我在android studio 0.8.2中有一个向导生成的应用程序,带有导航抽屉
我已经创建了一个片段,并用newInstance()添加了它,我得到了这个错误:
com.domain.myapp E/AndroidRuntime:致命异常: main java.lang.ClassCastException: com.domain.myapp.MainActivity@422fb8f0必须实现OnFragmentInteractionListener
我到处都找不到如何实现这个OnFragmentInteractionListener ??它甚至在android sdk文档中都找不到!
MainActivity.java
import android.app.Activity;
import android.app.ActionBar;
import android.app.Fragment;
import android.app.FragmentManager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.support.v4.widget.DrawerLayout;
public class MainActivity extends Activity
implements NavigationDrawerFragment.NavigationDrawerCallbacks {
/**
* Fragment managing the behaviors, interactions and presentation of the navigation drawer.
*/
private NavigationDrawerFragment mNavigationDrawerFragment;
/**
* Used to store the last screen title. For use in {@link #restoreActionBar()}.
*/
private CharSequence mTitle;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mNavigationDrawerFragment = (NavigationDrawerFragment)
getFragmentManager().findFragmentById(R.id.navigation_drawer);
mTitle = getTitle();
// Set up the drawer.
mNavigationDrawerFragment.setUp(
R.id.navigation_drawer,
(DrawerLayout) findViewById(R.id.drawer_layout));
}
@Override
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
FragmentManager fragmentManager = getFragmentManager();
switch (position) {
case 0: fragmentManager.beginTransaction()
.replace(R.id.container, PlaceholderFragment.newInstance(position + 1))
.commit(); break;
case 1: fragmentManager.beginTransaction()
.replace(R.id.container, AboutFragment.newInstance("test1", "test2"))
.commit(); break; // this crashes the app
case 2: fragmentManager.beginTransaction()
.replace(R.id.container, BrowseQuotesFragment.newInstance("test1", "test2"))
.commit(); break; // this crashes the app
}
}
public void onSectionAttached(int number) {
switch (number) {
case 1:
mTitle = getString(R.string.title_section1);
break;
case 2:
mTitle = getString(R.string.title_section2);
break;
case 3:
mTitle = getString(R.string.title_section3);
break;
}
}
public void restoreActionBar() {
ActionBar actionBar = getActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
actionBar.setDisplayShowTitleEnabled(true);
actionBar.setTitle(mTitle);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
if (!mNavigationDrawerFragment.isDrawerOpen()) {
// Only show items in the action bar relevant to this screen
// if the drawer is not showing. Otherwise, let the drawer
// decide what to show in the action bar.
getMenuInflater().inflate(R.menu.main, menu);
restoreActionBar();
return true;
}
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
/**
* Returns a new instance of this fragment for the given section
* number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
((MainActivity) activity).onSectionAttached(
getArguments().getInt(ARG_SECTION_NUMBER));
}
}
}
发布于 2014-10-21 03:22:06
此处发布的答案没有帮助,但以下链接提供了帮助:
定义接口
public class HeadlinesFragment extends ListFragment {
OnHeadlineSelectedListener mCallback;
// Container Activity must implement this interface
public interface OnHeadlineSelectedListener {
public void onArticleSelected(int position);
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception
try {
mCallback = (OnHeadlineSelectedListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnHeadlineSelectedListener");
}
}
...
}
例如,当用户单击列表项时,将调用片段中的以下方法。该片段使用回调接口将事件传递给父活动。
@Override
public void onListItemClick(ListView l, View v, int position, long id) {
// Send the event to the host activity
mCallback.onArticleSelected(position);
}
实现接口
例如,下面的活动实现了上述示例中的接口。
public static class MainActivity extends Activity
implements HeadlinesFragment.OnHeadlineSelectedListener{
...
public void onArticleSelected(int position) {
// The user selected the headline of an article from the HeadlinesFragment
// Do something here to display that article
}
}
API23:2015/8/31/的更新
重写的方法onAttach(Activity activity)
现在已在android.app.Fragment
中弃用,代码应升级到onAttach(Context context)
@Override
public void onAttach(Context context) {
super.onAttach(context);
}
@Override
public void onStart() {
super.onStart();
try {
mListener = (OnFragmentInteractionListener) getActivity();
} catch (ClassCastException e) {
throw new ClassCastException(getActivity().toString()
+ " must implement OnFragmentInteractionListener");
}
}
发布于 2014-12-27 17:33:42
对于那些在阅读了@meda answer后仍然不理解的人,这里是我对这个问题的简洁和完整的解释:
假设你有两个片段,Fragment_A
和Fragment_B
,它们是从应用程序中自动生成的。在您生成的片段的底部,您将找到以下代码:
public class Fragment_A extends Fragment {
//rest of the code is omitted
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
public void onFragmentInteraction(Uri uri);
}
}
public class Fragment_B extends Fragment {
//rest of the code is omitted
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
public void onFragmentInteraction(Uri uri);
}
}
为了解决这个问题,您必须将onFragmentInteraction
方法添加到您的活动中,在我的示例中,该方法的名称为MainActivity2
。在此之后,您需要像这样对MainActivity
中的所有片段执行implements
:
public class MainActivity2 extends ActionBarActivity
implements Fragment_A.OnFragmentInteractionListener,
Fragment_B.OnFragmentInteractionListener,
NavigationDrawerFragment.NavigationDrawerCallbacks {
//rest code is omitted
@Override
public void onFragmentInteraction(Uri uri){
//you can leave it empty
}
}
附言:简而言之,这种方法可以用于片段之间的通信。如果您想了解更多关于此方法的信息,请参考此link。
发布于 2014-07-16 18:51:51
查看由Android Studio创建的自动生成的Fragment
。当您创建新的Fragment
时,Studio为您保存了一大堆代码。在自动生成的模板的底部有一个名为OnFragmentInteractionListener
的内部接口定义。您的Activity
需要实现此接口。这是Fragment
向Activity
通知事件的推荐模式,这样它就可以采取适当的操作,例如加载另一个Fragment
。有关详细信息,请参阅此页面的“为活动创建事件回调”部分:http://developer.android.com/guide/components/fragments.html
https://stackoverflow.com/questions/24777985
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