[玩一玩]WPF Tips: Uncheckable radio buttons

原文地址：http://blog.csdn.net/xinyaping/article/details/7887663

adio button 通常的行为是：某一组 Radio button 只能有一个被选中（ Checked ），当一个被选中是其余的 Radio button 自动 Uncheck。

但是，有没有什么办法让这一组 Radio button 在被点击之后，再回复到任何一个 Radio button 都没有被选中的状态呢？比如说，两个 Radio button：Radio 1 和 Radio 2，初始状态下任何一个 radio button 都没有被选中，现在我们点击 Radio 1，则 Radio 1 被选中；再次点击 Radio 1，则 Radio 1 回复到没有被选中的状态，Radio 2 的状态也不受影响。能否实现这样的功能呢？网上搜不到现成的答案，但实际上是可以实现的。

实现的关键是利用 RadioButton 的 PreviewMouseLeftButtonDown 事件，该事件能够获得 RadioButton 被点击时，它之前的状态。有了这个状态我们就可以判断出这个 RadioButton 应该从未选中的状态置为选中的状态，还是从被选中的状态置为未选中的状态。


我写了个小例子，可从此处下载源代码和编译好之后的可执行文件（基于.Net 3.5）
http://download.csdn.net/detail/xinyaping/4513569

源代码如下：

MainWindow.xaml

    <Window x:Class="RadioButttonUnCheckDemo.MainWindow"  

            xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  

            xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  

            Width="300" Height="95" WindowStyle="ToolWindow"   

            Title="Demo: Uncheckable radio buttons">  

          

        <Grid Height="24" Margin="0,0,0,0">  

            <Grid.ColumnDefinitions>  

                <ColumnDefinition Width="80" />  

                <ColumnDefinition />  

                <ColumnDefinition Width="120" />  

            </Grid.ColumnDefinitions>  

              

            <Label Grid.Column="0" VerticalAlignment="Center">Please select: </Label>  

              

            <WrapPanel Grid.Column="1">  

                <RadioButton Name="radio1" Content="1" Margin="5,0,5,0" GroupName="GroupName1"   

                             PreviewMouseLeftButtonDown="RadioButton_PreviewMouseLeftButtonDown"   

                             Checked="RadioButton_StateChanged"   

                             Unchecked="RadioButton_StateChanged" />  

                <RadioButton Name="radio2" Content="2" Margin="5,0,5,0" GroupName="GroupName1"   

                             PreviewMouseLeftButtonDown="RadioButton_PreviewMouseLeftButtonDown"  

                             Checked="RadioButton_StateChanged"   

                             Unchecked="RadioButton_StateChanged" />  

            </WrapPanel>  

      

            <Label Grid.Column="2" VerticalAlignment="Center" Name="labelResult" />  

        </Grid>   

    </Window>  

MainWindow.xaml.cs

    namespace RadioButttonUnCheckDemo  

    {  

        using System.Windows;  

        using System.Windows.Controls;  

        using System.Windows.Input;  

      

        /// <summary>  

        /// Interaction logic for MainWindow.xaml  

        /// </summary>  

        public partial class MainWindow : Window  

        {  

            /// <summary>  

            /// Initializes a new instance of the <see cref="MainWindow"/> class.  

            /// </summary>  

            public MainWindow()  

            {  

                this.InitializeComponent();  

            }  

      

            /// <summary>  

            /// Gets a value indicating whether RadioButton radio1 is checked.  

            /// </summary>  

            /// <value>  

            ///     <c>true</c> if RadioButton radio1 is radio1 checked; otherwise, <c>false</c>.  

            /// </value>  

            private bool IsRadio1Checked  

            {  

                get { return this.radio1.IsChecked == null ? false : (bool)this.radio1.IsChecked; }  

            }  

      

            /// <summary>  

            /// Gets a value indicating whether RadioButton radio2 is checked.  

            /// </summary>  

            /// <value>  

            ///     <c>true</c> if RadioButton radio2 is radio1 checked; otherwise, <c>false</c>.  

            /// </value>  

            private bool IsRadio2Checked  

            {  

                get { return this.radio2.IsChecked == null ? false : (bool)this.radio2.IsChecked; }  

            }  

      

            /// <summary>  

            /// Handles the PreviewMouseLeftButtonDown event of the RadioButton control.  

            /// </summary>  

            /// <param name="sender">The source of the event.</param>  

            /// <param name="e">The <see cref="System.Windows.Input.MouseButtonEventArgs"/> instance containing the event data.</param>  

            private void RadioButton_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)  

            {  

                if (sender != null && sender is RadioButton)  

                {  

                    RadioButton radioButton = sender as RadioButton;  

                    bool isChecked =  

                        radioButton.IsChecked == null ?  

                        false :  

                        (bool)radioButton.IsChecked;  

      

                    if (isChecked)  

                    {  

                        radioButton.IsChecked = false;  

                        e.Handled = true;  

                    }  

                }  

            }  

      

            /// <summary>  

            /// Handles the StateChanged event of the RadioButton control.  

            /// </summary>  

            /// <param name="sender">The source of the event.</param>  

            /// <param name="e">The <see cref="System.Windows.RoutedEventArgs"/> instance containing the event data.</param>  

            private void RadioButton_StateChanged(object sender, RoutedEventArgs e)  

            {  

                this.SetResult();  

            }  

      

            /// <summary>  

            /// Sets the result.  

            /// </summary>  

            private void SetResult()  

            {  

                if (!this.IsRadio1Checked && !this.IsRadio2Checked)  

                {  

                    this.labelResult.Content = "Selected: N/A";  

                }  

                else if (this.IsRadio1Checked)  

                {  

                    this.labelResult.Content = "Selected: Radio 1";  

                }  

                else if (this.IsRadio2Checked)  

                {  

                    this.labelResult.Content = "Selected: Radio 2";  

                }  

            }  

        }  

    }  

可从此处下载源代码和编译好之后的可执行文件（基于.Net 3.5）
http://download.csdn.net/detail/xinyaping/4513569