Textbox为null时OutOfMemoryException

每次我在文本框中键入文字时,都会在picurebox中完美地绘制文字,但每当我删除所有字母或先键入[space]时,picturebox就会变成这样:

文本框文本更改事件

private void tbox_Text_TextChanged(object sender, EventArgs e)
    {
        _LayerType = (LayerClass.Type)System.Enum.Parse(typeof(LayerClass.Type), "Text");
        pictureBox_Canvass.Invalidate();
        text = tbox_Text.Text;
        UpdateFont();
        textRect = txt.MeasureCharacters(fontFamily, text);
    }

public RectangleF MeasureCharacters(Font f, string text)
    {
        RectangleF r = new RectangleF();
        GraphicsPath path = new GraphicsPath();
        path.AddString(text, f.FontFamily, (int)f.Style, f.Size, new PointF(250 - (r.Width / 2), 250 - (r.Height / 2)), StringFormat.GenericDefault);
        var bounds = path.GetBounds();
        r = new RectangleF(bounds.Left, bounds.Top, bounds.Width, bounds.Height);
        return r;
    }

文本绘图

public LayerClass DrawString(LayerClass.Type _text, string text, RectangleF rect, Font _fontStyle, Brush brush, float angle, PaintEventArgs e)
    {
        using (StringFormat string_format = new StringFormat())
        {
            SizeF stringSize = e.Graphics.MeasureString(text, _fontStyle);
            rect.Location = new PointF(Shape.center.X - (rect.Width / 2), Shape.center.Y - (rect.Height / 2));
            e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
            e.Graphics.CompositingQuality = CompositingQuality.HighQuality;

            //e.Graphics.DrawRectangle(Pens.Red, Rectangle.Round(rect));

            RectangleF r = new RectangleF(rect.Location, rect.Size); 
            GraphicsPath path = new GraphicsPath();

           //Exception thrown here
            path.AddString(text, _fontStyle.FontFamily, Convert.ToInt32(_fontStyle.Style),  r.Height, r.Location, string_format); 

            RectangleF text_rectf = path.GetBounds();
            PointF[] target_pts = {
                            new PointF(r.Left, r.Top),
                            new PointF(r.Right, r.Top),
                            new PointF(r.Left, r.Bottom)};
            Matrix m = new Matrix(text_rectf, target_pts);
            Matrix flip = new Matrix();
            flip.Translate(-stringSize.Width, 1);
            m.RotateAt(angle, new PointF(Shape.center.X - (r.Width/4.5f), Shape.center.Y));
            path.Transform(m);
            if (flipped)
                path.Transform(flip);
            if (!isOutlined)
                e.Graphics.FillPath(Brushes.Red, path);
            else
                e.Graphics.DrawPath(Pens.Red, path);


        }
        this._Text = text;
        this._TextRect = rect;
        this.brush = brush;
        this._Angle = angle;
        return new LayerClass(_text, this, text, rect);
    }

错误:

System.Drawing.dll中发生类型为“System.OutOfMemoryException”的第一次意外异常

path.AddString(text、\u fontStyle.fontfamine、Convert.ToInt32(\u fontStyle.Style)、r.高度、r.位置、字符串格式);

编辑:

public void Source(PaintEventArgs e)
    {
        switch (_LayerType)
        {
            case LayerClass.Type.Rectangle:
                shape.DrawRectangle(LayerClass.Type.Rectangle, rectangleColor, strokeRect, rectangleWidth, rectangleHeight, e.Graphics, rectRadius);
                break;
            case LayerClass.Type.Square:
                shape.DrawSquare(LayerClass.Type.Square, squareColor, strokeSquare, squareWidth, squareHeight, e.Graphics, squareRadius);
                break;
            case LayerClass.Type.Circle:
                shape.DrawCircle(LayerClass.Type.Circle, circleColor, strokeCircle, circleWidth, circleHeight, e.Graphics);
                break;
            case LayerClass.Type.Ellipse:
                shape.DrawEllipse(LayerClass.Type.Ellipse, ellipseColor, strokeEllipse, ellipseWidth, ellipseHeight, e.Graphics);
                break;
            case LayerClass.Type.Triangle:
                shape.DrawTriangle(LayerClass.Type.Triangle, triangleColor, strokeTriangle, triangleWidth, e.Graphics, triangleRadius);
                break;
            case LayerClass.Type.Image:
                img.ImageDrawing(LayerClass.Type.Image, ImageBitmap, imgRect, path, rotationAngle, e, newLoc, flipped);
                break;
            case LayerClass.Type.Text:
                txt.DrawString(LayerClass.Type.Text, text, textRect, fontFamily, brush, textAngle, e); //CALLS THE TEXT DRAWING
                break;
        }
    }