wpf 如何7步写一个badge控件-数字星空

首先看一下效果:

任意控件可以附加一个文字在控件的右上角，并带有红色背景

第一步，新建一个空的wpf项目:

第二步，创建一个类，取名为badge:

第三步，将badge的父类设置成 System.Windows.Documents.Adorner

    public class Badge : Adorner
    {
        public Badge(UIElement adornedElement) : base(adornedElement)
        {

        }
    }

里面的adornedElement表示badge后面附加的对象

关于Adorner这个类的说明，微软给了相应的教程 https://learn.microsoft.com/zh-cn/dotnet/desktop/wpf/controls/adorners-overview?view=netframeworkdesktop-4.8

也可以F11查看Adorner类的说明.

第4步，给badge添加一个Content的附加属性:

        public static readonly DependencyProperty ContentProperty;

        static Badge()
        {
            ContentProperty = DependencyProperty.RegisterAttached("Content", typeof(string), typeof(Badge),
                new FrameworkPropertyMetadata(string.Empty, new PropertyChangedCallback(ContentChangedCallBack)));
        }

　　　　　　public static string GetContent(DependencyObject obj)
　　　　　　{
　　　　　　　　　　return (string)obj.GetValue(ContentProperty);
　　　　　　}

　　　　　　public static void SetContent(DependencyObject obj, string value)
　　　　　　{
　　　　　　　　　　obj.SetValue(ContentProperty, value);
　　　　　　}

第5步，实现content的回调方法:

private static void ContentChangedCallBack(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    var target = d as FrameworkElement;
    if (target != null)
    {
        if (target.IsLoaded)
        {
            var layer = AdornerLayer.GetAdornerLayer(target);
            if (layer != null)
            {
                var Adorners = layer.GetAdorners(target);
                if (Adorners != null)
                {
                    foreach (var adorner in Adorners)
                    {
                        if (adorner is Badge)
                        {
                            layer.Remove(adorner);
                        }
                    }
                }
                layer.Add(new Badge(target));
            }
        }
        else
        {
            target.Loaded += (sender, ae) =>
            {
                var layer = AdornerLayer.GetAdornerLayer(target);
                if (layer != null)
                {
                    var Adorners = layer.GetAdorners(target);
                    if (Adorners != null)
                    {
                        foreach (var adorner in Adorners)
                        {
                            if (adorner is Badge)
                            {
                                layer.Remove(adorner);
                            }
                        }
                    }
                    layer.Add(new Badge(target));
                }
            };
        }
    }
}

第6步，重写一下OnRender方法:

        protected override void OnRender(DrawingContext drawingContext)
        {
            var element = this.AdornedElement as FrameworkElement;
            Rect adornedElementRect = new Rect(element.DesiredSize);
            var point = adornedElementRect.TopRight;
            point.X = adornedElementRect.Right - element.Margin.Left - element.Margin.Right;

            SolidColorBrush renderBrush = new SolidColorBrush(Colors.Red);
            Pen renderPen = new Pen(new SolidColorBrush(Colors.Red), 0.5);
            double renderRadius = 5;

            var content = this.AdornedElement.GetValue(Badge.ContentProperty).ToString();
            FormattedText formattedText = new FormattedText(content, CultureInfo.GetCultureInfo("zh-cn"), FlowDirection.LeftToRight, new Typeface("Verdana"), 10, Brushes.White);
            var textWidth = formattedText.Width;
            var textHeight = formattedText.Height;
            var rectangleSizeWidth = textWidth < 15 ? 15 : textWidth;
            var rectangleSizeHeight = textHeight < 15 ? 15 : textHeight;
            var size = new Size(rectangleSizeWidth, rectangleSizeHeight);
            Rect rect = new Rect(new Point(point.X - rectangleSizeWidth / 2, point.Y - rectangleSizeHeight / 2), size);

            drawingContext.DrawRoundedRectangle(renderBrush, renderPen, rect, renderRadius, renderRadius);
            drawingContext.DrawText(formattedText, new Point(point.X - textWidth / 2, point.Y - textHeight / 2));
        }

这段代码就是在目标控件的右上角绘制一个带圆角的rectangle，背景色为红色，再绘制一个文本用来显示content.

第7步，运用到项目中:

    <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
        <cc:CornerButton ButtonType="OutLine" Width="200" Height="30"
                         cc:Badge.Content="{Binding ElementName=textbox1, Path=Text, UpdateSourceTrigger=PropertyChanged}" Margin="10"/>
        <cc:CornerTextBox x:Name="textbox1" Width="200" Height="30" Text="12"
                          VerticalContentAlignment="Center" WaterText="BadgeContent"/>
    </StackPanel>