Android-- ArrayAdapter用法举例

在实际开发中LayoutInflater这个类还是非常有用的，它的作用类似于findViewById()。不同点是LayoutInflater是用来找res/layout/下的xml布局文件，并且实例化；而findViewById()是找xml布局文件下的具体widget控件(如Button、TextView等)。
具体作用：
1、对于一个没有被载入或者想要动态载入的界面，都需要使用LayoutInflater.inflate()来载入；

2、对于一个已经载入的界面，就可以使用Activiyt.findViewById()方法来获得其中的界面元素。

LayoutInflater 是一个抽象类，在文档中如下声明：

public<wbr></wbr>abstract<wbr></wbr>class<wbr>LayoutInflater<wbr></wbr></wbr>extends<wbr>Object<wbr><wbr></wbr></wbr></wbr>

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获得 LayoutInflater 实例的三种方式

1.LayoutInflater<wbr>inflater<wbr>=<wbr>getLayoutInflater();<wbr><wbr>//调用Activity的getLayoutInflater()</wbr></wbr></wbr></wbr></wbr>

2.LayoutInflater localinflater =<wbr>(LayoutInflater)context.getSystemService</wbr>

<wbr><wbr><wbr></wbr></wbr></wbr><wbr><strong><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></strong><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>(Context.LAYOUT_INFLATER_SERVICE);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

3.<wbr>LayoutInflater<wbr>inflater<wbr>=<wbr>LayoutInflater.from(context);<wbr><wbr><wbr><br></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

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其实，这三种方式本质是相同的，从源码中可以看出：

getLayoutInflater()：

Activity 的 getLayoutInflater() 方法是调用 PhoneWindow 的getLayoutInflater()方法，看一下该源代码：

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1. public<wbr>PhoneWindow(Context<wbr>context)<wbr>{<wbr><wbr></wbr></wbr></wbr></wbr></wbr>
2. <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><strong>super</strong><span style="word-wrap:normal; word-break:normal; line-height:18px; border-bottom-style:none; padding-bottom:0px; border-right-style:none; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px; padding-left:0px; padding-right:0px; border-top-style:none; color:black; border-left-style:none; padding-top:0px">(context);<wbr><wbr></wbr></wbr></span></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
3. <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>mLayoutInflater<wbr>=<wbr>LayoutInflater.from(context);<wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
4. }<wbr><wbr></wbr></wbr>

可以看出它其实是调用 LayoutInflater.from(context)。

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LayoutInflater.from(context)：

• public<wbr></wbr>static<wbr>LayoutInflater<wbr>from(Context<wbr>context)<wbr>{ <wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr>
• <wbr><wbr><wbr><wbr>LayoutInflater<wbr>LayoutInflater<wbr>= <wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
• <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>(LayoutInflater)<wbr>context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); <wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
• <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr>if<wbr>(LayoutInflater<wbr>==<wbr></wbr></wbr></wbr>null)<wbr>{ <wbr><wbr></wbr></wbr></wbr>
• <wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>throw<wbr></wbr>new<wbr>AssertionError(</wbr>"LayoutInflater<wbr>not<wbr>found."</wbr></wbr>); <wbr><wbr></wbr></wbr>
• <wbr><wbr><wbr><wbr>} <wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr>
• <wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr>return<wbr>LayoutInflater; <wbr><wbr></wbr></wbr></wbr>
• }<wbr></wbr>

可以看出它其实调用 context.getSystemService()。

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结论：所以这三种方式最终本质是都是调用的Context.getSystemService()。

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inflate 方法
通过 sdk 的 api 文档，可以知道该方法有以下几种过载形式，返回值均是 View 对象，如下：

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1. public<wbr>View<wbr>inflate<wbr>(</wbr></wbr></wbr>int<wbr>resource,<wbr>ViewGroup<wbr>root)<wbr><wbr></wbr></wbr></wbr></wbr></wbr>
2. public<wbr>View<wbr>inflate<wbr>(XmlPullParser<wbr>parser,<wbr>ViewGroup<wbr>root)<wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
3. <wbr><wbr></wbr></wbr>
4. public<wbr>View<wbr>inflate<wbr>(XmlPullParser<wbr>parser,<wbr>ViewGroup<wbr>root,<wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>boolean<wbr>attachToRoot)<wbr><wbr></wbr></wbr></wbr>
5. <wbr><wbr></wbr></wbr>
6. public<wbr>View<wbr>inflate<wbr>(</wbr></wbr></wbr>int<wbr>resource,<wbr>ViewGroup<wbr>root,<wbr></wbr></wbr></wbr></wbr>boolean<wbr>attachToRoot)<wbr><wbr></wbr></wbr></wbr>

示意代码：

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1. LayoutInflater<wbr>inflater<wbr>=<wbr>(LayoutInflater)</wbr></wbr></wbr>getSystemService(LAYOUT_INFLATER_SERVICE);<wbr><wbr></wbr></wbr>
2. <wbr><wbr></wbr></wbr>
3. View<wbr>view<wbr>=<wbr>inflater.inflate(R.layout.custom,<wbr></wbr></wbr></wbr></wbr>(ViewGroup)findViewById(R.id.test));<wbr><wbr></wbr></wbr>
4. <wbr><wbr></wbr></wbr>
5. //EditText<wbr>editText<wbr>=<wbr>(EditText)findViewById(R.id.content);//<wbr>error</wbr></wbr></wbr></wbr><wbr><wbr></wbr></wbr>
6. EditText<wbr>editText<wbr>=<wbr>(EditText)view.findViewById(R.id.content);<wbr><wbr></wbr></wbr></wbr></wbr></wbr>

对于上面代码，指定了第二个参数 ViewGroup root，当然你也可以设置为 null 值。

注意：

·inflate方法与 findViewById 方法不同；

·inflater 是用来找 res/layout 下的 xml 布局文件，并且实例化；

·findViewById() 是找具体 xml 布局文件中的具体 widget 控件(如:Button、TextView 等)。