1.首先贴上项目结构图：
2.先添加一个接口文件BackHandledInterface.java,定义一个setSelectedFragment方法用于设置当前加载的Fragment在栈顶，主界面MainActivity须实现此接口，代码如下：
package com.example.testdemo;public interface BackHandledInterface { public abstract void setSelectedFragment(BackHandledFragment selectedFragment); } 3.定义一个抽象类BackHandledFragment继承自Fragment，后面跳转的Fragment界面都要继承自BackHandledFragment。抽象类BackHandledFragment中定义一个返回值为boolean类型的onBackPressed方法，用于处理点击返回按键（物理Back键）时的逻辑，若该方法返回false，表示当前Fragment不消费返回事件，而由Fragment所属的FragmentActivity来处理这个事件。代码如下：
1 package com.example.testdemo; 2 3 import android.os.Bundle; 4 import android.support.v4.app.Fragment; 5 6 public abstract class BackHandledFragment extends Fragment { 7 8 protected BackHandledInterface mBackHandledInterface; 9 10 /** 11 * 所有继承BackHandledFragment的子类都将在这个方法中实现物理Back键按下后的逻辑 12 */ 13 protected abstract boolean onBackPressed(); 14 15 @Override 16 public void onCreate(Bundle savedInstanceState) { 17 super.onCreate(savedInstanceState); 18 if (!(getActivity() instanceof BackHandledInterface)) { 19 throw new ClassCastException( 20 "Hosting Activity must implement BackHandledInterface"); 21 } else { 22 this.mBackHandledInterface = (BackHandledInterface) getActivity(); 23 } 24 } 25 26 @Override 27 public void onStart() { 28 super.onStart(); 29 // 告诉FragmentActivity，当前Fragment在栈顶 30 mBackHandledInterface.setSelectedFragment(this); 31 } 32 33 } 4.主界面MainActivity要继承FragmentActivity才能调用getSupportFragmentManager()方法来处理Fragment。MainActivity还需重写onBackPressed方法用来捕捉返回键（Back Key）事件，代码如下：
1 package com.example.testdemo; 2 3 import android.os.Bundle; 4 import android.support.v4.app.FragmentActivity; 5 import android.support.v4.app.FragmentManager; 6 import android.support.v4.app.FragmentTransaction; 7 import android.view.View; 8 import android.view.View.OnClickListener; 9 import android.widget.Button; 10 11 public class MainActivity extends FragmentActivity implements 12 BackHandledInterface { 13 private static MainActivity mInstance; 14 private BackHandledFragment mBackHandedFragment; 15 private Button btnSecond; 16 17 @Override 18 public void onCreate(Bundle savedInstanceState) { 19 super.onCreate(savedInstanceState); 20 setContentView(R.layout.activity_main); 21 btnSecond = (Button) findViewById(R.id.btnSecond); 22 btnSecond.setOnClickListener(new OnClickListener() { 23 24 @Override 25 public void onClick(View v) { 26 FirstFragment first = new FirstFragment(); 27 loadFragment(first); 28 btnSecond.setVisibility(View.GONE); 29 } 30 }); 31 32 } 33 34 public static MainActivity getInstance() { 35 if (mInstance == null) { 36 mInstance = new MainActivity(); 37 } 38 return mInstance; 39 } 40 41 public void loadFragment(BackHandledFragment fragment) { 42 BackHandledFragment second = fragment; 43 FragmentManager fm = getSupportFragmentManager(); 44 FragmentTransaction ft = fm.beginTransaction(); 45 ft.replace(R.id.firstFragment, second, "other"); 46 ft.addToBackStack("tag"); 47 ft.commit(); 48 } 49 50 @Override 51 public void setSelectedFragment(BackHandledFragment selectedFragment) { 52 this.mBackHandedFragment = selectedFragment; 53 } 54 55 @Override 56 public void onBackPressed() { 57 if (mBackHandedFragment == null || !mBackHandedFragment.onBackPressed()) { 58 if (getSupportFragmentManager().getBackStackEntryCount() == 0) { 59 super.onBackPressed(); 60 } else { 61 if (getSupportFragmentManager().getBackStackEntryCount() == 1) { 62 btnSecond.setVisibility(View.VISIBLE); 63 } 64 getSupportFragmentManager().popBackStack(); 65 } 66 } 67 } 68 } 5.分别添加两个子级Fragment，FirstFragment.java和SecondFragment.java,代码分别如下：
FirstFragment.java
1 package com.example.testdemo; 2 3 import android.os.Bundle; 4 import android.support.annotation.Nullable; 5 import android.support.v4.app.FragmentManager; 6 import android.support.v4.app.FragmentTransaction; 7 import android.view.LayoutInflater; 8 import android.view.View; 9 import android.view.View.OnClickListener; 10 import android.view.ViewGroup; 11 import android.widget.Button; 12 13 public class FirstFragment extends BackHandledFragment { 14 private View myView; 15 private Button btnSecond; 16 17 @Override 18 public View onCreateView(LayoutInflater inflater, 19 @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 20 myView = inflater.inflate(R.layout.fragment_first, null); 21 initView(); 22 return myView; 23 } 24 25 private void initView() { 26 btnSecond = (Button) myView.findViewById(R.id.btnSecond); 27 btnSecond.setOnClickListener(new OnClickListener() { 28 29 @Override 30 public void onClick(View v) { 31 SecondFragment second = new SecondFragment(); 32 FragmentManager fm = getFragmentManager(); 33 FragmentTransaction ft = fm.beginTransaction(); 34 ft.replace(R.id.firstFragment, second); 35 ft.addToBackStack("tag"); 36 ft.commit(); 37 } 38 }); 39 } 40 41 @Override 42 protected boolean onBackPressed() { 43 return false; 44 } 45 46 } SecondFragment.java
1 package com.example.testdemo; 2 3 import android.os.Bundle; 4 import android.support.annotation.Nullable; 5 import android.view.LayoutInflater; 6 import android.view.View; 7 import android.view.ViewGroup; 8 9 public class SecondFragment extends BackHandledFragment { 10 11 private View mView; 12 13 @Override 14 public View onCreateView(LayoutInflater inflater, 15 @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { 16 mView = inflater.inflate(R.layout.fragment_second, null); 17 return mView; 18 } 19 20 @Override 21 protected boolean onBackPressed() { 22 return false; 23 } 24 25 } 6.三个布局文件代码如下：activity_main.xml
16 7 13 14 20 21 25 26 27
fragment_first.xml
fragment_second.xml
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7.最后奉上实例链接：