Android canvas.drawText文字居中（记录）

                Rect rect1 = new Rect(100,100,500,500);//画一个矩形
                Paint rectPaint = new Paint();
                rectPaint.setColor(Color.BLUE);
                rectPaint.setStyle(Paint.Style.FILL);
                canvas.drawRect(rect1, rectPaint);

                Paint textPaint = new Paint();
                textPaint.setColor(SPConstants.TITLE_COLOR);
                textPaint.setTextSize(SPConstants.TITLE_SIZE);
                textPaint.setStyle(Paint.Style.FILL);

                textPaint.setTextAlign(Paint.Align.CENTER);

                Paint.FontMetrics fontMetrics = textPaint.getFontMetrics();
                float top = fontMetrics.top;
                float bottom = fontMetrics.bottom;

                int baseLineY = (int) (rect.centerY() - top/2 - bottom/2);//基线中间点的y轴计算公式

                canvas.drawText(str,rect.centerX(),baseLineY,textPaint);