如何为自定义控件从资源中设置自定义字体？

Hi Arulpriya, let's walk through why your custom control's font isn't updating when using AddMemoryFont, and fix it step by step!

Common Missing Steps & Fixes #

1. Ensure You're Creating a Font Instance from the Loaded Memory Font

Calling AddMemoryFont only loads the font into the control's private font collection—it doesn't automatically set the control's font. You need to explicitly create a Font object using the loaded font family and assign it to your control's Font property.

Example code for loading and assigning:

protected override void OnCreateControl()
{
    base.OnCreateControl();

    // Load font bytes from resources
    byte[] fontResource = Properties.Resources.YourCustomFont;
    // Add to control's memory font collection
    IntPtr fontHandle = AddMemoryFont(fontResource, fontResource.Length);
    
    // Create a FontFamily from the loaded font handle
    FontFamily customFontFamily = FontFamily.FromHfont(fontHandle);
    // Assign a new Font instance to the control's Font property
    this.Font = new Font(customFontFamily, 10f, FontStyle.Regular);
}

2. Verify Your Font Property Override Triggers Redraws

When overriding the Font property, make sure you're not just calling the base setter—you need to trigger a control redraw to reflect the new font. Add Invalidate() to force the control to repaint with the updated font.

Example property override:

private Font _controlFont;

public override Font Font
{
    get => _controlFont ?? base.Font;
    set
    {
        if (_controlFont != value)
        {
            _controlFont = value;
            // Update the base font
            base.Font = value;
            // Force the control to redraw with the new font
            Invalidate();
            // Explicitly trigger FontChanged if needed
            OnFontChanged(EventArgs.Empty);
        }
    }
}

3. Check Your OnPaint Logic Uses the Current Font

If you've overridden OnPaint, double-check that you're using this.Font (not a hardcoded font) when drawing text. A common mistake is referencing a static font object instead of the control's dynamic Font property.

Correct OnPaint example:

protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);
    // Use the control's current Font for drawing
    e.Graphics.DrawString("Custom Text", this.Font, Brushes.Black, new Point(10, 10));
}

4. Re-Load Memory Fonts After Deserialization

Serialization typically only saves font metadata (name, size, style)—not the raw font bytes. After deserialization, you'll need to re-load the memory font from resources and re-assign it to the Font property.

Add this logic to your control's deserialization handler:

protected override void OnDeserialization(object sender)
{
    base.OnDeserialization(sender);
    // Re-load and assign the memory font here
    byte[] fontResource = Properties.Resources.YourCustomFont;
    IntPtr fontHandle = AddMemoryFont(fontResource, fontResource.Length);
    FontFamily customFontFamily = FontFamily.FromHfont(fontHandle);
    this.Font = new Font(customFontFamily, this.Font.Size, this.Font.Style);
}

5. Validate the Memory Font Loaded Successfully

Sometimes AddMemoryFont can fail silently (e.g., invalid font bytes). Add a check to ensure the FontFamily is valid before assigning:

FontFamily customFontFamily = FontFamily.FromHfont(fontHandle);
if (customFontFamily.IsStyleAvailable(FontStyle.Regular))
{
    this.Font = new Font(customFontFamily, 10f, FontStyle.Regular);
}
else
{
    // Fallback to default font if loading failed
    this.Font = SystemFonts.DefaultFont;
}

Final Notes #

• Avoid calling AddMemoryFont multiple times for the same font (it can cause memory leaks). Add a check to load it only once (e.g., in OnCreateControl with a boolean flag).
• Ensure your FontChanged event override properly calls base.OnFontChanged(e) to preserve base class behavior.

内容的提问来源于stack exchange，提问作者Arulpriya