Canvas繪製圓角矩形時的圓角粗邊問題

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ViewCompat.setBackground(findViewById(R.id.text_view),
                createCircleRect(5, Color.RED, 30));
    }

    public ShapeDrawable createCircleRect(final int strokeWidth, final int strokeColor, final int radius) {
        Shape shape = new Shape() {
            @Override
            public void draw(Canvas canvas, Paint paint) {
                paint.setStyle(Paint.Style.STROKE);
                paint.setStrokeWidth(strokeWidth);
                paint.setColor(strokeColor);
                RectF rectf= new RectF(0, 0, getWidth(), getHeight());
                canvas.drawRoundRect(rectf, radius, radius, paint);
            }
        };
        return new ShapeDrawable(shape);
    }

使用以上代碼繪製TextView的背景Shape，會發現，四個圓角的線寬要大於四邊直線線寬。如圖：

出現這種問題的原因是，使用Style.Stroke繪製粗線，基準線在中線，stroke邊由中線向內外擴展。以上代碼直接以矩形的最外一圈作爲基準線，導致直線邊只能繪製向裏的一半線寬。所以Shape中的draw方法應該做如下修改：

        Shape shape = new Shape() {
            @Override
            public void draw(Canvas canvas, Paint paint) {
                paint.setStyle(Paint.Style.STROKE);
                paint.setStrokeWidth(strokeWidth);
                paint.setColor(strokeColor);
                int d = strokeWidth / 2;
                RectF rectF= new RectF(d, d, getWidth()- d, getHeight()- d);
                canvas.drawRoundRect(rectF, radius, radius, paint);
            }
        };

這樣顯示的圓角矩形就正常了：

感謝文章：Android中Canvas繪圖基礎詳解（附源碼下載）給我的提示。