TextView源码解析

原文地址：https://github.com/7heaven/AndroidSdkSourceAnalysis/blob/master/article/textview%E6%BA%90%E7%A2%BC%E8%A7%A3%E6%9E%90.md

1.简介

TextView作为Android系统上显示和排版文字以及提供对文字的增删改查、图文混排等功能的控件，内部是相对比较复杂的。这么一个复杂的控件自然需要依赖于一些其他的辅助类，例如：Layout以及Layout的相关子类、Span相关的类、MovementMethod接口、TransformationMethod接口等。这篇文章主要介绍TextView的结构和内部处理文字的流程以及TextView相关的辅助类在TextView处理文字过程中的作用。

2.TextView的内部结构和辅助类

TextView内部除了继承自View的相关属性和measure、layout、draw步骤，还包括：

Layout: TextView的文字排版、折行策略以及文本绘制都是在Layout里面完成的，TextView的自身测量也受Layout的影响。Layout是TextView执行setText方法后，由TextView内部创建的实例，并不能由外部提供。可以用getLayout()方法获取。
TransformationMethod: 用来处理最终的显示结果的类，例如显示密码的时候把密码转换成圆点。这个类并不直接影响TextView内部储存的Text，只影响显示的结果。
MovementMethod: 用来处理TextView内部事件响应的类，可以针对TextView内文本的某一个区域做软键盘输入或者触摸事件的响应。
Drawables: TextView的静态内部类，用来处理和储存TextView的CompoundDrawables,包括TextView的上下左右的Drawable以及错误提示的Drawable。
Spans: Spans并不是特定的某一个类或者实现了某一个接口的类。它可以是任意类型，Spans实际上做的事情是在TextView的内部的text的某一个区域做标记。其中有部分Spans可以影响TextView的绘制和测量，如ImageSpan、BackgroundColorSpan、AbsoluteSizeSpan。还有可以响应点击事件的ClickableSpan。
Editor: TextView作为可编辑文本控件的时候(EditText)，使用Editor来处理文本的区域选择处理和判断、拼写检查、弹出文本菜单等。
InputConnection: EditText的文本输入部分是在TextView中完成的。而InputConnection是软键盘和TextView之间的桥梁，所有的软键盘的输入文字、修改文字和删除文字都是通过InputConnection传递给TextView的。

3.TextView的onTouchEvent处理

TextView内部能处理触摸事件的，包括自身的触摸处理、Editor的onTouchEvent、MovementMethod的onTouchEvent。Editor的onTouchEvent主要处理出于编辑状态下的触摸事件，比如点击选中、长按等。MovementMethod则主要负责文本内部有Span的时候的相关处理，比较常见的就是LinkMovementMethod处理ClickableSpan的点击事件。我们来看一下TextView内部对这些触摸事件的处理和优先级的分配：

public boolean onTouchEvent(MotionEvent event) {final int action = event.getActionMasked();//当Editor不为空的时候，给Editor的双击事件预设值if (mEditor != null && action == MotionEvent.ACTION_DOWN) {if (mFirstTouch && (SystemClock.uptimeMillis() - mLastTouchUpTime) <=ViewConfiguration.getDoubleTapTimeout()) {mEditor.mDoubleTap = true;mFirstTouch = false;} else {mEditor.mDoubleTap = false;mFirstTouch = true;}}if (action == MotionEvent.ACTION_UP) {mLastTouchUpTime = SystemClock.uptimeMillis();}//当Editor不为空，优先处理Editor的触摸事件if (mEditor != null) {mEditor.onTouchEvent(event);//由于Editor内部onTouchEvent实际上交给了mSelectionModifierCursorController处理，所以这边判断mSelectionModifierCursorController是否需要处理接下来的一系列事件，如果是则直接返回跳过下面的步骤if (mEditor.mSelectionModifierCursorController != null &&mEditor.mSelectionModifierCursorController.isDragAcceleratorActive()) {return true;}}final boolean superResult = super.onTouchEvent(event);//处理API 23新加入的InsertionActinoModeif (mEditor != null && mEditor.mDiscardNextActionUp && action == MotionEvent.ACTION_UP) {mEditor.mDiscardNextActionUp = false;if (mEditor.mIsInsertionActionModeStartPending) {mEditor.startInsertionActionMode();mEditor.mIsInsertionActionModeStartPending = false;}return superResult;}final boolean touchIsFinished = (action == MotionEvent.ACTION_UP) &&(mEditor == null || !mEditor.mIgnoreActionUpEvent) && isFocused();if ((mMovement != null || onCheckIsTextEditor()) && isEnabled()&& mText instanceof Spannable && mLayout != null) {boolean handled = false;//MovementMethod的触摸时间处理，如果MovementMethod类型是LinkMovementMethod则会处理文本内的所有ClickableSpan的点击if (mMovement != null) {handled |= mMovement.onTouchEvent(this, (Spannable) mText, event);}final boolean textIsSelectable = isTextSelectable();if (touchIsFinished && mLinksClickable && mAutoLinkMask != 0 && textIsSelectable) {//在文本可选择的情况下，默认是没有LinkMovementMethod来处理ClickableSpan相关的点击的，所以在文本可选择情况，TextView对所有的ClickableSpan进行统一处理ClickableSpan[] links = ((Spannable) mText).getSpans(getSelectionStart(),getSelectionEnd(), ClickableSpan.class);if (links.length > 0) {links[0].onClick(this);handled = true;}}if (touchIsFinished && (isTextEditable() || textIsSelectable)) {final InputMethodManager imm = InputMethodManager.peekInstance();viewClicked(imm);if (!textIsSelectable && mEditor.mShowSoftInputOnFocus) {handled |= imm != null && imm.showSoftInput(this, 0);}mEditor.onTouchUpEvent(event);handled = true;}if (handled) {return true;}}return superResult;}

4.TextView的创建Layout的过程

TextView内部并不仅仅只有一个用来显示文本内容的Layout，在设置了hint的时候，还需要有一个mHintLayout来处理hint的内容。如果设置了Ellipsize类型为Marquee时，还会有一个mSavedMarqueeModeLayout专门用来显示marquee效果。这些Layout都是通过内部的makeNewLayout方法来创建的：

protected void makeNewLayout(int wantWidth, int hintWidthBoringLayout.Metrics boring,BoringLayout.Metrics hintBoring,int ellipsisWidth, boolean bringIntoView) {//如果当前有marquee动画，则先停止动画
        stopMarquee();mOldMaximum = mMaximum;mOldMaxMode = mMaxMode;mHighlightPathBogus = true;if (wantWidth < 0) {wantWidth = 0;}if (hintWidth < 0) {hintWidth = 0;}//文本对齐方式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);//检测是否设置了ellipsizeboolean shouldEllipsize = mEllipsize != null && getKeyListener() == null;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;}//文本方向if (mTextDir == null) {mTextDir = getTextDirectionHeuristic();}//创建主LayoutmLayout = makeSingleLayout(wantWidth, boring, ellipsisWidth, alignment, shouldEllipsize,effectiveEllipsize, effectiveEllipsize == mEllipsize);//非常规的Marquee模式下，需要创建mSavedMarqueeModeLayout来保存marquee动画时所用的Layout，并且在动画期间把它和TextView的主Layout对换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;//判断是否需要创建hintLayoutif (mHint != null) {if (shouldEllipsize) hintWidth = wantWidth;if (hintBoring == UNKNOWN_BORING) {hintBoring = BoringLayout.isBoring(mHint, mTextPaint, mTextDir,mHintBoring);if (hintBoring != null) {mHintBoring = hintBoring;}}//判断是否为boring，如果是则创建BoringLayoutif (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);}}}//不是boring的状态下，用StaticLayout来创建if (mHintLayout == null) {StaticLayout.Builder builder = StaticLayout.Builder.obtain(mHint, 0,mHint.length(), mTextPaint, hintWidth).setAlignment(alignment).setTextDirection(mTextDir).setLineSpacing(mSpacingAdd, mSpacingMult).setIncludePad(mIncludePad).setBreakStrategy(mBreakStrategy).setHyphenationFrequency(mHyphenationFrequency);if (shouldEllipsize) {builder.setEllipsize(mEllipsize).setEllipsizedWidth(ellipsisWidth).setMaxLines(mMaxMode == LINES ? mMaximum : Integer.MAX_VALUE);}mHintLayout = builder.build();}}if (bringIntoView || (testDirChange && oldDir != mLayout.getParagraphDirection(0))) {registerForPreDraw();}//判断是否需要开始Marquee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;}}}if (mEditor != null) mEditor.prepareCursorControllers();}

TextView的布局创建过程涉及到一个boring的概念，boring是指布局所用的文本里面不包含任何Span，所有的文本方向都是从左到右的布局，并且仅需一行就能显示完全的布局。这种情况下，TextView会使用BoringLayout类来创建相关的布局，以节省不必要的文本测量以及文本折行、Span宽度、文本方向等的计算。下面我们来看一下makeNewLayout中使用频率比较高的makeSingleLayout的代码:

private Layout makeSingleLayout(int wantWidth, BoringLayout.Metrics boring, int ellipsisWidth,Layout.Alignment alignment, boolean shouldEllipsize, TruncateAt effectiveEllipsize,boolean useSaved) {Layout result = null;//判断是否Spannable，如果是则用DynamicLayout类来创建布局，DynamicLayout内部实际也是使用StaticLayout来做文本的测量绘制，并在StaticLayout的基础上增加了文本或者Span改变时的监听，及时对文本或者Span的变化做出反应。if (mText instanceof Spannable) {result = new DynamicLayout(mText, mTransformed, mTextPaint, wantWidth,alignment, mTextDir, mSpacingMult, mSpacingAdd, mIncludePad,mBreakStrategy, mHyphenationFrequency,getKeyListener() == null ? effectiveEllipsize : null, ellipsisWidth);} else {//如果boring是未知状态，则重新判断一次是否boringif (boring == UNKNOWN_BORING) {boring = BoringLayout.isBoring(mTransformed, mTextPaint, mTextDir, mBoring);if (boring != null) {mBoring = boring;}}//根据boring的属性来创建对应的布局，如果有mSavedLayout则从mSavedLayout创建if (boring != null) {if (boring.width <= wantWidth &&(effectiveEllipsize == null || boring.width <= ellipsisWidth)) {if (useSaved && mSavedLayout != null) {//从之前保存的Layout中创建result = mSavedLayout.replaceOrMake(mTransformed, mTextPaint,wantWidth, alignment, mSpacingMult, mSpacingAdd,boring, mIncludePad);} else {//创建新的Layoutresult = 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);}}}}//如果没有创建BoringLayout, 则使用StaticLayout类来创建布局if (result == null) {StaticLayout.Builder builder = StaticLayout.Builder.obtain(mTransformed,0, mTransformed.length(), mTextPaint, wantWidth).setAlignment(alignment).setTextDirection(mTextDir).setLineSpacing(mSpacingAdd, mSpacingMult).setIncludePad(mIncludePad).setBreakStrategy(mBreakStrategy).setHyphenationFrequency(mHyphenationFrequency);if (shouldEllipsize) {builder.setEllipsize(effectiveEllipsize).setEllipsizedWidth(ellipsisWidth).setMaxLines(mMaxMode == LINES ? mMaximum : Integer.MAX_VALUE);}result = builder.build();}return result;}

5.TextView的文字处理和绘制

TextView主要的文字排版和渲染并不是在TextView里面完成的，而是由Layout类来处理文字排版工作。在单纯地使用TextView来展示静态文本的时候，这件事情则是由Layout的子类StaticLayout来完成的。

StaticLayout接收到字符串后，首先做的事情是根据字符串里面的换行符对字符串进行拆分。

for (int paraStart = bufStart; paraStart <= bufEnd; paraStart = paraEnd) {paraEnd = TextUtils.indexOf(source, CHAR_NEW_LINE, paraStart, bufEnd);if (paraEnd < 0)paraEnd = bufEnd;elseparaEnd++;

拆分后的段落(Paragraph)被分配给辅助类MeasuredText进行测量得到每个字符的宽度以及每个段落的FontMetric。并通过LineBreaker进行折行的判断

//把段落载入到MeasuredText中，并分配对应的缓存空间
measured.setPara(source, paraStart, paraEnd, textDir, b);char[] chs = measured.mChars;float[] widths = measured.mWidths;byte[] chdirs = measured.mLevels;int dir = measured.mDir;boolean easy = measured.mEasy;//把相关属性传给JNI层的LineBreakernSetupParagraph(b.mNativePtr, chs, paraEnd - paraStart,firstWidth, firstWidthLineCount, restWidth,variableTabStops, TAB_INCREMENT, b.mBreakStrategy, b.mHyphenationFrequency);int fmCacheCount = 0;int spanEndCacheCount = 0;for (int spanStart = paraStart, spanEnd; spanStart < paraEnd; spanStart = spanEnd) {if (fmCacheCount * 4 >= fmCache.length) {int[] grow = new int[fmCacheCount * 4 * 2];System.arraycopy(fmCache, 0, grow, 0, fmCacheCount * 4);fmCache = grow;}if (spanEndCacheCount >= spanEndCache.length) {int[] grow = new int[spanEndCacheCount * 2];System.arraycopy(spanEndCache, 0, grow, 0, spanEndCacheCount);spanEndCache = grow;}if (spanned == null) {spanEnd = paraEnd;int spanLen = spanEnd - spanStart;//段落没有Span的情况下，把整个段落交给MeasuredText计算每个字符的宽度和FontMetric
                    measured.addStyleRun(paint, spanLen, fm);} else {spanEnd = spanned.nextSpanTransition(spanStart, paraEnd,MetricAffectingSpan.class);int spanLen = spanEnd - spanStart;MetricAffectingSpan[] spans =spanned.getSpans(spanStart, spanEnd, MetricAffectingSpan.class);spans = TextUtils.removeEmptySpans(spans, spanned, MetricAffectingSpan.class);//把对排版有影响的Span交给MeasuredText测量宽度并计算FontMetric
                    measured.addStyleRun(paint, spans, spanLen, fm);}//把测量后的FontMetric缓存下来方便后面使用fmCache[fmCacheCount * 4 + 0] = fm.top;fmCache[fmCacheCount * 4 + 1] = fm.bottom;fmCache[fmCacheCount * 4 + 2] = fm.ascent;fmCache[fmCacheCount * 4 + 3] = fm.descent;fmCacheCount++;spanEndCache[spanEndCacheCount] = spanEnd;spanEndCacheCount++;}nGetWidths(b.mNativePtr, widths);//计算段落中需要折行的位置，并返回折行的数量int breakCount = nComputeLineBreaks(b.mNativePtr, lineBreaks, lineBreaks.breaks,lineBreaks.widths, lineBreaks.flags, lineBreaks.breaks.length);

计算完每一行的测量相关信息、Span宽高以及折行位置，就可以开始按照最终的行数一行一行地保存下来，以供后面绘制和获取对应文本信息的时候使用。

for (int spanStart = paraStart, spanEnd; spanStart < paraEnd; spanStart = spanEnd) {spanEnd = spanEndCache[spanEndCacheIndex++];// 获取之前缓存的FontMetric信息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;}while (breakIndex < breakCount && paraStart + breaks[breakIndex] < spanStart) {breakIndex++;}while (breakIndex < breakCount && paraStart + breaks[breakIndex] <= spanEnd) {int endPos = paraStart + breaks[breakIndex];boolean moreChars = (endPos < bufEnd);//逐行把相关信息储存下来v = out(source, here, endPos,fmAscent, fmDescent, fmTop, fmBottom,v, spacingmult, spacingadd, chooseHt, chooseHtv, fm, flags[breakIndex],needMultiply, chdirs, dir, easy, bufEnd, includepad, trackpad,chs, widths, paraStart, ellipsize, ellipsizedWidth,lineWidths[breakIndex], paint, moreChars);if (endPos < spanEnd) {fmTop = fm.top;fmBottom = fm.bottom;fmAscent = fm.ascent;fmDescent = fm.descent;} else {fmTop = fmBottom = fmAscent = fmDescent = 0;}here = endPos;breakIndex++;if (mLineCount >= mMaximumVisibleLineCount) {return;}}}

这样StaticLayout的排版过程就完成了。文本的绘制则是交给父类Layout来做的，Layout的绘制分为两大部分，drawBackground和drawText。drawBackground做的事情是如果文本内有LineBackgroundSpan则绘制所有的LineBackgroundSpan，然后判断是否有高亮背景(文本选中的背景)，如果有则绘制高亮背景。

public void drawBackground(Canvas canvas, Path highlight, Paint highlightPaint,int cursorOffsetVertical, int firstLine, int lastLine) {//判断并绘制LineBackgroundSpanif (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;//逐行绘制LineBackgroundSpanfor (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) {spanEnd = mLineBackgroundSpans.getNextTransition(start, textLength);spansLength = 0;if (start != end || start == 0) {//排除不在绘制范围内的LineBackgroundSpanfor (int j = 0; j < mLineBackgroundSpans.numberOfSpans; j++) {if (mLineBackgroundSpans.spanStarts[j] >= end ||mLineBackgroundSpans.spanEnds[j] <= start) continue;spans = GrowingArrayUtils.append(spans, spansLength, mLineBackgroundSpans.spans[j]);spansLength++;}}}//对当前行内的LineBackgroundSpan进行绘制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();}//判断并绘制高亮背景(即选中的文本)if (highlight != null) {if (cursorOffsetVertical != 0) canvas.translate(0, cursorOffsetVertical);canvas.drawPath(highlight, highlightPaint);if (cursorOffsetVertical != 0) canvas.translate(0, -cursorOffsetVertical);}}

drawText用来逐行绘制Layout的文本、影响显示效果的Span、以及Emoji表情等。当有Emoji或者Span的时候，实际绘制工作交给TextLine类来完成。

public void drawText(Canvas canvas, int firstLine, int lastLine) {int previousLineBottom = getLineTop(firstLine);int previousLineEnd = getLineStart(firstLine);ParagraphStyle[] spans = NO_PARA_SPANS;int spanEnd = 0;TextPaint paint = mPaint;CharSequence buf = mText;Alignment paraAlign = mAlignment;TabStops tabStops = null;boolean tabStopsIsInitialized = false;//获取TextLine实例TextLine tl = TextLine.obtain();//逐行绘制文本for (int lineNum = firstLine; lineNum <= lastLine; lineNum++) {int start = previousLineEnd;previousLineEnd = getLineStart(lineNum + 1);int end = getLineVisibleEnd(lineNum, start, previousLineEnd);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();//检测是否段落的第一行boolean isFirstParaLine = (start == 0 || buf.charAt(start - 1) == '\n');//获得所有的段落风格相关的Spanif (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;}//获取影响行缩进的Spanfinal 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 (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);}}}}boolean hasTabOrEmoji = getLineContainsTab(lineNum);if (hasTabOrEmoji && !tabStopsIsInitialized) {if (tabStops == null) {tabStops = new TabStops(TAB_INCREMENT, spans);} else {tabStops.reset(TAB_INCREMENT, spans);}tabStopsIsInitialized = true;}//判断当前行的第五方式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;if (align == Alignment.ALIGN_NORMAL) {if (dir == DIR_LEFT_TO_RIGHT) {x = left + getIndentAdjust(lineNum, Alignment.ALIGN_LEFT);} else {x = right + getIndentAdjust(lineNum, Alignment.ALIGN_RIGHT);}} else {int max = (int)getLineExtent(lineNum, tabStops, false);if (align == Alignment.ALIGN_OPPOSITE) {if (dir == DIR_LEFT_TO_RIGHT) {x = right - max + getIndentAdjust(lineNum, Alignment.ALIGN_RIGHT);} else {x = left - max + getIndentAdjust(lineNum, Alignment.ALIGN_LEFT);}} else { // Alignment.ALIGN_CENTERmax = max & ~1;x = ((right + left - max) >> 1) +getIndentAdjust(lineNum, Alignment.ALIGN_CENTER);}}paint.setHyphenEdit(getHyphen(lineNum));Directions directions = getLineDirections(lineNum);if (directions == DIRS_ALL_LEFT_TO_RIGHT && !mSpannedText && !hasTabOrEmoji) {//没有任何Emoji或者span的时候，直接调用Canvas来绘制文本
                canvas.drawText(buf, start, end, x, lbaseline, paint);} else {//当有Emoji或者Span的时候，交给TextLine类来绘制
                tl.set(paint, buf, start, end, dir, directions, hasTabOrEmoji, tabStops);tl.draw(canvas, x, ltop, lbaseline, lbottom);}paint.setHyphenEdit(0);}TextLine.recycle(tl);}

我们下面再来看看TextLine是如何绘制有特殊情况的文本的

void draw(Canvas c, float x, int top, int y, int bottom) {//判断是否有Tab或者Emojiif (!mHasTabs) {if (mDirections == Layout.DIRS_ALL_LEFT_TO_RIGHT) {drawRun(c, 0, mLen, false, x, top, y, bottom, false);return;}if (mDirections == Layout.DIRS_ALL_RIGHT_TO_LEFT) {drawRun(c, 0, mLen, true, x, top, y, bottom, false);return;}}float h = 0;int[] runs = mDirections.mDirections;RectF emojiRect = null;int lastRunIndex = runs.length - 2;//逐个绘制for (int i = 0; i < runs.length; i += 2) {int runStart = runs[i];int runLimit = runStart + (runs[i+1] & Layout.RUN_LENGTH_MASK);if (runLimit > mLen) {runLimit = mLen;}boolean runIsRtl = (runs[i+1] & Layout.RUN_RTL_FLAG) != 0;int segstart = runStart;for (int j = mHasTabs ? runStart : runLimit; j <= runLimit; j++) {int codept = 0;Bitmap bm = null;if (mHasTabs && j < runLimit) {codept = mChars[j];if (codept >= 0xd800 && codept < 0xdc00 && j + 1 < runLimit) {codept = Character.codePointAt(mChars, j);if (codept >= Layout.MIN_EMOJI && codept <= Layout.MAX_EMOJI) {//获取Emoji对应的图像bm = Layout.EMOJI_FACTORY.getBitmapFromAndroidPua(codept);} else if (codept > 0xffff) {++j;continue;}}}if (j == runLimit || codept == '\t' || bm != null) {//绘制文字h += drawRun(c, segstart, j, runIsRtl, x+h, top, y, bottom,i != lastRunIndex || j != mLen);if (codept == '\t') {h = mDir * nextTab(h * mDir);} else if (bm != null) {float bmAscent = ascent(j);float bitmapHeight = bm.getHeight();float scale = -bmAscent / bitmapHeight;float width = bm.getWidth() * scale;if (emojiRect == null) {emojiRect = new RectF();}//调整emoji图像绘制矩形emojiRect.set(x + h, y + bmAscent,x + h + width, y);//绘制Emoji图像c.drawBitmap(bm, null, emojiRect, mPaint);h += width;j++;}segstart = j + 1;}}}}

这样就完成了文本的绘制工作，简单地总结就是：分析整体文本—>拆分为段落—>计算整体段落的文本包括Span的测量信息—>对文本进行折行—>根据最终行数把文本测量信息保存—>绘制文本的行背景—>判断并获取文本种的Span和Emoji图像—>绘制最终的文本和图像。当然我们省略了一部分内容，比如段落文本方向，单行的文本排版方向的计算，实际的处理要更为复杂。

接下来我们来看一下在测量过程中出现的FontMetrics，这是一个Paint的静态内部类。主要用来储存文字排版的Y轴相关信息。内部仅包含ascent、descent、top、bottom、leading五个数值。如下图:

除了leading以外，其他的数值都是相对于每一行的baseline的，也就是说其他的数值需要加上对应行的baseline才能得到最终真实的坐标。

6.TextView接收软键盘输入

Android上的标准文本编辑控件是EditText，而EditText对软键盘输入的处理，却是在TextView内部实现的。Android为所有的View预留了一个接收软键盘输入的接口类，叫InputConnection。软键盘以InputConnection为桥梁把文字输入、文字修改、文字删除等传递给View。任意View只要重写onCheckIsTextEditor()并返回true，然后重写onCreateInputConnection(EditorInfo outAttrs)返回一个InputConnection的实例，便可以接收软键盘的输入。TextView的软键盘输入接收，是通过EditableInputConnection类来实现的。

public InputConnection onCreateInputConnection(EditorInfo outAttrs) {//判断是否处于可编辑状态if (onCheckIsTextEditor() && isEnabled()) {mEditor.createInputMethodStateIfNeeded();//设置输入法相关的信息outAttrs.inputType = getInputType();if (mEditor.mInputContentType != null) {outAttrs.imeOptions = mEditor.mInputContentType.imeOptions;outAttrs.privateImeOptions = mEditor.mInputContentType.privateImeOptions;outAttrs.actionLabel = mEditor.mInputContentType.imeActionLabel;outAttrs.actionId = mEditor.mInputContentType.imeActionId;outAttrs.extras = mEditor.mInputContentType.extras;} else {outAttrs.imeOptions = EditorInfo.IME_NULL;}if (focusSearch(FOCUS_DOWN) != null) {outAttrs.imeOptions |= EditorInfo.IME_FLAG_NAVIGATE_NEXT;}if (focusSearch(FOCUS_UP) != null) {outAttrs.imeOptions |= EditorInfo.IME_FLAG_NAVIGATE_PREVIOUS;}if ((outAttrs.imeOptions&EditorInfo.IME_MASK_ACTION)== EditorInfo.IME_ACTION_UNSPECIFIED) {if ((outAttrs.imeOptions&EditorInfo.IME_FLAG_NAVIGATE_NEXT) != 0) {//把软键盘的enter设为下一步outAttrs.imeOptions |= EditorInfo.IME_ACTION_NEXT;} else {//把软键盘的enter设为完成outAttrs.imeOptions |= EditorInfo.IME_ACTION_DONE;}if (!shouldAdvanceFocusOnEnter()) {outAttrs.imeOptions |= EditorInfo.IME_FLAG_NO_ENTER_ACTION;}}if (isMultilineInputType(outAttrs.inputType)) {outAttrs.imeOptions |= EditorInfo.IME_FLAG_NO_ENTER_ACTION;}outAttrs.hintText = mHint;//判断TextView内部文本是否可编辑if (mText instanceof Editable) {//返回EditableInputConnection实例InputConnection ic = new EditableInputConnection(this);outAttrs.initialSelStart = getSelectionStart();outAttrs.initialSelEnd = getSelectionEnd();outAttrs.initialCapsMode = ic.getCursorCapsMode(getInputType());return ic;}}return null;}

我们再来看一下EditableInputConnection里面的几个主要的方法：

首先是commitText方法，这个方法接收输入法输入的字符并提交给TextView。

public boolean commitText(CharSequence text, int newCursorPosition) {//判断TextView是否为空if (mTextView == null) {return super.commitText(text, newCursorPosition);}//判断文本是否Span，来自输入法的Span一般只有SuggestionSpan，SuggestionSpan携带了输入法的错别字修正的词if (text instanceof Spanned) {Spanned spanned = ((Spanned) text);SuggestionSpan[] spans = spanned.getSpans(0, text.length(), SuggestionSpan.class);mIMM.registerSuggestionSpansForNotification(spans);}mTextView.resetErrorChangedFlag();//提交字符boolean success = super.commitText(text, newCursorPosition);mTextView.hideErrorIfUnchanged();//返回是否成功return success;}

getEditable方法，这个方法并不是InputConnection接口的一部分，而是EditableInputConnection的父类BaseInputConnection的方法，用来获取一个可编辑对象，EditableInputConnection里面的所有修改都针对这个可编辑对象来做。

public Editable getEditable() {TextView tv = mTextView;if (tv != null) {//返回TextView的可编辑对象return tv.getEditableText();}return null;}

deleteSurroundingText方法，这个方法用来删除光标前后的内容：

public boolean deleteSurroundingText(int beforeLength, int afterLength) {if (DEBUG) Log.v(TAG, "deleteSurroundingText " + beforeLength+ " / " + afterLength);final Editable content = getEditable();if (content == null) return false;//批量删除标记
        beginBatchEdit();//获取当前已选择的文本的位置int a = Selection.getSelectionStart(content);int b = Selection.getSelectionEnd(content);if (a > b) {int tmp = a;a = b;b = tmp;}int ca = getComposingSpanStart(content);int cb = getComposingSpanEnd(content);if (cb < ca) {int tmp = ca;ca = cb;cb = tmp;}if (ca != -1 && cb != -1) {if (ca < a) a = ca;if (cb > b) b = cb;}int deleted = 0;//删除光标之前的文本if (beforeLength > 0) {int start = a - beforeLength;if (start < 0) start = 0;content.delete(start, a);deleted = a - start;}//删除光标之后的文本if (afterLength > 0) {b = b - deleted;int end = b + afterLength;if (end > content.length()) end = content.length();content.delete(b, end);}//结束批量编辑
        endBatchEdit();return true;}

commitCompletion和commitCorrection方法，即是用来补全单词和修正错别字的方法，这两个方法内部都是调用TextView对应的方法来实现的。

public boolean commitCompletion(CompletionInfo text) {if (DEBUG) Log.v(TAG, "commitCompletion " + text);mTextView.beginBatchEdit();mTextView.onCommitCompletion(text);mTextView.endBatchEdit();return true;}@Overridepublic boolean commitCorrection(CorrectionInfo correctionInfo) {if (DEBUG) Log.v(TAG, "commitCorrection" + correctionInfo);mTextView.beginBatchEdit();mTextView.onCommitCorrection(correctionInfo);mTextView.endBatchEdit();return true;}

8.总结

一个展示文本+文本编辑器功能的控件需要做的事情很多，要对文本进行排版、处理不同的段落风格、处理段落内的不同emoji和span、进行折行计算，然后还需要做文本编辑、文本选择等。而TextView把这些事情明确分工给不同的类。这样不仅仅把复杂问题拆分成了一个个简单的小功能，同时也大大增加了可扩展性。