关于Window.ShowDialog()方法，有一个常见的容易犯的错误。下面给出这个错误的例子：
DemoA：错误的例子
1. 在WPF项目中，创建一个Windows：DialogWindow
DialogWindow.xaml
<Window x:Class="DemoA.DialogWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"Title="I am a dialog window" Height="200" Width="300"><Grid><Grid.RowDefinitions><RowDefinition Height="140" /><RowDefinition Height="60" /></Grid.RowDefinitions><Label Grid.Row="0" Margin="12" Content="Hello!" /><WrapPanel Grid.Row="1" Margin="0" HorizontalAlignment="Center"><Button Content="OK" Margin="5,0,5,0" Width="60" /><Button Content="Cancel" Margin="5,0,5,0" Width="60"Click="ButtonCancelOnClick"/></WrapPanel></Grid>
</Window>
DialogWindow.xaml.cs
using System.Windows;namespace DemoA
{/// <summary>/// Interaction logic for DialogWindow.xaml/// </summary>public partial class DialogWindow : Window{public DialogWindow(){InitializeComponent();}private void ButtonCancelOnClick(object sender, RoutedEventArgs e){this.Close();}}
}
然后在MainWindow里面去调用它：
MainWindow.xaml
<Window x:Class="DemoA.MainWindow"xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"Title="MainWindow" Height="350" Width="525"><Grid><Button Width="Auto" Height="Auto" Content="Show dialog" Click="ButtonClick" /></Grid>
</Window>
MainWindow.xaml.cs
using System.Windows;namespace DemoA
{/// <summary>/// Interaction logic for MainWindow.xaml/// </summary>public partial class MainWindow : Window{private DialogWindow dialogWindow = new DialogWindow();public MainWindow(){this.InitializeComponent();}private void ButtonClick(object sender, RoutedEventArgs e){dialogWindow.ShowDialog();}}
}
这个例子似乎非常寻常。看出它有什么问题了吗？如果您看出问题来了，那么本文对您来说纯属浪费时间，请移步其它文章，谢谢。
好，下面我们运行它。运行时，点击MainWindow窗口的按钮，第一次点击，弹出了DialogWindow对话框，没什么问题。点击“Cancel”按钮关闭DialogWindow对话框，再次点击MainWindow窗口的按钮，这时候问题出现了，抛出了以下异常：
An unhandled exception of type 'System.InvalidOperationException' occurred in PresentationFramework.dllAdditional information: Cannot set Visibility or call Show, ShowDialog, or WindowInteropHelper.EnsureHandle after a Window has closed.如何解决这个问题呢？解决方案如下：DemoB
DialogWindow.xaml.cs
using System.Windows;namespace DemoB
{/// <summary>/// Interaction logic for DialogWindow.xaml/// </summary>public partial class DialogWindow : Window{private static DialogWindow staticInstance = null;public DialogWindow(){this.InitializeComponent();this.Closed += WindowOnClosed;}public static DialogWindow GetInstance(){if (staticInstance == null){staticInstance = new DialogWindow();}return staticInstance;}private void ButtonCancelOnClick(object sender, RoutedEventArgs e){this.Close();}private void WindowOnClosed(object sender, System.EventArgs e){staticInstance = null;}}
}
MainWindow.xaml.cs
using System.Windows;namespace DemoB
{/// <summary>/// Interaction logic for MainWindow.xaml/// </summary>public partial class MainWindow : Window{public MainWindow(){this.InitializeComponent();}private void ButtonClick(object sender, RoutedEventArgs e){DialogWindow.GetInstance().ShowDialog();}}
}
这样，每次调用Window.ShowDialog()方法的时候，都创建了一个新的DialogWindow实例，所以问题得以解决。
参考：
同样的疑问，在StackOverflow上的讨论如下：
《WPF: Cannot reuse window after it has been closed》
http://stackoverflow.com/questions/3568233/wpf-cannot-reuse-window-after-it-has-been-closed
