Activty可以直接响应返回键,而Fragment却不行,可用如下方式:
创建一个抽象类BackHandledFragment,该类中有一个抽象方法onBackPress(),所有BackHandledFragment的子类在onBackPress()中处理各自对Back事件的响应逻辑。onBackPress()返回boolean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是否需要消费改时间,如果没有Fragment消费才会自己消费。
/**
* Fragment响应返回键
* @author Administrator
*
*/
public abstract class BackHandledFragment extends Fragment{
protected BackHandledInterface mBackHandledInterface;
public abstract boolean onBackPressed(); @Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(!(getActivity() instanceof BackHandledInterface)){
throw new ClassCastException("Hosting Activity must implement BackHandledInterface");
}else{
this.mBackHandledInterface = (BackHandledInterface)getActivity();
}
} @Override
public void onStart() {
super.onStart();
//告诉FragmentActivity,当前Fragment在栈顶
mBackHandledInterface.setSelectedFragment(this);
}
}
宿主FragmentActivity需实现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.
public interface BackHandledInterface {
public abstract void setSelectedFragment(BackHandledFragment selectedFragment);
}
所以在Fragment的onCreate()中会判断宿主FragmentActivity是否已实现了该接口。在Fragment的onStart()方法中就会调用该接口告诉宿主Fragment自己是当前屏幕可见的Fragment。
宿主FragmentActivity就可以在onBackPressed()方法中对Back时间进行判断处理了。
public class MainActivity extends FragmentActivity implements BackHandledInterface{
private BackHandledFragment mBackHandedFragment;
private boolean hadIntercept;
private Button mBtn; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
this.mBtn = (Button)findViewById(R.id.btn);
this.mBtn.setOnClickListener(new OnClickListener() { @Override
public void onClick(View v) {
MyFragment f = new MyFragment();
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.replace(R.id.container, f);
ft.addToBackStack("tag");
ft.commit();
}
});
} @Override
public void setSelectedFragment(BackHandledFragment selectedFragment) {
this.mBackHandedFragment = selectedFragment;
} @Override
public void onBackPressed() {
if(mBackHandedFragment == null || !mBackHandedFragment.onBackPressed()){
if(getSupportFragmentManager().getBackStackEntryCount() == 0){
super.onBackPressed();
}else{
getSupportFragmentManager().popBackStack();
}
}
}
}
在Fragment中的使用
public class MyFragment extends BackHandledFragment {
private boolean hadIntercept;
@Override
public View onCreateView(LayoutInflater inflater,
@Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
return getLayoutInflater(savedInstanceState).inflate(R.layout.fragment_a, null);
} @Override
protected boolean onBackPressed() {
if(hadIntercept){
return false;
}else{
Toast.makeText(getActivity(), "Click MyFragment", Toast.LENGTH_SHORT).show();
hadIntercept = true;
return true;
}
} }