我有一个导航抽屉，其中的项目正在打开碎片，但当我尝试使用导航抽屉上的项目打开另一个活动时，它会崩溃并打开所述活动。这是我的代码：
MainActivity.java
package application.cedie.myapplication;
import android.app.Activity;
import android.content.Intent;
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.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.NotificationCompat;
import android.text.InputType;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.inputmethod.EditorInfo;
import android.widget.EditText;
import layout.BlankFragment;
import layout.DrugList;
import layout.HerbalMedicineList;
import layout.Home;
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener, Home.OnFragmentInteractionListener, BlankFragment.OnFragmentInteractionListener, DrugList.OnFragmentInteractionListener
, HerbalMedicineList.OnFragmentInteractionListener{
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
Fragment fragment = null;
Class fragmentClass = null;
fragmentClass = BlankFragment.class;
try {
fragment = (Fragment) fragmentClass.newInstance();
}catch (Exception e){
e.printStackTrace();
}
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.Fragment_container, fragment).commit();
NavigationView nw = (NavigationView)
findViewById(R.id.nav_view);
nw.setItemIconTintList(null);
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();
}
});
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
drawer.setDrawerListener(toggle);
toggle.syncState();
NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
navigationView.setNavigationItemSelectedListener(this);
}
@Override
public void onBackPressed() {
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
if (drawer.isDrawerOpen(GravityCompat.START)) {
drawer.closeDrawer(GravityCompat.START);
} else {
super.onBackPressed();
}
}
@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
// 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
return super.onOptionsItemSelected(item);
}
@SuppressWarnings("StatementWithEmptyBody")
@Override
public boolean onNavigationItemSelected(MenuItem item) {
// Handle navigation view item clicks here.
int id = item.getItemId();
Fragment fragment = null;
Class fragmentClass = null;
if (id == R.id.nav_home) {
fragmentClass = Home.class;
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.Fragment_container,fragment).commit();
} else if (id == R.id.nav_reminder) {
fragmentClass = BlankFragment.class;
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.Fragment_container,fragment).commit();
} else if (id == R.id.nav_druglist) {
fragmentClass = DrugList.class;
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.Fragment_container,fragment).commit();
} else if (id == R.id.nav_herbdrug) {
fragmentClass = HerbalMedicineList.class;
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.Fragment_container,fragment).commit();
} else if (id == R.id.nav_settings) {
} else if (id == R.id.nav_help) {
} else if (id == R.id.nav_about) {
Intent newAct = new Intent(getApplicationContext(), About.class);
startActivity(newAct);
}
try {
fragment = (Fragment) fragmentClass.newInstance();
}catch (Exception e){
e.printStackTrace();
}
DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
drawer.closeDrawer(GravityCompat.START);
return true;
}
@Override
public void onFragmentInteraction(Uri uri) {
}
}
About.java
package application.cedie.myapplication;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
public class About extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_about);
}
}
logcat的
07-06 03:28:23.426 1760-1760/application.cedie.myapplication I/Process: Sending signal. PID: 1760 SIG: 9
07-06 03:28:30.049 3855-3876/application.cedie.myapplication I/OpenGLRenderer: Initialized EGL, version 1.4
07-06 03:28:30.049 3855-3876/application.cedie.myapplication W/OpenGLRenderer: Failed to choose config with EGL_SWAP_BEHAVIOR_PRESERVED, retrying without...
07-06 03:28:30.059 3855-3876/application.cedie.myapplication D/OpenGLRenderer: Enabling debug mode 0
07-06 03:28:33.043 3855-3855/application.cedie.myapplication V/Monotype: SetAppTypeFace- try to flip, app = application.cedie.myapplication
07-06 03:28:33.044 3855-3855/application.cedie.myapplication V/Monotype: Typeface getFontPathFlipFont - systemFont = /data/data/flipfont/app_fonts/Felbridge#Felbridge
07-06 03:28:33.256 3855-3855/application.cedie.myapplication W/art: Before Android 4.1, method android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter, android.content.res.ColorStateList, android.graphics.PorterDuff$Mode) would have incorrectly overridden the package-private method in android.graphics.drawable.Drawable
07-06 03:28:34.020 3855-3871/application.cedie.myapplication W/art: Suspending all threads took: 6.224ms
07-06 03:28:38.532 3855-3855/application.cedie.myapplication D/AndroidRuntime: Shutting down VM
07-06 03:28:38.533 3855-3855/application.cedie.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: application.cedie.myapplication, PID: 3855
java.lang.NullPointerException: Attempt to write to field 'android.support.v4.app.FragmentManagerImpl android.support.v4.app.Fragment.mFragmentManager' on a null object reference
at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:418)
at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:453)
at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:445)
at application.cedie.myapplication.MainActivity.onNavigationItemSelected(MainActivity.java:128)
at android.support.design.widget.NavigationView$1.onMenuItemSelected(NavigationView.java:151)
at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:811)
at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152)
at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:958)
at android.support.design.internal.NavigationMenuPresenter$1.onClick(NavigationMenuPresenter.java:318)
at android.view.View.performClick(View.java:4756)
at android.view.View$PerformClick.run(View.java:19761)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5253)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:949)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:744)
片段类： Home.java
package layout;
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.EditText;
import application.cedie.myapplication.R;
/**
* A simple {@link Fragment} subclass.
* Activities that contain this fragment must implement the
* {@link Home.OnFragmentInteractionListener} interface
* to handle interaction events.
* Use the {@link Home#newInstance} factory method to
* create an instance of this fragment.
*/
public class Home 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;
public Home() {
// 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 Home.
*/
// TODO: Rename and change types and number of parameters
public static Home newInstance(String param1, String param2) {
Home fragment = new Home();
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_home, 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(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);
}
}
答案 0 :(得分：1)
试试这个
Fragment fragment = null;
if (id == R.id.nav_home) {
fragment = Home.class;
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.Fragment_container,fragment ).comit();
} else if (id == R.id.nav_reminder) {
fragment = BlankFragment.class;
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.Fragment_container,fragment ).comit();
} else if (id == R.id.nav_druglist) {
fragment = DrugList.class;
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.Fragment_container,fragment ).comit();
} else if (id == R.id.nav_herbdrug) {
fragment = HerbalMedicineList.class;
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.Fragment_container,fragment ).commit();
} else if (id == R.id.nav_settings) {
} else if (id == R.id.nav_help) {
} else if (id == R.id.nav_about) {
Intent newAct = new Intent(getApplicationContext(), About.class);
startActivity(newAct);
}
答案 1 :(得分：1)
这解决了我的问题：
DATE每当我打开一个片段时，我都会把它放进去。