如何在不改变表单背后的代码的情况下每秒动态更新表单中的子控件？

Question

我在一个表格中有一个儿童控制器，显示了WiFi信号的强度。因为这个应用程序将在平板电脑上使用在车​​辆周围的移动车辆上。 我想在我的WPF应用程序的每个形式中都有这个控件，我希望它每秒刷新一次，而不必更改它所在的每个表单后面的代码。

通过调用signalQualityView.Refresh（），可以使用父窗体的代码来刷新此控件。 每秒钟，但希望在SignalQualityView用户控件中实现此功能。

public partial class SignalQualityView : UserControl, INotifyPropertyChanged
    {
        // wifi signal indicator taken from from https://stackoverflow.com/questions/20085284/c-sharp-wpf-rating-control-similar-to-wifi-signal-indicator

        private NetworkInformationService _networkInformationService;

        public SignalQualityView()
        {
            InitializeComponent();
            DataContext = this;
            _networkInformationService = new NetworkInformationService();
            Refresh();

        }

        public void Refresh()
        {
            Task.Run(() =>
            {
                WirelessNetwork wirelessNetwork = _networkInformationService.GetWirelessNetworkDetails();
                var signalQuality = wirelessNetwork.SignalQuality;

                if (signalQuality >= 80)
                    RatingValue = 5;
                else if (signalQuality >= 60)
                    RatingValue = 4;
                else if (signalQuality >= 40)
                    RatingValue = 3;
                else if (signalQuality >= 20)
                    RatingValue = 2;
                else if (signalQuality >= 1)
                    RatingValue = 1;
                else
                    RatingValue = 0;
                Task.Delay(1000);
                Refresh();
            });
        }



        public int RatingValue
        {
            get { return (int)GetValue(RatingValueProperty); }
            set
            {
                SetValue(RatingValueProperty, value);
                OnPropertyChanged();
            }
        }

        // Using a DependencyProperty as the backing store for RatingValue.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty RatingValueProperty =
            DependencyProperty.Register("RatingValue", typeof(int), typeof(SignalQualityView), new UIPropertyMetadata(0));

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public class RatingConverter : IValueConverter
    {
        public Brush OnBrush { get; set; }
        public Brush OffBrush { get; set; }

        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            int rating = 0;
            int number = 0;
            if (int.TryParse(value.ToString(), out rating) && int.TryParse(parameter.ToString(), out number))
            {
                if (rating >= number)
                {
                    return OnBrush;
                }
                return OffBrush;
            }
            return Brushes.Transparent;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

<UserControl x:Class="App.PlugIn.Controls.SignalQualityView"
             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:local="clr-namespace:DPWorld.PlugIn.Controls"
             mc:Ignorable="d" 
            Height="40" Width="60">


    <Grid Background="black"  >
        <Grid.Resources>
            <local:RatingConverter x:Key="RatingConverter" OnBrush="LightBlue" OffBrush="Black" />
            <Style TargetType="Rectangle">
                <Setter Property="HorizontalAlignment" Value="Left" />
                <Setter Property="VerticalAlignment" Value="Bottom" />
                <Setter Property="Margin" Value="5,0,0,0" />
            </Style>
        </Grid.Resources>

        <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" Background="Black" VerticalAlignment="Center">
            <Rectangle Width="5" Height="5" Fill="{Binding RatingValue, Converter={StaticResource RatingConverter}, ConverterParameter=1}"/>
            <Rectangle Width="5" Height="10" Fill="{Binding RatingValue, Converter={StaticResource RatingConverter}, ConverterParameter=2}"/>
            <Rectangle Width="5" Height="15" Fill="{Binding RatingValue, Converter={StaticResource RatingConverter}, ConverterParameter=3}"/>
            <Rectangle Width="5" Height="20" Fill="{Binding RatingValue, Converter={StaticResource RatingConverter}, ConverterParameter=4}"/>
            <Rectangle Width="5" Height="25" Fill="{Binding RatingValue, Converter={StaticResource RatingConverter}, ConverterParameter=5}"/>
        </StackPanel>
        <Label Content="SIGNAL" Foreground="LightBlue" VerticalAlignment="Top" Height="15" FontSize="8" Margin="10,0,18,0" Padding="0,0,0,0"/>
    </Grid>
</UserControl>

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
 xmlns:pi="clr-namespace:App.PlugIn.Controls;assembly=PlugIn"
    Title="Window1" Height="300" Width="300">
    <Grid>
   <pi:SignalQualityView Name="signalQualityView" />
    </Grid>
</Window>

根据信号强度突出显示信号条的数量，但突出显示0条。

Answer 1

使用WPF时，更改窗口上的数据应来自绑定对象的IObservable属性。 属性更改时，显示值会更改。 使用每秒运行一次的任务将当前值放入共享对象的属性中。 在所有绑定对象之间共享对象，不需要后面的代码。

您可以从一个可以共享和观察的类开始：

   public class WiFiStrength : IObservable<int>
   {
      private int _signalQuality;
      private int _ratingValue;

      private class Unsubscriber : IDisposable
      {
         private List<IObserver<int>> _observers;
         private readonly IObserver<int> _observer;

         public Unsubscriber(List<IObserver<int>> observers, IObserver<int> observer)
         {
            _observers = observers;
            _observer = observer;
         }

         public void Dispose()
         {
            if (_observers != null)
            {
               _observers.Remove(_observer);
               _observers = null;
            }
         }
      }

      private List<IObserver<int>> _observers = new List<IObserver<int>>();

      private void SetAndRaiseIfChanged(int newRating)
      {
         if (_ratingValue != newRating)
         {
            _ratingValue = newRating;
            foreach (var observer in _observers)
            {
               observer.OnNext(newRating);
            }
         }
      }

      private static WiFiStrength _sharedInstance;
      private static Task _updater;
      private static CancellationTokenSource cts;

      private static void UpdateStrength(WiFiStrength model, CancellationToken ct)
      {
         var rnd = new Random();
         while (!ct.IsCancellationRequested)
         {
            model.SignalQuality = rnd.Next(100);
            Thread.Sleep(1000);
         }
      }

      public static WiFiStrength SharedInstance()
      {
         if (_sharedInstance == null)
         {
            _sharedInstance = new WiFiStrength();
            cts = new CancellationTokenSource();
            _updater = new Task(() => UpdateStrength(_sharedInstance, cts.Token));
            _updater.Start();
         }

         return _sharedInstance;
      }

      public int SignalQuality
      {
         get => _signalQuality;
         set
         {
            _signalQuality = value;
            if (_signalQuality >= 80)
            {
               SetAndRaiseIfChanged(5);
            }
            else if (_signalQuality >= 60)
            {
               SetAndRaiseIfChanged(4);
            }
            else if (_signalQuality >= 40)
            {
               SetAndRaiseIfChanged(3);
            }
            else if (_signalQuality >= 20)
            {
               SetAndRaiseIfChanged(2);
            }
            else if (_signalQuality >= 1)
            {
               SetAndRaiseIfChanged(1);
            }
            else
            {
               SetAndRaiseIfChanged(0);
            }
         }
      }

      public int SignalRating => _ratingValue;

      public IDisposable Subscribe(IObserver<int> observer)
      {
         _observers.Add(observer);
         return new Unsubscriber(_observers, observer);
      }
   }

您将它附加到您的绑定类：

   public class ViewModel1 : INotifyPropertyChanged
   {
      public string TextField { get; set; }
      public WiFiStrength WiFi { get; set; }

      private IObserver<int> _observer;

      private class WiFiObserver : IObserver<int>
      {
         private readonly ViewModel1 _parent;
         private readonly IDisposable _unsubscribe;

         public WiFiObserver(ViewModel1 parent, WiFiStrength observed)
         {
            _parent = parent;
            _unsubscribe = parent.WiFi.Subscribe(this);
         }

         public void OnNext(int value)
         {
            _parent.NotifyPropertyChanged("WiFi");
         }

         public void OnError(Exception error)
         {
            _unsubscribe.Dispose();
         }

         public void OnCompleted()
         {
            _unsubscribe.Dispose();
         }
      }

      public ViewModel1()
      {
         WiFi = WiFiStrength.SharedInstance();
         _observer = new WiFiObserver(this, WiFi);
      }

      public event PropertyChangedEventHandler PropertyChanged;

      private void NotifyPropertyChanged(string propertyName)
      {
         PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
      }
   }

您的班级会查找更改，并在更改时通知拥有的表单。

您的XAML只需绑定到属性，如下所示：

         <Label Content="{Binding WiFi.SignalRating, Mode=OneWay}"/>

使用尽可能多的表单。

Answer 2

定期更新的简单UserControl将使用带有Tick事件处理程序的DispatcherTimer来更新控件的依赖项属性。 控件的XAML中的元素将通过RelativeSource绑定绑定控件属性。

以简单的数字时钟为例：

<UserControl ...>
    <Grid>
        <TextBlock Text="{Binding Time,
            RelativeSource={RelativeSource AncestorType=UserControl}}"/>
    </Grid>
</UserControl>

代码背后：

public partial class Clock : UserControl
{
    public Clock()
    {
        InitializeComponent();

        var timer = new DispatcherTimer { Interval = TimeSpan.FromSeconds(0.5) };
        timer.Tick += (s, e) => Time = DateTime.Now.ToString("HH:mm:ss");
        timer.Start();
    }

    public static readonly DependencyProperty TimeProperty =
        DependencyProperty.Register(nameof(Time), typeof(string), typeof(Clock));

    public string Time
    {
        get { return (string)GetValue(TimeProperty); }
        set { SetValue(TimeProperty, value); }
    }
}