I get error: name cannot be found in the name scope of - When moving from page to page in an MVVMLight application

Question

我有一个 MVVMLight 多页应用程序，它有两个页面，我可以通过单击相应的按钮从一个页面导航到另一个页面。

在第二页中，我有一个加载器动画，每次在 textBox 字段中输入内容时都会触发该动画。一切正常；我可以从第一页转到第二页，然后在 textBox 中输入内容，动画开始。问题是，如果我转到第二页，然后返回第一页，然后再次转到第二页并在 textBox 中键入内容，我收到一条错误消息，指出loader 不存在，有趣的是，直到我离开页面再回来，我才收到这个错误。

知道为什么动画在离开页面并返回后停止工作吗？

编辑：这里是link一个完整的项目。 https://www.dropbox.com/sh/yf87shw5rzxtxen/AAClTesIGpLKl6IzV-6pjfEfa?dl=0

要复制错误，请执行以下操作...

下载并打开应用程序。
转到第 2 页。
在文本框中输入内容（动画应该开始）。
返回第 1 页，什么都不做。
再次转到第 2 页并尝试在文本框中键入内容（您应该会在此处看到错误）。

错误：

Additional information: 'rectangleLoader' name cannot be found in the name scope of 'TwoViews.Views.SecondView'.

XAML

<UserControl x:Class="TwoViews.Views.SecondView"
             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"
             d:DesignHeight="300"
             d:DesignWidth="300"
             mc:Ignorable="d">
    <Grid>
        <Rectangle x:Name="rectangleLoader" Fill="#FFB2B2FF" HorizontalAlignment="Left" Height="19" Margin="26,89,0,0" VerticalAlignment="Top" Width="248"/>
        <TextBox x:Name="textBoxFileName" 
                     HorizontalAlignment="Left" 
                     Height="35" Width="180" 
                     Margin="26,125,0,0" 
                     VerticalAlignment="Top" 
                     Text="{Binding InputFileNameChanged, UpdateSourceTrigger=PropertyChanged}" FontSize="18"/>
    </Grid>
</UserControl>

SecondView.xaml.cs

namespace TwoViews.Views
{
    public partial class SecondView : UserControl
    {
        private Storyboard loaderStoryboard;

        public SecondView()
        {
            InitializeComponent();

            Messenger.Default.Register<MessageSearchStatus>(this, messageSearchStatus => ReceivedSearchStatus(messageSearchStatus));

            /// Animation for loader
            DoubleAnimation myDoubleAnimation = new DoubleAnimation();
            myDoubleAnimation.From = 100;
            myDoubleAnimation.To = 0;
            myDoubleAnimation.Duration = new Duration(TimeSpan.FromSeconds(.1));
            myDoubleAnimation.AutoReverse = true;
            myDoubleAnimation.RepeatBehavior = RepeatBehavior.Forever;

            loaderStoryboard = new Storyboard();
            loaderStoryboard.Children.Add(myDoubleAnimation);
            Storyboard.SetTargetName(myDoubleAnimation, rectangleLoader.Name);
            Storyboard.SetTargetProperty(myDoubleAnimation, new PropertyPath(Rectangle.WidthProperty));
        }

        private void ReceivedSearchStatus(MessageSearchStatus message)
        {
            loaderStoryboard.Begin(this, true);
        }

        /// I manually stop the animation before going to other screens
        private void stopAnimation_Click(object sender, System.Windows.RoutedEventArgs e)
        {
           loaderStoryboard.Stop(this);
        }

    }
}

视图模型

namespace TwoViews.ViewModels
{
    public class SecondViewModel : ViewModelBase
    {
        private string _inputFileName;

        public string InputFileNameChanged
        {
            get { return _inputFileName; }
            set {
                // send message to start animation everytime the textBox changes
                Messenger.Default.Send<MessageSearchStatus>(new MessageSearchStatus { isSearchingFile = true });
            }
        }
    }
}

~~请注意，在我的代码中我没有显示停止动画的代码。~~

同样，动画效果很好，直到用户离开动画所在的页面并返回。

谢谢！

Answer 1

仅供参考 - 问题似乎是我在动画中使用的 Storyboard。删除了 Storyboard，一切正常。

SecondView.xaml.cs

using System.Windows;
using System.Windows.Controls;
using System.Windows.Media.Animation;
using System;
using System.Windows.Input;
using GalaSoft.MvvmLight.Messaging;
using GalaSoft.MvvmLight.Threading;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Collections.Specialized;
using System.Linq;
using System.Windows.Shapes;
using TwoViews.Models;
using System.Windows.Media;

namespace TwoViews.Views
{
    public partial class SecondView : UserControl
    {
        private DoubleAnimation myDoubleAnimation;

        public SecondView()
        {
            InitializeComponent();

            Messenger.Default.Register<MessageSearchStatus>(this, messageSearchStatus => ReceivedSearchStatus(messageSearchStatus));

            /// Animation for loader
            myDoubleAnimation = new DoubleAnimation();
            myDoubleAnimation.From = 100;
            myDoubleAnimation.To = 0;
            myDoubleAnimation.Duration = new Duration(TimeSpan.FromSeconds(.1));
            myDoubleAnimation.AutoReverse = true;
            myDoubleAnimation.RepeatBehavior = RepeatBehavior.Forever;
        }

        private void ReceivedSearchStatus(MessageSearchStatus message)
        {
            rectangleLoader.BeginAnimation(Rectangle.WidthProperty, myDoubleAnimation);
        }

        private void stopAnimation_Click(object sender, System.Windows.RoutedEventArgs e)
        {
            rectangleLoader.BeginAnimation(Rectangle.WidthProperty, null);
        }
    }
}

I get error: name cannot be found in the name scope of - When moving from page to page in an MVVMLight application

I get error: name cannot be found in the name scope of - When moving from page to page in an MVVMLight application

c#

wpf

mvvm

mvvm-light

错误：

XAML

SecondView.xaml.cs

视图模型

SecondView.xaml.cs