1、背景
如圖,在圖片中,要實現ListFragment中點擊的不同,就要實現對DetailFragment的更新,在DetailFragment中的內容出現變化時,ListFragment也要做相應的變化,那麼如何,實現DetailFragment與ListFragment之間的通信呢?
2、實現方式
爲了保持Fragment的獨立性,我們可以在Fragment中定義回調接口,委託託管的Activity來完成那些不應該由Fragment處理的任務,託管activity將實現回調接口,履行託管Fragment的任務
1、在ListFragment中定義了一個內部接口,
public class CrimeListFragment extends ListFragment {
private Callbacks mCallbacks;
public interface Callbacks{
void onCrimeSelected(Crime crime);
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
mCallbacks=(Callbacks) activity;
}
@Override
public void onDetach() {
// TODO Auto-generated method stub
super.onDetach();
mCallbacks=null;
}
2、同時在託管的Activty中實現這個接口,並重寫了接口中的onCrimeSelected(Crime crime)方法,該方法主要用於當點擊ListFragment中的item時,更新DetailFragment,public class CrimeListActivity extends SingleFragmentActivity implements CrimeListFragment.Callbacks{
@Override
public void onCrimeSelected(Crime crime) {
FragmentManager fm=getSupportFragmentManager();
FragmentTransaction ft=fm.beginTransaction();
Fragment oldDetail=fm.findFragmentById(R.id.detailFragmentContainer);
Fragment newDetial=CrimeFragment.newInstance(crime.getId());
if(oldDetail!=null){
ft.remove(oldDetail);
}
ft.add(R.id.detailFragmentContainer, newDetial);
ft.commit();
}
}
}
3、那麼如何在ListFragment中實現呢?首先在ListFragment被託管在Activity時,實例化mCallback對象,當Fragment被託管的Activity移除時,設置mCallback對象爲空,因爲ListFragment不被託管時,更新界面是不起作用的。同時當點擊ListFragment中的數據時,調用mCallback.onCrimeSelected()方法
<pre name="code" class="java">public class CrimeListFragment extends ListFragment {
public void onListItemClick(ListView l, View v, int position, long id) {
// get the Crime from the adapter
Crime c = ((CrimeAdapter)getListAdapter()).getItem(position);
// start an instance of CrimePagerActivity
// Intent i = new Intent(getActivity(), CrimePagerActivity.class);
// i.putExtra(CrimeFragment.EXTRA_CRIME_ID, c.getId());
// startActivityForResult(i, 0);
mCallbacks.onCrimeSelected(c);
public interface Callbacks{
void onCrimeSelected(Crime crime);
}
public void UpdateUI(){
((CrimeAdapter)getListAdapter()).notifyDataSetChanged();
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
mCallbacks=(Callbacks) activity;
}
@Override
public void onDetach() {
// TODO Auto-generated method stub
super.onDetach();
mCallbacks=null;
}
}
mCallback對象其實還是一個Activity對象,所以在此方法中調用的onCrimeSelected()方法就是activity中被重寫的onCrimeSelected()方法,那麼ListFragment更新Detail界面的流程就是這樣。同理,在DetailFragment中更新ListFragment中的數據,只需要在DetailFragment中聲明一個接口,同時在Activity中實現,在實現的過程中調用ListFragment中的
UpdateUI方法,就可以實現DetailFragment中的數據變化後ListFragment中的界面也會相應的進行改變,具體代碼如下:
public class CrimeFragment extends Fragment {
/**
*
* @author user
* Required interface for hosting activites.
*/
public interface CallBacks{
void onCrimeUpdated(Crime crime);
}
@Override
public void onAttach(Activity activity) {
// TODO Auto-generated method stub
super.onAttach(activity);
mCallbacks=(CallBacks) activity;
}
@Override
public void onDetach() {
// TODO Auto-generated method stub
super.onDetach();
mCallbacks=null;
}
{
在Activity中重寫DetailFragment中的方法
public class CrimeListActivity extends SingleFragmentActivity implements CrimeListFragment.Callbacks,CrimeFragment.CallBacks {
@Override
public void onCrimeUpdated(Crime crime) {
// TODO Auto-generated method stub
FragmentManager fm=getSupportFragmentManager();
CrimeListFragment listFragment=(CrimeListFragment) fm.findFragmentById(R.id.fragmentContainer);
listFragment.UpdateUI();
}
}