转载：http://blog.csdn.net/lvxiangan/article/details/8540774

关于Canvas.drawText中xy位置问题

        分类：            Android2013-01-25 10:1411007人阅读评论(2)收藏举报

问：canvas.drawText("3", x, y, paint);  x和y是指画得时候数字3中心的坐标吗？还是左上角的坐标？
答：x默认是‘3’这个字符的左边在屏幕的位置，如果设置了paint.setTextAlign(Paint.Align.CENTER);那就是字符的中心，y是指定这个字符baseline在屏幕上的位置。

public void drawText (String text, float x, float y, Paint paint)
Since: API Level 1 Draw the text, with origin at (x,y), using the specified paint.
The origin is interpreted based on the Align setting in the paint.
Parameters
text The text to be drawn
x The x-coordinate of the origin of the text being drawn
y The y-coordinate of the origin of the text being drawn
paint The paint used for the text (e.g. color, size, style)

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

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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.    String text = "abcdefghijklmnopqrstu"; 
8.  
9.    // 计算每一个坐标 
10.    float baseX = 0; 
11.    float baseY = 100; 
12.    float topY = baseY + fontMetrics.top; 
13.    float ascentY = baseY + fontMetrics.ascent; 
14.    float descentY = baseY + fontMetrics.descent; 
15.    float bottomY = baseY + fontMetrics.bottom; 
16.  
17.    // 绘制文本 
18.    canvas.drawText( text, baseX, baseY, textPaint); 
19.  
20.    // BaseLine描画 
21.    Paint baseLinePaint =new Paint( Paint.ANTI_ALIAS_FLAG);> 
22.    baseLinePaint.setColor( Color.RED); 
23.    canvas.drawLine(0, baseY, getWidth(), baseY, baseLinePaint); 
24.  
25.    // Base描画 
26.    canvas.drawCircle( baseX, baseY, 5, baseLinePaint); 
27.  
28.    // TopLine描画 
29.    Paint topLinePaint =new Paint( Paint.ANTI_ALIAS_FLAG); 
30.    topLinePaint.setColor( Color.LTGRAY); 
31.    canvas.drawLine(0, topY, getWidth(), topY, topLinePaint); 
32.  
33.    // AscentLine描画 
34.    Paint ascentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG); 
35.    ascentLinePaint.setColor( Color.GREEN); 
36.    canvas.drawLine(0, ascentY, getWidth(), ascentY, ascentLinePaint); 
37.  
38.    // DescentLine描画 
39.    Paint descentLinePaint =new Paint( Paint.ANTI_ALIAS_FLAG); 
40.    descentLinePaint.setColor( Color.YELLOW); 
41.    canvas.drawLine(0, descentY, getWidth(), descentY, descentLinePaint); 
42.  
43.    // ButtomLine描画 
44.    Paint bottomLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG); 
45.    bottomLinePaint.setColor( Color.MAGENTA); 
46.    canvas.drawLine(0, bottomY, getWidth(), bottomY, bottomLinePaint); 

   Paint textPaint = new Paint( Paint.ANTI_ALIAS_FLAG);   textPaint.setTextSize( 35);   textPaint.setColor( Color.WHITE);   // FontMetrics对象   FontMetrics fontMetrics = textPaint.getFontMetrics();   String text = "abcdefghijklmnopqrstu";   // 计算每一个坐标   float baseX = 0;   float baseY = 100;   float topY = baseY + fontMetrics.top;   float ascentY = baseY + fontMetrics.ascent;   float descentY = baseY + fontMetrics.descent;   float bottomY = baseY + fontMetrics.bottom;   // 绘制文本   canvas.drawText( text, baseX, baseY, textPaint);   // BaseLine描画   Paint baseLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);>   baseLinePaint.setColor( Color.RED);   canvas.drawLine(0, baseY, getWidth(), baseY, baseLinePaint);   // Base描画   canvas.drawCircle( baseX, baseY, 5, baseLinePaint);   // TopLine描画   Paint topLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);   topLinePaint.setColor( Color.LTGRAY);   canvas.drawLine(0, topY, getWidth(), topY, topLinePaint);   // AscentLine描画   Paint ascentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);   ascentLinePaint.setColor( Color.GREEN);   canvas.drawLine(0, ascentY, getWidth(), ascentY, ascentLinePaint);   // DescentLine描画   Paint descentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);   descentLinePaint.setColor( Color.YELLOW);   canvas.drawLine(0, descentY, getWidth(), descentY, descentLinePaint);   // ButtomLine描画   Paint bottomLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);   bottomLinePaint.setColor( Color.MAGENTA);   canvas.drawLine(0, bottomY, getWidth(), bottomY, bottomLinePaint);

drawText画字符串是baseline对齐的。所以要特别注意这点，不然画文字可能画到其它地方而误以为没有画出来。

如果baseline对齐的话：底端的Y坐标是：(行高-字体高度)/2+字体高度 ，但是字符串并不居中，经过测试如果：(行高-字体高度)/2+字体高度-6 ，就稍微居中了一点。 以上的方法只是一个取巧的做法，网上也没有找到设置文字居中的方法。

按上面办法会有误差。加上那段距离应该就行了:

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1. FontMetrics fontMetrics =mPaint.getFontMetrics(); 
2. float fontTotalHeight = fontMetrics.bottom - fontMetrics.top; 
3. float offY = fontTotalHeight / 2 - fontMetrics.bottom; 
4. float newY = baseY + offY; 
5. canvas.drawText(text, baseX, newY, paint);