android自定义View绘制的时候，会有很多情况下要与字体打交道，涉及到字体宽度、高度的时候要特别注意一下几个概念，见图：

baseLine：一行文字的底线。

Ascent： 字符顶部到baseLine的距离。

Descent： 字符底部到baseLine的距离。

Leading： 字符行间距。

Java代码  

1. public class TestOnDraw extends Activity {
2. @Override
3. protected void onCreate(Bundle savedInstanceState) {
4. // TODO Auto-generated method stub
5. super.onCreate(savedInstanceState);
6. MyView v = new MyView(this);
7. this.setContentView(v);
8. }
9. }
10. class MyView extends View
11. {
12. public MyView(Context context) {
13. super(context);
14. }
15. @Override
16. protected void onDraw(Canvas canvas) {
17. super.onDraw(canvas);
18. Paint p = new Paint();
19. p.setColor(Color.WHITE);
20. p.setTextSize(50);
21. p.setAntiAlias(true);
22. FontMetrics fm = p.getFontMetrics();
23. System.out.println("top = "+ fm.top);
24. System.out.println("ascent = "+ fm.ascent);
25. System.out.println("descent = "+ fm.descent);
26. System.out.println("bottom = "+ fm.bottom);
27. System.out.println("leading = "+ fm.leading);
28. int textHeight = (int) (Math.ceil(fm.descent - fm.ascent) + 2);
29. System.out.println("textHeight = "  + textHeight);
30. float width =500;
31. float baseline = 100f;
32. float offsetAscent = baseline + fm.ascent;
33. float offsetDescent = baseline +fm.descent;
34. float offsetTop = baseline + fm.top;
35. float offsetBottom = baseline + fm.bottom;
36. canvas.drawText("中国 bp Android", 0, baseline, p);
37. canvas.drawLine(0, baseline, width, baseline, p);//baseline
38. canvas.drawLine(0, offsetAscent, width, offsetAscent, p);//ascent
39. canvas.drawLine(0, offsetDescent, width, offsetDescent, p);//descent
40. canvas.drawLine(0, offsetTop, width, offsetTop, p);//top
41. canvas.drawLine(0, offsetBotton, width, offsetBottom, p);//bottom
42. }
43. }

public class TestOnDraw extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
MyView v = new MyView(this);
this.setContentView(v);
}
}
class MyView extends View
{
public MyView(Context context) {
super(context);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Paint p = new Paint();
p.setColor(Color.WHITE);
p.setTextSize(50);
p.setAntiAlias(true);
FontMetrics fm = p.getFontMetrics();
System.out.println("top = "+ fm.top);
System.out.println("ascent = "+ fm.ascent);
System.out.println("descent = "+ fm.descent);
System.out.println("bottom = "+ fm.bottom);
System.out.println("leading = "+ fm.leading);
int textHeight = (int) (Math.ceil(fm.descent - fm.ascent) + 2);
System.out.println("textHeight = "  + textHeight);
float width =500;
float baseline = 100f;
float offsetAscent = baseline + fm.ascent;
float offsetDescent = baseline +fm.descent;
float offsetTop = baseline + fm.top;
float offsetBottom = baseline + fm.bottom;
canvas.drawText("中国 bp Android", 0, baseline, p);
canvas.drawLine(0, baseline, width, baseline, p);//baseline
canvas.drawLine(0, offsetAscent, width, offsetAscent, p);//ascent
canvas.drawLine(0, offsetDescent, width, offsetDescent, p);//descent
canvas.drawLine(0, offsetTop, width, offsetTop, p);//top
canvas.drawLine(0, offsetBotton, width, offsetBottom, p);//bottom
}
}

运行效果：

这是程序的输出结果：

得出结论： canvas drawText() 的startX是从左下角的baseline的底线开始绘画的，如果我们要得到字体的高度需要关注descent - ascent (ascent线在baseline上面，所以是负数)