学步园

画一个圆，圆心为(cx,cy),并以此为中心，写数字：

通常情况下，drawText(text,cx,xy,paint)中，点(cx,cy)是文字的起始点，如下：

即使使用paint.setTextAlign(Paint.Align.CENTER),是文字横向居中，但是纵向不会居中。如果能得到文字高度，再向下位移一半，就可以居中了：

先要取得text的边界，paint.getTextBounds(,,,textBounds);

取得了边界，就可计算高度,宽度。

Paint countPaint = new Paint(Paint.ANTI_ALIAS_FLAG
				| Paint.DEV_KERN_TEXT_FLAG);
		countPaint.setColor(Color.BLUE);
		countPaint.setTextSize(20f);
		countPaint.setTypeface(Typeface.DEFAULT_BOLD);
		countPaint.setTextAlign(Paint.Align.CENTER);
		Rect textBounds = new Rect();
		String numberStr = String.valueOf(number);
		countPaint.getTextBounds(numberStr, 0, numberStr.length(), textBounds);//get text bounds, that can get the text width and height
		int textHeight = textBounds.bottom - textBounds.top;
		Log.i("TAG","bounds: left = "+textBounds.left + ", right = "+textBounds.right+", top = "+textBounds.top+", bottom = "+textBounds.bottom);
		canvas.drawText(numberStr, cx, cy + textHeight/2,
				countPaint);