WPF 中 TextBlock 设置TextTrimming 后，并根据需要自动显示 ToolTip

第一种方式：在 TextBlock 中使用附加属性

实现 TextBlockUtils 类，定义 AutoTooltip 附加属性：

public class TextBlockUtils
    {
        /// <summary>
        /// Gets the value of the AutoTooltipProperty dependency property
        /// </summary>
        public static bool GetAutoTooltip(DependencyObject obj)
        {
            return (bool)obj.GetValue(AutoTooltipProperty);
        }

        /// <summary>
        /// Sets the value of the AutoTooltipProperty dependency property
        /// </summary>
        public static void SetAutoTooltip(DependencyObject obj, bool value)
        {
            obj.SetValue(AutoTooltipProperty, value);
        }

        /// <summary>
        /// Identified the attached AutoTooltip property. When true, this will set the TextBlock TextTrimming
        /// property to WordEllipsis, and display a tooltip with the full text whenever the text is trimmed.
        /// </summary>
        public static readonly DependencyProperty AutoTooltipProperty = DependencyProperty.RegisterAttached("AutoTooltip",
                typeof(bool), typeof(TextBlockUtils), new PropertyMetadata(false, OnAutoTooltipPropertyChanged));

        private static void OnAutoTooltipPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            TextBlock textBlock = d as TextBlock;
            if (textBlock == null)
                return;

            if (e.NewValue.Equals(true))
            {
                textBlock.TextTrimming = TextTrimming.WordEllipsis;
                ComputeAutoTooltip(textBlock);
                textBlock.SizeChanged += TextBlock_SizeChanged;
            }
            else
            {
                textBlock.SizeChanged -= TextBlock_SizeChanged;
            }
        }

        private static void TextBlock_SizeChanged(object sender, SizeChangedEventArgs e)
        {
            TextBlock textBlock = sender as TextBlock;
            ComputeAutoTooltip(textBlock);
        }

        /// <summary>
        /// Assigns the ToolTip for the given TextBlock based on whether the text is trimmed
        /// </summary>
        private static void ComputeAutoTooltip(TextBlock textBlock)
        {
#if !Silverlight
            textBlock.Measure(new Size(Double.PositiveInfinity, Double.PositiveInfinity));
            var width = textBlock.DesiredSize.Width;

            if (textBlock.ActualWidth < width)
            {
                ToolTipService.SetToolTip(textBlock, textBlock.Text);
            }
            else
            {
                ToolTipService.SetToolTip(textBlock, null);
            }

#else
            FrameworkElement parentElement = VisualTreeHelper.GetParent(textBlock) as FrameworkElement;
            if (parentElement != null)
            {
                if (textBlock.ActualWidth > parentElement.ActualWidth)
                {
                    ToolTipService.SetToolTip(textBlock, textBlock.Text);
                }
                else
                {
                    ToolTipService.SetToolTip(textBlock, null);
                }
            }
#endif
        }
    }

View Code