【Android开发经验】LayoutInflater——80%的Android程序员对它并不了解甚至错误使用
2015-03-11 14:41
746 查看
这个标题起的有点夸张哈，但是LayoutInflater这个类的一些用法，在Android开发者使用的过程中，确实存在着一些很普遍的误区，最起码我研究的这么多小项目的源代码，基本上都在错误的使用这个类。今天，看到了一篇文章讲LayoutInflater的用法，瞬间感觉自己对这个类确实不够了解，于是简单的看了下LayoutInflater类的源代码，对这个类有了新的认识。
首先，LayoutInflater这个类是用来干嘛的呢？
我们最常用的便是LayoutInflater的inflate方法，这个方法重载了四种调用方式，分别为：
1. public View inflate(int resource, ViewGroup root)
2.
public View inflate(int resource, ViewGroup root, boolean attachToRoot)
3.public View inflate(XmlPullParser
parser, ViewGroup root)
4.public View inflate(XmlPullParser
parser, ViewGroup root, boolean attachToRoot)
这四种使用方式中，我们最常用的是第一种方式，inflate方法的主要作用就是将xml转换成一个View对象，用于动态的创建布局。虽然重载了四个方法，但是这四种方法最终调用的，还是第四种方式。第四种方式也很好理解，内部实现原理就是利用Pull解析器，对Xml文件进行解析，然后返回View对象。
我们以我们经常使用的第一种形式为例，你在重写BaseAdapter的getView方法的时候是否这样做过
[java]
view plaincopyprint?
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = inflate(R.layout.item_row,
null);
}
return convertView;
}
1.resource布局的资源id
2.root填充的根视图
3.attachToRoot是否将载入的视图绑定到根视图中
在这个例子中，我们将root参数设为空，功能确实实现了，但是这里还隐藏着一个隐患，这种方式并不是inflate正确的使用姿势，下面我们通过一个Demo，来说一下这样使用造成的弊端。
首先，我们建立一个这样的项目
这里三个界面，一个主界面，两个测试界面，布局文件中，主界面只负责界面跳转，两个测试界面都是一个简单的Listview，item布局显示效果如下
对应的布局文件如下
[html]
view plaincopyprint?
<?xml
version="1.0"
encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="60dp"
android:background="@android:color/holo_orange_light"
android:gravity="center"
android:orientation="vertical"
>
<TextView
android:id="@+id/tv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="11"
android:textColor="@android:color/black"
android:textSize="22sp"
/>
</LinearLayout>
OneActivity的代码如下
[java]
view plaincopyprint?
public class OneActivity
extends Activity {
private ListView list1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_one);
list1 = (ListView) findViewById(R.id.list1);
list1.setAdapter(new MyAdapter(this));
}
private class MyAdapter
extends BaseAdapter {
private LayoutInflater inflater;
MyAdapter(Context context) {
inflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
return
20;
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView ==
null) {
convertView = inflater.inflate(R.layout.item_list,
null);
}
TextView tv = (TextView) convertView.findViewById(R.id.tv);
tv.setText(position+"");
return convertView;
}
}
}
TwoActivity的代码如下
[java]
view plaincopyprint?
public class TwoActivity
extends Activity {
private ListView list2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_two);
list2 = (ListView) findViewById(R.id.list2);
list2.setAdapter(new MyAdapter(this));
}
private class MyAdapter
extends BaseAdapter {
private LayoutInflater inflater;
MyAdapter(Context context) {
inflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
return 20;
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView ==
null) {
convertView = inflater.inflate(R.layout.item_list, parent,false);
}
TextView tv = (TextView) convertView.findViewById(R.id.tv);
tv.setText(position + "");
return convertView;
}
}
}
两个文件最关键的区别就一句话，
在getView方法中，OneActivity是
convertView = inflater.inflate(R.layout.item_list, null);
在getView方法中，TwoActivity是
convertView = inflater.inflate(R.layout.item_list,
parent,false);
我们先看一下显示效果，再说两者的区别
OneActivity效果
TwoActivity的显示效果
我们可以很明显的看出来，使用第一种方式，根布局的高度设置60dp没有起作用，系统还是按照包裹内容的方式加载的，为什么会产生这种效果呢？我们从需要inflate方法的源代码中找一下答案。
首先，方式一的源代码实现
[java]
view plaincopyprint?
public View inflate(XmlPullParser parser, ViewGroup root) {
return inflate(parser, root, root !=
null);
}
当我们使用方式一，并且第二个参数传入null的时候，默认调用的是下面的方法，并且attachToRoot是false
[java]
view plaincopyprint?
public View inflate(int resource, ViewGroup root,
boolean attachToRoot) {
if (DEBUG) System.out.println("INFLATING from resource: " + resource);
XmlResourceParser parser = getContext().getResources().getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}
在这一个方法中，pull解析器将资源id转化成XmlResourceParser对象，又传给了第四种方式，所以我们需要重点看的还是第四种方式是如何实现的
[java]
view plaincopyprint?
public View inflate(XmlPullParser parser, ViewGroup root,
boolean attachToRoot) {
synchronized (mConstructorArgs) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW,
"inflate");
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 xml
View 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 supplied
params = 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
rInflate(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;
}
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
return result;
}
}
代码比较长，我们重点关注下面的代码
[java]
view plaincopyprint?
if (root != null) {
if (DEBUG) {
System.out.println("Creating params from root: " +
root);
}
// Create layout params that match root, if supplied
params = 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);
}
}
这些代码的意思就是，当我们传进来的root参数不是空的时候，并且attachToRoot是false的时候，也就是上面的TwoActivity的实现方式的时候，会给temp设置一个LayoutParams参数。那么这个temp又是干嘛的呢？
[java]
view plaincopyprint?
<pre name="code"
class="java">// 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;
}
现在应该明白了吧，当我们传进来的root不是null，并且第三个参数是false的时候，这个temp就被加入到了root中，并且把root当作最终的返回值返回了。而当我们设置root为空的时候，没有设置LayoutParams参数的temp对象，作为返回值返回了。
因此，我们可以得出下面的结论：
1.若我们采用convertView
= inflater.inflate(R.layout.item_list, null);方式填充视图，item布局中的根视图的layout_XX属性会被忽略掉，然后设置成默认的包裹内容方式
2.如果我们想保证item的视图中的参数不被改变，我们需要使用convertView
= inflater.inflate(R.layout.item_list, parent,false);这种方式进行视图的填充
3.除了使用这种方式，我们还可以设置item布局的根视图为包裹内容，然后设置内部控件的高度等属性，这样就不会修改显示方式了。
最后，给出那篇文章的链接http://blog.jobbole.com/72156/大家可以去看看
首先，LayoutInflater这个类是用来干嘛的呢？
我们最常用的便是LayoutInflater的inflate方法，这个方法重载了四种调用方式，分别为：
1. public View inflate(int resource, ViewGroup root)
2.
public View inflate(int resource, ViewGroup root, boolean attachToRoot)
3.public View inflate(XmlPullParser
parser, ViewGroup root)
4.public View inflate(XmlPullParser
parser, ViewGroup root, boolean attachToRoot)
这四种使用方式中，我们最常用的是第一种方式，inflate方法的主要作用就是将xml转换成一个View对象，用于动态的创建布局。虽然重载了四个方法，但是这四种方法最终调用的，还是第四种方式。第四种方式也很好理解，内部实现原理就是利用Pull解析器，对Xml文件进行解析，然后返回View对象。
我们以我们经常使用的第一种形式为例，你在重写BaseAdapter的getView方法的时候是否这样做过
[java]
view plaincopyprint?
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = inflate(R.layout.item_row,
null);
}
return convertView;
}
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = inflate(R.layout.item_row, null);
}
return convertView;
}inflate方法有三个参数，分别是1.resource布局的资源id
2.root填充的根视图
3.attachToRoot是否将载入的视图绑定到根视图中
在这个例子中，我们将root参数设为空，功能确实实现了，但是这里还隐藏着一个隐患，这种方式并不是inflate正确的使用姿势，下面我们通过一个Demo，来说一下这样使用造成的弊端。
首先，我们建立一个这样的项目
这里三个界面，一个主界面，两个测试界面，布局文件中，主界面只负责界面跳转，两个测试界面都是一个简单的Listview，item布局显示效果如下
对应的布局文件如下
[html]
view plaincopyprint?
<?xml
version="1.0"
encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="60dp"
android:background="@android:color/holo_orange_light"
android:gravity="center"
android:orientation="vertical"
>
<TextView
android:id="@+id/tv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="11"
android:textColor="@android:color/black"
android:textSize="22sp"
/>
</LinearLayout>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="60dp"
android:background="@android:color/holo_orange_light"
android:gravity="center"
android:orientation="vertical" >
<TextView
android:id="@+id/tv"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="11"
android:textColor="@android:color/black"
android:textSize="22sp" />
</LinearLayout>OneActivity的代码如下
[java]
view plaincopyprint?
public class OneActivity
extends Activity {
private ListView list1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_one);
list1 = (ListView) findViewById(R.id.list1);
list1.setAdapter(new MyAdapter(this));
}
private class MyAdapter
extends BaseAdapter {
private LayoutInflater inflater;
MyAdapter(Context context) {
inflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
return
20;
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView ==
null) {
convertView = inflater.inflate(R.layout.item_list,
null);
}
TextView tv = (TextView) convertView.findViewById(R.id.tv);
tv.setText(position+"");
return convertView;
}
}
}
public class OneActivity extends Activity {
private ListView list1;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_one);
list1 = (ListView) findViewById(R.id.list1);
list1.setAdapter(new MyAdapter(this));
}
private class MyAdapter extends BaseAdapter {
private LayoutInflater inflater;
MyAdapter(Context context) {
inflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
return 20;
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = inflater.inflate(R.layout.item_list, null);
}
TextView tv = (TextView) convertView.findViewById(R.id.tv);
tv.setText(position+"");
return convertView;
}
}
}TwoActivity的代码如下
[java]
view plaincopyprint?
public class TwoActivity
extends Activity {
private ListView list2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_two);
list2 = (ListView) findViewById(R.id.list2);
list2.setAdapter(new MyAdapter(this));
}
private class MyAdapter
extends BaseAdapter {
private LayoutInflater inflater;
MyAdapter(Context context) {
inflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
return 20;
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView ==
null) {
convertView = inflater.inflate(R.layout.item_list, parent,false);
}
TextView tv = (TextView) convertView.findViewById(R.id.tv);
tv.setText(position + "");
return convertView;
}
}
}
public class TwoActivity extends Activity {
private ListView list2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_two);
list2 = (ListView) findViewById(R.id.list2);
list2.setAdapter(new MyAdapter(this));
}
private class MyAdapter extends BaseAdapter {
private LayoutInflater inflater;
MyAdapter(Context context) {
inflater = LayoutInflater.from(context);
}
@Override
public int getCount() {
return 20;
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
convertView = inflater.inflate(R.layout.item_list, parent,false);
}
TextView tv = (TextView) convertView.findViewById(R.id.tv);
tv.setText(position + "");
return convertView;
}
}
}两个文件最关键的区别就一句话，
在getView方法中，OneActivity是
convertView = inflater.inflate(R.layout.item_list, null);
在getView方法中，TwoActivity是
convertView = inflater.inflate(R.layout.item_list,
parent,false);
我们先看一下显示效果，再说两者的区别
OneActivity效果
TwoActivity的显示效果
我们可以很明显的看出来，使用第一种方式，根布局的高度设置60dp没有起作用，系统还是按照包裹内容的方式加载的，为什么会产生这种效果呢？我们从需要inflate方法的源代码中找一下答案。
首先，方式一的源代码实现
[java]
view plaincopyprint?
public View inflate(XmlPullParser parser, ViewGroup root) {
return inflate(parser, root, root !=
null);
}
public View inflate(XmlPullParser parser, ViewGroup root) {
return inflate(parser, root, root != null);
}当我们使用方式一，并且第二个参数传入null的时候，默认调用的是下面的方法，并且attachToRoot是false
[java]
view plaincopyprint?
public View inflate(int resource, ViewGroup root,
boolean attachToRoot) {
if (DEBUG) System.out.println("INFLATING from resource: " + resource);
XmlResourceParser parser = getContext().getResources().getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}
public View inflate(int resource, ViewGroup root, boolean attachToRoot) {
if (DEBUG) System.out.println("INFLATING from resource: " + resource);
XmlResourceParser parser = getContext().getResources().getLayout(resource);
try {
return inflate(parser, root, attachToRoot);
} finally {
parser.close();
}
}在这一个方法中，pull解析器将资源id转化成XmlResourceParser对象，又传给了第四种方式，所以我们需要重点看的还是第四种方式是如何实现的
[java]
view plaincopyprint?
public View inflate(XmlPullParser parser, ViewGroup root,
boolean attachToRoot) {
synchronized (mConstructorArgs) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW,
"inflate");
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 xml
View 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 supplied
params = 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
rInflate(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;
}
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
return result;
}
}
public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {
synchronized (mConstructorArgs) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "inflate");
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 xml
View 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 supplied
params = 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
rInflate(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;
}
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
return result;
}
}代码比较长，我们重点关注下面的代码
[java]
view plaincopyprint?
if (root != null) {
if (DEBUG) {
System.out.println("Creating params from root: " +
root);
}
// Create layout params that match root, if supplied
params = 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 (root != null) {
if (DEBUG) {
System.out.println("Creating params from root: " +
root);
}
// Create layout params that match root, if supplied
params = 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);
}
}这些代码的意思就是，当我们传进来的root参数不是空的时候，并且attachToRoot是false的时候，也就是上面的TwoActivity的实现方式的时候，会给temp设置一个LayoutParams参数。那么这个temp又是干嘛的呢？
[java]
view plaincopyprint?
<pre name="code"
class="java">// 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;
}
<pre name="code" class="java">// 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;
}现在应该明白了吧，当我们传进来的root不是null，并且第三个参数是false的时候，这个temp就被加入到了root中，并且把root当作最终的返回值返回了。而当我们设置root为空的时候，没有设置LayoutParams参数的temp对象，作为返回值返回了。
因此，我们可以得出下面的结论：
1.若我们采用convertView
= inflater.inflate(R.layout.item_list, null);方式填充视图，item布局中的根视图的layout_XX属性会被忽略掉，然后设置成默认的包裹内容方式
2.如果我们想保证item的视图中的参数不被改变，我们需要使用convertView
= inflater.inflate(R.layout.item_list, parent,false);这种方式进行视图的填充
3.除了使用这种方式，我们还可以设置item布局的根视图为包裹内容，然后设置内部控件的高度等属性，这样就不会修改显示方式了。
最后，给出那篇文章的链接http://blog.jobbole.com/72156/大家可以去看看
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