Fragment的一些介绍

Fragment的产生：Fragment是android3.0的产物，在Android3.0之前，手机、平板电脑 的适配是个令人头疼的问题，Fragment也因此而产生。
那么我们一般使用Fragment来干些啥呢，通过查找资料得知，它有以下几个用法：

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1.解决手机、平板电脑等各种设备的适配
2.多个Activity之间切换性能问题
3.模块化，即复用

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Fragment的生命周期

——生命周期图片—-

—-Fragment与Activity生命周期对比图——

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——生命周期—-

/**
* Called when a fragment is first attached to its activity.
* {@link #onCreate(Bundle)} will be called after this.
*/
onAttach：Fragment绑定到它的父Activity中的时候被调用，我们可以在这里保存它和Activity之间的引用。

/**
* Called to have the fragment instantiate its user interface view.
* This is optional, and non-graphical fragments can return null (which
* is the default implementation). This will be called between
* {@link #onCreate(Bundle)} and {@link #onActivityCreated(Bundle)}.
*/
onCreateView:在Fragment创建自己的视图结构的时候被调用，在这个方法中我们会载入Fragment的布局文件，在这个过程中，我们不能保证父Activity是否已经创建，所以有一些操作我们不能在这里完成.

/**
* Called to do initial creation of a fragment. This is called after
* {@link #onAttach(Activity)} and before
* {@link #onCreateView(LayoutInflater, ViewGroup, Bundle)}
*

Note that this can be called while the fragment’s activity is
* still in the process of being created. As such, you can not rely
* on things like the activity’s content view hierarchy being initialized
* at this point. If you want to do work once the activity itself is
* created, see {@link #onActivityCreated(Bundle)}.
*/
onCreate:Fragment就是在这一步中产生的，可以用这个方法来启动其它线程来检索数据，比如从远程服务器中启动.

/**
* Called when the Fragment is visible to the user. This is generally
* tied to {@link Activity#onStart() Activity.onStart} of the containing
* Activity’s lifecycle.
*/
onStart:fragment完全可见时，但是还不能和用户进行交互。

/**
* Called when the fragment is visible to the user and actively running.
* This is generally
* tied to {@link Activity#onResume() Activity.onResume} of the containing
* Activity’s lifecycle.
*/
onResume：fragment完全可见，并且可以和用户进行交互，这时，Fragment就已经启动并运行起来了。

/**
* Called when the Fragment is no longer resumed. This is generally
* tied to {@link Activity#onPause() Activity.onPause} of the containing
* Activity’s lifecycle.
*/
onPause：Activity被暂停

/**
* Called when the Fragment is no longer started. This is generally
* tied to {@link Activity#onStop() Activity.onStop} of the containing
* Activity’s lifecycle.
*/
onStop：fragment完全停止。

/**
* Called when the fragment’s activity has been created and this
* fragment’s view hierarchy instantiated. It can be used to do final
* initialization once these pieces are in place, such as retrieving
* views or restoring state. It is also useful for fragments that use
* {@link #setRetainInstance(boolean)} to retain their instance,
* as this callback tells the fragment when it is fully associated with
* the new activity instance. This is called after {@link #onCreateView}
* and before {@link #onViewStateRestored(Bundle)}.
*/
onActivityCreated:当activity的onCreated()方法返回后调用此方法

/**
* Called when the view previously created by {@link #onCreateView} has
* been detached from the fragment. The next time the fragment needs
* to be displayed, a new view will be created. This is called
* after {@link #onStop()} and before {@link #onDestroy()}. It is called
* regardless of whether {@link #onCreateView} returned a
* non-null view. Internally it is called after the view’s state has
* been saved but before it has been removed from its parent.
*/
onDestroyView：系统销毁Fragment的视图显示，

/**
* Called when the fragment is no longer in use. This is called
* after {@link #onStop()} and before {@link #onDetach()}.
*/
onDestroy：Fragment完全销毁

/**
* Called when the fragment is no longer attached to its activity. This
* is called after {@link #onDestroy()}.
*/
onDetach：Fragment解绑

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Activity与Fragment之间的通信

有以下几种方式：

1.通过handler传值
2.通过发送广播来传递消息
3.通过接口传递消息

以上三种方式，缺点都比较多，隆重介绍接下来的一种消息传递方式。
这种方式，我理解为是“第三者插足法”，即首先新建一个公共类AppContext，在这个类里面创建对Fragment或者是Activity进行初始化的方法:initFragment(Fragment fragment)、initActivity(Activity activity)。然后在Fragment或者是Activity里面调用AppContext类中的初始化方法。
这样，我们就可以在第三者，即AppContext里面进行传值了。
fragment里面:

AppContext.getInstance().initOrderFragment(this);

AppContext:

private class AppContext{     private OrderFragment mOrderFragment; /**     * 订单对象初始化     * @param fragment     */    public void initOrderFragment(OrderFragment fragment){        this.mOrderFragment = fragment;    }    /**     * 展示待竞价界面     */    public void showWaitBidMenu(){        if(mOrderFragment != null && mPager != null){            mPager.setCurrentItem(1);            mOrderFragment.showWaitBidMenu();        }    }}

这样就可以进行传值了。