How can I show a Balloon Tip over a textbox?

Question

I have a C# WPF application using XAML and MVVM. My question is: How can I show a balloon tooltip above a text box for some invalid data entered by the user?

I want

Answer 1

This BalloonDecorator Project is one that I am using on a current project to show help hints and error notifications. I know you could modify your error template to show this decorator, just like you could show an icon instead of the red borders. The benefit of using a decorator is you can make it look however you'd like, and won't have to depend on WinForms.

BalloonDecorator.cs

using System;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;

namespace MyNamespace
{
public class BalloonDecorator : Decorator
{
    private static double _thickness = 0;
    private static int OpeningGap = 10;

    public static readonly DependencyProperty BackgroundProperty =
        DependencyProperty.Register("Background", typeof (Brush), typeof (BalloonDecorator));

    public static readonly DependencyProperty BorderBrushProperty =
        DependencyProperty.Register("BorderBrush", typeof (Brush), typeof (BalloonDecorator));

    public static readonly DependencyProperty PointerLengthProperty = 
        DependencyProperty.Register("PointerLength", typeof (double), typeof (BalloonDecorator),
        new FrameworkPropertyMetadata(10.0, FrameworkPropertyMetadataOptions.AffectsRender |
        FrameworkPropertyMetadataOptions.AffectsMeasure));

    public static readonly DependencyProperty CornerRadiusProperty = 
        DependencyProperty.Register("CornerRadius", typeof (double), typeof (BalloonDecorator),
        new FrameworkPropertyMetadata(10.0, FrameworkPropertyMetadataOptions.AffectsRender |
        FrameworkPropertyMetadataOptions.AffectsMeasure));

    public Brush Background
    {
        get { return (Brush) GetValue(BackgroundProperty); }
        set { SetValue(BackgroundProperty, value); }
    }

    public Brush BorderBrush
    {
        get { return (Brush) GetValue(BorderBrushProperty); }
        set { SetValue(BorderBrushProperty, value); }
    }

    public double PointerLength
    {
        get { return (double) GetValue(PointerLengthProperty); }
        set { SetValue(PointerLengthProperty, value); }
    }

    public double CornerRadius
    {
        get { return (double) GetValue(CornerRadiusProperty); }
        set { SetValue(CornerRadiusProperty, value); }
    }

    protected override Size ArrangeOverride(Size arrangeSize)
    {
        UIElement child = Child;
        if (child != null)
        {
            double pLength = PointerLength;
            Rect innerRect =
                Rect.Inflate(new Rect(pLength, 0, Math.Max(0, arrangeSize.Width - pLength), arrangeSize.Height),
                             -1 * _thickness, -1 * _thickness);
            child.Arrange(innerRect);
        }

        return arrangeSize;
    }

    protected override Size MeasureOverride(Size constraint)
    {
        UIElement child = Child;
        Size size = new Size();
        if (child != null)
        {
            Size innerSize = new Size(Math.Max(0, constraint.Width - PointerLength), constraint.Height);
            child.Measure(innerSize);
            size.Width += child.DesiredSize.Width;
            size.Height += child.DesiredSize.Height;
        }

        Size borderSize = new Size(2 * _thickness, 2 * _thickness);
        size.Width += borderSize.Width + PointerLength;
        size.Height += borderSize.Height;

        return size;
    }

    protected override void OnRender(DrawingContext dc)
    {
        Rect rect = new Rect(0, 0, RenderSize.Width, RenderSize.Height);

        dc.PushClip(new RectangleGeometry(rect));
        dc.DrawGeometry(Background, new Pen(BorderBrush, _thickness), CreateBalloonGeometry(rect));
        dc.Pop();
    }

    private StreamGeometry CreateBalloonGeometry(Rect rect)
    {
        double radius = Math.Min(CornerRadius, rect.Height / 2);
        double pointerLength = PointerLength;

        // All the points on the path
        Point[] points =
            {
                new Point(pointerLength + radius, 0), new Point(rect.Width - radius, 0), // Top
                new Point(rect.Width, radius), new Point(rect.Width, rect.Height - radius), // Right
                new Point(rect.Width - radius, rect.Height), // Bottom
                new Point(pointerLength + radius, rect.Height), // Bottom
                new Point(pointerLength, rect.Height - radius), // Left
                new Point(pointerLength, radius) // Left
            };

        StreamGeometry geometry = new StreamGeometry();
        geometry.FillRule = FillRule.Nonzero;
        using (StreamGeometryContext ctx = geometry.Open())
        {
            ctx.BeginFigure(points[0], true, true);
            ctx.LineTo(points[1], true, false);
            ctx.ArcTo(points[2], new Size(radius, radius), 0, false, SweepDirection.Clockwise, true, false);
            ctx.LineTo(points[3], true, false);
            ctx.ArcTo(points[4], new Size(radius, radius), 0, false, SweepDirection.Clockwise, true, false);
            ctx.LineTo(points[5], true, false);

            ctx.ArcTo(points[6], new Size(radius, radius), 0, false, SweepDirection.Clockwise, true, false);

            // Pointer
            if (pointerLength > 0)
            {
                ctx.LineTo(rect.BottomLeft, true, false);
                ctx.LineTo(new Point(pointerLength, rect.Height - radius - OpeningGap), true, false);
            }
            ctx.LineTo(points[7], true, false);

            ctx.ArcTo(points[0], new Size(radius, radius), 0, false, SweepDirection.Clockwise, true, false);
        }
        return geometry;
    }
}
}

Just make sure that this class's namespace is loaded into the XAML imports (I use a namespace called "Framework"), and it is simple to use:

Obviously, I tie the visibility to a binding, but you could just set it to true and put this inside your Validation.ErrorTemplate.

Hope this helps!