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 > )
            {
                this.textBox1.ToolTip = Validation.GetErrors(this.textBox1)[].ErrorContent.ToString();
            }
        }
    }

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

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

完成后运行程序，当输入0到100之间的值时程序正常显示，但输入这个区间之外的值或不能被解析的值时 TextBox 会显示红色边框，表示值是错误的，不能把它传递给 Source。

　Binding 进行校验时的默认行为是认为来自 Source 的数据总是正确的，只有来自 Target 的数据（因为 Target 多为 UI 控件，所以等价于用户输入的数据）才有可能有问题，为了不让有问题的数据污染 Source 所以需要校验。换句话说，Binding 只在 Target 被外部方法更新时校验数据，而来自 Binding 的 Source 数据更新 Target 时是不会进行校验的。如果想改变这种行为，或者说当来自 Source 的数据也有可能出现问题时，我们就需要将校验的条件的 ValidateOnTargetUpdated 属性设为 true。

2. Binding 的数据转换

当数据从 Binding 的 Source 流向 Target 时，Convert 方法将被调用；反之，ConvertBack 方法将被调用。这两个方法的参数列表一模一样：第一个参数为 object，最大限度地保证了 Converter 的重用性（可以在方法体内对实际类型进行判断）；第二个参数用于确定方法的返回类型（个人认为形参名字叫 outputType 比 targetType 要好，可以避免与 Binding  的 Target 混淆）；第三个参数用于把额外的信息传入方法，若需要传递多个信息则可把信息放入一个集合对象来传入方法。

　Binding 对象的 Mode 属性会影响到这两个方法的调用。如果 Mode 为 TwoWay 或 Default 行为与 TwoWay 一致则两个方法都有可能被调用；如果 Mode 为 OneWay 或 Default 行为与 OneWay 一致则只有 Convert 方法会被调用；其他情况同理。

<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; }
    }

3. MultiBinding（多路 Binding）

<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 Background="LightBlue">
        <TextBox x:Name="textBox1" Height="23" Margin="5"/>
        <TextBox x:Name="textBox2" Height="23" Margin="5,0"/>
        <TextBox x:Name="textBox3" Height="23" Margin="5"/>
        <TextBox x:Name="textBox4" Height="23" Margin="5,0"/>
        <Button x:Name="button1" Content="Submit" Width="80" Margin="5"/>
    </StackPanel>
</Window>

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

            this.SetMultiBinding();
        }

        private void SetMultiBinding()
        {
            //准备基础Binding
            Binding b1 = new Binding("Text") { Source = this.textBox1 };
            Binding b2 = new Binding("Text") { Source = this.textBox2 };
            Binding b3 = new Binding("Text") { Source = this.textBox3 };
            Binding b4 = new Binding("Text") { Source = this.textBox4 };

            //准备MultiBinding
            MultiBinding mb = new MultiBinding() { Mode = BindingMode.OneWay };
            mb.Bindings.Add(b1); //注意:MultiBinding对Add子Binding的顺序是敏感的
            mb.Bindings.Add(b2);
            mb.Bindings.Add(b3);
            mb.Bindings.Add(b4);
            mb.Converter = new LogonMultiBindingConverters();

            //将 Button 与 MultiBinding 对象关联
            this.button1.SetBinding(Button.IsEnabledProperty, mb);
        }
    }

public class LogonMultiBindingConverters : IMultiValueConverter
    {
        public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
        {
            if(!values.Cast<string>().Any(text=>string.IsNullOrEmpty(text))
                && values[].ToString() == values[].ToString()
                && values[].ToString() == values[].ToString())
            {
                return true;
            }
            return false;
        }

        public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

转自：《深入浅出 WPF》 第六章