我一直在尝试让片段正常工作，但行为不一致，很难调试。我用xml文件和类文件创建了两个片段。据我所知，这两个frag是以完全相同的方式实现的。
当我在MainActivity中添加"BlankFragment_frag1"时，它就会运行。当我添加BlankFragment2_frag2时，当代码退出MainActivity.onCreate方法时，它会崩溃。
我在一个更复杂的应用程序中遇到了这个问题，所以我去掉了所有无关的东西，用我能用的最简单的应用程序实现了它。。。。仍然会发生。
我在下面附上了.java文件和.xml文件。我会包含整个项目的zip，但我没有看到附加文件对话框。如果有人向我发送请求，我可以通过电子邮件发送该项目darrylctx@gmail.com.
在MainActivity.onCreate方法中，有两行：
_ft.add(R.id.container, _frag1);
_ft.add(R.id.container, _frag2);
如果我注释掉_ft.add（R.id.container，_frag2）；并取消注释//_ft.add（R.id.container，_frag1）；然后运行良好。也就是说，_frag1运行良好。
如果我注释掉_ft.add（R.id.container，_frag1）；和取消注释_ft.add（R.id.container，_frag2）；它在从onCreate方法退出时崩溃。也就是说，_frag2不运行。
据我所知，frag1和frag2的实现之间没有区别，但我一定遗漏了一些东西。
// MainActivity.java ------------------------------------------------------------
package com.example.dcornish.TestFrag;
import android.net.Uri;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
//import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.view.ViewGroup;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity implements BlankFragment.OnFragmentInteractionListener {
BlankFragment _frag1 = new BlankFragment();
BlankFragment2 _frag2 = new BlankFragment2();
FragmentManager _fm;
FragmentTransaction _ft;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
// get the viewgroup for this activity
ViewGroup view = (ViewGroup) findViewById(android.R.id.content);
//Fragment Help: add fragment to main activity
if (savedInstanceState == null) {
//getSupportFragmentManager().beginTransaction().add(R.id.container, new BlankFragment()).commit();
_fm = getSupportFragmentManager();
_ft = _fm.beginTransaction();
// comment out one or the other of the _ft.add methods below to change fragments
//_ft.add(R.id.container, _frag1);
_ft.add(R.id.container, _frag2);
_ft.commit();
}
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
public void onFragmentInteraction(Uri uri){
Toast toast = Toast.makeText(this, "Wheeee!",Toast.LENGTH_SHORT);
toast.show();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@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();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
//BlankFragment.java---------------------------------------
package com.example.dcornish.TestFrag;
import android.content.Context;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
/**
* A simple {@link Fragment} subclass.
* Activities that contain this fragment must implement the
* {@link BlankFragment.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {@link BlankFragment#newInstance} factory method to
* create an instance of this fragment.
*/
public class BlankFragment extends Fragment implements Button.OnClickListener{
// 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;
private Button mButton; //Add at the top of the fragment
public BlankFragment() {
// Required empty public constructor
}
/**
* 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 BlankFragment.
*/
// TODO: Rename and change types and number of parameters
public static BlankFragment newInstance(String param1, String param2) {
BlankFragment fragment = new BlankFragment();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
//return inflater.inflate(R.layout.fragment_blank, container, false);
View view = null;
view = inflater.inflate(R.layout.fragment_blank, container, false);
mButton = (Button) view.findViewById(R.id.button);
mButton.setOnClickListener(this);
return view;
}
// 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(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.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
void onFragmentInteraction(Uri uri);
}
//Fragment Help: Have to figure out what mListener.onFragmentInteraction(null) does
public void onClick(View v){
//Nothing here yet
mListener.onFragmentInteraction(null);
}
}
//BlankFragment2.java----------------------------------------------------
package com.example.dcornish.TestFrag;
import android.content.Context;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
/**
* A simple {@link Fragment} subclass.
* Activities that contain this fragment must implement the
* {@link BlankFragment2.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {@link BlankFragment2#newInstance} factory method to
* create an instance of this fragment.
*/
public class BlankFragment2 extends Fragment implements Button.OnClickListener{
// 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;
private Button _button;
public BlankFragment2() {
// Required empty public constructor
}
/**
* 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 BlankFragment2.
*/
// TODO: Rename and change types and number of parameters
public static BlankFragment2 newInstance(String param1, String param2) {
BlankFragment2 fragment = new BlankFragment2();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = null;
view = inflater.inflate(R.layout.fragment_blank_2, container, false);
_button = (Button) view.findViewById(R.id.whee_button);
_button.setOnClickListener(this);
return view;
}
// 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(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.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
void onFragmentInteraction(Uri uri);
}
public void onClick(View v){
//Nothing here yet
mListener.onFragmentInteraction(null);
}
}
//activity_main.xml----------------------------------------------------
<!-- fragment instructions: android:id = "@+id/container" -->
<!-- give id to the mainActivity layout so it can be referenced as container for fragments -->
<android.support.design.widget.CoordinatorLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id = "@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:context="com.example.dcornish.TestFrag.MainActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<include layout="@layout/content_main" />
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="@dimen/fab_margin"
android:src="@android:drawable/ic_dialog_email" />
</android.support.design.widget.CoordinatorLayout>
// content_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:orientation="vertical"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="com.example.dcornish.TestFrag.MainActivity"
tools:showIn="@layout/activity_main">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!" />
</RelativeLayout>
//fragment_blank.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.dcornish.TestFrag.BlankFragment">
<!-- TODO: Update blank fragment layout -->
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="@string/hello_blank_fragment" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Whee"
android:id="@+id/button"
android:layout_gravity="center" />
</FrameLayout>
//fragment_blank_2.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=".BlankFragment2">
<!-- TODO: Update blank fragment layout -->
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:text="@string/hello_blank_fragment" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="TrajMgr"
android:id="@+id/whee_button"
android:layout_gravity="center" />
</FrameLayout>
//menu_main.xml-----------------------------------------------------------
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
tools:context="com.example.dcornish.TestFrag.MainActivity">
<item
android:id="@+id/mnu_edit_profile"
android:orderInCategory="100"
android:title="Edit Profile"
app:showAsAction="never" />
<item
android:id="@+id/mnu_load_profile"
android:orderInCategory="100"
android:title="Load Profile"
app:showAsAction="never" />
<item
android:id="@+id/mnu_save_profile"
android:orderInCategory="100"
android:title="Save Profile"
app:showAsAction="never" />
<item
android:id="@+id/action_settings"
android:orderInCategory="100"
android:title="@string/action_settings"
app:showAsAction="never" />
<item
android:id="@+id/mnu_help"
android:orderInCategory="100"
android:title="Help"
app:showAsAction="never" />
<item
android:id="@+id/mnu_dash1"
android:orderInCategory="100"
android:title="------------"
app:showAsAction="never" />
<item
android:id="@+id/mnu_exit"
android:orderInCategory="100"
android:title="Exit"
app:showAsAction="never" />
<item
android:id="@+id/mnu_test"
android:orderInCategory="100"
android:title="Test"
app:showAsAction="never" />
</menu>
我想我可能知道是什么导致了崩溃。当您添加BlankFragment2时，您还必须在MainActivity 中实现它的侦听器OnFragmentInteractionListener
@Override
public void onFragmentInteraction(Uri uri) {
}
它应该看起来像这个
public class MainActivity extends AppCompatActivity implements BlankFragment.OnFragmentInteractionListener, BlankFragment2.OnFragmentInteractionListener {
BlankFragment _frag1 = new BlankFragment();
BlankFragment2 _frag2 = new BlankFragment2();
FragmentManager _fm;
FragmentTransaction _ft;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
// get the viewgroup for this activity
ViewGroup view = (ViewGroup) findViewById(android.R.id.content);
//Fragment Help: add fragment to main activity
if (savedInstanceState == null) {
//getSupportFragmentManager().beginTransaction().add(R.id.container, new BlankFragment()).commit();
_fm = getSupportFragmentManager();
_ft = _fm.beginTransaction();
// comment out one or the other of the _ft.add methods below to change fragments
// _ft.add(R.id.container, _frag1);
_ft.add(R.id.container, _frag2);
_ft.commit();
}
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@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();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onFragmentInteraction(Uri uri) {
}
}