Fragment生命周期及add、replace、remove、hide&show方法分析

最近做项目时，发现未能完全的理解Fragment的生命周期，以致在处理逻辑上踩到到了一些坑。所以花了点时间去分析，也顺便整理下，下次再碰到Fragment时就可以避免一些坑了（大笑）。

项目有一个Activity类和3个Fragment类。Activity 中放置3个按钮（实质TextView）可以切换到不同的Fragment上。下面将给出Activity 和Fragment的代码和layout。

1-1 Fragment1

public class Fragment1 extends Fragment {    final  String TAG  = " test  Fragment1";    public Fragment1() {        // Required empty public constructor    }    @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");    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,                             Bundle savedInstanceState) {        View view = inflater.inflate(R.layout.fragment1_layout, null);        Log.d(TAG,"onCreateView");        return view;    }    @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");    }}

1-2 fragment1_layout.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:background="#888"    android:gravity="center">    <TextView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:textSize="30sp"        android:text="Fragment1"/></LinearLayout>

2-1 Fragment2

public class Fragment2 extends Fragment {    final  String TAG  = " test  Fragment2";    public Fragment2() {        // Required empty public constructor    }    @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");    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,                             Bundle savedInstanceState) {        View view = inflater.inflate(R.layout.fragment2_layout, null);        Log.d(TAG,"onCreateView");        return view;    }    @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");    }}

2-2 fragment2_layout.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:background="#888"    android:gravity="center"><TextView    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:textSize="30sp"    android:text="Fragment2"/></LinearLayout>

3-1 Fragment3

public class Fragment3 extends Fragment {    final  String TAG  = " test  Fragment3";    public Fragment3() {        // Required empty public constructor    }    @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");    }    @Override    public View onCreateView(LayoutInflater inflater, ViewGroup container,                             Bundle savedInstanceState) {        View view = inflater.inflate(R.layout.fragment3_layout, null);        Log.d(TAG,"onCreateView");        return view;    }    @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");    }}

3-2 fragment3_layout.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:background="#888"    android:gravity="center"><TextView    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:textSize="30sp"    android:text="Fragment3"/></LinearLayout>

4-1 MainActivity

public class MainActivity extends Activity{    final String TAG = " test  MainActivity";    TextView mFragment1Tv ;    TextView mFragment2Tv ;    TextView mFragment3Tv ;    FrameLayout mainll ;    FragmentManager manager ;    FragmentTransaction transaction;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        this.setContentView(R.layout.activity_main);        initView();        initListener();        initData();        Log.d(TAG,"onCreate");    }    private void initListener() {        mFragment1Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Fragment1 fragment1= new Fragment1();                transaction = manager.beginTransaction();                transaction.add(R.id.main_ll, fragment1,"1");                transaction.commit();            }        });        mFragment2Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Fragment2 fragment2= new Fragment2();                transaction = manager.beginTransaction();                transaction.add(R.id.main_ll, fragment2,"2");                transaction.commit();            }        });        mFragment3Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Fragment3 fragment3= new Fragment3();                transaction = manager.beginTransaction();                transaction.add(R.id.main_ll, fragment3,"3");                transaction.commit();            }        });    }    private void initData() {        manager = getFragmentManager();    }    private void initView() {        mFragment1Tv = (TextView) findViewById(R.id.fragment1_tv);        mFragment2Tv = (TextView) findViewById(R.id.fragment2_tv);        mFragment3Tv = (TextView) findViewById(R.id.fragment3_tv);        mainll  = (FrameLayout) findViewById(R.id.main_ll);    }    @Override    protected void onStart() {        super.onStart();        Log.d(TAG,"onCreate");    }    @Override    protected void onRestart() {        super.onRestart();        Log.d(TAG,"onRestart");    }    @Override    protected void onResume() {        super.onResume();        Log.d(TAG,"onResume");    }    @Override    protected void onPause() {        super.onPause();        Log.d(TAG,"onPause");    }    @Override    protected void onStop() {        super.onStop();        Log.d(TAG,"onStop");    }    @Override    protected void onDestroy() {        super.onDestroy();        Log.d(TAG,"onDestroy");    }}

4-2 activity_main.xml

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/activity_main"    android:layout_width="match_parent"    android:layout_height="match_parent">    <LinearLayout        android:id="@+id/index"        android:layout_width="match_parent"        android:layout_height="40dp"        android:orientation="horizontal">        <TextView            android:id="@+id/fragment1_tv"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_margin="5dp"            android:background="#bbb"            android:text="Fragment1"            android:textSize="22sp" />        <TextView            android:id="@+id/fragment2_tv"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_margin="5dp"            android:background="#bbb"            android:text="Fragment2"            android:textSize="22sp" />        <TextView            android:id="@+id/fragment3_tv"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_margin="5dp"            android:background="#bbb"            android:text="Fragment3"            android:textSize="22sp" />    </LinearLayout>    <View        android:layout_below="@id/index"        android:layout_width="match_parent"        android:layout_height="1dp"        android:background="#aaa"/>    <LinearLayout        android:id="@+id/main_ll"        android:layout_width="match_parent"        android:layout_height="match_parent"        android:orientation="vertical"        android:layout_alignParentBottom="true"        android:layout_alignParentStart="true">    </LinearLayout></RelativeLayout>

5 测试生命周期
(一) add 方法分析
1.启动app，log如图：

界面如下：

2.点击Fragment1，log如下:

界面如下：

3点击fragment2 log如下： (这里并没有触发fragment1的生命周期)

界面如下：

4点击fragment3 log如下：

界面如下：

5 在此时分为两次不同的操作：

5-1 测试返回
操作：点击返回键，此时应用已经退出。log如下：

5-2 home键测试
操作：（1）点击home键，app退到后台，log如下:

（2）点击应用图标重新打开app，log如下:

6 回退栈测试
再回到5-1 ，如果想要点击返回键回到上一个Fragment的话，那么就需要加入到会退栈。
修改 MainActivity 的方法initListener如下：

private void initListener() {        mFragment1Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Fragment1 fragment1= new Fragment1();                transaction = manager.beginTransaction();                transaction.add(R.id.main_ll, fragment1,"1");                transaction.addToBackStack(null);                transaction.commit();            }        });        mFragment2Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Fragment2 fragment2= new Fragment2();                transaction = manager.beginTransaction();                transaction.add(R.id.main_ll, fragment2,"2");                transaction.addToBackStack(null);                transaction.commit();            }        });        mFragment3Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Fragment3 fragment3= new Fragment3();                transaction = manager.beginTransaction();                transaction.add(R.id.main_ll, fragment3,"3");                transaction.addToBackStack(null);                transaction.commit();            }        });    }

操作：执行 1.打开app,2.点击Fragment，3.点击Fragment2，4.点击Fragment3。
此时清空LogCat，再点击返回键Log如下：

此时界面回到Fragment2，而其他Fragment和Activity的生命周期是没有变化的。若再点击返回键将回到Fragment1界面，再点击返回键就是回到Activity界面了。

(二) replace方法分析
修改 MainActivity 的方法initListener如下：（主要是替换add为replace）

private void initListener() {        mFragment1Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Fragment1 fragment1= new Fragment1();                transaction = manager.beginTransaction();                transaction.replace(R.id.main_ll, fragment1,"1");               //transaction.add(R.id.main_ll, fragment1,"1");             // transaction.addToBackStack(null);                transaction.commit();            }        });        mFragment2Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Fragment2 fragment2= new Fragment2();                transaction = manager.beginTransaction();                transaction.replace(R.id.main_ll, fragment2,"2");                //transaction.add(R.id.main_ll, fragment2,"2");              // transaction.addToBackStack(null);                transaction.commit();            }        });        mFragment3Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Fragment3 fragment3= new Fragment3();                transaction = manager.beginTransaction();                transaction.replace(R.id.main_ll, fragment3,"3");                //transaction.add(R.id.main_ll, fragment3,"3");                //transaction.addToBackStack(null);                transaction.commit();            }        });    }

1.测试replace
操作：启动app，然后点击Fragment1，再点击Fragment2，log如下：

2.测试返回键
在上一步骤的基础上点击物理返回键Log如下：（应用程序已经退出了）

3.在（二）1的基础上点击home键，再重新打开app，log如下:

4．此时看下会退栈的情况。
修改 MainActivity 的方法initListener，主要是取消

// transaction.addToBackStack(null);

的注释。

操作：打开app，点击Fragment1，点击Fragment2，清空logCat，再点击返回键，此时log如下：

可见replace 是会销毁掉被replace 的Fragment。

(三) hide &show方法分析。
修改 MainActivity如下：（在activity的oncreate中add Fragment1和Fragment2，修改mFragment2Tv的点击事件。）

public class MainActivity extends Activity{    final String TAG = "testFragment  MainActivity";    TextView mFragment1Tv ;    TextView mFragment2Tv ;    TextView mFragment3Tv ;    FrameLayout mainll ;    FragmentManager manager ;    FragmentTransaction transaction;    Fragment1 fragment1;    Fragment2 fragment2;    Fragment3 fragment3;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        this.setContentView(R.layout.activity_main);        initView();        initListener();        initData();        Log.d(TAG,"onCreate");    }    private void initListener() {        mFragment1Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                transaction = manager.beginTransaction();                transaction.add(R.id.main_ll, fragment1,"1");                transaction.commit();            }        });        mFragment2Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                transaction = manager.beginTransaction();                transaction.hide(fragment1).show(fragment2);                transaction.commit();            }        });        mFragment3Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                transaction = manager.beginTransaction();                transaction.replace(R.id.main_ll, fragment3,"3");//                transaction.add(R.id.main_ll, fragment3,"3");                transaction.addToBackStack(null);                transaction.commit();            }        });    }    private void initData() {        manager = getFragmentManager();        fragment1= new Fragment1();        fragment2= new Fragment2();        fragment3= new Fragment3();        transaction = manager.beginTransaction();        transaction.add(R.id.main_ll, fragment2,"2");        transaction.add(R.id.main_ll, fragment1,"1");        transaction.commit();    }    private void initView() {        mFragment1Tv = (TextView) findViewById(R.id.fragment1_tv);        mFragment2Tv = (TextView) findViewById(R.id.fragment2_tv);        mFragment3Tv = (TextView) findViewById(R.id.fragment3_tv);        mainll  = (FrameLayout) findViewById(R.id.main_ll);    }    @Override    protected void onStart() {        super.onStart();        Log.d(TAG,"onStart");    }    @Override    protected void onRestart() {        super.onRestart();        Log.d(TAG,"onRestart");    }    @Override    protected void onResume() {        super.onResume();        Log.d(TAG,"onResume");    }    @Override    protected void onPause() {        super.onPause();        Log.d(TAG,"onPause");    }    @Override    protected void onStop() {        super.onStop();        Log.d(TAG,"onStop");    }    @Override    protected void onDestroy() {        super.onDestroy();        Log.d(TAG,"onDestroy");    }}

操作：启动app ，log如下图，代码里面是先add Fragment2 再add Fragment1，此时显示的界面是Fragment1 的界面，然后点击TextView mFragment2Tv，界面切换到了Fragment2上，而log无任何的信息打印，可见hide &show 方法不触发Fragment生命周期，只影响它的显示。

(四) remove方法分析
在 (三)hide&show方法分析 的代码基础上修改MainActivity 如下：
(其他代码不变，只修改为remove方法)

mFragment2Tv.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                transaction = manager.beginTransaction();                transaction.remove(fragment1).show(fragment2);                transaction.commit();            }        });

启动app 时的log:

此时点击Fragment2，log如下:

本以为分析下Fragment会很简单，想不到分析Fragment+一篇文章 能耗那么多时间，看来得加个卤蛋犒劳犒劳自己了（偷笑中…）