Graphics.DrawString()

如何解决Graphics.DrawString()

我有一个 Windows 窗体，上面有一些数字（此时只有一个数字）并定期刷新它们（数字是随机生成的）。更新过程与应用程序在一个单独的线程中进行，因此表单可以接收用户单击按钮、调整窗口大小等事件。 主要方法：

class Program {       
        static void Main(string[] args) {
            Form o = new Overlay();
            Application.Run(o);
        }
    }

表单类：

public partial class Overlay : Form {
        Graphics g;
        Drawer drawer;
        public Overlay() {
            InitializeComponent();
            TopMost = true;
            TransparencyKey = Color.Black;
            BackColor = TransparencyKey;
            CheckForIllegalCrossThreadCalls = false;

            g = CreateGraphics();
            drawer = new Drawer();
        }

        protected override void OnLoad(EventArgs e) {
            base.OnLoad(e);
            Thread upd = new Thread(mainLoop);
            upd.Start();
        }

        void mainLoop() {
            while (true) {
                NetCoreEx.Geometry.Rectangle r;
                GetWindowRect(Handle,out r);
                Refresh();
                drawer.Update(g,new Rectangle(r.Left,r.Top,r.Width,r.Height));
            }
        }

抽屉：

class Drawer {
        Font font;

        public Drawer() {
            string workingDir = Environment.CurrentDirectory;
            string projDir = Directory.GetParent(workingDir).Parent.FullName;
            PrivateFontCollection collection = new PrivateFontCollection();
            collection.AddFontFile(projDir + "\\Resources\\Athelas-Regular.ttf");
            FontFamily fontFamily = new FontFamily("Athelas",collection);
            font = new Font(fontFamily,16);
        }

        
        public void Update(Graphics g,Rectangle rect) {
            string stats = new Random().NextDouble().ToString();
            g.DrawString(stats,font,Brushes.Aqua,rect.Width / 2,(int)(rect.Height * 0.75));
        }
    }

代码对我来说看起来很简单，但是由于某种原因，在正常运行 5-10 秒后，应用程序突然崩溃，并在 DrawString 方法上出现 System.AccessViolateException... 堆栈跟踪

at System.Drawing.SafeNativeMethods.Gdip.GdipDrawString(HandleRef graphics,String textString,Int32 length,HandleRef font,GPRECTF& layoutRect,HandleRef stringFormat,HandleRef brush)
   at System.Drawing.Graphics.DrawString(String s,Font font,Brush brush,RectangleF layoutRectangle,StringFormat format)
   at System.Drawing.Graphics.DrawString(String s,Single x,Single y)
   at OverlayStatistics.Scripts.Drawer.Update(Graphics g,Rectangle rect) in C:\Users\Гриша\source\repos\OverlayStatistics\Scripts\Drawer.cs:line 30
   at OverlayStatistics.Overlay.mainLoop() in C:\Users\Гриша\source\repos\OverlayStatistics\Scripts\Overlay.cs:line 50
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext,ContextCallback callback,Object state,Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext,Object state)
   at System.Threading.ThreadHelper.ThreadStart()

我花了很多时间调试，但仍然不知道我做错了什么，有什么帮助吗？

解决方法

发生的情况是 FontFamily 实例被释放并导致内部 GDI 调用崩溃。您可以像这样加速行为：

public void Update(Graphics g,Rectangle rect)
{
    string stats = new Random().NextDouble().ToString();
    g.DrawString(stats,font,Brushes.Aqua,rect.Width / 2,(int)(rect.Height * 0.75));
    GC.Collect(); // a good way to check for dispose issues
}

有多种方法可以修复它，例如只需确保 FontFamily 实例也是 Drawer 的成员，即：

class Drawer {
    Font font;
    FontFamily fontFamily;


    public Drawer() {
        ...
        fontFamily = new FontFamily("Athelas",collection);
        font = new Font(fontFamily,16);
    }

    public void Update(Graphics g,Rectangle rect) {
        string stats = new Random().NextDouble().ToString();
        g.DrawString(stats,(int)(rect.Height * 0.75));
    }
}