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");
}
}
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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>
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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");
}
}
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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>
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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");
}
}
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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>
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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");
}
}
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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>
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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 *** 作：
5-1 测试返回
*** 作：点击返回键，此时应用已经退出。log如下：
5-2 home键测试
*** 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();
}
});
}
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*** 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();
}
});
}
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1.测试replace
*** 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);
1
的注释。
*** 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");
}
}
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*** 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();
}
});
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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…）
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版权声明：本文为CSDN博主「hdcanta」的原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/u014699958/article/details/52996143
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