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Fragment生命周期探索

标签:
Android

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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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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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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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

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