转载请标明出处：， 本文出自：1、题外话
相信大家对LayoutInflate都不陌生，特别在ListView的Adapter的getView方法中基本都会出现，使用inflate方法去加载一个布局，用于ListView的每个Item的布局。Inflate有三个参数，我在初学Android的时候这么理解的：
对于Inflate的三个参数(int resource, ViewGroup root, boolean attachToRoot)
如果inflate(layoutId, null )则layoutId的最外层的控件的宽高是没有效果的
如果inflate(layoutId, root, false ) 则认为和上面效果是一样的
如果inflate(layoutId, root, true ) 则认为这样的话layoutId的最外层控件的宽高才能正常显示
如果你也这么认为，那么你有就必要好好阅读这篇文章，因为这篇文章首先会验证上面的理解是错误的，然后从源码角度去解释，最后会从ViewGroup与View的角度去解释。
2、实践是验证真理的唯一标准
下面我写一个特别常见的例子来验证上面的理解是错误的，一个特别简单的ListView，每个Item中放一个按钮：
Activity的布局文件：
<ListView xmlns:android=""xmlns:tools=""android:id="@+id/id_listview"android:layout_width="fill_parent"android:layout_height="wrap_content" ></ListView>ListView的Item的布局文件：<Button xmlns:android=""xmlns:tools=""android:id="@+id/id_btn"android:layout_width="120dp"android:layout_height="120dp" ></Button>
ListView的适配器：
package com.example.zhy_layoutinflater;import java.util.List;import android.content.Context;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.Button;public class MyAdapter extends BaseAdapter{private LayoutInflater mInflater;private List<String> mDatas;public MyAdapter(Context context, List<String> datas){mInflater = LayoutInflater.from(context);mDatas = datas;}@Overridepublic int getCount(){return mDatas.size();}@Overridepublic Object getItem(int position){return mDatas.get(position);}@Overridepublic long getItemId(int position){return position;}@Overridepublic View getView(int position, View convertView, ViewGroup parent){ViewHolder holder = null;if (convertView == null){holder = new ViewHolder();convertView = mInflater.inflate(R.layout.item, null);//convertView = mInflater.inflate(R.layout.item, parent ,false);//convertView = mInflater.inflate(R.layout.item, parent ,true);holder.mBtn = (Button) convertView.findViewById(R.id.id_btn);convertView.setTag(holder);} else{holder = (ViewHolder) convertView.getTag();}holder.mBtn.setText(mDatas.get(position));return convertView;}private final class ViewHolder{Button mBtn;}}主Activity:package com.example.zhy_layoutinflater;import java.util.Arrays;import java.util.List;import android.app.Activity;import android.os.Bundle;import android.widget.ListView;public class MainActivity extends Activity{private ListView mListView;private MyAdapter mAdapter;private List<String> mDatas = Arrays.asList("Hello", "Java", "Android");@Overrideprotected void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mListView = (ListView) findViewById(R.id.id_listview);mAdapter = new MyAdapter(this, mDatas);mListView.setAdapter(mAdapter);}}好了，相信大家对这个例子都再熟悉不过了，没啥好说的，我们主要关注getView里面的inflate那行代码：下面我依次把getView里的写成：1、convertView = mInflater.inflate(R.layout.item, null);2、convertView = mInflater.inflate(R.layout.item, parent ,false);3、convertView = mInflater.inflate(R.layout.item, parent ,true);分别看效果图：图1：
图2：
图3：
FATAL EXCEPTION: mainjava.lang.UnsupportedOperationException: addView(View, LayoutParams) is not supported in AdapterView嗯，没错没有图3，第三种写法会报错。
由上面三行代码的变化，产生3个不同的结果，可以看到
inflater(resId, null )的确不能正确处理宽高的值，但是inflater(resId,parent,false)并非和inflater(resId, null )效果一致，它可以看出完美的显示了宽和高。
而inflater(resId,parent,true)报错了（错误的原因在解析源码的时候说）。
由此可见：文章开始提出的理解是绝对错误的。
3、源码解析
下面我通过源码来解释，这三种写法真正的差异
这三个方法，最终都会执行下面的代码：
public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {synchronized (mConstructorArgs) {final AttributeSet attrs = Xml.asAttributeSet(parser);Context lastContext = (Context)mConstructorArgs[0];mConstructorArgs[0] = mContext;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, attrs, false);} else {// Temp is the root view that was found in the xmlView temp;if (TAG_1995.equals(name)) {temp = new BlinkLayout(mContext, attrs);} else {temp = createViewFromTag(root, name, 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 temprInflate(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 (IOException 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;}return result;}}第6行：首先声明了View result = root ；//最终返回值为result
第43行执行了：temp = createViewFromTag(root, name, attrs);创建了View
所有的胜利，与征服自己的胜利比起来，都是微不足道
