FontMetrics ----- 绘制文本，获取文本高度

Canvas 绘制文本时，使用FontMetrics对象，计算位置的坐标。

 1 public static class FontMetrics {  2 /**  3  * The maximum distance above the baseline for the tallest glyph in  4  * the font at a given text size.  5 */  6 public float top;  7 /**  8  * The recommended distance above the baseline for singled spaced text.  9 */ 10 public float ascent; 11 /** 12  * The recommended distance below the baseline for singled spaced text. 13 */ 14 public float descent; 15 /** 16  * The maximum distance below the baseline for the lowest glyph in 17  * the font at a given text size. 18 */ 19 public float bottom; 20 /** 21  * The recommended additional space to add between lines of text. 22 */ 23 public float leading; 24 }

它的各基准线可以参考下图：

 1 /** 绘制FontMetrics对象的各种线 */  2 mPaint.reset();  3 mPaint.setColor(Color.WHITE);  4 mPaint.setTextSize(80);  5 // FontMetrics对象  6 FontMetrics fontMetrics = mPaint.getFontMetrics();  7 String text = "abcdefg";  8 // 计算每一个坐标  9 float textWidth = mPaint.measureText(text); 10 float baseX = 30; 11 float baseY = 700; 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 // 绘制文本 17 canvas.drawText(text, baseX, baseY, mPaint); 18 // BaseLine描画 19 mPaint.setColor(Color.RED); 20 canvas.drawLine(baseX, baseY, baseX + textWidth, baseY, mPaint); 21 mPaint.setTextSize(20); 22 canvas.drawText("base", baseX + textWidth, baseY, mPaint); 23 // Base描画 24 canvas.drawCircle(baseX, baseY, 5, mPaint); 25 // TopLine描画 26 mPaint.setColor(Color.LTGRAY); 27 canvas.drawLine(baseX, topY, baseX + textWidth, topY, mPaint); 28 canvas.drawText("top", baseX + textWidth, topY, mPaint); 29 // AscentLine描画 30 mPaint.setColor(Color.GREEN); 31 canvas.drawLine(baseX, ascentY, baseX + textWidth, ascentY, mPaint); 32 canvas.drawText("ascent", baseX + textWidth, ascentY + 10, mPaint); 33 // DescentLine描画 34 mPaint.setColor(Color.YELLOW); 35 canvas.drawLine(baseX, descentY, baseX + textWidth, descentY, mPaint); 36 canvas.drawText("descent", baseX + textWidth, descentY, mPaint); 37 // ButtomLine描画 38 mPaint.setColor(Color.MAGENTA); 39 canvas.drawLine(baseX, bottomY, baseX + textWidth, bottomY, mPaint); 40 canvas.drawText("buttom", baseX + textWidth, bottomY + 10, mPaint);

相信通过以上程序，能够很好的理解topLine，buttomLine，baseLine，ascentLine，descentLine。

另外：Paint类有两个方法

 1 /**  2  * Return the distance above (negative) the baseline (ascent) based on the  3  * current typeface and text size.  4  *  5  * @return the distance above (negative) the baseline (ascent) based on the  6  * current typeface and text size.  7 */  8 public native float ascent();  9 10 /** 11  * Return the distance below (positive) the baseline (descent) based on the 12  * current typeface and text size. 13  * 14  * @return the distance below (positive) the baseline (descent) based on 15  * the current typeface and text size. 16 */ 17 public native float descent();

ascent()：the distance above the baseline（baseline以上的height）

descent()：the distance below the baseline（baseline以下的height）

所以ascent() + descent() 可以看成文字的height。

到此为止，怎么获取文字的height和width都已经揭晓了：

获取height ： mPaint.ascent() + mPaint.descent()

获取width ： mPaint.measureText(text)