Google文档中的描述：
/**
* Class that describes the various各种 metrics指标 for a font at a given text size.
* Remember, Y values increase going down, so those values will be positive正数,
* and values that measure distances距离 going up will be negative负数. This class
* is returned by getFontMetrics().
*/
public static class FontMetrics {
//The maximum distance above the baseline for the tallest glyph in the font at a given text size.
public float top;
//【字符顶部】The recommended推荐的 distance above the baseline for singled spaced text.
public float ascent;
//【字符底部】The recommended distance below the baseline for singled spaced text.
public float descent;
//The maximum distance below the baseline for the lowest glyph in the font at a given text size.
public float bottom;
//【字符行间距】The recommended additional额外的 space to add between lines两行之间 of text.
public float leading;
}
该类描述给定文本大小的字体的各种度量。记住，Y值向下增加，所以这些值为正值，测量向上距离的值为负值。此类由GetFontMetrics（）返回。
网上找的各种模型图
要点如下：
- 基准点是baseline
- Ascent是baseline之上至字符最高处的距离
- Descent是baseline之下至字符最低处的距离
- 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
- Top指的是指的是最高字符到baseline的值，即ascent的最大值
- bottom指的是最下字符到baseline的值，即descent的最大值
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。
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Paint的ascent和descent方法--算高度
这两个是native方法
//Return the distance above (negative) the baseline (ascent) based on the current typeface字体 and text size.
public native float ascent();
//Return the distance below (positive) the baseline (descent) based on the current typeface and text size.
public native float descent();
可以通过 mPaint.ascent()+ mPaint.descent() 获取文字高度
Paint的measureText方法--获取宽度
image
/**
* Return the width of the text.
*
* @param text The text to measure. Cannot be null.
* @param start The index of the first character to start measuring
* @param end 1 beyond the index of the last character to measure
* @return The width of the text
*/
public float measureText(String text, int start, int end) {
if (text == null) throw new IllegalArgumentException("text cannot be null");
if ((start | end | (end - start) | (text.length() - end)) < 0) throw new IndexOutOfBoundsException();
if (text.length() == 0 || start == end) return 0f;
if (!mHasCompatScaling) return (float) Math.ceil(native_measureText(text, start, end, mBidiFlags));
final float oldSize = getTextSize();
setTextSize(oldSize*mCompatScaling);
float w = native_measureText(text, start, end, mBidiFlags);
setTextSize(oldSize);
return (float) Math.ceil(w*mInvCompatScaling);
}
通过这个方法即可以轻松的获取到文字的的宽度
Paint的getTextBounds方法--获取边界
image
/**
* Return in bounds (allocated by the caller 由调用者分配) the smallest最小的 rectangle that
* encloses围起来 all of the characters, with an implied origin默认的起始位置 at (0,0).
* @param text String to measure and return its bounds
* @param start Index of the first char in the string to measure
* @param end 1 past the last char in the string measure
* @param bounds Returns the unioned bounds of all the text. Must be allocated by the caller.
*/
public void getTextBounds(String text, int start, int end, Rect bounds) {
if ((start | end | (end - start) | (text.length() - end)) < 0) throw new IndexOutOfBoundsException();
if (bounds == null) throw new NullPointerException("need bounds Rect");
nativeGetStringBounds(mNativePaint, mNativeTypeface, text, start, end, mBidiFlags, bounds);
}
这个方法需要提供一个参数 Rect 矩形区域，这个方法将文字的区域传递到 Rect
Paint的获取
比如对于TextView，要通过TextView的getPaint()得到Paint，而不能new一个或者拿其他不相干的Paint
/**
* @return the base paint used for the text. Please use this only to
* consult查阅 the Paint's properties属性 and not to change them.
*/
public TextPaint getPaint() {
return mTextPaint;
}
如果是在自定义View 中，则可以直接通过Paint调用相关方法去获取文字的宽高等信息
测试代码
public class MainActivity extends Activity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
String text = "aA bB fF gG";
TextView tv_info = new TextView(this);
tv_info.setTextColor(Color.BLUE);
tv_info.setBackgroundColor(0x5500ff00);
tv_info.setTextSize(TypedValue.COMPLEX_UNIT_SP, 18);
tv_info.setText(text);
setContentView(tv_info);
tv_info.measure(0, 0);//必须手动调用测量方法，否则getMeasuredHeight获取不到值。另外，即使测量过了getHeight也获取不到值
Paint mPaint = tv_info.getPaint();
Log.i("bqt", "ascent()的值为" + mPaint.ascent() + "，descent()的值为" + mPaint.descent());//-33.398438， 8.7890625
Log.i("bqt", "字符的高度为" + (-mPaint.ascent() + mPaint.descent()) + "，字符的长度为" + mPaint.measureText(text));//42.1875，190.0
Log.i("bqt", "测量的高度为" + tv_info.getMeasuredHeight() + "，测量的宽度为" + tv_info.getMeasuredWidth());//49，190
Rect mRect = new Rect();
mPaint.getTextBounds(text, 0, text.length(), mRect);
Log.i("bqt", "字符的边界为" + mRect.left + "，" + mRect.top + "，" + mRect.right + "，" + mRect.bottom);//1，-28，187，8
Log.i("bqt", "字符的高度为" + (mRect.bottom - mRect.top) + "，字符的长度为" + (mRect.right - mRect.left));//36，186
}
}
