Android之繪制文本（FontMetrics） 獲取文本高度

Canvas 作為繪制文本時，使用FontMetrics對象，計算位置的坐標。

它的思路和java.awt.FontMetrics的基本相同。

FontMetrics對象

它以四個基本坐標為基准，分別為：

・FontMetrics.top
・FontMetrics.ascent
・FontMetrics.descent
・FontMetrics.bottom

該圖片將如下

1. Paint textPaint = new Paint( Paint.ANTI_ALIAS_FLAG);
2. textPaint.setTextSize( 35);
3. textPaint.setColor( Color.WHITE);
5. // FontMetrics對象
6. FontMetrics fontMetrics = textPaint.getFontMetrics();
8. String text = "abcdefghijklmnopqrstu";
10. // 計算每一個坐標
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;
18. // 繪制文本
19. canvas.drawText( text, baseX, baseY, textPaint);
21. // BaseLine描畫
22. Paint baseLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);>
23. baseLinePaint.setColor( Color.RED);
24. canvas.drawLine(0, baseY, getWidth(), baseY, baseLinePaint);
26. // Base描畫
27. canvas.drawCircle( baseX, baseY, 5, baseLinePaint);
29. // TopLine描畫
30. Paint topLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);
31. topLinePaint.setColor( Color.LTGRAY);
32. canvas.drawLine(0, topY, getWidth(), topY, topLinePaint);
34. // AscentLine描畫
35. Paint ascentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);
36. ascentLinePaint.setColor( Color.GREEN);
37. canvas.drawLine(0, ascentY, getWidth(), ascentY, ascentLinePaint);
39. // DescentLine描畫
40. Paint descentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);
41. descentLinePaint.setColor( Color.YELLOW);
42. canvas.drawLine(0, descentY, getWidth(), descentY, descentLinePaint);
44. // ButtomLine描畫
45. Paint bottomLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);
46. bottomLinePaint.setColor( Color.MAGENTA);
47. canvas.drawLine(0, bottomY, getWidth(), bottomY, bottomLinePaint);