Fragment静态使用

在Android中，Fragment是比价常用的一个类，注意，Fragment是个类，只实现了两个接口：

1.ComponentCallbacks

2.OnCreateContextMenuListener

第一个接口：官方文档上解释，Called by the system when the device configuration changes while your

component is running。什么意思呢，当你的应用正在运行，这个时候你的设备配置改变了，系统会自动调用这个接口。

这个接口里面就两个回调方法：

A void onConfigurationChanged(Configuration newConfig);--->当配置改变的时候调用

B void onLowMemory(); --->当内存低的时候调用此方法。

第二个接口：OnCreateContextMenuListener，官方文档解释，Interface definition for a callback to be invoked when the context menu for this view is being built. 当前view的上下文菜单创建的时候调用。

这个接口里面就一个回调：

void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo);

当创建上下文菜单的时候调用。

Fragment第一次出现时在谷歌的平板上，因为平板设备比较大，如果仅仅显示简单的布局有点浪费，为了充分利用那么大的屏幕，Fragment出现了。Fragment是碎片的意思，一听就知道这个类是比较小的，一般比较小的东西消耗资源就比价小，对于手机这种小型设备，资源是非常宝贵的，所以先在Fragment在手机中的应用也很广泛。Fragment在一定程度上可以替代Activity进行页面的显示。我就把Fragment理解为一个轻量级的Activity，基本上能够满足所有需要在Activity上进行的东西，比如显示view，请求网络，页面跳转等。

下面说下Fragment的生命周期：

Fragment是依赖于Activity存在的，有点像盆栽，首先你的花盆得有，然后才能种盆栽么。

所以Fragment得生命周期有点多：

官方文档如下（如果想看中文的可以百度下，但是建议看英文的，因为很多技术文档还是英文的，掌握一门外语也不错哈哈）：

The core series of lifecycle methods that are called to bring a fragment up to resumed state (interacting with the user) are:

onAttach(Activity) called once the fragment is associated with its activity.
onCreate(Bundle) called to do initial creation of the fragment.
onCreateView(LayoutInflater, ViewGroup, Bundle) creates and returns the view hierarchy associated with the fragment.
onActivityCreated(Bundle) tells the fragment that its activity has completed its own Activity.onCreate().
onViewStateRestored(Bundle) tells the fragment that all of the saved state of its view hierarchy has been restored.
onStart() makes the fragment visible to the user (based on its containing activity being started).
onResume() makes the fragment interacting with the user (based on its containing activity being resumed).

As a fragment is no longer being used, it goes through a reverse series of callbacks:

onPause() fragment is no longer interacting with the user either because its activity is being paused or a fragment operation is modifying it in the activity.
onStop() fragment is no longer visible to the user either because its activity is being stopped or a fragment operation is modifying it in the activity.
onDestroyView() allows the fragment to clean up resources associated with its View.
onDestroy() called to do final cleanup of the fragment's state.
onDetach() called immediately prior to the fragment no longer being associated with its activity.

下面，我来说下Fragment怎么使用：

1.在布局文件中使用，这个时候需要name属性和fragment标签。

首先建立Fragment类：

public class DemoFragment extends Fragment{
    	public View onCreateView(LayoutInflater inflater,ViewGroup container, Bundle    savedInstanceState) {
        TextView textView=new TextView(getActivity());
        textView.setText("静态使用Fragment");
        return textView;
    }
}

接着布局文件：

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

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

    	<TextView
       	 	android:layout_width="match_parent"
       	 	android:layout_height="30dp"
        	android:textSize="30dp"
        	android:gravity="center"
        	android:background="#66FF0000"
        	android:text="Fragment的静态使用" />
    	<fragment
        	android:layout_width="match_parent"
        	android:layout_height="0dp"
        	android:layout_weight="1"
        	android:name="com.example.fragmentdemo.DemoFragment"
        	/>
	</LinearLayout>

直接运行，Fragment就被加载到应用中。

需要注意的是，使用这种方式，Fragment就相当于在布局文件中的view，里面的控件可以直接通过findViewById（）找到。比较方便，但是如果有切换页面的时候就显得不那么灵活了。

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