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

1 <?xml version="1.0" encoding="utf-8"?>
2
3 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
4               android:orientation="vertical"
5               android:layout_width="match_parent"
6               android:layout_height="match_parent"
7               android:background="@color/white">
8
9     <TextView
10             android:layout_width="match_parent"
11             android:layout_height="wrap_content"
12             android:id="@+id/textViewTitle"
13             android:textColor="@color/black"
14             android:gravity="center" android:textSize="26dp"/>
15
16     <TextView
17             android:layout_width="match_parent"
18             android:layout_height="wrap_content"
19             android:id="@+id/textViewAuthor"
20             android:layout_gravity="left" android:textColor="@android:color/darker_gray" android:textSize="16dp"/>
21
22     <ImageView
23             android:layout_width="wrap_content"
24             android:layout_height="wrap_content"
25             android:id="@+id/imageView"
26             android:layout_gravity="center_horizontal"
27             android:scaleType="center"/>
28
29     <TextView
30             android:layout_width="match_parent"
31             android:layout_height="wrap_content"
32             android:id="@+id/textViewContent"
33             android:layout_gravity="center_horizontal" android:textColor="@color/black" android:textSize="20dp"/>
34
35     <LinearLayout
36             android:layout_width="fill_parent"
37             android:layout_height="2dp"
38             android:layout_gravity="center"
39             android:background="@color/black">
40     </LinearLayout>
41
42     <TextView
43             android:layout_width="match_parent"
44             android:layout_height="wrap_content"
45             android:id="@+id/textViewOtherInfo"
46             android:layout_gravity="left" android:clickable="true" android:textColor="@android:color/darker_gray"
47             android:textSize="16dp"/>
48 </LinearLayout>

对应的类是

1 public class ContentItemView extends LinearLayout {
2
3     private TextView title;
4     private TextView author;
5     private TextView content;
6     private TextView otherInfo;
7     private ImageView contentImage;
8
9     private ContentInfo info;
10
11     public ContentItemView(Context context) {
12         super(context);
13         init(context);
14     }
15
16     private void init(Context context) {
17         LinearLayout convertView =
18         (LinearLayout) LayoutInflater.from(context).inflate(R.layout.contentitem, null);
19         title = (TextView) convertView.findViewById(R.id.textViewTitle);
20         author = (TextView) convertView.findViewById(R.id.textViewAuthor);
21         content = (TextView) convertView.findViewById(R.id.textViewContent);
22         otherInfo = (TextView) convertView.findViewById(R.id.textViewOtherInfo);
23         contentImage = (ImageView) convertView.findViewById(R.id.imageView);
24     }
25 }

这个自定义view我想将它添加到一个listview中。

1     public void add(final ContentInfo info) {
2         ContentItemView contentItemView  = new ContentItemView(context);
3         contentItemView.setContentInfo(info);
4         contentItemView.setLayoutParams(new AbsListView.LayoutParams(AbsListView.LayoutParams.MATCH_PARENT, AbsListView.LayoutParams.WRAP_CONTENT));
5
6         data.add(contentItemView);
7     }
8
9     @Override
10     public View getView(int position, View convertView, ViewGroup parent) {
11         return data.get(position);
12     }

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

1     public View inflate(int resource, ViewGroup root) {
2         return inflate(resource, root, root != null);
3     }
4
5     public View inflate(int resource, ViewGroup root, boolean attachToRoot) {
6         if (DEBUG) System.out.println("INFLATING from resource: " + resource);
7         XmlResourceParser parser = getContext().getResources().getLayout(resource);
8         try {
9             return inflate(parser, root, attachToRoot);
10         } finally {
11             parser.close();
12         }
13     }
14     public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot) {
15 ........
16                 if (TAG_MERGE.equals(name)) {
17                     if (root == null || !attachToRoot) {
18                         throw new InflateException("<merge /> can be used only with a valid "
19                                 + "ViewGroup root and attachToRoot=true");
20                     }
21
22                     rInflate(parser, root, attrs, false);
23                 } else {
24                     // Temp is the root view that was found in the xml
25                     View temp;
26                     if (TAG_1995.equals(name)) {
27                         temp = new BlinkLayout(mContext, attrs);
28                     } else {
29                         temp = createViewFromTag(root, name, attrs);
30                     }
31
32                     ViewGroup.LayoutParams params = null;
33
34                     if (root != null) {
35                         if (DEBUG) {
36                             System.out.println("Creating params from root: " +
37                                     root);
38                         }
39                         // Create layout params that match root, if supplied
40                         params = root.generateLayoutParams(attrs);
41                         if (!attachToRoot) {
42                             // Set the layout params for temp if we are not
43                             // attaching. (If we are, we use addView, below)
44                             temp.setLayoutParams(params);
45                         }
46                     }
47
48                   ..............
49                     if (root != null && attachToRoot) {
50                         root.addView(temp, params);
51                     }
52
53                     // Decide whether to return the root that was passed in or the
54                     // top view found in xml.
55                     if (root == null || !attachToRoot) {
56                         result = temp;
57                     }
58                 }
59 .....
60 }

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。