一年多以前看過(guò)源碼，感覺(jué)了解比較透徹了，長(zhǎng)時(shí)間不經(jīng)大腦思考，靠曾經(jīng)總結(jié)的經(jīng)驗(yàn)使用inflate方法，突然發(fā)現(xiàn)不知道什么時(shí)候忘記其中的原理了，上網(wǎng)查了一些資料，還各有不同，反而把我搞糊涂了，還是自己看源碼來(lái)的實(shí)在。

inflate有多個(gè)重載方法，不過(guò)殊途同歸，最后的歸宿都是下面這個(gè)家伙：

public View inflate(XmlPullParser parser, @Nullable ViewGroup root, boolean attachToRoot) {synchronized (mConstructorArgs) {Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");final Context inflaterContext = mContext;final AttributeSet attrs = Xml.asAttributeSet(parser);Context lastContext = (Context) mConstructorArgs[0];mConstructorArgs[0] = inflaterContext;View result = root;try {// Look for the root node.int type;while ((type = parser.next()) != XmlPullParser.START_TAG &&type != XmlPullParser.END_DOCUMENT) {// Empty }if (type != XmlPullParser.START_TAG) {throw new InflateException(parser.getPositionDescription()+ ": No start tag found!");}final String name = parser.getName();if (DEBUG) {System.out.println("**************************");System.out.println("Creating root view: "+ name);System.out.println("**************************");}if (TAG_MERGE.equals(name)) {if (root == null || !attachToRoot) {throw new InflateException("<merge /> can be used only with a valid "+ "ViewGroup root and attachToRoot=true");}rInflate(parser, root, inflaterContext, attrs, false);} else {// Temp is the root view that was found in the xmlfinal View temp = createViewFromTag(root, name, inflaterContext, attrs);ViewGroup.LayoutParams params = null;if (root != null) {if (DEBUG) {System.out.println("Creating params from root: " +root);}// Create layout params that match root, if suppliedparams = root.generateLayoutParams(attrs);if (!attachToRoot) {// Set the layout params for temp if we are not// attaching. (If we are, we use addView, below) temp.setLayoutParams(params);}}if (DEBUG) {System.out.println("-----> start inflating children");}// Inflate all children under temp against its context.rInflateChildren(parser, temp, attrs, true);if (DEBUG) {System.out.println("-----> done inflating children");}// We are supposed to attach all the views we found (int temp)// to root. Do that now.if (root != null && attachToRoot) {root.addView(temp, params);}// Decide whether to return the root that was passed in or the// top view found in xml.if (root == null || !attachToRoot) {result = temp;}}} catch (XmlPullParserException e) {InflateException ex = new InflateException(e.getMessage());ex.initCause(e);throw ex;} catch (Exception e) {InflateException ex = new InflateException(parser.getPositionDescription()+ ": " + e.getMessage());ex.initCause(e);throw ex;} finally {// Don't retain static reference on context.mConstructorArgs[0] = lastContext;mConstructorArgs[1] = null;}Trace.traceEnd(Trace.TRACE_TAG_VIEW);return result;}}

1.首先來(lái)看看 root!=null && attachToRoot==true的情況：

if (root != null && attachToRoot) {root.addView(temp, params);}

直接將layout添加至root中，此方法相當(dāng)于將layout的代碼直接放置在root布局的根布局下。

此方法的返回值為root。

2.再看看root!=null && attachToRoot==false的情況：

if (root != null) {params = root.generateLayoutParams(attrs);if (!attachToRoot) {temp.setLayoutParams(params);}}

此方法返回的值為layout，且layout中設(shè)置了自己的layoutParams。

3.最后就是root==null的情況了：

此方法返回的也是layout，與第二種情況不同的是layout中不含layoutParams。

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注：與第1中情況不同，第2和第3種情況需自己調(diào)用addview方法添加至相應(yīng)布局中。

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總結(jié)：

1.?root!=null && attachToRoot==true ?-----> ?將layout完全地添加到root中，返回root。

2.?root!=null && attachToRoot==false------> ?返回的layout（包含layoutParams）

3.?root==nul -------------------------------> ?返回layout（不包含layoutParams）

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轉(zhuǎn)載于:https://www.cnblogs.com/zhisuoyu/p/5924396.html

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