android中LayoutInflater.from(context).inflate的分析

在应用中自定义一个view，需要获取这个view的布局，需要用到

(LinearLayout) LayoutInflater.from(context).inflate(R.layout.contentitem, null);

这个方法。

一般的资料中的第二个参数会是一个null。通常情况下没有问题，但是如果我想给这个view设置一个对应的类，然后通过这个类来操作的话就会出问题。

先看下面的例子

 <?xml version="1.0" encoding="utf-8"?>

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
               android:orientation="vertical"
               android:layout_width="match_parent"
               android:layout_height="match_parent"
               android:background="@color/white">

     <TextView
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             android:id="@+id/textViewTitle"
             android:textColor="@color/black"
             android:gravity="center" android:textSize="26dp"/>

     <TextView
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             android:id="@+id/textViewAuthor"
             android:layout_gravity="left" android:textColor="@android:color/darker_gray" android:textSize="16dp"/>

     <ImageView
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:id="@+id/imageView"
             android:layout_gravity="center_horizontal"
             android:scaleType="center"/>

     <TextView
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             android:id="@+id/textViewContent"
             android:layout_gravity="center_horizontal" android:textColor="@color/black" android:textSize="20dp"/>

     <LinearLayout
             android:layout_width="fill_parent"
             android:layout_height="2dp"
             android:layout_gravity="center"
             android:background="@color/black">
     </LinearLayout>

     <TextView
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             android:id="@+id/textViewOtherInfo"
             android:layout_gravity="left" android:clickable="true" android:textColor="@android:color/darker_gray"
             android:textSize="16dp"/>
 </LinearLayout>

对应的类是

 public class ContentItemView extends LinearLayout {

     private TextView title;
     private TextView author;
     private TextView content;
     private TextView otherInfo;
     private ImageView contentImage;

     private ContentInfo info;

     public ContentItemView(Context context) {
         super(context);
         init(context);
     }

     private void init(Context context) {
         LinearLayout convertView =
         (LinearLayout) LayoutInflater.from(context).inflate(R.layout.contentitem, null);
         title = (TextView) convertView.findViewById(R.id.textViewTitle);
         author = (TextView) convertView.findViewById(R.id.textViewAuthor);
         content = (TextView) convertView.findViewById(R.id.textViewContent);
         otherInfo = (TextView) convertView.findViewById(R.id.textViewOtherInfo);
         contentImage = (ImageView) convertView.findViewById(R.id.imageView);
     }
 }

这个自定义view我想将它添加到一个listview中。

     public void add(final ContentInfo info) {
         ContentItemView contentItemView  = new ContentItemView(context);
         contentItemView.setContentInfo(info);
         contentItemView.setLayoutParams(new AbsListView.LayoutParams(AbsListView.LayoutParams.MATCH_PARENT, AbsListView.LayoutParams.WRAP_CONTENT));

         data.add(contentItemView);
     }

     @Override
     public View getView(int position, View convertView, ViewGroup parent) {
         return data.get(position);
     }

程序运行起来以后，没有任何问题，但是界面没有显示出来，仅仅是在listview中多了一系列黑色的条条

如果将

(LinearLayout) LayoutInflater.from(context).inflate(R.layout.contentitem, null);

修改为

(LinearLayout) LayoutInflater.from(context).inflate(R.layout.contentitem, this);

显示就会正常

上面的东西很多资料里面都有，但是原因是什么？我在网络上找了很久都没有找到，于是就自己研究了下代码

     public View inflate(int resource, ViewGroup root) {
         return inflate(resource, root, root != null);
     }

     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(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {
 ........
                 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 (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;
                     }
                 }
 .....
 }

可以看到在inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot)函数中，只有root不等于空的情况下才能够真正的把view添加到listview中。

看看参数root的含义：@param root Optional view to be the parent of the generated hierarchy

就是说这个表示的事view的容器是什么。如果不告诉SDK你要把这个view放到哪里，当然就不能生成view了。