在单独的控件中绘制 ListBox 项的行号

Question

我想在 ListBox 的左侧绘制行号，非常类似于 AvalonEdit does with LineNumberMargin. When ShowLineNumbers is true, it creates LineNumberMargin like this。

无论如何，我看了一下他们是如何做到的，并理解了，现在我正在尝试应用类似的东西，但使用 ListBox（及其项目）作为绘图的来源。

我的控件是这样工作的：我有一个单独的 ItemsControl 停靠在 ListBox 的左侧。每个 ItemsControl 的项目都是一个 UIElement。 DesignerLineNumberMargin 是 ItemsControl 的项目之一，当设置了 ListBox 的 ItemsSource 时，我将 ListBox 附加到 DesignerLineNumberMargin。呈现 DesignerLineNumberMargin 时，我遍历 ListBox 的项目并绘制行号。

DesignerLineNumberMargin.cs

public interface IMetadataAware
{
    void Attach(ItemsControl control);
    void Detach(ItemsControl control);
}

public class DesignerLineNumberMargin : FrameworkElement, IMetadataAware
{
    private ItemsControl control;
    private Typeface typeface;
    private double emSize;
    private int maxLineNumberLength = 2;

    static DesignerLineNumberMargin()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(DesignerLineNumberMargin),
            new FrameworkPropertyMetadata(typeof(DesignerLineNumberMargin)));
    }

    protected override Size MeasureOverride(Size availableSize)
    {
        typeface = CreateTypeface();
        emSize = (double)GetValue(TextBlock.FontSizeProperty);

        var text = CreateText(new string('9', maxLineNumberLength));

        return new Size(text.Width, 0);
    }

    private FormattedText CreateText(string text)
    {
        return
            new FormattedText(
            text,
            CultureInfo.CurrentCulture,
            FlowDirection.LeftToRight,
            typeface,
            emSize,
            (Brush)GetValue(Control.ForegroundProperty));
    }

    protected override void OnRender(DrawingContext drawingContext)
    {
        if (control == null)
            return;

        var renderSize = RenderSize;
        var foreground = (Brush)GetValue(Control.ForegroundProperty);

        for (int index = 0; index < control.Items.Count; index++)
        {
            var item = control.Items[index];
            var container = (FrameworkElement)control.ItemContainerGenerator.ContainerFromItem(item);

            var text = CreateText((index + 1).ToString(CultureInfo.CurrentCulture));
            //var y = container.Height;
            var y = RenderSize.Height / (double)control.Items.Count;

            drawingContext.DrawText(text, new Point(renderSize.Width - text.Width, y + index));
        }
    }

    private Typeface CreateTypeface()
    {
        var element = this;
        return new Typeface(
            (FontFamily)element.GetValue(TextBlock.FontFamilyProperty),
            (FontStyle)element.GetValue(TextBlock.FontStyleProperty),
            (FontWeight)element.GetValue(TextBlock.FontWeightProperty),
            (FontStretch)element.GetValue(TextBlock.FontStretchProperty));
    }

    public void Attach(ItemsControl control)
    {
        this.control = control;

        var descriptor = TypeDescriptor.GetProperties(control)["ItemsSource"];
        descriptor.AddValueChanged(control, OnItemsSourceChanged);
    }

    private void OnItemsSourceChanged(object sender, EventArgs e)
    {
        if (this.control.ItemsSource is INotifyCollectionChanged)
            (this.control.ItemsSource as INotifyCollectionChanged).CollectionChanged += CollectionChanged;
    }

    private void CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        InvalidateVisual();
    }

    public void Detach(ItemsControl control)
    {
        if (this.control == control)
        {
            var descriptor = TypeDescriptor.GetProperties(control)["ItemsSource"];
            descriptor.RemoveValueChanged(control, OnItemsSourceChanged);

            if (this.control.ItemsSource is INotifyCollectionChanged)
                (this.control.ItemsSource as INotifyCollectionChanged).CollectionChanged -= CollectionChanged;
            this.control = null;
        }

        InvalidateVisual();
    }
}

我的问题是找出 y 坐标。调用OnRender时我不知道ListBoxItem的Height：Height、ActualHeight、DesiredSize始终为0。

有什么见解吗？

Answer 1

我想那是因为你的 MeasureOverride() returns 一个 Size 只有一个 Width，但是 Height 设置为零。

尝试将 return 语句更改为：

 return new Size(text.Width, text.Height);

在单独的控件中绘制 ListBox 项的行号

Draw line number of ListBox items in a separated control

c#

wpf

listbox

wpf-controls

avalonedit