Android110509: LayoutInflater注记

zcatt

Android110509: LayoutInflater注记


Email:    zcatt@163.com
Blog    http://zcatt.blog.chinaunix.net
 
内容提要
LayoutInflater及<merge>, <include>和<requestFocus>用法简记.以供备忘和参考。

声明
仅限学习交流，禁止商业用途。转载需注明出处。

版本记录
Date        Ver        Note
2011-05-09    0.1        Draft.  zcatt, Beijing
 
LayoutInflater根据layout xml文件, 递归调用xml tag相应的viewClass, 例如<FrameLayout>对应FrameLayout, 的构造函数生成viewClass的实例. 调用的viewClass的构造函数的signature如下,

1. public View(Context context, AttributeSet attrs);

通常使用LayoutInflater的步骤是两步:

1) 取得LayoutInflater实例.

1. private LayoutInflater mInflater;
   
2. mInflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

    或

1. private LayoutInflater mInflater;
   
2. mInflater = LayoutInflater.from(context);

在contextImpl.java我们可以找到如下代码,

1. ... ... ...
   
2.     public Object getSystemService(String name) {
   
3.         if (WINDOW_SERVICE.equals(name)) {
   
4.             return WindowManagerImpl.getDefault();
   
5.         } else if (LAYOUT_INFLATER_SERVICE.equals(name)) {
   
6.             synchronized (mSync) {
   
7.                 LayoutInflater inflater = mLayoutInflater;
   
8.                 if (inflater != null) {
   
9.                     return inflater;
   
10.                 }
    
11.                 mLayoutInflater = inflater =
    
12.                     PolicyManager.makeNewLayoutInflater(getOuterContext());
    
13.                 return inflater;
    
14.             }
    
15.         } else if (ACTIVITY_SERVICE.equals(name)) {
    
16.             return getActivityManager();
    
17.     ... ... ...

而PolicyManager.makeNewLayoutInflater()实际是调用 Policy.makeNewLayoutInflater()

1. public class Policy implements IPolicy {
   
2.     ... ... ...
   
3. 
   
4.     public PhoneLayoutInflater makeNewLayoutInflater(Context context) {
   
5.         return new PhoneLayoutInflater(context);
   
6.     }
   
7.     ... ... ...
   
8. }

也就是说,Android中实际使用的是LayoutInflater的子类 PhoneLayoutInflater.

    LayoutInflater
        PhoneLayoutInflater

2) 调用LayoutInflater.infate()载入指定的layout xml, 生成对应的View. inflate()入口参数可以控制是否将生成的view加到root中. 这里罗列LayoutInflater的几个inflate().

1. public View inflate(int resource, ViewGroup root);
   
2. public View inflate(XmlPullParser parser, ViewGroup root);
   
3. public View inflate(int resource, ViewGroup root, boolean attachToRoot);
   
4. public View inflate(XmlPullParser parser, ViewGroup root, boolean attachToRoot);

在LayoutInflater可以设置Filter, 不满足Filter条件的view将不会生成, 并抛例外exception, 较少用到, 不赘述, 可参考RemoteView.

LayoutInflater提供了对<merge>, <include>, 和<requestFocus>计3个xml tag的支持. 其中的<include>和<merge>可以用来更好的组织layout xml脚本.

<include>类似C的#include语句. 粘贴[1]中的例子

1. <com.android.launcher.Workspace
   
2.     android:id="@+id/workspace"
   
3.     android:layout_width="fill_parent"
   
4.     android:layout_height="fill_parent"
   
5. 
   
6.     launcher:defaultScreen="1">
   
7. 
   
8.     <include android:id="@+id/cell1" layout="@layout/workspace_screen" />
   
9.     <include android:id="@+id/cell2" layout="@layout/workspace_screen" />
   
10.     <include android:id="@+id/cell3" layout="@layout/workspace_screen" />
    
11. 
    
12. </com.android.launcher.Workspace>

<merge>比较特殊, 只能用在xml的root tag上, 是用来消除xml的root node冗余的. 如果xml的root node同父节点是一样的, 就可以直接使用父节点做为容器, 没必要再创建一个root node. 粘贴[2]中的例子.

1. <merge xmlns:android="http://schemas.android.com/apk/res/android">
   
2. 
   
3.     <ImageView
   
4.         android:layout_width="fill_parent"
   
5.         android:layout_height="fill_parent"
   
6.     
   
7.         android:scaleType="center"
   
8.         android:src="@drawable/golden_gate" />
   
9.     
   
10.     <TextView
    
11.         android:layout_width="wrap_content"
    
12.         android:layout_height="wrap_content"
    
13.         android:layout_marginBottom="20dip"
    
14.         android:layout_gravity="center_horizontal|bottom"
    
15. 
    
16.         android:padding="12dip"
    
17.         
    
18.         android:background="#AA000000"
    
19.         android:textColor="#ffffffff"
    
20.         
    
21.         android:text="Golden Gate" />
    
22. 
    
23. </merge>

参考文档[1]和[2]分别详述了<include>和<merge>的使用.
    


参考
[1] ANDROID_SDK/docs/resources/articles/layout-tricks-merge.html
[2] ANDROID_SDK/docs/resources/articles/layout-tricks-reuse.html
[3] froyo src