Fragment监听返回键

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/