添加內容時，使ViewModel屬性系結的RichTextBox自動滾動到底部

感謝您對我的問題的徹底和解釋清楚的回答！

我有一個 WPF UserControl 與BindableRichTextBox：

xmlns:controls="clr-namespace:SysadminsLV.WPF.OfficeTheme.Controls;assembly=Wpf.OfficeTheme"
.
.
.
<controls:BindableRichTextBox Background="Black"
                              Foreground="White"
                              FontFamily="Consolas"
                              FontSize="12"
                              IsReadOnly="True"
                              IsReadOnlyCaretVisible="True"
                              VerticalScrollBarVisibility="Auto"
                              IsUndoEnabled="False"
                              Document="{Binding Contents}"/>

內容由 ViewModel 屬性控制Document：

using System.Windows.Documents;

class MyViewModel : ILogServerContract 
{
    readonly Paragraph _paragraph;

    public MyViewModel() 
    {
        _paragraph = new Paragraph();
        Contents = new FlowDocument(_paragraph);
    }

    public FlowDocument Contents { get; }

    //Log Server Contract Write method (accessed via NetPipe)
    public void WriteLine(string text, int debugLevel) 
    {
        //figure out formatting stuff based on debug level. not important
        _paragraph.Inlines.Add(new Run(text) {
            //set text color
        });
    }
}

如您所見，RichTextBoxDocument屬性系結到Contents來自 的屬性MyViewModel。Contents反過來，該屬性是通過 NetPipes 通過方法寫入的，該WriteLine()方法是ILogServerContract介面的一部分。

我正在努力的是：

• 如何在 RichTextBox 的內容更新時引發事件，然后
• 按照這個更簡單的問題中的建議呼叫ScrollToEnd()RichTextBox 上的方法。由于 RichTextBox 是在 XAML 而不是代碼中宣告的，所以我不知道該怎么做。

有人可以幫忙嗎？

uj5u.com熱心網友回復：

您不應該在視圖模型類中實作這種與視圖相關的邏輯。滾動邏輯必須是您控制的一部分。
此外，Run是一個純視圖類。它 extends FrameworkElement，它應該給你一個提示，如果可能的話，避免在你的視圖模型中處理這個 UI 元素。

由于您正在實作一個簡單的訊息視圖，RichTextBox因此不是正確的控制元件。TextBlock會更合適（它還支持為文本著色Inline等元素）。 現在您想要顯示多行文本，您應該基于 a 實作您的視圖，該視圖借助 a 呈現其專案。 這種方法的主要優點是性能優越得多。在顯示大量訊息的情況下，它為您提供開箱即用的 UI 虛擬化 - 它始終會平滑滾動。重物很快變得呆滯。Run
ListBoxTextBlock
ListBoxRichTextBox

由于您的視圖模型只能處理資料，因此第一步是引入資料模型，例如LogMessage及其相關型別：

日志訊息.cs

// If you plan to modify existing messages e.g. in order to append text,
// the Message property must have a set() and must raise the PropertyChanged event.
public class LogMessage : INotifyPropertyChanged
{
  public LogMessage(string message, LogLevel logLevel)
  {
    this.Message = message;
    this.LogLevel = logLevel;
  }

  public string Message { get; }
  public LogLevel LogLevel { get; }
  public bool IsNewLine { get; init; }

  public event PropertyChangedEventHandler PropertyChanged;
}

日志級別.cs

public enum LogLevel
{
  Default = 0,
  Debug,
  Info
}

主視圖模型.cs

class MainViewModel : INotifyPropertyChanged
{
  public ObservableCollection<LogMessage> LogMessages { get; }
  public event PropertyChangedEventHandler PropertyChanged;

  public MainViewModel()
  {
    this.LogMessages = new ObservableCollection<LogMessage>();

    WriteLine("Debug test message.", LogLevel.Debug);
    WriteLine("Info test message.", LogLevel.Info);
  }
 
  // To implement Write() to avoid line breaks, 
  // simply append the new message text to the previous message.
  public void WriteLine(string message, LogLevel logLevel) 
  {
    var newMessage = new LogMessage(message, logLevel) { IsNewLine = true };
    this.LogMessages.Add(newMessage);
  }
}

Then implement the view that displays the messages. Although this example uses a UserControl, I highly recommend to create a custom control by extending Control instead:

LogLevelToBrushConverter.cs

public class LogLevelToBrushConverter : IValueConverter
{
  public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
  {
    return value switch
    {
      LogLevel.Debug => Brushes.Blue,
      LogLevel.Info => Brushes.Gray,
      _ => Brushes.Black
    };
  }

  public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) 
    => throw new NotSupportedException();
}

LogOutputBox.xaml.cs

public partial class LogOutputBox : UserControl
{
  public IList<LogMessage> LogMessagesSource
  {
    get => (IList<LogMessage>)GetValue(LogMessagesSourceProperty);
    set => SetValue(LogMessagesSourceProperty, value);
  }

  public static readonly DependencyProperty LogMessagesSourceProperty = DependencyProperty.Register(
    "LogMessagesSource", 
    typeof(IList<LogMessage>), 
    typeof(LogOutputBox), 
    new PropertyMetadata(default(IList<LogMessage>), OnLogMessagesSourceChanged));

  public LogOutputBox()
  {
    InitializeComponent();
  }

  private static void OnLogMessagesSourceChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) 
    => (d as LogOutputBox).OnLogMessagesSourceChanged(e.OldValue as IList<LogMessage>, e.NewValue as IList<LogMessage>);

  // Listen to CollectionChanged events 
  // in order to always keep the last and latest item in view.
  protected virtual void OnLogMessagesSourceChanged(IList<LogMessage> oldMessages, IList<LogMessage> newMessages)
  {
    if (oldMessages is INotifyCollectionChanged oldObservableCollection)
    {
      oldObservableCollection.CollectionChanged -= OnLogMessageCollectionChanged;
    }
    if (newMessages is INotifyCollectionChanged newObservableCollection)
    {
      newObservableCollection.CollectionChanged  = OnLogMessageCollectionChanged;
    }
  }

  private void OnLogMessageCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
  {
    LogMessage item = this.LogMessagesSource.LastOrDefault();
    ListBox listBox = this.Output;
    Dispatcher.InvokeAsync(
      () => listBox.ScrollIntoView(item), 
      DispatcherPriority.Background);
  }
}

LogOutputBox.xaml

<UserControl>
  <UserControl.Resources>
    <local:LogLevelToBrushConverter x:Key="LogLevelToBrushConverter" />
  </UserControl.Resources>
  
  <ListBox x:Name="Output" 
           ItemsSource="{Binding RelativeSource={RelativeSource AncestorType=UserControl}, Path=LogMessagesSource}">
    <ListBox.ItemTemplate>
      <DataTemplate DataType="{x:Type local:LogMessage}">
        <TextBlock>

          <!-- If you expect Message to change, adjust the Binding.Mode to OneWay. 
               Otherwise leave it as OneTime to improve performance 
          -->
          <Run Text="{Binding Message, Mode=OneTime}"
               Foreground="{Binding LogLevel, Mode=OneTime, Converter={StaticResource LogLevelToBrushConverter}}" />
        </TextBlock>
      </DataTemplate>
    </ListBox.ItemTemplate>
  </ListBox>
</UserControl>

Usage example

MainWindow.xaml

<Window>
  <Window.DataContext>
    <MainViewModel />
  </Window.DataContext>

  <LogOutputBox LogMessagesSource="{Binding LogMessages}" />
</Window>

標籤：C＃ wpf xml

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