c# - 为什么我的用户控件会导致 Visual Studio 崩溃？

Question

我花了一整天的时间试图弄清楚为什么这个用户控件会导致 VS2010(Windows Phone 7.1 开发)崩溃。应用程序运行此控件没有问题，但当我进入 MainPage.xaml 中的设计模式时 - VS 崩溃。

<UserControl x:Class="blabla.Controls.Tile"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}">

    <UserControl.Resources>
        <Storyboard x:Name="SwitchSidesAnimation">
            <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.Projection).(PlaneProjection.RotationX)" Storyboard.TargetName="FrontSide">
                <EasingDoubleKeyFrame KeyTime="0" Value="0"/>
                <EasingDoubleKeyFrame KeyTime="0:0:0.2" Value="90"/>
                <EasingDoubleKeyFrame KeyTime="0:0:0.4" Value="90"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause1" KeyTime="0:0:6" Value="-90"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause2" KeyTime="0:0:6.2" Value="-90"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause3" KeyTime="0:0:6.4" Value="0"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause4" KeyTime="0:0:12" Value="0"/>
            </DoubleAnimationUsingKeyFrames>
            <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.Projection).(PlaneProjection.RotationX)" Storyboard.TargetName="BackSide">
                <EasingDoubleKeyFrame KeyTime="0" Value="-90"/>
                <EasingDoubleKeyFrame KeyTime="0:0:0.2" Value="-90"/>
                <EasingDoubleKeyFrame KeyTime="0:0:0.4" Value="0"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause5" KeyTime="0:0:6" Value="0"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause6" KeyTime="0:0:6.2" Value="90"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause7" KeyTime="0:0:6.4" Value="90"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause8" KeyTime="0:0:12" Value="90"/>
            </DoubleAnimationUsingKeyFrames>
            <ObjectAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.Visibility)" Storyboard.TargetName="FrontSide">
                <DiscreteObjectKeyFrame KeyTime="0:0:0.2">
                    <DiscreteObjectKeyFrame.Value>
                        <Visibility>Visible</Visibility>
                    </DiscreteObjectKeyFrame.Value>
                </DiscreteObjectKeyFrame>
                <DiscreteObjectKeyFrame KeyTime="0:0:0.4">
                    <DiscreteObjectKeyFrame.Value>
                        <Visibility>Collapsed</Visibility>
                    </DiscreteObjectKeyFrame.Value>
                </DiscreteObjectKeyFrame>
                <DiscreteObjectKeyFrame x:Name="MoveThisForPause9" KeyTime="0:0:6">
                    <DiscreteObjectKeyFrame.Value>
                        <Visibility>Visible</Visibility>
                    </DiscreteObjectKeyFrame.Value>
                </DiscreteObjectKeyFrame>
                <DiscreteObjectKeyFrame x:Name="MoveThisForPause10" KeyTime="0:0:6.4">
                    <DiscreteObjectKeyFrame.Value>
                        <Visibility>Visible</Visibility>
                    </DiscreteObjectKeyFrame.Value>
                </DiscreteObjectKeyFrame>
                <DiscreteObjectKeyFrame x:Name="MoveThisForPause11" KeyTime="0:0:12">
                    <DiscreteObjectKeyFrame.Value>
                        <Visibility>Visible</Visibility>
                    </DiscreteObjectKeyFrame.Value>
                </DiscreteObjectKeyFrame>
            </ObjectAnimationUsingKeyFrames>
            <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.RenderTransform).(CompositeTransform.TranslateX)" Storyboard.TargetName="FrontSide">
                <EasingDoubleKeyFrame KeyTime="0:0:0.4" Value="0"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause12" KeyTime="0:0:6" Value="0"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause13" KeyTime="0:0:6.2" Value="0"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause14" KeyTime="0:0:6.4" Value="0"/>
                <EasingDoubleKeyFrame x:Name="MoveThisForPause15" KeyTime="0:0:12" Value="0"/>
            </DoubleAnimationUsingKeyFrames>
        </Storyboard>
    </UserControl.Resources>

    <Grid x:Name="LayoutRoot">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="1*" />
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="1*" />
        </Grid.RowDefinitions>

        <!-- Front side -->
        <Grid x:Name="FrontSide" Grid.Column="0" Grid.Row="0"
              Background="{Binding FrontBackground}">
            <Image Source="{Binding FrontImage}" />
        </Grid>
        <!-- /Front side -->

        <!-- Back side -->
        <Grid x:Name="BackSide" Grid.Column="0" Grid.Row="0"
              Background="{Binding BackBackground}">
            <Grid.Projection>
                <PlaneProjection RotationX="-90" />
            </Grid.Projection>
            <Image Source="{Binding BackImage}" />
        </Grid>
        <!-- /Back side -->
    </Grid>
</UserControl>

现在是代码。

namespace blabla.Controls
{
    public partial class Tile : UserControl
    {
        /// <summary>
        /// Defines if the tile has two sides.
        /// </summary>
        public bool IsTwoSided
        {
            get { return (bool)GetValue(IsTwoSidedProperty); }
            set
            {
                SetValue(IsTwoSidedProperty, value);

                this.startAnimations();
            }
        }

        /// <summary>
        /// Image that will be displayed on front side.
        /// </summary>
        public BitmapImage FrontImage
        {
            get { return (BitmapImage)GetValue(FrontImageProperty); }
            set { SetValue(FrontImageProperty, value); }
        }

        /// <summary>
        /// Image that ill be displayed on back side.
        /// </summary>
        public BitmapImage BackImage
        {
            get { return (BitmapImage)GetValue(BackImageProperty); }
            set { SetValue(BackImageProperty, value); }
        }

        /// <summary>
        /// Brush that will be used as background for front side.
        /// </summary>
        public Brush FrontBackground
        {
            get { return (Brush)GetValue(FrontBackgroundProperty); }
            set { SetValue(FrontBackgroundProperty, value); }
        }

        /// <summary>
        /// Brush that will be used as background for back side.
        /// </summary>
        public Brush BackBackground
        {
            get { return (Brush)GetValue(BackBackgroundProperty); }
            set { SetValue(BackBackgroundProperty, value); }
        }

        ///////////////////////////////////////////////////////////////////////////////////////////////////////

        public static readonly DependencyProperty IsTwoSidedProperty =
            DependencyProperty.Register("IsTwoSided", typeof(bool), typeof(Tile), new PropertyMetadata(false));

        public static readonly DependencyProperty FrontImageProperty =
            DependencyProperty.Register("FrontImage", typeof(BitmapImage), typeof(Tile), new PropertyMetadata(null));

        public static readonly DependencyProperty BackImageProperty =
            DependencyProperty.Register("BackImage", typeof(BitmapImage), typeof(Tile), new PropertyMetadata(null));

        public static readonly DependencyProperty FrontBackgroundProperty =
            DependencyProperty.Register("FrontBackground", typeof(Brush), typeof(Tile),
            new PropertyMetadata(new SolidColorBrush((Color)Application.Current.Resources["PhoneAccentColor"])));

        public static readonly DependencyProperty BackBackgroundProperty =
            DependencyProperty.Register("BackBackground", typeof(Brush), typeof(Tile),
            new PropertyMetadata(new SolidColorBrush((Color)Application.Current.Resources["PhoneAccentColor"])));

        ///////////////////////////////////////////////////////////////////////////////////////////////////////

        public Tile()
        {
            InitializeComponent();
            this.LayoutRoot.DataContext = this;
        }

        ///////////////////////////////////////////////////////////////////////////////////////////////////////

        /// <summary>
        /// Modifies animation frames' KeyTime to adjust time for new timing.
        /// <param name="pauseTime">Lenght of the pause.</param>
        /// </summary>
        private void setPauses(TimeSpan pauseTime)
        {
            // Sets pauses.
            EasingDoubleKeyFrame frameToModify;

            for(int i = 0; true; i++)
            {
                if(this.FindName("MoveThisForPause" + i) != null)
                {
                    frameToModify = (EasingDoubleKeyFrame)this.FindName("MoveThisForPause" + i);
                    frameToModify.KeyTime = KeyTime.FromTimeSpan(frameToModify.KeyTime.TimeSpan - TimeSpan.FromSeconds(5) + pauseTime);
                }
                else
                {
                    break;
                }
            }
        }

        /// <summary>
        /// Starts animations.
        /// </summary>
        /// <param name="beginTime">Usually delay before first-time animation.</param>
        private void startAnimations()
        {
            // We start animations only if the tile is two sided.
            if(this.IsTwoSided)
            {
                // Stopping previous animation.
                this.SwitchSidesAnimation.Stop();

                // Sets correct pauses.
                this.setPauses(TimeSpan.FromSeconds(new Random().Next(5, 10)));

                // Starts animation.
                this.SwitchSidesAnimation.BeginTime = TimeSpan.FromSeconds(new Random().Next(2, 15));
                this.SwitchSidesAnimation.RepeatBehavior = RepeatBehavior.Forever;
                this.SwitchSidesAnimation.Begin();
            }
            else
            {
                this.SwitchSidesAnimation.Stop();
            }
        }
    }
}

Answer 1

我已经能够重现此崩溃，诚然使用非电话版本的 Silverlight，并且在 Visual Web Dev Express 中而不是完整版本的 VS。

问题最终归结为这两个依赖属性声明中指定的默认值:

    public static readonly DependencyProperty FrontBackgroundProperty =
        DependencyProperty.Register("FrontBackground", typeof(Brush), typeof(Tile),
        new PropertyMetadata(new SolidColorBrush((Color)Application.Current.Resources["PhoneAccentColor"])));

    public static readonly DependencyProperty BackBackgroundProperty =
        DependencyProperty.Register("BackBackground", typeof(Brush), typeof(Tile),
        new PropertyMetadata(new SolidColorBrush((Color)Application.Current.Resources["PhoneAccentColor"])));

在我用 null 替换默认值后，崩溃消失了(使用 Notepad++ 作为 Visual Web Dev Express 崩溃)，删除了项目的 bin和 obj文件夹并重新启动 Visual Web Dev Express。当我重新启动 VWDX 时，它提示找不到类型 Tile , 但那是因为我删除了 bin和 obj文件夹。重建解决了这个问题。

我只能猜测究竟是什么问题。在 Tile 点正在静态初始化类，Application.Current可能是 null , Application.Current.Resources可能是 null , 或 Application.Current.Resources["PhoneAccentColor"]可能是 null (这会导致转换为 Color 失败，因为 Color 是 struct )。可能 VS 设计者没有很好地处理在类型的静态初始化期间抛出的异常？

顺便说一下，我还想指出另外几个潜在的问题。首先，这是您的 IsTwoSided属性:

    /// <summary>
    /// Defines if the tile has two sides.
    /// </summary>
    public bool IsTwoSided
    {
        get { return (bool)GetValue(IsTwoSidedProperty); }
        set
        {
            SetValue(IsTwoSidedProperty, value);

            this.startAnimations();
        }
    }

看起来你想要 startAnimations每当您的 IsTwoSided 时调用的方法依赖属性更改。您在上面编写的代码不会实现这一点。

当 Silverlight 更改依赖属性的值时，它不会调用您的属性 setter 来执行此操作。如果您希望在依赖属性的值更改时发生某些事情，请使用 property-changed callback相反。

其次，在Tile.xaml , 你声明 Storyboard在<UserControl.Resources>如下:

    <Storyboard x:Name="SwitchSidesAnimation">

我建议使用 x:Key而不是 x:Name ，有两个原因:

• 资源字典中的所有项目(隐式样式除外)必须具有 x:Key或 x:Name识别他们。 VS 支持使用 x:Name代替 x:Key , 但它以 legacy support mechanism 的形式存在仅。

• 使用 x:Name在用户控件的元素中 XAML 导致 VS 在 InitializeComponent() 中创建一个具有该名称的字段在您的 Tile 的自动生成部分类(在 obj\Debug 中的 Tile.g.cs 中)。然而，就因为你能坚持x:Name在一个元素上并不一定意味着您将能够访问生成字段中的相应对象。因为没有名为 SwitchSidesAnimation 的 UIElement在你的Tile.xaml ( Storyboard不是 UIElements)，SwitchSidesAnimation字段将始终为 null .

  的确，MSDN documentation for the x:Key attribute (也链接到上面)提到

  A FindName call using a key value will not retrieve a keyed resource

  (FindName 是用于按名称查找控件的方法。如果您查看 Tile.g.cs，您会看到它在那里使用。)

我建议始终使用 x:Key在资源字典中，这样您就不会相信您可以直接在代码隐藏中访问这个 Storyboard。

要在代码隐藏中访问 Storyboard，请使用

    this.Resources["SwitchSidesAnimation"] as Storyboard

事实上，如果您添加以下属性，则不必更改您的 startAnimations方法:

    private Storyboard SwitchSidesAnimation
    {
        get { return this.Resources["SwitchSidesAnimation"] as Storyboard; }
    }