首先创建一个抽象类BackHandledFragment，该类有一个抽象方法onBackPressed()，所有BackHandledFragment的子类在onBackPressed方法中处理各自对Back事件的消费逻辑。onBackPressed返回布尔值，宿主FragmentActivity将会根据该方法的返回值判断子Fragment是否有消费Back事件。此外，宿主FragmentActivity还会保持一份当前Fragment的引用，当用户按下Back键时，宿主Activity会判断当前Fragment是否需要消费该事件，如果没有Fragment消费才会自己消费。
1 public abstract class BackHandledFragment extends Fragment {
2
3 protected BackHandledInterface mBackHandledInterface;
4
5 /**
6 * 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
7 * FragmentActivity捕捉到物理返回键点击事件后会首先询问Fragment是否消费该事件
8 * 如果没有Fragment消息时FragmentActivity自己才会消费该事件
9 */
10 protected abstract boolean onBackPressed();
11
12 @Override
13 public void onCreate(Bundle savedInstanceState) {
14 super.onCreate(savedInstanceState);
15 if(!(getActivity() instanceof BackHandledInterface)){
16 throw new ClassCastException("Hosting Activity must implement BackHandledInterface");
17 }else{
18 this.mBackHandledInterface = (BackHandledInterface)getActivity();
19 }
20 }
21
22 @Override
23 public void onStart() {
24 super.onStart();
25 //告诉FragmentActivity，当前Fragment在栈顶
26 mBackHandledInterface.setSelectedFragment(this);
27 }
28
29 }
宿主FragmentActivity需要继承BackHandledIntegerface，子Fragment会通过该接口告诉宿主FragmentActivity自己是当前屏幕可见的Fragment。
1 public interface BackHandledInterface {
2 public abstract void setSelectedFragment(BackHandledFragment selectedFragment);
3 }
所以在Fragment的onCreate中会判断宿主FragmentActivity是否已继承了该接口。在Fragment的onStart()方法中就会调用该接口告诉宿主FragmentActivity自己是当前屏幕可见的Fragment。
宿主FragmentActivity就可以在onBackPressed()方法中对Back事件进行判断处理了。
1 public class MainActivity extends FragmentActivity implements BackHandledInterface{
2
3 private BackHandledFragment mBackHandedFragment;
4 private boolean hadIntercept;
5
6 @Override
7 public void setSelectedFragment(BackHandledFragment selectedFragment) {
8 this.mBackHandedFragment = selectedFragment;
9 }
10
11 @Override
12 public void onBackPressed() {
13 if(mBackHandedFragment == null || !mBackHandedFragment.onBackPressed()){
14 if(getSupportFragmentManager().getBackStackEntryCount() == 0){
15 super.onBackPressed();
16 }else{
17 getSupportFragmentManager().popBackStack();
18 }
19 }
20 }
21 }
DEMO完整下载地址：https://github.com/mxy1228/FragmentHandleBackDemo/
http://vinsol.com/blog/2014/10/01/handling-back-button-press-inside-fragments/