android实现富文本
android要实现富文本有一下几种方法：
- Spannable
- Html.fromHtml
- 第三方库（RichText） GitHub地址：https://github.com/zzhoujay/RichText
这里简单分析一下SpannableUtils和Html.fromHtml的实现
一、SpannableStringBuilder分析
要用Spannable离不开SpannableStringBuilder
首先看他的源码：实现GraphicsOperations接口，实现此接口CharSequence可以快速绘制/测量/宽度
public class SpannableStringBuilder implements CharSequence, GetChars, Spannable, Editable,
Appendable, GraphicsOperations {
SpannableStringBuilder有一个setSpan方法，作用是设置Spannable
为什么TextView设置text为Spannable就可以实现富文本呢？
再看看TextView的setText()方法
private void setText(CharSequence text, BufferType type,
boolean notifyBefore, int oldlen) {
mTextFromResource = false;
if (text == null) {
text = "";
}
// If suggestions are not enabled, remove the suggestion spans from the text
if (!isSuggestionsEnabled()) {
text = removeSuggestionSpans(text);
}
if (!mUserSetTextScaleX) mTextPaint.setTextScaleX(1.0f);
if (text instanceof Spanned
&& ((Spanned) text).getSpanStart(TextUtils.TruncateAt.MARQUEE) >= 0) {
if (ViewConfiguration.get(mContext).isFadingMarqueeEnabled()) {
setHorizontalFadingEdgeEnabled(true);
mMarqueeFadeMode = MARQUEE_FADE_NORMAL;
} else {
setHorizontalFadingEdgeEnabled(false);
mMarqueeFadeMode = MARQUEE_FADE_SWITCH_SHOW_ELLIPSIS;
}
setEllipsize(TextUtils.TruncateAt.MARQUEE);
}
int n = mFilters.length;
for (int i = 0; i < n; i++) {
CharSequence out = mFilters[i].filter(text, 0, text.length(), EMPTY_SPANNED, 0, 0);
if (out != null) {
text = out;
}
}
if (notifyBefore) {
if (mText != null) {
oldlen = mText.length();
sendBeforeTextChanged(mText, 0, oldlen, text.length());
} else {
sendBeforeTextChanged("", 0, 0, text.length());
}
}
boolean needEditableForNotification = false;
if (mListeners != null && mListeners.size() != 0) {
needEditableForNotification = true;
}
if (type == BufferType.EDITABLE || getKeyListener() != null
|| needEditableForNotification) {
createEditorIfNeeded();
mEditor.forgetUndoRedo();
Editable t = mEditableFactory.newEditable(text);
text = t;
setFilters(t, mFilters);
InputMethodManager imm = InputMethodManager.peekInstance();
if (imm != null) imm.restartInput(this);
} else if (type == BufferType.SPANNABLE || mMovement != null) {
text = mSpannableFactory.newSpannable(text);
} else if (!(text instanceof CharWrapper)) {
text = TextUtils.stringOrSpannedString(text);
}
if (mAutoLinkMask != 0) {
Spannable s2;
if (type == BufferType.EDITABLE || text instanceof Spannable) {
s2 = (Spannable) text;
} else {
s2 = mSpannableFactory.newSpannable(text);
}
if (Linkify.addLinks(s2, mAutoLinkMask)) {
text = s2;
type = (type == BufferType.EDITABLE) ? BufferType.EDITABLE : BufferType.SPANNABLE;
/*
* We must go ahead and set the text before changing the
* movement method, because setMovementMethod() may call
* setText() again to try to upgrade the buffer type.
*/
mText = text;
// Do not change the movement method for text that support text selection as it
// would prevent an arbitrary cursor displacement.
if (mLinksClickable && !textCanBeSelected()) {
setMovementMethod(LinkMovementMethod.getInstance());
}
}
}
mBufferType = type;
mText = text;
if (mTransformation == null) {
mTransformed = text;
} else {
mTransformed = mTransformation.getTransformation(text, this);
}
final int textLength = text.length();
if (text instanceof Spannable && !mAllowTransformationLengthChange) {
Spannable sp = (Spannable) text;
// Remove any ChangeWatchers that might have come from other TextViews.
final ChangeWatcher[] watchers = sp.getSpans(0, sp.length(), ChangeWatcher.class);
final int count = watchers.length;
for (int i = 0; i < count; i++) {
sp.removeSpan(watchers[i]);
}
if (mChangeWatcher == null) mChangeWatcher = new ChangeWatcher();
sp.setSpan(mChangeWatcher, 0, textLength, Spanned.SPAN_INCLUSIVE_INCLUSIVE
| (CHANGE_WATCHER_PRIORITY << Spanned.SPAN_PRIORITY_SHIFT));
if (mEditor != null) mEditor.addSpanWatchers(sp);
if (mTransformation != null) {
sp.setSpan(mTransformation, 0, textLength, Spanned.SPAN_INCLUSIVE_INCLUSIVE);
}
if (mMovement != null) {
mMovement.initialize(this, (Spannable) text);
/*
* Initializing the movement method will have set the
* selection, so reset mSelectionMoved to keep that from
* interfering with the normal on-focus selection-setting.
*/
if (mEditor != null) mEditor.mSelectionMoved = false;
}
}
if (mLayout != null) {
checkForRelayout();
}
sendOnTextChanged(text, 0, oldlen, textLength);
onTextChanged(text, 0, oldlen, textLength);
notifyViewAccessibilityStateChangedIfNeeded(AccessibilityEvent.CONTENT_CHANGE_TYPE_TEXT);
if (needEditableForNotification) {
sendAfterTextChanged((Editable) text);
} else {
// Always notify AutoFillManager - it will return right away if autofill is disabled.
notifyAutoFillManagerAfterTextChangedIfNeeded();
}
// SelectionModifierCursorController depends on textCanBeSelected, which depends on text
if (mEditor != null) mEditor.prepareCursorControllers();
}代码中很清晰的看到CharSequence为Spannable 时同样可添加到text中，具体它是怎么绘制这里就不分析，想了解的话可以看一下TextView的绘制。
二、Html.fromHtml分析
public static Spanned fromHtml(String source, Html.ImageGetter imageGetter,
Html.TagHandler tagHandler) {
//创建HTML解析器
Parser parser = new Parser();
try {
parser.setProperty(Parser.schemaProperty, HtmlParser.schema);
} catch (org.xml.sax.SAXNotRecognizedException e) {
// Should not happen.
throw new RuntimeException(e);
} catch (org.xml.sax.SAXNotSupportedException e) {
// Should not happen.
throw new RuntimeException(e);
}
//HTML数据转换成span
HtmlToSpannedConverter converter =
new HtmlToSpannedConverter(source, imageGetter, tagHandler,
parser);
return converter.convert();
} private void handleStartTag(String tag, Attributes attributes) {
if (tag.equalsIgnoreCase("br")) {
// We don't need to handle this. TagSoup will ensure that there's a for each
// so we can safely emite the linebreaks when we handle the close tag.
} else if (tag.equalsIgnoreCase("p")) {
handleP(mSpannableStringBuilder);
} else if (tag.equalsIgnoreCase("div")) {
handleP(mSpannableStringBuilder);
} else if (tag.equalsIgnoreCase("em")) {
start(mSpannableStringBuilder, new Bold());
} else if (tag.equalsIgnoreCase("b")) {
start(mSpannableStringBuilder, new Bold());
} else if (tag.equalsIgnoreCase("strong")) {
start(mSpannableStringBuilder, new Italic());
} else if (tag.equalsIgnoreCase("cite")) {
start(mSpannableStringBuilder, new Italic());
} else if (tag.equalsIgnoreCase("dfn")) {
start(mSpannableStringBuilder, new Italic());
} else if (tag.equalsIgnoreCase("i")) {
start(mSpannableStringBuilder, new Italic());
} else if (tag.equalsIgnoreCase("big")) {
start(mSpannableStringBuilder, new Big());
} else if (tag.equalsIgnoreCase("small")) {
start(mSpannableStringBuilder, new Small());
} else if (tag.equalsIgnoreCase("font")) {
startFont(mSpannableStringBuilder, attributes);
} else if (tag.equalsIgnoreCase("blockquote")) {
handleP(mSpannableStringBuilder);
start(mSpannableStringBuilder, new Blockquote());
}
*****省略代码
}
private static void startFont(SpannableStringBuilder text,
Attributes attributes) {
String color = attributes.getValue("", "color");
String face = attributes.getValue("", "face");
int len = text.length();
text.setSpan(new Font(color, face), len, len, Spannable.SPAN_MARK_MARK);
}原来Html.fromHtml也是通过spannable来实现富文本
问题延伸：
若文本中存在：右到左的语言（如阿拉伯语），这时候会导致文本顺序错乱
解决方案：
在文本最前面创建一个透明占位符：
/**
* 消息占位符
*
* @param msg
* @return
*/
public static SpannableStringBuilder placeHolderTextSp(String msg) {
final SpannableStringBuilder mStringBuilder = new SpannableStringBuilder(msg);
mStringBuilder.setSpan(new ForegroundColorSpan(Color.TRANSPARENT), 0, msg.length(), Spanned.SPAN_EXCLUSIVE_EXCLUSIVE);
return mStringBuilder;
}