C＃WPF连续不停地调用OnRender

Question

我正在为我的WPF应用程序创建自定义控件。这是我的代码：

MainWindow.xaml.cs：

public sealed class MainTimer : FrameworkElement
{
    public DispatcherTimer Timer = new DispatcherTimer();

    public MainTimer()
    {
        Timer.Tick += delegate 
        {
            UpdateLayout();

            // No luck
            // Dispatcher.Invoke(delegate { },DispatcherPriority.Render);

            // InvalidateVisual();
        };
        Timer.Interval = new TimeSpan(10);
        Timer.Start();
    }

    protected override void OnRender(DrawingContext drawingContext)
    {
        string mode = "12";

        Console.WriteLine("RENDERING");


        if (Application.Current.MainWindow != null)
        {
            if (mode == "24")
            {
                //drawingContext.DrawRectangle(new SolidColorBrush(Color.FromArgb(50,150,255,255)), null, BoundsRelativeTo(this, Application.Current.MainWindow));
                drawingContext.DrawText(new FormattedText(DateTime.Now.ToLongTimeString(), System.Globalization.CultureInfo.CurrentCulture, FlowDirection.LeftToRight, new Typeface("Microsoft PhagsPa"), 50, new SolidColorBrush(Color.FromArgb(50, 235, 255, 255))), new Point(0, -15));
            }
            else
            {
                string st = "";

                if (DateTime.Now.Hour > 12)
                {
                    st = ((DateTime.Now.Hour - 12).ToString("00") + " : " + DateTime.Now.Minute.ToString("00") + " : " + DateTime.Now.Second.ToString("00")) + " pm" ;
                }
                else
                {
                    st = ((DateTime.Now.Hour).ToString("00") + " : " + DateTime.Now.Minute.ToString("00") + " : " + DateTime.Now.Second.ToString("00")) + " am";
                }


                drawingContext.DrawText(new FormattedText(st, System.Globalization.CultureInfo.CurrentCulture, FlowDirection.LeftToRight, new Typeface("Microsoft PhagsPa"), 40, new SolidColorBrush(Color.FromArgb(50, 200, 255, 255))), new Point(0, -12));
            }
        }
        //Dispatcher.Invoke(new Action(() => { }), DispatcherPriority.ContextIdle, null);

    }

    public static Rect BoundsRelativeTo(FrameworkElement element,Visual relativeTo)
    {
        return
          element.TransformToVisual(relativeTo)
                 .TransformBounds(LayoutInformation.GetLayoutSlot(element));
    }

}

MainWindow.xaml：

<Window x:Class="WpfApp1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:WpfApp1"
    mc:Ignorable="d"
    ShowInTaskbar="False"
    AllowsTransparency="True" WindowStyle="None"  
    WindowStartupLocation="Manual"
    Left="1168"
    Top="120"
    ResizeMode="NoResize"
    WindowState="Normal"
    Title="MainWindow" Height="75.132" Width="283.621" FontFamily="Microsoft PhagsPa">
<Window.Background>
    <SolidColorBrush Opacity="0" Color="LightCyan"/>
</Window.Background>

<local:MainTimer Loaded="Grid_Loaded"/>

问题是消息“RENDERING”应该每秒出现在控制台中，但它只出现一次！我希望我的控件每秒重新渲染一次。 我尝试使用InvalidateVisual()，但该程序占用了近70％-80％的CPU资源。 如何在不使用大量系统资源的情况下重新渲染控件？ 在WinForm中是否有类似“Refresh（）”的方法？

提前致谢 ：）

Answer 1

你的设置使这个非常微弱，但你可以看到时间，如果你知道要寻找什么：

以下代码工作正常：

using System;

namespace WpfApp1
{
    using System.Windows;
    using System.Windows.Media;
    using System.Windows.Threading;

    public sealed class MainTimer : FrameworkElement
    {
        private DispatcherTimer Timer = new DispatcherTimer();

        public MainTimer()
        {
            // what you are looking for is InvalidateVisual
            this.Timer.Tick += (sender, args) => this.InvalidateVisual();

            // changed your timespan to a more appropriate value
            this.Timer.Interval = TimeSpan.FromSeconds(1);
            this.Timer.Start();
        }

        protected override void OnRender(DrawingContext drawingContext)
        {
            string mode = "12";

            System.Diagnostics.Trace.WriteLine("Rendering");

            if (Application.Current.MainWindow != null)
            {
                if (mode == "24")
                {
                    drawingContext.DrawText(new FormattedText(DateTime.Now.ToLongTimeString(), System.Globalization.CultureInfo.CurrentCulture, FlowDirection.LeftToRight, new Typeface("Microsoft PhagsPa"), 50, new SolidColorBrush(Color.FromArgb(50, 235, 255, 255))), new Point(0, -15));
                }
                else
                {
                    string st = "";

                    if (DateTime.Now.Hour > 12)
                    {
                        st = ((DateTime.Now.Hour - 12).ToString("00") + " : " + DateTime.Now.Minute.ToString("00") + " : " + DateTime.Now.Second.ToString("00")) + " pm";
                    }
                    else
                    {
                        st = ((DateTime.Now.Hour).ToString("00") + " : " + DateTime.Now.Minute.ToString("00") + " : " + DateTime.Now.Second.ToString("00")) + " am";
                    }


                    drawingContext.DrawText(new FormattedText(st, System.Globalization.CultureInfo.CurrentCulture, FlowDirection.LeftToRight, new Typeface("Microsoft PhagsPa"), 40, new SolidColorBrush(Color.FromArgb(50, 200, 255, 255))), new Point(0, -12));
                }
            }
        }
    }
}

使用XAML：

<Window x:Class="WpfApp1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp1"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <local:MainTimer/>
    </Grid>
</Window>

它每秒渲染一次。

我仍然认为这不是自定义渲染的意思，您可以在XAML中使用更改viewmodel值的计时器来执行此操作。但是，如果它变得更复杂，您可能会对this other thread以及详细说明如何使用绘图组提高性能的答案感兴趣。