Android字符串进阶之三：字体属性及测量（FontMetrics）
最近的一个模块正好用到字体的相关内容，整理出来。
(一) 字体的几个参数 ，以Android API文档定义为准，见下图
要点如下：
1. 基准点是baseline
2. Ascent是baseline之上至字符最高处的距离
3. Descent是baseline之下至字符最低处的距离
4. Leading文档说的很含糊，其实是上一行字符的descent到下一行的ascent之间的距离
5. Top指的是指的是最高字符到baseline的值，即ascent的最大值
6. 同上，bottom指的是最下字符到baseline的值，即descent的最大值
Note:网上有很多错误的图，如果有疑问，就参看文档，区分对错。
为了帮助理解，我特此搜索了不同的示意图。对照示意图，会很容易理解FontMetrics的参数。
pic-1
pic-2
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pic-5
pic-6
(二) 测试
1，测试的代码直接使用网上的代码，因为重复着众多，无所给出原始出处，故不注出。
我增加了Bitmap作为输出显示，完整代码如下：
public class FontMetricsDemoActivity extends Activity {
private Canvas canvas;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Paint textPaint = new Paint( Paint.ANTI_ALIAS_FLAG);
textPaint.setTextSize( 55);
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;
float leading = baseY + fontMetrics.leading;
Log.d("fontMetrics", "baseX is:" + 0);
Log.d("fontMetrics", "baseY is:" + 100);
Log.d("fontMetrics", "topY is:" + topY);
Log.d("fontMetrics", "ascentY is:" + ascentY);
Log.d("fontMetrics", "descentY is:" + descentY);
Log.d("fontMetrics", "bottomY is:" + bottomY);
Log.d("fontMetrics", "leading is:" + leading);
Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.fontmetrics);
Bitmap mutableBitmap = bitmap.copy(Bitmap.Config.ARGB_8888, true);
canvas = new Canvas(mutableBitmap);
// 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, canvas.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, canvas.getWidth(), topY, topLinePaint);
// AscentLine描画
Paint ascentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);
ascentLinePaint.setColor( Color.GREEN);
canvas.drawLine(0, ascentY, canvas.getWidth(), ascentY, ascentLinePaint);
// DescentLine描画
Paint descentLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);
descentLinePaint.setColor( Color.YELLOW);
canvas.drawLine(0, descentY, canvas.getWidth(), descentY, descentLinePaint);
// ButtomLine描画
Paint bottomLinePaint = new Paint( Paint.ANTI_ALIAS_FLAG);
bottomLinePaint.setColor( Color.MAGENTA);
canvas.drawLine(0, bottomY, canvas.getWidth(), bottomY, bottomLinePaint);
ImageView imageView = (ImageView) findViewById(R.id.imageView1);
imageView.setImageBitmap(mutableBitmap);
}
}
2，以上是根据paint设置，获取相关的FontMetrics属性，并且只绘制了一行字符串，我们猜想，如果是多行，是否可以获得行间距leanding，代码如下：
//test_multiply_lines
TextView textView = (TextView) findViewById(R.id.textView1);
String textMultiLines = "abcdefghijklmnopqrstuabcdefghijklmnopqrstuabcdefghijklmnopqrstuabcdefghijklmnopqrstuabcdefghijklmnopqrstu";
textView.setTextSize(55);
textView.setText(textMultiLines);
FontMetrics fontMetrics2 = textView.getPaint().getFontMetrics();
// 计算每一个坐标
float topY = fontMetrics2.top;
float ascentY = fontMetrics2.ascent;
float descentY = fontMetrics2.descent;
float bottomY = fontMetrics2.bottom;
float leading = fontMetrics2.leading;
Log.d("fontMetrics", "topY is:" + topY);
Log.d("fontMetrics", "ascentY is:" + ascentY);
Log.d("fontMetrics", "descentY is:" + descentY);
Log.d("fontMetrics", "bottomY is:" + bottomY);
Log.d("fontMetrics", "leading is:" + leading);
3，如果text是单行，获得各个属性将会怎样，代码如下：
String text = "abcdefghijklmnopqrstu"; TextView textView = (TextView) findViewById(R.id.textView1); textView.setTextSize(55); textView.setText(text); FontMetrics fontMetrics = textView.getPaint().getFontMetrics(); // 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; float leading = fontMetrics.leading; Log.d("fontMetrics", "topY is:" + fontMetrics.top); Log.d("fontMetrics", "ascentY is:" + fontMetrics.ascent); Log.d("fontMetrics", "descentY is:" + fontMetrics.descent); Log.d("fontMetrics", "bottomY is:" + fontMetrics.bottom); Log.d("fontMetrics", "leading is:" + fontMetrics.leading);
结论：
A:虽然paint和textView所设置的textSize均为55，且为相同的字符串，但是两个获得的FontMetrics属性值并不相同。但是，我们发现，做除法之后，均为1.5倍关系。做出猜测，即Paint下，为mdpi对应的size，而TextView的size已经关联到了显示屏幕本身的320dip。所以获得属性值均为整1.5倍数
B:各种情况下，均未获得leading值。
转自：http://mikewang.blog.51cto.com/3826268/871765/