文字尺寸、宽高的测量 Paint FontMetrics

Paint.FontMetrics类简介

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;
}

网上找的各种模型图

注意Y坐标基准点是在BaseLine那个位置，而非AscentLine或Top那个位置

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

/**
 * 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

/**
 * 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

    }

}