Android TextView源码浅析之Layout
2020-07-21 本文已影响0人
ChrisChanSysu
OverView
在上一篇从顶层整体流程分析TextView时能看到Layout这个重要概念，无论是onMeasure()过程还是onDraw()过程，主要工作都是由Layout来完成。
Layout类负责的作用是，完成TextView的排版，包括折行、省略等等。
TextView.makeNewLayout()
在上一篇的分析中，在onMeasure()过程，会调用到TextView的makeNewLayout()方法，现在来看下它的实现：
public void makeNewLayout(int wantWidth, int hintWidth,
BoringLayout.Metrics boring,
BoringLayout.Metrics hintBoring,
int ellipsisWidth, boolean bringIntoView) {
// 暂停走马灯动画
stopMarquee();
mOldMaximum = mMaximum;
mOldMaxMode = mMaxMode;
mHighlightPathBogus = true;
if (wantWidth < 0) {
wantWidth = 0;
}
if (hintWidth < 0) {
hintWidth = 0;
}
// 1.获取对齐方式
Layout.Alignment alignment = getLayoutAlignment();
final boolean testDirChange = mSingleLine && mLayout != null
&& (alignment == Layout.Alignment.ALIGN_NORMAL
|| alignment == Layout.Alignment.ALIGN_OPPOSITE);
int oldDir = 0;
if (testDirChange) oldDir = mLayout.getParagraphDirection(0);
boolean shouldEllipsize = mEllipsize != null && getKeyListener() == null;
// 2.处理省略方式
final boolean switchEllipsize = mEllipsize == TruncateAt.MARQUEE
&& mMarqueeFadeMode != MARQUEE_FADE_NORMAL;
TruncateAt effectiveEllipsize = mEllipsize;
if (mEllipsize == TruncateAt.MARQUEE
&& mMarqueeFadeMode == MARQUEE_FADE_SWITCH_SHOW_ELLIPSIS) {
effectiveEllipsize = TruncateAt.END_SMALL;
}
// 3.获取文字方向
if (mTextDir == null) {
mTextDir = getTextDirectionHeuristic();
}
// 4.通过上述信息，构建mLayout
mLayout = makeSingleLayout(wantWidth, boring, ellipsisWidth, alignment, shouldEllipsize,
effectiveEllipsize, effectiveEllipsize == mEllipsize);
if (switchEllipsize) {
TruncateAt oppositeEllipsize = effectiveEllipsize == TruncateAt.MARQUEE
? TruncateAt.END : TruncateAt.MARQUEE;
mSavedMarqueeModeLayout = makeSingleLayout(wantWidth, boring, ellipsisWidth, alignment,
shouldEllipsize, oppositeEllipsize, effectiveEllipsize != mEllipsize);
}
shouldEllipsize = mEllipsize != null;
mHintLayout = null;
// 5.构建出用于显示hint的Layout
if (mHint != null) {
if (shouldEllipsize) hintWidth = wantWidth;
if (hintBoring == UNKNOWN_BORING) {
hintBoring = BoringLayout.isBoring(mHint, mTextPaint, mTextDir,
mHintBoring);
if (hintBoring != null) {
mHintBoring = hintBoring;
}
}
if (hintBoring != null) {
if (hintBoring.width <= hintWidth
&& (!shouldEllipsize || hintBoring.width <= ellipsisWidth)) {
if (mSavedHintLayout != null) {
mHintLayout = mSavedHintLayout.replaceOrMake(mHint, mTextPaint,
hintWidth, alignment, mSpacingMult, mSpacingAdd,
hintBoring, mIncludePad);
} else {
mHintLayout = BoringLayout.make(mHint, mTextPaint,
hintWidth, alignment, mSpacingMult, mSpacingAdd,
hintBoring, mIncludePad);
}
mSavedHintLayout = (BoringLayout) mHintLayout;
} else if (shouldEllipsize && hintBoring.width <= hintWidth) {
if (mSavedHintLayout != null) {
mHintLayout = mSavedHintLayout.replaceOrMake(mHint, mTextPaint,
hintWidth, alignment, mSpacingMult, mSpacingAdd,
hintBoring, mIncludePad, mEllipsize,
ellipsisWidth);
} else {
mHintLayout = BoringLayout.make(mHint, mTextPaint,
hintWidth, alignment, mSpacingMult, mSpacingAdd,
hintBoring, mIncludePad, mEllipsize,
ellipsisWidth);
}
}
}
if (mHintLayout == null) {
StaticLayout.Builder builder = StaticLayout.Builder.obtain(mHint, 0,
mHint.length(), mTextPaint, hintWidth)
.setAlignment(alignment)
.setTextDirection(mTextDir)
.setLineSpacing(mSpacingAdd, mSpacingMult)
.setIncludePad(mIncludePad)
.setUseLineSpacingFromFallbacks(mUseFallbackLineSpacing)
.setBreakStrategy(mBreakStrategy)
.setHyphenationFrequency(mHyphenationFrequency)
.setJustificationMode(mJustificationMode)
.setMaxLines(mMaxMode == LINES ? mMaximum : Integer.MAX_VALUE);
if (shouldEllipsize) {
builder.setEllipsize(mEllipsize)
.setEllipsizedWidth(ellipsisWidth);
}
mHintLayout = builder.build();
}
}
if (bringIntoView || (testDirChange && oldDir != mLayout.getParagraphDirection(0))) {
registerForPreDraw();
}
// 6.重启走马灯动画
if (mEllipsize == TextUtils.TruncateAt.MARQUEE) {
if (!compressText(ellipsisWidth)) {
final int height = mLayoutParams.height;
if (height != LayoutParams.WRAP_CONTENT && height != LayoutParams.MATCH_PARENT) {
startMarquee();
} else {
mRestartMarquee = true;
}
}
}
// CursorControllers need a non-null mLayout
if (mEditor != null) mEditor.prepareCursorControllers();
}
在这个函数中，最重要的是第4点的通过调用makeSingleLayout()方法构建出主Layout，但第5点构建hint的Layout也很值得学习，因为涉及了BoringLayout和StaticLayout这两个重要的概念：
BoringLayout和StaticLayout都是Layout的子类，其中BoringLayout是指不包含Span而且文本都是左到右而且能够一行展示下的文本，这种情况下使用BoringLayout能够节省不必要的计算；当hint不满足BoringLayout的条件时，会使用StaticLayout来进行布局
TextView.makeSingleLayout()方法
protected Layout makeSingleLayout(int wantWidth, BoringLayout.Metrics boring, int ellipsisWidth,
Layout.Alignment alignment, boolean shouldEllipsize, TruncateAt effectiveEllipsize,
boolean useSaved) {
Layout result = null;
// 这个方法的内部会判断文本是否是Spannable，是的话会使用DynamicLayout
if (useDynamicLayout()) {
final DynamicLayout.Builder builder = DynamicLayout.Builder.obtain(mText, mTextPaint,
wantWidth)
.setDisplayText(mTransformed)
.setAlignment(alignment)
.setTextDirection(mTextDir)
.setLineSpacing(mSpacingAdd, mSpacingMult)
.setIncludePad(mIncludePad)
.setUseLineSpacingFromFallbacks(mUseFallbackLineSpacing)
.setBreakStrategy(mBreakStrategy)
.setHyphenationFrequency(mHyphenationFrequency)
.setJustificationMode(mJustificationMode)
.setEllipsize(getKeyListener() == null ? effectiveEllipsize : null)
.setEllipsizedWidth(ellipsisWidth);
result = builder.build();
} else {
// 判断是否确定了是不是Boring
if (boring == UNKNOWN_BORING) {
boring = BoringLayout.isBoring(mTransformed, mTextPaint, mTextDir, mBoring);
if (boring != null) {
mBoring = boring;
}
}
// 这个条件如果成立，则证明是Boring
if (boring != null) {
// 根据boring的不同属性，创建对应的Layout，if-else分支里都会尝试从mSavedLayout中创建，拿不到再调用BoringLayout.make()来创建新的
if (boring.width <= wantWidth
&& (effectiveEllipsize == null || boring.width <= ellipsisWidth)) {
if (useSaved && mSavedLayout != null) {
result = mSavedLayout.replaceOrMake(mTransformed, mTextPaint,
wantWidth, alignment, mSpacingMult, mSpacingAdd,
boring, mIncludePad);
} else {
result = BoringLayout.make(mTransformed, mTextPaint,
wantWidth, alignment, mSpacingMult, mSpacingAdd,
boring, mIncludePad);
}
if (useSaved) {
mSavedLayout = (BoringLayout) result;
}
} else if (shouldEllipsize && boring.width <= wantWidth) {
if (useSaved && mSavedLayout != null) {
result = mSavedLayout.replaceOrMake(mTransformed, mTextPaint,
wantWidth, alignment, mSpacingMult, mSpacingAdd,
boring, mIncludePad, effectiveEllipsize,
ellipsisWidth);
} else {
result = BoringLayout.make(mTransformed, mTextPaint,
wantWidth, alignment, mSpacingMult, mSpacingAdd,
boring, mIncludePad, effectiveEllipsize,
ellipsisWidth);
}
}
}
}
// 在这里result依然为null，证明不是Boring，需要用StaticLayout
if (result == null) {
StaticLayout.Builder builder = StaticLayout.Builder.obtain(mTransformed,
0, mTransformed.length(), mTextPaint, wantWidth)
.setAlignment(alignment)
.setTextDirection(mTextDir)
.setLineSpacing(mSpacingAdd, mSpacingMult)
.setIncludePad(mIncludePad)
.setUseLineSpacingFromFallbacks(mUseFallbackLineSpacing)
.setBreakStrategy(mBreakStrategy)
.setHyphenationFrequency(mHyphenationFrequency)
.setJustificationMode(mJustificationMode)
.setMaxLines(mMaxMode == LINES ? mMaximum : Integer.MAX_VALUE);
if (shouldEllipsize) {
builder.setEllipsize(effectiveEllipsize)
.setEllipsizedWidth(ellipsisWidth);
}
result = builder.build();
}
return result;
}
StaticLayout.generate()
在调用StaticLayout.Builder.build()方法之后，最终会调用到StaticLayout的generate()方法来构建出真正对应的Layout，generate()方法很长，还是采取分部分的方式来看：
final CharSequence source = b.mText;
final int bufStart = b.mStart;
final int bufEnd = b.mEnd;
TextPaint paint = b.mPaint;
int outerWidth = b.mWidth;
TextDirectionHeuristic textDir = b.mTextDir;
final boolean fallbackLineSpacing = b.mFallbackLineSpacing;
float spacingmult = b.mSpacingMult;
float spacingadd = b.mSpacingAdd;
float ellipsizedWidth = b.mEllipsizedWidth;
TextUtils.TruncateAt ellipsize = b.mEllipsize;
final boolean addLastLineSpacing = b.mAddLastLineLineSpacing;
LineBreaks lineBreaks = new LineBreaks();
FloatArray widths = new FloatArray();
mLineCount = 0;
mEllipsized = false;
mMaxLineHeight = mMaximumVisibleLineCount < 1 ? 0 : DEFAULT_MAX_LINE_HEIGHT;
int v = 0;
boolean needMultiply = (spacingmult != 1 || spacingadd != 0);
Paint.FontMetricsInt fm = b.mFontMetricsInt;
int[] chooseHtv = null;
- 第1部分是变量的初始化
final int[] indents;
if (mLeftIndents != null || mRightIndents != null) {
final int leftLen = mLeftIndents == null ? 0 : mLeftIndents.length;
final int rightLen = mRightIndents == null ? 0 : mRightIndents.length;
final int indentsLen = Math.max(leftLen, rightLen);
indents = new int[indentsLen];
for (int i = 0; i < leftLen; i++) {
indents[i] = mLeftIndents[i];
}
for (int i = 0; i < rightLen; i++) {
indents[i] += mRightIndents[i];
}
} else {
indents = null;
}
final long nativePtr = nInit(
b.mBreakStrategy, b.mHyphenationFrequency,
b.mJustificationMode != Layout.JUSTIFICATION_MODE_NONE,
indents, mLeftPaddings, mRightPaddings);
- 第2部分是对文本缩进的处理，最终处理调用的是native函数实现，但实际这个if代码块，暂时还没有找到能够判断为true的地方
PrecomputedText.ParagraphInfo[] paragraphInfo = null;
final Spanned spanned = (source instanceof Spanned) ? (Spanned) source : null;
if (source instanceof PrecomputedText) {
PrecomputedText precomputed = (PrecomputedText) source;
if (precomputed.canUseMeasuredResult(bufStart, bufEnd, textDir, paint,
b.mBreakStrategy, b.mHyphenationFrequency)) {
paragraphInfo = precomputed.getParagraphInfo();
}
}
if (paragraphInfo == null) {
final PrecomputedText.Params param = new PrecomputedText.Params(paint, textDir,
b.mBreakStrategy, b.mHyphenationFrequency);
paragraphInfo = PrecomputedText.createMeasuredParagraphs(source, param, bufStart,
bufEnd, false);
}
- 第3部分是分析文本的段落信息，这里涉及到的PrecomputedText是包含了文本测量信息的类，通过它来构建文本能够节省一些开销
接下来的部分，是根据段落信息，逐段地分析段落里的文本内容
for (int paraIndex = 0; paraIndex < paragraphInfo.length; paraIndex++) {
final int paraStart = paraIndex == 0
? bufStart : paragraphInfo[paraIndex - 1].paragraphEnd;
final int paraEnd = paragraphInfo[paraIndex].paragraphEnd;
// ……
}
下面这几段的代码都发生在这个大的for循环中
int firstWidthLineCount = 1;
int firstWidth = outerWidth;
int restWidth = outerWidth;
LineHeightSpan[] chooseHt = null;
if (spanned != null) {
LeadingMarginSpan[] sp = getParagraphSpans(spanned, paraStart, paraEnd,
LeadingMarginSpan.class);
for (int i = 0; i < sp.length; i++) {
LeadingMarginSpan lms = sp[i];
firstWidth -= sp[i].getLeadingMargin(true);
restWidth -= sp[i].getLeadingMargin(false);
// LeadingMarginSpan2 is odd. The count affects all
// leading margin spans, not just this particular one
if (lms instanceof LeadingMarginSpan2) {
LeadingMarginSpan2 lms2 = (LeadingMarginSpan2) lms;
firstWidthLineCount = Math.max(firstWidthLineCount,
lms2.getLeadingMarginLineCount());
}
}
- 首先是宽度方面的分析，解析LeadingMarginSpan和LeadingMargin2
chooseHt = getParagraphSpans(spanned, paraStart, paraEnd, LineHeightSpan.class);
if (chooseHt.length == 0) {
chooseHt = null; // So that out() would not assume it has any contents
} else {
if (chooseHtv == null || chooseHtv.length < chooseHt.length) {
chooseHtv = ArrayUtils.newUnpaddedIntArray(chooseHt.length);
}
for (int i = 0; i < chooseHt.length; i++) {
int o = spanned.getSpanStart(chooseHt[i]);
if (o < paraStart) {
// starts in this layout, before the
// current paragraph
chooseHtv[i] = getLineTop(getLineForOffset(o));
} else {
// starts in this paragraph
chooseHtv[i] = v;
}
}
}
}
- 然后是行高的分析，通过解析LineHeightSpan来实现
int[] variableTabStops = null;
if (spanned != null) {
TabStopSpan[] spans = getParagraphSpans(spanned, paraStart,
paraEnd, TabStopSpan.class);
if (spans.length > 0) {
int[] stops = new int[spans.length];
for (int i = 0; i < spans.length; i++) {
stops[i] = spans[i].getTabStop();
}
Arrays.sort(stops, 0, stops.length);
variableTabStops = stops;
}
}
- 这一段通过解析TabStopSpan来获取tabStop，排序后存储在variableTabStop中
final MeasuredParagraph measuredPara = paragraphInfo[paraIndex].measured;
final char[] chs = measuredPara.getChars();
final int[] spanEndCache = measuredPara.getSpanEndCache().getRawArray();
final int[] fmCache = measuredPara.getFontMetrics().getRawArray();
widths.resize(chs.length);
- 这部分作用是从段落信息paragraphInfo[paraIndex]中取出测量相关的信息，后面准备使用
int breakCount = nComputeLineBreaks(
nativePtr,
// Inputs
chs,
measuredPara.getNativePtr(),
paraEnd - paraStart,
firstWidth,
firstWidthLineCount,
restWidth,
variableTabStops,
TAB_INCREMENT,
mLineCount,
// Outputs
lineBreaks,
lineBreaks.breaks.length,
lineBreaks.breaks,
lineBreaks.widths,
lineBreaks.ascents,
lineBreaks.descents,
lineBreaks.flags,
widths.getRawArray());
final int[] breaks = lineBreaks.breaks;
final float[] lineWidths = lineBreaks.widths;
final float[] ascents = lineBreaks.ascents;
final float[] descents = lineBreaks.descents;
final int[] flags = lineBreaks.flags;
- 这一段是根据前述步骤的宽度、行宽等信息，调用native的方法进行了折行处理，处理后的结果在lineBreaks中
final int remainingLineCount = mMaximumVisibleLineCount - mLineCount;
final boolean ellipsisMayBeApplied = ellipsize != null
&& (ellipsize == TextUtils.TruncateAt.END
|| (mMaximumVisibleLineCount == 1
&& ellipsize != TextUtils.TruncateAt.MARQUEE));
if (0 < remainingLineCount && remainingLineCount < breakCount
&& ellipsisMayBeApplied) {
// Calculate width and flag.
float width = 0;
int flag = 0; // XXX May need to also have starting hyphen edit
for (int i = remainingLineCount - 1; i < breakCount; i++) {
if (i == breakCount - 1) {
width += lineWidths[i];
} else {
for (int j = (i == 0 ? 0 : breaks[i - 1]); j < breaks[i]; j++) {
width += widths.get(j);
}
}
flag |= flags[i] & TAB_MASK;
}
// Treat the last line and overflowed lines as a single line.
breaks[remainingLineCount - 1] = breaks[breakCount - 1];
lineWidths[remainingLineCount - 1] = width;
flags[remainingLineCount - 1] = flag;
breakCount = remainingLineCount;
}
- 这里主要是对末行以及省略的相应处理
int here = paraStart;
int fmTop = 0, fmBottom = 0, fmAscent = 0, fmDescent = 0;
int fmCacheIndex = 0;
int spanEndCacheIndex = 0;
int breakIndex = 0;
for (int spanStart = paraStart, spanEnd; spanStart < paraEnd; spanStart = spanEnd) {
// retrieve end of span
spanEnd = spanEndCache[spanEndCacheIndex++];
// retrieve cached metrics, order matches above
fm.top = fmCache[fmCacheIndex * 4 + 0];
fm.bottom = fmCache[fmCacheIndex * 4 + 1];
fm.ascent = fmCache[fmCacheIndex * 4 + 2];
fm.descent = fmCache[fmCacheIndex * 4 + 3];
fmCacheIndex++;
if (fm.top < fmTop) {
fmTop = fm.top;
}
if (fm.ascent < fmAscent) {
fmAscent = fm.ascent;
}
if (fm.descent > fmDescent) {
fmDescent = fm.descent;
}
if (fm.bottom > fmBottom) {
fmBottom = fm.bottom;
}
// skip breaks ending before current span range
while (breakIndex < breakCount && paraStart + breaks[breakIndex] < spanStart) {
breakIndex++;
}
while (breakIndex < breakCount && paraStart + breaks[breakIndex] <= spanEnd) {
int endPos = paraStart + breaks[breakIndex];
boolean moreChars = (endPos < bufEnd);
final int ascent = fallbackLineSpacing
? Math.min(fmAscent, Math.round(ascents[breakIndex]))
: fmAscent;
final int descent = fallbackLineSpacing
? Math.max(fmDescent, Math.round(descents[breakIndex]))
: fmDescent;
v = out(source, here, endPos,
ascent, descent, fmTop, fmBottom,
v, spacingmult, spacingadd, chooseHt, chooseHtv, fm,
flags[breakIndex], needMultiply, measuredPara, bufEnd,
includepad, trackpad, addLastLineSpacing, chs, widths.getRawArray(),
paraStart, ellipsize, ellipsizedWidth, lineWidths[breakIndex],
paint, moreChars);
if (endPos < spanEnd) {
// preserve metrics for current span
fmTop = fm.top;
fmBottom = fm.bottom;
fmAscent = fm.ascent;
fmDescent = fm.descent;
} else {
fmTop = fmBottom = fmAscent = fmDescent = 0;
}
here = endPos;
breakIndex++;
if (mLineCount >= mMaximumVisibleLineCount && mEllipsized) {
return;
}
}
}
if (paraEnd == bufEnd) {
break;
}
}
- 这一段是对段落中的Span和这行进行处理，其中fmCache是前面PrecomputeText在测量时已经测算好的各个Span在top/bottom/ascent/descent这几个维度上的值，并缓存在fmCache中，因此在这里需要计算某个段落的字体属性时，直接从fmCache中取出即可
if ((bufEnd == bufStart || source.charAt(bufEnd - 1) == CHAR_NEW_LINE)
&& mLineCount < mMaximumVisibleLineCount) {
final MeasuredParagraph measuredPara =
MeasuredParagraph.buildForBidi(source, bufEnd, bufEnd, textDir, null);
paint.getFontMetricsInt(fm);
v = out(source,
bufEnd, bufEnd, fm.ascent, fm.descent,
fm.top, fm.bottom,
v,
spacingmult, spacingadd, null,
null, fm, 0,
needMultiply, measuredPara, bufEnd,
includepad, trackpad, addLastLineSpacing, null,
null, bufStart, ellipsize,
ellipsizedWidth, 0, paint, false);
}
- 注意最后这一段的成立条件：结束为止和起始位置相等，并且前一个字符是换行符，那证明是一个新的空白段落，也需要作为一个单独的段落进行单独处理
StaticLayout.out()
上面已经看完了整体的StaticLayout.generate()函数，其中看到有对out()函数的调用，out()函数完整的签名如下：
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 int flags, final boolean needMultiply, @NonNull final MeasuredParagraph measured,
final int bufEnd, final boolean includePad, final boolean trackPad,
final boolean addLastLineLineSpacing, final char[] chs, final float[] widths,
final int widthStart, final TextUtils.TruncateAt ellipsize, final float ellipsisWidth,
final float textWidth, final TextPaint paint, final boolean moreChars)
参数非常多，但看参数名基本能看出和此前的generate()函数基本是对应的
接下来分段看下它做了什么
final int j = mLineCount;
final int off = j * mColumns;
final int want = off + mColumns + TOP;
int[] lines = mLines;
final int dir = measured.getParagraphDir();
if (want >= lines.length) {
final int[] grow = ArrayUtils.newUnpaddedIntArray(GrowingArrayUtils.growSize(want));
System.arraycopy(lines, 0, grow, 0, lines.length);
mLines = grow;
lines = grow;
}
if (j >= mLineDirections.length) {
final Directions[] grow = ArrayUtils.newUnpaddedArray(Directions.class,
GrowingArrayUtils.growSize(j));
System.arraycopy(mLineDirections, 0, grow, 0, mLineDirections.length);
mLineDirections = grow;
}
- 第1部分是判断mLines/mLineDirections数组是否需要扩容以及在需要时进行扩容操作，mLines数组中存储的是每行的信息，包括每一行的信息包括START/TOP/DESCENT/HYPHEN/ELLIPSIS_START/ELLIPSIS_COUNT
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);
}
}
above = fm.ascent;
below = fm.descent;
top = fm.top;
bottom = fm.bottom;
}
第2部分是对高度进行处理，得到的结果存储在above/below/top/bottom变量中
if (ellipsize != null) {
// If there is only one line, then do any type of ellipsis except when it is MARQUEE
// if there are multiple lines, just allow END ellipsis on the last line
boolean forceEllipsis = moreChars && (mLineCount + 1 == mMaximumVisibleLineCount);
boolean doEllipsis =
(((mMaximumVisibleLineCount == 1 && moreChars) || (firstLine && !moreChars)) &&
ellipsize != TextUtils.TruncateAt.MARQUEE) ||
(!firstLine && (currentLineIsTheLastVisibleOne || !moreChars) &&
ellipsize == TextUtils.TruncateAt.END);
if (doEllipsis) {
calculateEllipsis(start, end, widths, widthStart,
ellipsisWidth, ellipsize, j,
textWidth, paint, forceEllipsis);
}
}
- 第3部分是对省略的计算和处理
final boolean lastLine;
if (mEllipsized) {
lastLine = true;
} else {
final boolean lastCharIsNewLine = widthStart != bufEnd && bufEnd > 0
&& text.charAt(bufEnd - 1) == CHAR_NEW_LINE;
if (end == bufEnd && !lastCharIsNewLine) {
lastLine = true;
} else if (start == bufEnd && lastCharIsNewLine) {
lastLine = true;
} else {
lastLine = false;
}
}
if (firstLine) {
if (trackPad) {
mTopPadding = top - above;
}
if (includePad) {
above = top;
}
}
int extra;
if (lastLine) {
if (trackPad) {
mBottomPadding = bottom - below;
}
if (includePad) {
below = bottom;
}
}
if (needMultiply && (addLastLineLineSpacing || !lastLine)) {
double ex = (below - above) * (spacingmult - 1) + spacingadd;
if (ex >= 0) {
extra = (int)(ex + EXTRA_ROUNDING);
} else {
extra = -(int)(-ex + EXTRA_ROUNDING);
}
} else {
extra = 0;
}
- 第4部分是对首行末行的特殊处理，因为要考虑上下留白；还有对行间距的特殊处理
lines[off + START] = start;
lines[off + TOP] = v;
lines[off + DESCENT] = below + extra;
lines[off + EXTRA] = extra;
// special case for non-ellipsized last visible line when maxLines is set
// store the height as if it was ellipsized
if (!mEllipsized && currentLineIsTheLastVisibleOne) {
// below calculation as if it was the last line
int maxLineBelow = includePad ? bottom : below;
// similar to the calculation of v below, without the extra.
mMaxLineHeight = v + (maxLineBelow - above);
}
v += (below - above) + extra;
lines[off + mColumns + START] = end;
lines[off + mColumns + TOP] = v;
lines[off + TAB] |= flags & TAB_MASK;
lines[off + HYPHEN] = flags;
lines[off + DIR] |= dir << DIR_SHIFT;
mLineDirections[j] = measured.getDirections(start - widthStart, end - widthStart);
mLineCount++;
return v;
- 第5部分就是将处理完的每一行的信息，都记录到lines数组中了
从这里就能看出out函数的作用是对Layout中的每一行文本进行分析，最重要的产出就是得到mLines数组
Layout.draw()
在上一篇TextView的整体流程中我们看到，TextView的onDraw()执行过程中，最终实际上是通过Layout.draw()函数完成的，而在Layout前面的分析中我们已经得到了每一行的信息，所以接下来看下Layout.draw()函数是怎么执行的。
public void draw(Canvas canvas, Path highlight, Paint highlightPaint,
int cursorOffsetVertical) {
final long lineRange = getLineRangeForDraw(canvas);
int firstLine = TextUtils.unpackRangeStartFromLong(lineRange);
int lastLine = TextUtils.unpackRangeEndFromLong(lineRange);
if (lastLine < 0) return;
drawBackground(canvas, highlight, highlightPaint, cursorOffsetVertical,
firstLine, lastLine);
drawText(canvas, firstLine, lastLine);
}
Layout.draw()实际上分成了两部分，drawBackground()和drawText()，下面看下它们的实现：
Layout.drawBackground()
public void drawBackground(Canvas canvas, Path highlight, Paint highlightPaint,
int cursorOffsetVertical, int firstLine, int lastLine) {
// First, draw LineBackgroundSpans.
// LineBackgroundSpans know nothing about the alignment, margins, or
// direction of the layout or line. XXX: Should they?
// They are evaluated at each line.
if (mSpannedText) {
if (mLineBackgroundSpans == null) {
mLineBackgroundSpans = new SpanSet<LineBackgroundSpan>(LineBackgroundSpan.class);
}
Spanned buffer = (Spanned) mText;
int textLength = buffer.length();
mLineBackgroundSpans.init(buffer, 0, textLength);
if (mLineBackgroundSpans.numberOfSpans > 0) {
int previousLineBottom = getLineTop(firstLine);
int previousLineEnd = getLineStart(firstLine);
ParagraphStyle[] spans = NO_PARA_SPANS;
int spansLength = 0;
TextPaint paint = mPaint;
int spanEnd = 0;
final int width = mWidth;
for (int i = firstLine; i <= lastLine; i++) {
int start = previousLineEnd;
int end = getLineStart(i + 1);
previousLineEnd = end;
int ltop = previousLineBottom;
int lbottom = getLineTop(i + 1);
previousLineBottom = lbottom;
int lbaseline = lbottom - getLineDescent(i);
if (start >= spanEnd) {
// These should be infrequent, so we'll use this so that
// we don't have to check as often.
spanEnd = mLineBackgroundSpans.getNextTransition(start, textLength);
// All LineBackgroundSpans on a line contribute to its background.
spansLength = 0;
// Duplication of the logic of getParagraphSpans
if (start != end || start == 0) {
// Equivalent to a getSpans(start, end), but filling the 'spans' local
// array instead to reduce memory allocation
for (int j = 0; j < mLineBackgroundSpans.numberOfSpans; j++) {
// equal test is valid since both intervals are not empty by
// construction
if (mLineBackgroundSpans.spanStarts[j] >= end ||
mLineBackgroundSpans.spanEnds[j] <= start) continue;
spans = GrowingArrayUtils.append(
spans, spansLength, mLineBackgroundSpans.spans[j]);
spansLength++;
}
}
}
for (int n = 0; n < spansLength; n++) {
LineBackgroundSpan lineBackgroundSpan = (LineBackgroundSpan) spans[n];
lineBackgroundSpan.drawBackground(canvas, paint, 0, width,
ltop, lbaseline, lbottom,
buffer, start, end, i);
}
}
}
mLineBackgroundSpans.recycle();
}
// There can be a highlight even without spans if we are drawing
// a non-spanned transformation of a spanned editing buffer.
if (highlight != null) {
if (cursorOffsetVertical != 0) canvas.translate(0, cursorOffsetVertical);
canvas.drawPath(highlight, highlightPaint);
if (cursorOffsetVertical != 0) canvas.translate(0, -cursorOffsetVertical);
}
}
- 代码不长，可以看到Layout的drawBackground()实际上是通过LineBackgroundSpan.drawBackground()来完成的，而LineBackgroundSpan只是一个接口，在Android源码中并没有实现类，因此drawBackground()的实际绘制效果是使用时自己定义的
Layout.drawText()
image.png
drawText()方法整体内容如图，主要的工作在for循环中，从注释中能看出，drawText()的过程是，逐行绘制，下面看下这个for循环内部的逻辑：
int start = previousLineEnd;
previousLineEnd = getLineStart(lineNum + 1);
final boolean justify = isJustificationRequired(lineNum);
int end = getLineVisibleEnd(lineNum, start, previousLineEnd);
paint.setHyphenEdit(getHyphen(lineNum));
int ltop = previousLineBottom;
int lbottom = getLineTop(lineNum + 1);
previousLineBottom = lbottom;
int lbaseline = lbottom - getLineDescent(lineNum);
int dir = getParagraphDirection(lineNum);
int left = 0;
int right = mWidth;
if (mSpannedText) {
Spanned sp = (Spanned) buf;
int textLength = buf.length();
boolean isFirstParaLine = (start == 0 || buf.charAt(start - 1) == '\n');
// New batch of paragraph styles, collect into spans array.
// Compute the alignment, last alignment style wins.
// Reset tabStops, we'll rebuild if we encounter a line with
// tabs.
// We expect paragraph spans to be relatively infrequent, use
// spanEnd so that we can check less frequently. Since
// paragraph styles ought to apply to entire paragraphs, we can
// just collect the ones present at the start of the paragraph.
// If spanEnd is before the end of the paragraph, that's not
// our problem.
if (start >= spanEnd && (lineNum == firstLine || isFirstParaLine)) {
spanEnd = sp.nextSpanTransition(start, textLength,
ParagraphStyle.class);
spans = getParagraphSpans(sp, start, spanEnd, ParagraphStyle.class);
paraAlign = mAlignment;
for (int n = spans.length - 1; n >= 0; n--) {
if (spans[n] instanceof AlignmentSpan) {
paraAlign = ((AlignmentSpan) spans[n]).getAlignment();
break;
}
}
tabStopsIsInitialized = false;
}
// Draw all leading margin spans. Adjust left or right according
// to the paragraph direction of the line.
final int length = spans.length;
boolean useFirstLineMargin = isFirstParaLine;
for (int n = 0; n < length; n++) {
if (spans[n] instanceof LeadingMarginSpan2) {
int count = ((LeadingMarginSpan2) spans[n]).getLeadingMarginLineCount();
int startLine = getLineForOffset(sp.getSpanStart(spans[n]));
// if there is more than one LeadingMarginSpan2, use
// the count that is greatest
if (lineNum < startLine + count) {
useFirstLineMargin = true;
break;
}
}
}
for (int n = 0; n < length; n++) {
if (spans[n] instanceof LeadingMarginSpan) {
LeadingMarginSpan margin = (LeadingMarginSpan) spans[n];
if (dir == DIR_RIGHT_TO_LEFT) {
margin.drawLeadingMargin(canvas, paint, right, dir, ltop,
lbaseline, lbottom, buf,
start, end, isFirstParaLine, this);
right -= margin.getLeadingMargin(useFirstLineMargin);
} else {
margin.drawLeadingMargin(canvas, paint, left, dir, ltop,
lbaseline, lbottom, buf,
start, end, isFirstParaLine, this);
left += margin.getLeadingMargin(useFirstLineMargin);
}
}
}
}
- 第1部分，主要是判断是不是Spanned，是的话需要获取影响ParagraphStyle的Span，然后判断其中是否有LeadingMarginSpan，有的话会调用其drawLeadingMargin()方法来绘制其段首的缩进效果
boolean hasTab = getLineContainsTab(lineNum);
// Can't tell if we have tabs for sure, currently
if (hasTab && !tabStopsIsInitialized) {
if (tabStops == null) {
tabStops = new TabStops(TAB_INCREMENT, spans);
} else {
tabStops.reset(TAB_INCREMENT, spans);
}
tabStopsIsInitialized = true;
}
// Determine whether the line aligns to normal, opposite, or center.
Alignment align = paraAlign;
if (align == Alignment.ALIGN_LEFT) {
align = (dir == DIR_LEFT_TO_RIGHT) ?
Alignment.ALIGN_NORMAL : Alignment.ALIGN_OPPOSITE;
} else if (align == Alignment.ALIGN_RIGHT) {
align = (dir == DIR_LEFT_TO_RIGHT) ?
Alignment.ALIGN_OPPOSITE : Alignment.ALIGN_NORMAL;
}
int x;
final int indentWidth;
if (align == Alignment.ALIGN_NORMAL) {
if (dir == DIR_LEFT_TO_RIGHT) {
indentWidth = getIndentAdjust(lineNum, Alignment.ALIGN_LEFT);
x = left + indentWidth;
} else {
indentWidth = -getIndentAdjust(lineNum, Alignment.ALIGN_RIGHT);
x = right - indentWidth;
}
} else {
int max = (int)getLineExtent(lineNum, tabStops, false);
if (align == Alignment.ALIGN_OPPOSITE) {
if (dir == DIR_LEFT_TO_RIGHT) {
indentWidth = -getIndentAdjust(lineNum, Alignment.ALIGN_RIGHT);
x = right - max - indentWidth;
} else {
indentWidth = getIndentAdjust(lineNum, Alignment.ALIGN_LEFT);
x = left - max + indentWidth;
}
} else { // Alignment.ALIGN_CENTER
indentWidth = getIndentAdjust(lineNum, Alignment.ALIGN_CENTER);
max = max & ~1;
x = ((right + left - max) >> 1) + indentWidth;
}
}
Directions directions = getLineDirections(lineNum);
- 第2部分，确定该行中是否有Tab，以及对其方式
if (directions == DIRS_ALL_LEFT_TO_RIGHT && !mSpannedText && !hasTab && !justify) {
// XXX: assumes there's nothing additional to be done
canvas.drawText(buf, start, end, x, lbaseline, paint);
} else {
tl.set(paint, buf, start, end, dir, directions, hasTab, tabStops);
if (justify) {
tl.justify(right - left - indentWidth);
}
tl.draw(canvas, x, ltop, lbaseline, lbottom);
}
- 第3部分，根据前面的信息，如果是布局从左到右并且是普通文本而且没有tab而且不需要对齐，则调用canvas.drawText来绘制，否则调用的是TextLine的draw()方法来进行绘制
