>
    <StackPanel Background="LightBlue">
        <ListBox x:Name="listBoxPanel" 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="5,5" Click="ButtonSave_Click"/>
    </StackPanel>
</Window>

　　 public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        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 }
            };

            this.listBoxPanel.ItemsSource = planeList;
        }

        private void ButtonSave_Click(object sender, RoutedEventArgs e)
        {
            StringBuilder sb = new StringBuilder();
            foreach(Plane p in listBoxPanel.Items)
            {
                sb.AppendLine(string.Format("Category={0},Name={1},State={2}", p.Category, p.Name, p.State));
            }
            File.WriteAllText(@"D:\PlaneList.txt", sb.ToString());
        }
    }

    // Converters
    public class CategoryToSourceConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo cultureinfo)
        {
            Category c = (Category)value;
            switch (c)
            {
                case Category.Bomber:
                    return @"\Icons\Bomber.png";
                case Category.Fighter:
                    return @"\Icons\Fighter.png";
                default:
                    return null;
            }
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo cultureinfo)
        {
            throw new NotImplementedException();
        }
    }

    public class StateToNullableBoolConverter : IValueConverter
    {
        // 将 State 转换为 bool?
        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;
            }
        }

        // 将 bool? 转换为 State
        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;
            }
        }
    }

　　//种类
    public enum Category
    {
        Bomber,
        Fighter
    }

    //状态
    public enum State
    {
        Available,
        Locked,
        Unknown
    }

    //飞机
    public class Plane
    {
        public Category Category { get; set; }
        public string Name { get; set; }
        public State State { get; set; }
    }

    转自：《深入浅出 WPF》 第六章