[英]App Crashes when replacing Android Fragments, android studio
I am new to android programming and I am trying to write a simple application that switches between two Fragments. 我是android编程的新手,我试图编写一个在两个Fragment之间切换的简单应用程序。 I started a new project with a blank activity template that already included a Fragment. 我使用空白活动模板(其中已经包含片段)开始了一个新项目。 I think this could be where I am going wrong, but I am lost. 我认为这可能是我出问题的地方,但我迷路了。 Every time I launch and click the button the app crashes. 每当我启动并单击按钮时,应用程序就会崩溃。 It throws a must implement OnFragmentInteractionListener error from MyFragment2's onAttach method. 它从MyFragment2的onAttach方法引发必须实现的OnFragmentInteractionListener错误。 If I comment that method out it add's the new Fragment on top of the old one. 如果我注释掉该方法,它将在旧方法的基础上添加新的Fragment。 I have been through just about every tutorial I can find. 我几乎遍历了所有可以找到的教程。 I do not see where my code is going wrong. 我看不到我的代码出了什么问题。 I'm sure it is something easy and I am going to feel pretty stupid when I finally figure it out. 我敢肯定这很容易,当我终于弄清楚这一点时,我会感到非常愚蠢。 Any help would be appreciated. 任何帮助,将不胜感激。 Thanks in advance. 提前致谢。
My main activity: 我的主要活动:
package com.example.misanthropic.fragments;
import android.app.Activity;
import android.app.ActionBar;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.FragmentTransaction;
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.os.Build;
public class Main extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// matically 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);
}
public void buttonClicked(View v){
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
Fragment2 myFragment = new Fragment2();
fragmentTransaction.replace(R.id.fragment_main, myFragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends 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;
}
}
}
The MyFragment2 I would like to swap in: 我想交换MyFragment2:
package com.example.misanthropic.fragments;
import android.app.Activity;
import android.net.Uri;
import android.os.Bundle;
import android.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
/**
* A simple {@link Fragment} subclass.
* Activities that contain this fragment must implement the
* {@link Fragment2.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {@link Fragment2#newInstance} factory method to
* create an instance of this fragment.
*
*/
public class Fragment2 extends Fragment {
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
private OnFragmentInteractionListener mListener;
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment Fragment2.
*/
// TODO: Rename and change types and number of parameters
public static Fragment2 newInstance(String param1, String param2) {
Fragment2 fragment = new Fragment2();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
public Fragment2() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_fragment2, container, false);
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
mListener = (OnFragmentInteractionListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnFragmentInteractionListener");
}
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
public void onFragmentInteraction(Uri uri);
}
}
My main xml: 我的主要xml:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".Main"
tools:ignore="MergeRootFrame" />
My Initial Fragment XML: 我的初始片段XML:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".Main$PlaceholderFragment"
android:id="@+id/fragment_main">
<TextView
android:text="@string/hello_world"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/textView" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="New Button"
android:id="@+id/button"
android:layout_below="@+id/textView"
android:layout_centerHorizontal="true"
android:layout_marginTop="165dp"
android:onClick="buttonClicked" />
</RelativeLayout>
The replacement Fragment XML: 替换片段XML:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.misanthropic.fragments.Fragment2">
<!-- TODO: Update blank fragment layout -->
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="@string/hello_blank_fragment" />
</FrameLayout>
Figured it out. 弄清楚了。 I was calling the wrong id in the replace method. 我在replace方法中调用了错误的ID。
fragmentTransaction.replace(R.id.fragment_main, myFragment);
should have been: 本来应该:
fragmentTransaction.replace(R.id.container, myFragment);
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