Canvas 作为绘制文本时，使用FontMetrics对象，计算位置的坐标。
它的思路和java.awt.FontMetrics的基本相同。
FontMetrics对象
它以四个基本坐标为基准，分别为：
・FontMetrics.top
・FontMetrics.ascent
・FontMetrics.descent
・FontMetrics.bottom
该图片将如下
绘制文字的代码
1 Paint textPaint = new Paint( Paint.ANTI_ALIAS_FLAG); 2 textPaint.setTextSize( 35); 3 textPaint.setColor( Color.WHITE); 4 5 // FontMetrics对象 6 FontMetrics fontMetrics = textPaint.getFontMetrics(); 7 8 String text = "abcdefghijklmnopqrstu"; 9 10 // 计算每一个坐标 11 float baseX = 0; 12 float baseY = 100; 13 float topY = baseY + fontMetrics.top; 14 float ascentY = baseY + fontMetrics.ascent; 15 float descentY = baseY + fontMetrics.descent; 16 float bottomY = baseY + fontMetrics.bottom; 17 18 // 绘制文本 19 canvas.drawText( text, baseX, baseY, textPaint); 20 21 // BaseLine描画 22 Paint baseLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);> 23 baseLinePaint.setColor( Color.RED); 24 canvas.drawLine(0, baseY, getWidth(), baseY, baseLinePaint); 25 26 // Base描画 27 canvas.drawCircle( baseX, baseY, 5, baseLinePaint); 28 29 // TopLine描画 30 Paint topLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG); 31 topLinePaint.setColor( Color.LTGRAY); 32 canvas.drawLine(0, topY, getWidth(), topY, topLinePaint); 33 34 // AscentLine描画 35 Paint ascentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG); 36 ascentLinePaint.setColor( Color.GREEN); 37 canvas.drawLine(0, ascentY, getWidth(), ascentY, ascentLinePaint); 38 39 // DescentLine描画 40 Paint descentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG); 41 descentLinePaint.setColor( Color.YELLOW); 42 canvas.drawLine(0, descentY, getWidth(), descentY, descentLinePaint); 43 44 // ButtomLine描画 45 Paint bottomLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG); 46 bottomLinePaint.setColor( Color.MAGENTA); 47 canvas.drawLine(0, bottomY, getWidth(), bottomY, bottomLinePaint);
这个是从别处转载的，图片是精华，谢谢原作者！