<TextView
        android:id="@+id/title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="虽然此视图的实际布局取决于其父视图和任何同级视图中的其他属性。虽然。。。"
        android:textSize="16dp"/>

<TextView
        android:id="@+id/title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="虽然此视图的实际布局取决于其父视图和任何同级视图中的其他属性。虽然。。。"
        android:textSize="24dp"/>

/**
 * Class that describes the various metrics for a font at a given text size.
 * Remember, Y values increase going down, so those values will be positive,
 * and values that measure distances going up will be negative. 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;
    /**
     * The recommended distance above the baseline for singled spaced text.
     */
    public float   ascent;
    /**
     * 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;
    /**
     * The recommended additional space to add between lines of text.
     */
    public float   leading;
}

private int out(final CharSequence text, final int start, final int end, int above, int below,
        int top, int bottom, int v, final float spacingmult, final float spacingadd,
        final LineHeightSpan[] chooseHt, final int[] chooseHtv, final Paint.FontMetricsInt fm,
        final boolean hasTab, final int hyphenEdit, final boolean needMultiply,
        @NonNull final MeasuredParagraph measured,
        final int bufEnd, final boolean includePad, final boolean trackPad,
        final boolean addLastLineLineSpacing, final char[] chs,
        final int widthStart, final TextUtils.TruncateAt ellipsize, final float ellipsisWidth,
        final float textWidth, final TextPaint paint, final boolean moreChars) {
    final int j = mLineCount;
    // 偏移量，标识当前的行号
    final int off = j * mColumns;
    final int want = off + mColumns + TOP;
    // 一维数组，保存了TextView各行文字的计算出来的坐标信息。
    int[] lines = mLines;
    final int dir = measured.getParagraphDir();
  
    // 将所有的字体的度量信息存入fm变量中，然后通过LineHeightSpan接口将fm变量传递出去.
    // 这就给外部提供了一个接口去修改字体的度量信息。
    if (chooseHt != null) {
        fm.ascent = above;
        fm.descent = below;
        fm.top = top;
        fm.bottom = bottom;

        for (int i = 0; i < chooseHt.length; i++) {
            if (chooseHt[i] instanceof LineHeightSpan.WithDensity) {
                ((LineHeightSpan.WithDensity) chooseHt[i])
                        .chooseHeight(text, start, end, chooseHtv[i], v, fm, paint);
            } else {
                chooseHt[i].chooseHeight(text, start, end, chooseHtv[i], v, fm);
            }
        }
        // 获取修改后的字体度量属性
        above = fm.ascent;
        below = fm.descent;
        top = fm.top;
        bottom = fm.bottom;
    }
    
    if (firstLine) {
        if (trackPad) {
            mTopPadding = top - above;
        }

        if (includePad) {
            // 如果当前行是TextView的第一行文字，above(ascent)值使用top替代。
            above = top;
        }
    }

    int extra;

    if (lastLine) {
        if (trackPad) {
            mBottomPadding = bottom - below;
        }

        if (includePad) {
            // 如果当前行是TextView的最后一行文字，below(descent)值使用bottom替代。
            below = bottom;
        }
    }

    if (needMultiply && (addLastLineLineSpacing || !lastLine)) {
        // 计算行间距
        // spacingmult变量对应lineSpacingMultiplier属性配置的值
        // spacingadd变量对应lineSpacingExtra属性配置的值。
        double ex = (below - above) * (spacingmult - 1) + spacingadd;

        if (ex >= 0) {
            extra = (int)(ex + EXTRA_ROUNDING);
        } else {
            extra = -(int)(-ex + EXTRA_ROUNDING);
        }
    } else {
        extra = 0;
    }

    // 将当前行的坐标信息存入mLines[]数组中
    lines[off + START] = start;
    lines[off + TOP] = v;
    lines[off + DESCENT] = below + extra;
    lines[off + EXTRA] = extra;

    // 计算下一行的的top值
    v += (below - above) + extra;
    
    mLineCount++;
    return v;
}

public class ExcludeInnerLineSpaceSpan implements LineHeightSpan {
    // TextView行高
    private final  int mHeight;

    public ExcludeInnerPaddingSpan(int height) {
        mHeight = height;
    }

    @Override
    public void chooseHeight(CharSequence text, int start, int end,
                             int spanstartv, int lineHeight,
                             Paint.FontMetricsInt fm) {
        // 原始行高
        final int originHeight = fm.descent - fm.ascent;
        if (originHeight <= 0) {
            return;
        }
        // 计算比例值
        final float ratio = mHeight * 1.0f / originHeight;
        // 根据最新行高，修改descent
        fm.descent = Math.round(fm.descent * ratio);
        // 根据最新行高，修改ascent
        fm.ascent = fm.descent - mHeight;
    }
}

public class ETextView extends TextView {
    /**
     * 排除每行文字间的padding
     *
     * @param text
     */
    public void setCustomText(CharSequence text) {
        if (text == null) {
            return;
        }

        // 获得视觉定义的每行文字的行高
        int lineHeight = (int) getTextSize();

        SpannableStringBuilder ssb ;
        if (text instanceof SpannableStringBuilder) {
            ssb = (SpannableStringBuilder) text;
            // 设置LineHeightSpan
            ssb.setSpan(new ExcludeInnerLineSpaceSpan(lineHeight),
                    0, text.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
        } else {
            ssb = new SpannableStringBuilder(text);
            // 设置LineHeightSpan
            ssb.setSpan(new ExcludeInnerLineSpaceSpan(lineHeight),
                    0, text.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
        }

        // 调用系统setText()方法
        setText(ssb);
    }
}