編輯：關於Android編程
看段Android官方的簡介
Class Overview
Displays text to the user and optionally allows them to edit it. A TextView is a complete text editor, however the basic class is configured to not allow editing; see EditText for a subclass that configures the text view for editing.
To allow users to copy some or all of the TextView’s value and paste it somewhere else, set the XML attribute android:textIsSelectable to “true” or call setTextIsSelectable(true). The textIsSelectable flag allows users to make selection gestures in the TextView, which in turn triggers the system’s built-in copy/paste controls.
TextView主要用於給用戶展示文字，並且讓用戶隨意的可以對文字進行編輯。但是普通的TextView是不允許用來編輯的，只有EditText才可以。
如果在XML中設置了android:textIsSelectable 或者在Java代碼中調用了setTextIsSelectable(true)方法，就可以允許對TextView的部分或者全部文字進行復制，然後粘貼到其他地方。textIsSelectable 標簽是允許用戶在TextView上使用選擇手勢。
順便提下，大家如果想看API文檔的話，可以在
file:///E:/AndroidEnvironment/SDK/docs/reference/android/widget/TextView.html
你安裝SDK的目錄下/docs/reference/android/widget/TextView.html找到你想要查看控件的API
一般自定義view都需要滿足2個條件，展示我們期望的UI，正確傳遞或者接收處理點擊或者觸摸事件。
所以對於TextView的分析也從這三個地方展開
繪制過程
onMeasure()
onLayout()
onDraw()
事件接收處理
由於TextView繼承於View，所以主要分析onTouchEvent()方法就好了
一些和TextView有關的類如何實現，比如Spans，Layout,接收輸入的InputConnection
本文基於Android SDK API-19的基礎上分析
在分析之前，我們先來看個小彩蛋
![這裡寫圖片描述](https://android.yunyiwangluo.com/Android/UploadFiles_5356/201702/2017022309502228.png "\")
不知道這個//TODO是某個哥們自問自答呢，還是別人在對他的代碼review的時候給注上的
再分析之前，順便拋出一個問題供大家思考下，maxEms這個屬性到底是用來做什麼的？
網上的答案五花八門，在下面的源碼中我們可以一窺究竟。
首先來看onMeasure()部分代碼
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
//首先接收到父容器傳遞過來的MeasureSpec
//關於MeasureSpec是如果計算的，可以查看之前的博文
//[LinearLayout源碼解析](http://blog.csdn.net/wz249863091/article/details/51702980)
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
int width;
int height;
//這裡解釋下什麼叫作boring
//A BoringLayout is a very simple Layout implementation for text that
//fits on a single line and is all left-to-right characters.
//boring就是指布局所用的文本裡面不包含任何Span，所有的文本方向都是從左到右的布局，
//並且僅需一行就能顯示完全的布局
//這裡將TextView和Hint的boring初始化
BoringLayout.Metrics boring = UNKNOWN_BORING;
BoringLayout.Metrics hintBoring = UNKNOWN_BORING;
//獲得文字的排序方式。一共有6種
//FIRSTSTRONG_RTL,FIRSTSTRONG_LTR Unicode雙向算法
//ANYRTL_LTR
//LTR,RTL 左到右或者右到左排序
//LOCALE
//first strong算法 有興趣的同學可以自行研究下，一般情況下都是左到右排序
if (mTextDir == null) {
mTextDir = getTextDirectionHeuristic();
}
int des = -1;
boolean fromexisting = false;
//如果寬度是精確模式了，那就那父容器給的寬度當作當前TextView的寬度
if (widthMode == MeasureSpec.EXACTLY) {
// Parent has told us how big to be. So be it.
width = widthSize;
} else {
if (mLayout != null && mEllipsize == null) {
//首先計算下期望值，如果行數大於1就返回-1，否則返回單行寬度
//具體代碼貼在下面
des = desired(mLayout);
}
//如果小於0，即行數大於1行，就去判斷是否是boring
//isBoring()這個方法也在下面有詳細分析，大家可以閱讀後
//再回過頭來看看
if (des < 0) {
boring = BoringLayout.isBoring(mTransformed, mTextPaint, mTextDir, mBoring);
//閱讀過下面的方法，就知道boring是一個Metrics矩陣，
//包含了文本樣式 width, ascent, and descen等
if (boring != null) {
mBoring = boring;
}
} else {
fromexisting = true;
}
//再次判斷boring是否為null
//這裡有2種情況會為null
//1.des>0,即Textview只顯示一行文字，就不會去計算boring的值了
//2.Textview包含的內容不是boring的，多行，有縮進或者包含spann
if (boring == null || boring == UNKNOWN_BORING) {
//如果是多行文字的
if (des < 0) {
des = (int) FloatMath.ceil(Layout.getDesiredWidth(mTransformed, mTextPaint));
}
width = des;
} else {
//如果是boring模式的就很簡單了，把boring剛測量得到的width賦給TextView
//即文字的寬度
width = boring.width;
}
//這裡就是加上Drawable的寬度
final Drawables dr = mDrawables;
if (dr != null) {
width = Math.max(width, dr.mDrawableWidthTop);
width = Math.max(width, dr.mDrawableWidthBottom);
}
//這裡會再計算一次hint的寬度，流程和上面的一模一樣，就不再重復了
if (mHint != null) {
int hintDes = -1;
int hintWidth;
if (mHintLayout != null && mEllipsize == null) {
hintDes = desired(mHintLayout);
}
if (hintDes < 0) {
hintBoring = BoringLayout.isBoring(mHint, mTextPaint, mTextDir, mHintBoring);
if (hintBoring != null) {
mHintBoring = hintBoring;
}
}
if (hintBoring == null || hintBoring == UNKNOWN_BORING) {
if (hintDes < 0) {
hintDes = (int) FloatMath.ceil(Layout.getDesiredWidth(mHint, mTextPaint));
}
hintWidth = hintDes;
} else {
hintWidth = hintBoring.width;
}
if (hintWidth > width) {
width = hintWidth;
}
}
//這裡再加上padding的值
//順便說一句，padding的值是在子view裡自己算的
//margin的值是在父容器裡算的
//在自定義view和viewgroup的時候，千萬注意
//width += getCompoundPaddingLeft() + getCompoundPaddingRight();
//在這，就能解答之前的疑問，EMS這個屬性到底是干嘛的
//如果我們設置了maxEms這個屬性
//public void setMaxEms(int maxems) {
// mMaxWidth = maxems;
//mMaxWidthMode = EMS;
//requestLayout();
//invalidate();
//}
//mMaxWidth的值就是EMS的值
//如果設置了maxLength，那麼mMaxWidth的值就是maxWidth的值
//然後再來看如果是EMS模式
//Math.min(width, mMaxWidth * getLineHeight())
//我們的最大寬度就是EMS的值乘以lineHeight的值
//而lineHeight的值 官方是這麼解釋的
//return the height of one standard line in pixels
//public int getLineHeight() {
// return FastMath.round(mTextPaint.getFontMetricsInt(null) *
//mSpacingMult + mSpacingAdd);
//就是行間距乘以字體大小
//所以在不同行間距和字體大小下，EMS所產生的mMaxWidth也是不同的
}
if (mMaxWidthMode == EMS) {
width = Math.min(width, mMaxWidth * getLineHeight());
} else {
width = Math.min(width, mMaxWidth);
}
if (mMinWidthMode == EMS) {
width = Math.max(width, mMinWidth * getLineHeight());
} else {
width = Math.max(width, mMinWidth);
}
// Check against our minimum width
width = Math.max(width, getSuggestedMinimumWidth());
//如果是Wrap的，會在父容器給的size和實際最大size中取小的
if (widthMode == MeasureSpec.AT_MOST) {
width = Math.min(widthSize, width);
}
}
//最後根據上面計算得到的size-padding的值就是我們單行text實際可以展示的大小
int want = width - getCompoundPaddingLeft() - getCompoundPaddingRight();
int unpaddedWidth = want;
//如果是水平方向可以scroll的，那麼寬度就是無限大了，因為可以滑嘛
if (mHorizontallyScrolling) want = VERY_WIDE;
int hintWant = want;
int hintWidth = (mHintLayout == null) ? hintWant : mHintLayout.getWidth();
//這裡會牽扯到makeNewLayout（...）這個方法，也會在下面得到詳細分析
if (mLayout == null) {
makeNewLayout(want, hintWant, boring, hintBoring,
width - getCompoundPaddingLeft() - getCompoundPaddingRight(), false);
} else {
final boolean layoutChanged = (mLayout.getWidth() != want) ||
(hintWidth != hintWant) ||
(mLayout.getEllipsizedWidth() !=
width - getCompoundPaddingLeft() - getCompoundPaddingRight());
final boolean widthChanged = (mHint == null) &&
(mEllipsize == null) &&
(want > mLayout.getWidth()) &&
(mLayout instanceof BoringLayout || (fromexisting && des >= 0 && des <= want));
final boolean maximumChanged = (mMaxMode != mOldMaxMode) || (mMaximum != mOldMaximum);
if (layoutChanged || maximumChanged) {
if (!maximumChanged && widthChanged) {
mLayout.increaseWidthTo(want);
} else {
makeNewLayout(want, hintWant, boring, hintBoring,
width - getCompoundPaddingLeft() - getCompoundPaddingRight(), false);
}
} else {
// Nothing has changed
}
}
//然後開始計算高度，這部分代碼相對於寬度，就簡單的多了
//如果是精確模式，那麼高度就等於TextView要求的高度
if (heightMode == MeasureSpec.EXACTLY) {
// Parent has told us how big to be. So be it.
height = heightSize;
mDesiredHeightAtMeasure = -1;
} else {
//計算下想要的高度
//這裡邏輯比較簡單
//只需要比較下文字高度和hint的高度，取大的那個值就可以了
//至於文字高度和hint高度的計算：
//1.當行高度*行數
//如果設置了Drawable的話，比較2個值得大小，取大的
//如果設置了maxLines或者maxHeight計算下當前高度有沒超過最大高度，超過的話取最大高度
//如果設置了minLines或者minHeight的話，比較下當前高度和最小高度，取小的
int desired = getDesiredHeight();
height = desired;
mDesiredHeightAtMeasure = desired;
//如果是warp模式，就取父容器算的和實際需要小的值
if (heightMode == MeasureSpec.AT_MOST) {
height = Math.min(desired, heightSize);
}
}
int unpaddedHeight = height - getCompoundPaddingTop() - getCompoundPaddingBottom();
if (mMaxMode == LINES && mLayout.getLineCount() > mMaximum) {
unpaddedHeight = Math.min(unpaddedHeight, mLayout.getLineTop(mMaximum));
}
/*
* We didn't let makeNewLayout() register to bring the cursor into view,
* so do it here if there is any possibility that it is needed.
*/
//這裡就是處理下滾動條
if (mMovement != null ||
mLayout.getWidth() > unpaddedWidth ||
mLayout.getHeight() > unpaddedHeight) {
registerForPreDraw();
} else {
scrollTo(0, 0);
}
setMeasuredDimension(width, height);
}
desire()方法
private static int desired(Layout layout) {
//首先獲得行數
int n = layout.getLineCount();
CharSequence text = layout.getText();
float max = 0;
// if any line was wrapped, we can't use it.
// but it's ok for the last line not to have a newline
//如果行數大於1，就返回-1
for (int i = 0; i < n - 1; i++) {
if (text.charAt(layout.getLineEnd(i) - 1) != '\n')
return -1;
}
//將寬度和0比較，如果大於0，就取寬度
for (int i = 0; i < n; i++) {
max = Math.max(max, layout.getLineWidth(i));
}
return (int) FloatMath.ceil(max);
}
isBoring()實現
/**
* Returns null if not boring; the width, ascent, and descent in the
* provided Metrics object (or a new one if the provided one was null)
* if boring.
* @hide
*/
//如果是boring模式的就返回Metrics object，不是就返回null
//什麼是boring模式 開頭已經講過了，根據他的定義也不難猜到這個方法有幾個條件判斷
public static Metrics isBoring(CharSequence text, TextPaint paint,
TextDirectionHeuristic textDir, Metrics metrics) {
//首先獲得一個char型數組，這裡值得一提的是TextUtils.obtain(500)這個方法
//在我們自己寫代碼的時候也可以借鑒，減少內存的交換
//這裡把字符串分成了以500個字符為一組
char[] temp = TextUtils.obtain(500);
int length = text.length();
boolean boring = true;
outer:
for (int i = 0; i < length; i += 500) {
int j = i + 500;
//首先判斷是否當前組的字符串是否有500個
//沒有就取實際長度
if (j > length)
j = length;
//根據長度取出字符串的子串
TextUtils.getChars(text, i, j, temp, 0);
//子串的長度
int n = j - i;
//遍歷整個子串
for (int a = 0; a < n; a++) {
char c = temp[a];
//這裡有3個條件
//1.如果有換行 \n
//2.如果有縮進 \t
//3.如果不是LTR 左到右模式
//如果有其中1種情況，就視為不是boring模式
if (c == '\n' || c == '\t' || c >= FIRST_RIGHT_TO_LEFT) {
boring = false;
break outer;
}
}
if (textDir != null && textDir.isRtl(temp, 0, n)) {
boring = false;
break outer;
}
}
//把temp回收
TextUtils.recycle(temp);
//如果包含了span，那麼也視為不是boring模式
if (boring && text instanceof Spanned) {
Spanned sp = (Spanned) text;
Object[] styles = sp.getSpans(0, length, ParagraphStyle.class);
if (styles.length > 0) {
boring = false;
}
}
//如果是boring模式，那就返回Metrics對象
if (boring) {
Metrics fm = metrics;
//首先判斷傳進來的Metrics是否為空，如果為空，就新建一個對象
if (fm == null) {
fm = new Metrics();
}
//設置TextLine，文本樣式
TextLine line = TextLine.obtain();
line.set(paint, text, 0, length, Layout.DIR_LEFT_TO_RIGHT,
Layout.DIRS_ALL_LEFT_TO_RIGHT, false, null);
fm.width = (int) FloatMath.ceil(line.metrics(fm));
TextLine.recycle(line);
return fm;
} else {
return null;
}
}
makeNewLayout（…）方法
/**
* The width passed in is now the desired layout width,
* not the full view width with padding.
* {@hide}
*/
protected void makeNewLayout(int wantWidth, int hintWidth,
BoringLayout.Metrics boring,
BoringLayout.Metrics hintBoring,
int ellipsisWidth, boolean bringIntoView) {
//首先，如果有跑馬燈效果，先把跑馬燈停了
stopMarquee();
// Update "old" cached values
//把最大寬度和最大行數先保存起來
mOldMaximum = mMaximum;
mOldMaxMode = mMaxMode;
mHighlightPathBogus = true;
if (wantWidth < 0) {
wantWidth = 0;
}
if (hintWidth < 0) {
hintWidth = 0;
}
//獲得對其方式
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);
//是否需要省略號，這個值是根據我們在XML中寫的Ellipsize來定的
boolean shouldEllipsize = mEllipsize != null && getKeyListener() == null;
//省略號主要分開始位置，中間位置和結束位置3個常規位置
//還有跑馬燈這種非常規位置
//mMarqueeFadeMode分為3種效果
//MARQUEE_FADE_NORMAL
//MARQUEE_FADE_SWITCH_SHOW_ELLIPSIS
//MARQUEE_FADE_SWITCH_SHOW_FADE
//這裡判斷是否為常規的marquee
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;
}
//獲得排序方向，一般是LTR 左到右
if (mTextDir == null) {
mTextDir = getTextDirectionHeuristic();
}
//獲得一個singleLayout,這個方法在下面分析
mLayout = makeSingleLayout(wantWidth, boring, ellipsisWidth, alignment, shouldEllipsize,
effectiveEllipsize, effectiveEllipsize == mEllipsize);
//如果是非常規的跑馬燈，需要再創建一個mSavedMarqueeModeLayout，在播放跑馬燈的時候
//把這個layout作為mLayout
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;
//如果有默認提示，還要計算hintLayout
if (mHint != null) {
//如果有省略號，那麼提示文字的寬度就是實際能分配的寬度
if (shouldEllipsize) hintWidth = wantWidth;
//這段代碼看著眼熟不？就是剛在onLayout()裡分析的那段
if (hintBoring == UNKNOWN_BORING) {
//如果hint只是單行，無縮進，無spann那麼就是把boring的矩陣賦值hintBoring
hintBoring = BoringLayout.isBoring(mHint, mTextPaint, mTextDir,
mHintBoring);
if (hintBoring != null) {
mHintBoring = hintBoring;
}
}
//這裡有3層if嵌套，如果不仔細看，很容易暈
//主要分為3層邏輯
//最外層當前的hint是否是boring的，即單行無span
//第二層主要判斷是否需要省略號，當前hint實際需要寬度是否大於計算得到的寬度
//如果仔細看了前面分析可以知道wantWidth,hintWidth和ellipsisWidth
//其實都是一個值 width-paddingleft-paddingRight
//即實際可以提供的寬度
//然後最裡面那層就是判斷mSavedHintLayout是否為null
//如果為null就make一個新的，不為null就把老的值更新
//先看如果是boring模式
if (hintBoring != null) {
//首先判斷hint需要寬度是否小於實際給的寬度
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;
//如果不滿足上面的要求
//再判斷是否需要省略號，並且需要寬度是否小於實際給的寬度
//如果進入這個if條件的，都是設置了省略號，但是不需要顯示的
} 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);
}
//如果還是不滿足
//到了這就應該是需要省略號，但是需要寬度是大於實際給的寬度
//那麼就應該顯示省略號了
} else if (shouldEllipsize) {
mHintLayout = new StaticLayout(mHint,
0, mHint.length(),
mTextPaint, hintWidth, alignment, mTextDir, mSpacingMult,
mSpacingAdd, mIncludePad, mEllipsize,
ellipsisWidth, mMaxMode == LINES ? mMaximum : Integer.MAX_VALUE);
} else {
mHintLayout = new StaticLayout(mHint, mTextPaint,
hintWidth, alignment, mTextDir, mSpacingMult, mSpacingAdd,
mIncludePad);
}
//到了這開始處理不是boring的hint
//如果不是boring的，需要省略號
} else if (shouldEllipsize) {
mHintLayout = new StaticLayout(mHint,
0, mHint.length(),
mTextPaint, hintWidth, alignment, mTextDir, mSpacingMult,
mSpacingAdd, mIncludePad, mEllipsize,
ellipsisWidth, mMaxMode == LINES ? mMaximum : Integer.MAX_VALUE);
//如果不是boring的，不需要省略號
} else {
mHintLayout = new StaticLayout(mHint, mTextPaint,
hintWidth, alignment, mTextDir, mSpacingMult, mSpacingAdd,
mIncludePad);
}
}
//如果文字方向發生變化了，就重新注冊OnPreDrawListener
//OnPreDrawListener回調的時機是
//即將繪制視圖樹時執行的回調函數。這時所有的視圖都測量完成並確定了框架。 客戶端可以
//使用該方法來調整滾動邊框，甚至可以在繪制之前請求新的布局。
if (bringIntoView || (testDirChange && oldDir != mLayout.getParagraphDirection(0))) {
registerForPreDraw();
}
//這裡開始處理跑馬燈
//如果需要播放跑馬燈
if (mEllipsize == TextUtils.TruncateAt.MARQUEE) {
if (!compressText(ellipsisWidth)) {
final int height = mLayoutParams.height;
// If the size of the view does not depend on the size of the text, try to
// start the marquee immediately
//這裡值得稍微留意是
//如果當前TextView的寬度不需要依賴內部文字的話
//直接就可以播放跑馬燈了
if (height != LayoutParams.WRAP_CONTENT && height != LayoutParams.MATCH_PARENT) {
startMarquee();
} else {
// Defer the start of the marquee until we know our width (see setFrame())
mRestartMarquee = true;
}
}
}
// CursorControllers need a non-null mLayout
if (mEditor != null) mEditor.prepareCursorControllers();
}
分析到這onMeasure()就結束了
讓我們來看下onLayout()是如何實現的
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
//這裡主要的邏輯就是bringPointIntoView
if (mDeferScroll >= 0) {
int curs = mDeferScroll;
mDeferScroll = -1;
bringPointIntoView(Math.min(curs, mText.length()));
}
}
最後我們看下onDraw()的實現，看看文字是如何被繪制到屏幕上的
@Override
protected void onDraw(Canvas canvas) {
restartMarqueeIfNeeded();
// Draw the background for this view
super.onDraw(canvas);
//首先先計算padding和scorll的值
//還有判斷是LTR還是RTS方向
final int compoundPaddingLeft = getCompoundPaddingLeft();
final int compoundPaddingTop = getCompoundPaddingTop();
final int compoundPaddingRight = getCompoundPaddingRight();
final int compoundPaddingBottom = getCompoundPaddingBottom();
final int scrollX = mScrollX;
final int scrollY = mScrollY;
final int right = mRight;
final int left = mLeft;
final int bottom = mBottom;
final int top = mTop;
final boolean isLayoutRtl = isLayoutRtl();
final int offset = getHorizontalOffsetForDrawables();
final int leftOffset = isLayoutRtl ? 0 : offset;
final int rightOffset = isLayoutRtl ? offset : 0 ;
//如果有drawable，那麼先繪制draw
final Drawables dr = mDrawables;
if (dr != null) {
/*
* Compound, not extended, because the icon is not clipped
* if the text height is smaller.
*/
//計算水平和垂直空間
int vspace = bottom - top - compoundPaddingBottom - compoundPaddingTop;
int hspace = right - left - compoundPaddingRight - compoundPaddingLeft;
// IMPORTANT: The coordinates computed are also used in invalidateDrawable()
// Make sure to update invalidateDrawable() when changing this code.
//開始繪制DrawableLeft
if (dr.mDrawableLeft != null) {
//這裡簡單介紹下canvas.save()和canvas.restore()
//調用save之後，可以對canvas進行平移和旋轉，確定新的原點然後繪制
//等繪制完了之後，可以把原點恢復原狀
canvas.save();
canvas.translate(scrollX + mPaddingLeft + leftOffset,
scrollY + compoundPaddingTop +
(vspace - dr.mDrawableHeightLeft) / 2);
//個人認為TextView整個控件寫了十分出彩
//TextView需要繪制背景，文字，Drawable
//谷歌在處理這個控件的時候，把不同的事交給不同的類去完成，充分解耦
//文字部分用Editor和layout處理
//圖片部分用Drawable自行繪制
//整個TextView其實只是充當了容器作用
dr.mDrawableLeft.draw(canvas);
canvas.restore();
}
// IMPORTANT: The coordinates computed are also used in invalidateDrawable()
// Make sure to update invalidateDrawable() when changing this code.
if (dr.mDrawableRight != null) {
canvas.save();
canvas.translate(scrollX + right - left - mPaddingRight
- dr.mDrawableSizeRight - rightOffset,
scrollY + compoundPaddingTop + (vspace - dr.mDrawableHeightRight) / 2);
dr.mDrawableRight.draw(canvas);
canvas.restore();
}
// IMPORTANT: The coordinates computed are also used in invalidateDrawable()
// Make sure to update invalidateDrawable() when changing this code.
if (dr.mDrawableTop != null) {
canvas.save();
canvas.translate(scrollX + compoundPaddingLeft +
(hspace - dr.mDrawableWidthTop) / 2, scrollY + mPaddingTop);
dr.mDrawableTop.draw(canvas);
canvas.restore();
}
// IMPORTANT: The coordinates computed are also used in invalidateDrawable()
// Make sure to update invalidateDrawable() when changing this code.
if (dr.mDrawableBottom != null) {
canvas.save();
canvas.translate(scrollX + compoundPaddingLeft +
(hspace - dr.mDrawableWidthBottom) / 2,
scrollY + bottom - top - mPaddingBottom - dr.mDrawableSizeBottom);
dr.mDrawableBottom.draw(canvas);
canvas.restore();
}
}
int color = mCurTextColor;
//如果layout為null，通過剛分析的makeNewLayout()方法，再去獲得一個Layout
if (mLayout == null) {
assumeLayout();
}
Layout layout = mLayout;
//如果當前沒有文字，並且設置了hint，那麼就顯示hint
if (mHint != null && mText.length() == 0) {
if (mHintTextColor != null) {
color = mCurHintTextColor;
}
layout = mHintLayout;
}
mTextPaint.setColor(color);
mTextPaint.drawableState = getDrawableState();
canvas.save();
//感覺寫TextView控件這位工程師對自己寫的代碼不是很自信，留下了很多疑問
//也許是Review之後忘了刪除了，自己看的時候有時候會和有代入感，感覺在給別人review代碼
/* Would be faster if we didn't have to do this. Can we chop the
(displayable) text so that we don't need to do this ever?
*/
int extendedPaddingTop = getExtendedPaddingTop();
int extendedPaddingBottom = getExtendedPaddingBottom();
final int vspace = mBottom - mTop - compoundPaddingBottom - compoundPaddingTop;
final int maxScrollY = mLayout.getHeight() - vspace;
//計算矩陣的上下左右4個坐標值
float clipLeft = compoundPaddingLeft + scrollX;
float clipTop = (scrollY == 0) ? 0 : extendedPaddingTop + scrollY;
float clipRight = right - left - compoundPaddingRight + scrollX;
float clipBottom = bottom - top + scrollY -
((scrollY == maxScrollY) ? 0 : extendedPaddingBottom);
//這裡是處理文字陰影
if (mShadowRadius != 0) {
clipLeft += Math.min(0, mShadowDx - mShadowRadius);
clipRight += Math.max(0, mShadowDx + mShadowRadius);
clipTop += Math.min(0, mShadowDy - mShadowRadius);
clipBottom += Math.max(0, mShadowDy + mShadowRadius);
}
//在畫布中裁剪出剛計算出來的矩陣大小
canvas.clipRect(clipLeft, clipTop, clipRight, clipBottom);
int voffsetText = 0;
int voffsetCursor = 0;
// translate in by our padding
/* shortcircuit calling getVerticaOffset() */
if ((mGravity & Gravity.VERTICAL_GRAVITY_MASK) != Gravity.TOP) {
voffsetText = getVerticalOffset(false);
voffsetCursor = getVerticalOffset(true);
}
canvas.translate(compoundPaddingLeft, extendedPaddingTop + voffsetText);
final int layoutDirection = getLayoutDirection();
final int absoluteGravity = Gravity.getAbsoluteGravity(mGravity, layoutDirection);
//如果有跑馬燈，並且不是MARQUEE_FADE_SWITCH_SHOW_ELLIPSIS模式的話
if (mEllipsize == TextUtils.TruncateAt.MARQUEE &&
mMarqueeFadeMode != MARQUEE_FADE_SWITCH_SHOW_ELLIPSIS) {
//如果當前只有1行顯示，並且不是SingleLine的，也不是Gravity.LEFT
if (!mSingleLine && getLineCount() == 1 && canMarquee() &&
(absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK) != Gravity.LEFT) {
final int width = mRight - mLeft;
final int padding = getCompoundPaddingLeft() + getCompoundPaddingRight();
//dx值就是layout的寬度減去實際寬度再減去padding的值，主要是給RTL模式計算偏移量
final float dx = mLayout.getLineRight(0) - (width - padding);
canvas.translate(isLayoutRtl ? -dx : +dx, 0.0f);
}
if (mMarquee != null && mMarquee.isRunning()) {
final float dx = -mMarquee.getScroll();
canvas.translate(isLayoutRtl ? -dx : +dx, 0.0f);
}
}
final int cursorOffsetVertical = voffsetCursor - voffsetText;
//這裡終於開始繪制文字了
Path highlight = getUpdatedHighlightPath();
//如果是EditText的就交給mEditor繪制，普通TextView，就交給layout處理
if (mEditor != null) {
mEditor.onDraw(canvas, layout, highlight, mHighlightPaint, cursorOffsetVertical);
} else {
layout.draw(canvas, highlight, mHighlightPaint, cursorOffsetVertical);
}
if (mMarquee != null && mMarquee.shouldDrawGhost()) {
final int dx = (int) mMarquee.getGhostOffset();
canvas.translate(isLayoutRtl ? -dx : dx, 0.0f);
layout.draw(canvas, highlight, mHighlightPaint, cursorOffsetVertical);
}
canvas.restore();
}
上文中主要分析了TextView的整個繪制流程，主要是從過程的角度分析了幾個比較重要的階段。
在下一篇TextView源碼分析（二）中會具體分析Layout,Editor和Drawable是如何完成繪制，排版。
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