在按鈕上繪制字符串

Question

我想在帶有 PlatformEffect 的按鈕的右下角繪制一個自定義字符串。 更喜歡使用更靈活的效果，並將其僅應用於特定按鈕而不是應用程序范圍。 這些按鈕是在沒有 xaml 的情況下動態創建的。

這是可能的還是我需要創建一個自定義按鈕+渲染器？

謝謝。

Answer 1

您可以創建自定義按鈕，然后通過自定義渲染器設置文本對齊方式。

[assembly: ExportRenderer(typeof(Xamarin.Forms.Button), typeof(ButtonCustomRenderer))]//set the Button as your custom button
namespace App3.Droid
{
public class ButtonCustomRenderer : ButtonRenderer
{
    public ButtonCustomRenderer(Context context) : base(context)
    {

    }
    protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.Button> e)
    {
        base.OnElementChanged(e);
        Control.Gravity = GravityFlags.End // Set the horizontal text alignment to right 
                       | GravityFlags.Bottom; // Set the vertical text alignment to bottom
    }
  }
}

Answer 2

我通過創建一個覆蓋 Draw 方法的渲染器來解決它。

public class HotkeyButtonRenderer : ButtonRenderer
{
    HotkeyButton element;

    public HotkeyButtonRenderer(Context ctx) : base(ctx)
    {

    }

    protected override void OnElementChanged(ElementChangedEventArgs<Button> e)
    {
        base.OnElementChanged(e);
        element = Element as HotkeyButton;
        SetWillNotDraw(false);
    }

    protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
    {
        base.OnElementPropertyChanged(sender, e);
        if (element != null && e.PropertyName == HotkeyButton.HotkeyTextProperty.PropertyName)
        {
            Invalidate();
        }
    }

    public override void Draw(Canvas canvas)
    {
        base.Draw(canvas);
        if (element != null && !string.IsNullOrEmpty(element.HotkeyText))
        {
            string textToDraw = string.Format("({0})", element.HotkeyText);
            float textSize = Control.TextSize / 1.5f;
            SizeF measuredTextSize = GetTextSize(textToDraw, element.FontFamily, textSize);
            float x = 5;
            float y = Height-measuredTextSize.Height/2;

            canvas.DrawText(textToDraw,
                x,
                y,
                new TextPaint
                {
                    Color = element.BorderColor.ToAndroid(),
                    TextSize = textSize
                });
        }
    }

    private SizeF GetTextSize(string text, string fontFamily, float textSize)
    {
        var textPaint = new SKPaint(new SKFont(SKTypeface.FromFamilyName(fontFamily), textSize));
        SKRect textBounds = new SKRect(); 
        textPaint.MeasureText(text, ref textBounds);
        return new SizeF(textBounds.Width, textBounds.Height);
    }
}

public class HotkeyButton : Button
{
    public static readonly BindableProperty HotkeyTextProperty = BindableProperty.Create(
        propertyName: nameof(HotkeyText),
        returnType: typeof(string),
        declaringType: typeof(MobileEntry),
        defaultValue: string.Empty);

    public string HotkeyText
    {
        get { return (string)GetValue(HotkeyTextProperty); }
        set { SetValue(HotkeyTextProperty, value); }
    }
}