Fragment生命周期探索

Fragment和Activity类似，也有自己的生命周期，并且fragment的生命周期和activity的生命周期特别相似。

Activity的生命周期由四种状态，运行、暂停、停止、和销毁，类似的，Fragment也有这四种状态，只是在一些细小的地方有所不同。

Fragment生命周期图(来自Android官网)

下面直接通过工程来认识Fragment的生命周期

首先新建FragmentDemo工程。

MainActivity.java

[代码]java代码：

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package com.marktony.fragmentdemo; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentTransaction; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.util.Log; import android.view.View; import android.widget.Button; public class MainActivity   extends AppCompatActivity   {     private Button btnAddFragment;     private FragmentManager fragmentManager;     private FragmentTransaction fragmentTransaction;     public static final String   TAG = "MainActivity";     @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         initViews();         initData();         btnAddFragment.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View v) {                 MyFragment   fragment = new MyFragment();                 fragmentTransaction.replace(R.id.container,fragment);                 fragmentTransaction.commit();             }         });         Log.d(TAG,"onCreate");     }     private void initData() {         fragmentManager   = getSupportFragmentManager();         fragmentTransaction   = fragmentManager.beginTransaction();     }     private void initViews() {         btnAddFragment   = (Button) findViewById(R.id.btn_add_fragment);     } }

 

代码很简单，加载相应的布局，通过监听button的点击事件，加载fragment。

activity_main.xml

[代码]xml代码：

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<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:id="@+id/container"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:paddingBottom="@dimen/activity_vertical_margin"     android:paddingLeft="@dimen/activity_horizontal_margin"     android:paddingRight="@dimen/activity_horizontal_margin"     android:paddingTop="@dimen/activity_vertical_margin"     tools:context="com.marktony.fragmentdemo.MainActivity">     <Button         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:id="@+id/btn_add_fragment"         android:text="add_fragment"/> </RelativeLayout>

 

MyFragment.java

[代码]java代码：

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package com.marktony.fragmentdemo; import android.content.Context; import android.os.Bundle; import android.support.annotation.Nullable; import android.support.v4.app.Fragment; import android.util.Log; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; /**  * Created by lizhaotailang on   2016/6/13.  */ public class MyFragment   extends Fragment   {     public static final String   TAG = "MY_FRAGMENT";     // empty   constructor     public MyFragment(){     }     @Override     public void onAttach(Context context) {         super.onAttach(context);         Log.d(TAG,"onAttach");     }     @Override     public void onCreate(@Nullable Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         Log.d(TAG,"onCreate");     }     @Nullable     @Override     public View onCreateView(LayoutInflater   inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {         Log.d(TAG,"onCreateView");         return inflater.inflate(R.layout.fragment_my,container,false);     }     @Override     public void onActivityCreated(@Nullable Bundle savedInstanceState) {         super.onActivityCreated(savedInstanceState);         Log.d(TAG,"onActivityCreated");     }     @Override     public void onStart() {         super.onStart();         Log.d(TAG,"onStart");     }     @Override     public void onResume() {         super.onResume();         Log.d(TAG,"onResume");     }     @Override     public void onPause() {         super.onPause();         Log.d(TAG,"onPause");     }     @Override     public void onStop() {         super.onStop();         Log.d(TAG,"onStop");     }     @Override     public void onDestroyView() {         super.onDestroyView();         Log.d(TAG,"onDestroyView");     }     @Override     public void onDestroy() {         super.onDestroy();         Log.d(TAG,"onDestroy");     }     @Override     public void onDetach() {         super.onDetach();         Log.d(TAG,"onDetach");     } }

 

MyFragment中复写了一些方法，每个方法被调用时打印日志。

ok，大功告成，现在就跑到手机上。

观察打印日志，可以看到:

[代码]java代码：

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1	com.marktony.fragmentdemo D/MainActivity:   onCreate

 

按下按钮时

[代码]java代码：

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com.marktony.fragmentdemo D/MY_FRAGMENT:   onAttach com.marktony.fragmentdemo D/MY_FRAGMENT:   onCreate com.marktony.fragmentdemo D/MY_FRAGMENT:   onCreateView com.marktony.fragmentdemo D/MY_FRAGMENT:   onActivityCreated com.marktony.fragmentdemo D/MY_FRAGMENT:   onStart com.marktony.fragmentdemo D/MY_FRAGMENT:   onResume

 

此时按下home键

[代码]java代码：

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1 2	com.marktony.fragmentdemo D/MY_FRAGMENT:   onPause com.marktony.fragmentdemo D/MY_FRAGMENT:   onStop

 

重新回到应用

[代码]java代码：

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1 2	com.marktony.fragmentdemo D/MY_FRAGMENT:   onStart com.marktony.fragmentdemo D/MY_FRAGMENT:   onResume

 

按下back键，此时fragment和activity均被销毁。

[代码]java代码：

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com.marktony.fragmentdemo D/MY_FRAGMENT:   onPause com.marktony.fragmentdemo D/MY_FRAGMENT:   onStop com.marktony.fragmentdemo D/MY_FRAGMENT:   onDestroyView com.marktony.fragmentdemo D/MY_FRAGMENT:   onDestroy com.marktony.fragmentdemo D/MY_FRAGMENT:   onDetach

 

观察日志，不难发现。

当fragment被创建时，会依次经历以下状态：

·         onAttach()

·         onCreate()

·         onCreateView()

·         onActivityCreated()

当fragment处于可见状态时，会经历

·         onStart()

·         onResume()

不可见时，经历了

·         onPause()

·         onStop()

当fragment被销毁时（或相应的activity被销毁时）

·         onPause()

·         onStop()

·         onDestroyView()

·         onDestroy()

·         onDetach()

由此可见，fragment的生命周期和activity的生命周期真的非常的相似，只是增加了一些新的状态。

在fragment中也是可以通过onSaveInstanceState()方法保存数据的，因为进入停止状态的fragment可能由于系统内存不足而被回收，保存下来数据可以在onCreate(),onCreateView(),onActivityCreate()三个方法中重新得到，他们都含有一个Bundle类型的saveInstanceState参数。

原文链接：http://www.apkbus.com/blog-705730-62669.html