(WPF, MVVM) Slider Binding.
对于Button的Command的绑定可以通过实现ICommand接口来进行，但是Slider并没有Command属性。
另外如果要实现MVVM模式的话，需要将一些Method和Slider的Event进行绑定，如何进行呢？
（对于UIElement的一些Event进行绑定一定有一些通用的方法，目前还没有深入研究。）
首先，Slider Value的绑定是很简单的, 绑定Slider的Value属性即可。
（1）ViewModel
public class SliderViewModel : ViewModelBase { private string selectedValue; public SliderViewModel() { } public string SelectedValue { get { return this.selectedValue; } set { if (this.selectedValue != value) { this.selectedValue = value; base.OnPropertyChanged("SelectedValue"); } } } }
(2) View, 设定 DataContext 为ViewModel， 绑定SelectValue到 Slider的Value 和TextBlock的Text属性上。
这样当拖动Slider时，Slider的值会传给SelectedValue, 然后SelectValue会传给TexBlock上。
x:Class="WpfApplication2.View.SliderView" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:vm="clr-namespace:WpfApplication2.ViewModel" mc:Ignorable="d" d:DesignHeight="300" d:DesignWidth="300"> <UserControl.DataContext> <vm:SliderViewModel /> </UserControl.DataContext> <Grid> <Slider HorizontalAlignment="Left" Margin="28,102,0,0" VerticalAlignment="Top" Width="158" Minimum="0" Maximum="100" Value="{Binding SelectedValue}"/> <TextBlock HorizontalAlignment="Left" Margin="203,102,0,0" TextWrapping="Wrap" Text="{Binding SelectedValue}" VerticalAlignment="Top" /> </Grid> </UserControl>
效果如下：
如果不想显示double值，可以设定Slider的属性。
TickFrequency="1"
IsSnapToTickEnabled="True"
TickPlacement="None" />
其次， 当用鼠标或者键盘移动滑块结束的时候，需要进行一些处理。如果不用MVVM的方式的话，可以在Slider的Event里面增加处理。
用MVVM的话，就稍微麻烦一些。
（1）下载或者复制C:\Program Files (x86)\Microsoft SDKs\Expression\Blend\.NETFramework\v4.0\Libraries\System.Windows.Interactivity.dll
在工程中Reference 这个dll，命名空间里面增加：using System.Windows.Interactivity
（2）新写个SliderValueChangedBehavior 继承Behavior<Slider>
/// <summary> /// Helps find the user-selected value of a slider only when the keyboard/mouse gesture has ended. /// </summary> public class SliderValueChangedBehavior : Behavior<Slider> { /// <summary> /// Keys down. /// </summary> private int keysDown; /// <summary> /// Indicate whether to capture the value on latest key up. /// </summary> private bool applyKeyUpValue; #region Dependency property Value /// <summary> /// DataBindable value. /// </summary> public double Value { get { return (double)GetValue(ValueProperty); } set { SetValue(ValueProperty, value); } } public static readonly DependencyProperty ValueProperty = DependencyProperty.Register( "Value", typeof(double), typeof(SliderValueChangedBehavior), new PropertyMetadata(default(double), OnValuePropertyChanged)); #endregion #region Dependency property Value /// <summary> /// DataBindable Command /// </summary> public ICommand Command { get { return (ICommand)GetValue(CommandProperty); } set { SetValue(CommandProperty, value); } } public static readonly DependencyProperty CommandProperty = DependencyProperty.Register( "Command", typeof(ICommand), typeof(SliderValueChangedBehavior), new PropertyMetadata(null)); #endregion /// <summary> /// On behavior attached. /// </summary> protected override void OnAttached() { this.AssociatedObject.KeyUp += this.OnKeyUp; this.AssociatedObject.KeyDown += this.OnKeyDown; this.AssociatedObject.ValueChanged += this.OnValueChanged; base.OnAttached(); } /// <summary> /// On behavior detaching. /// </summary> protected override void OnDetaching() { base.OnDetaching(); this.AssociatedObject.KeyUp -= this.OnKeyUp; this.AssociatedObject.KeyDown -= this.OnKeyDown; this.AssociatedObject.ValueChanged -= this.OnValueChanged; } /// <summary> /// On Value dependency property change. /// </summary> private static void OnValuePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { var me = (SliderValueChangedBehavior)d; if (me.AssociatedObject != null) me.Value = (double)e.NewValue; } /// <summary> /// Occurs when the slider's value change. /// </summary> /// <param name="sender"></param> /// <param name="e"></param> private void OnValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e) { if (Mouse.Captured != null) { this.AssociatedObject.LostMouseCapture += this.OnLostMouseCapture; } else if (this.keysDown != 0) { this.applyKeyUpValue = true; } else { this.ApplyValue(); } } private void OnLostMouseCapture(object sender, MouseEventArgs e) { this.AssociatedObject.LostMouseCapture -= this.OnLostMouseCapture; this.ApplyValue(); } private void OnKeyUp(object sender, KeyEventArgs e) { if (this.keysDown-- != 0) { this.ApplyValue(); } } private void OnKeyDown(object sender, KeyEventArgs e) { this.keysDown++; } /// <summary> /// Applies the current value in the Value dependency property and raises the command. /// </summary> private void ApplyValue() { this.Value = this.AssociatedObject.Value; if (this.Command != null) this.Command.Execute(this.Value); } }
（3） 在View中为Slider的行为添加Command
<i:Interaction.Behaviors> <helper:SliderValueChangedBehavior Command="{Binding ValueChangedCommand}" /> </i:Interaction.Behaviors>
（4）在ViewModel中实现当Slider值个改变的时候进行一些处理。
public ICommand ValueChangedCommand { get { if (this.valueChangedCommmand == null) { this.valueChangedCommmand = new RelayCommand( param => this.PopValue(), null); } return this.valueChangedCommmand; } } private void PopValue() { MessageBox.Show(String.Format("Selected value is {0}", this.selectedValue)); }
最后，进行调试，发现ValueChangedCommand当每次Silder值变更的时候都会被执行。
那么如何实现最后一次值变更时，才执行Command呢？