System.Drawing.Graphics.DrawString - “参数无效” 例外

Question

有时，微软的异常消息毫无帮助，令人恼火。 我创建了一个很好的 MVC 小方法来渲染文本。 方法主体如下。 当它到达“DrawString”方法时，我收到一个异常，提示“参数无效”。

请注意，据我所知，字体的构造正确（我只是使用 10pt 的 Arial），矩形大小为正且看起来有效，画笔是白色 SolidBrush，格式标志不会影响输出；即如果我从调用中排除格式标志，我仍然会收到错误，

DrawString 调用就在底部附近。

public ActionResult RenderText(
    string fontFamily,
    float pointSize,
    string foreColor,
    string backColor,
    bool isBold,
    bool isItalic,
    bool isVertical,
    string align,
    string[] allText,
    int textIndex)
{
    // method renders a horizontal or vertical text image, taking all the text strings that will be rendered in each image
    // and sizing the final bitmap according to which text would take the most space, thereby making it possible to render
    // a selection of text images all at the same size.

    Response.ContentType = "image/png";

    var fmt = StringFormat.GenericTypographic;
    if(isVertical)
        fmt.FormatFlags = StringFormatFlags.DirectionVertical;

    Func<string,StringAlignment> getAlign = (s => {
        switch(s.ToLower())
        {
            case "right": return StringAlignment.Far;
            case "center": return StringAlignment.Center;
            default: return StringAlignment.Near;
        }
    });
    fmt.LineAlignment = isVertical ? StringAlignment.Center : getAlign(align);
    fmt.Alignment = isVertical ? getAlign(align) : StringAlignment.Center;

    var strings = (allText ?? new string[0]).Where(t => t.Length > 0).ToList();
    if(strings.Count == 0)
        strings.Add("[Missing Text]");

    FontStyle style = FontStyle.Regular;
    if(isBold)
        if(isItalic)
            style = FontStyle.Bold | FontStyle.Italic;
        else
            style = FontStyle.Bold;
    else if(isItalic)
        style = FontStyle.Italic;

    Font font = new Font(fontFamily, pointSize, style, GraphicsUnit.Point);
    Color fc = foreColor.IsHexColorString() ? foreColor.ToColorFromHex() : foreColor.ToColor();
    Color bc = backColor.IsHexColorString() ? backColor.ToColorFromHex() : backColor.ToColor();

    var maxSize = new Size(0,0);
    using(var tmp = new Bitmap(100, 200))
        using(var gfx = Graphics.FromImage(tmp))
            foreach(var txt in strings)
            {
                var size = gfx.MeasureString(txt, font, 1000, fmt);
                maxSize = new Size(
                    Math.Max(Convert.ToInt32(isVertical ? size.Height : size.Width), maxSize.Width),
                    Math.Max(Convert.ToInt32(isVertical ? size.Width : size.Height), maxSize.Width)
                );
            }

    using(var bmp = new Bitmap(maxSize.Width, maxSize.Height))
    {
        using(var gfx = Graphics.FromImage(bmp))
        {
            gfx.CompositingMode = CompositingMode.SourceCopy;
            gfx.CompositingQuality = CompositingQuality.HighQuality;
            gfx.SmoothingMode = SmoothingMode.HighQuality;
            gfx.InterpolationMode = InterpolationMode.HighQualityBicubic;

            var rect = new RectangleF(new PointF(0,0), maxSize);
            gfx.FillRectangle(new SolidBrush(bc), rect);
            gfx.DrawString(strings[textIndex], font, new SolidBrush(fc), rect, fmt);
        }
        bmp.Save(Response.OutputStream, ImageFormat.Png);
    }
    return new EmptyResult();
}

Answer 1

好吧，我找到了问题的原因。 非常晦涩难懂的东西。 当我删除这一行时，代码有效：

gfx.CompositingMode = CompositingMode.SourceCopy;

Answer 2

在调试时有帮助的是使方法更小。 例如，您可以替换

FontStyle style = FontStyle.Regular;
if(isBold)
    if(isItalic)
        style = FontStyle.Bold | FontStyle.Italic;
    else
        style = FontStyle.Bold;
else if(isItalic)
    style = FontStyle.Italic;

为

FontStyle style = GetFontStyle(isBold, isItalic);

and

public FontStyle GetFontStyle(bool isBold, bool isItalic)
{
    if(isBold)
        if(isItalic)
            return FontStyle.Bold | FontStyle.Italic;
        else
            return FontStyle.Bold;
    else if(isItalic)
        return FontStyle.Italic;
    else
        return FontStyle.Regular;
}

它使您的代码更具可读性，并且其他人更容易帮助您。

真的没有冒犯的意思！

亲切的问候，
安斯·弗鲁格