我有一个从 Firebase 获取数据的列表 Activity ，我有取消选中所有复选框的菜单项。第一次进入 Activity 时它工作正常，但是当我从此 Activity 退出应用程序并且当我返回应用程序时应用程序进入休眠状态时，我得到
Exception java.lang.NullPointerException: Attempt to write to field 'int android.app.Fragment.mNextAnim' on a null object reference android.app.BackStackRecord.run (BackStackRecord.java:779) android.app.FragmentManagerImpl.execPendingActions (FragmentManager.java:1582) android.app.FragmentManagerImpl$1.run (FragmentManager.java:483) android.os.Handler.handleCallback (Handler.java:751) android.os.Handler.dispatchMessage (Handler.java:95) android.os.Looper.loop (Looper.java:154) android.app.ActivityThread.main (ActivityThread.java:6688) java.lang.reflect.Method.invoke (Method.java) com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run (ZygoteInit.java:1468) com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1358)
我试图理解为什么我得到 null 但没有成功，我调试了我的应用程序，问题出在函数 setIconPercent()
我的 Activity :
package com.nadav.weddingcalc.activity_best_list;
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Handler;
import android.support.design.widget.FloatingActionButton;
import android.support.v4.app.NavUtils;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Gravity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.Toast;
import com.google.android.gms.ads.AdRequest;
import com.google.android.gms.ads.AdView;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.joanfuentes.hintcase.HintCase;
import com.joanfuentes.hintcase.RectangularShape;
import com.joanfuentes.hintcaseassets.hintcontentholders.SimpleHintContentHolder;
import com.joanfuentes.hintcaseassets.shapeanimators.RevealRectangularShapeAnimator;
import com.joanfuentes.hintcaseassets.shapeanimators.UnrevealRectangularShapeAnimator;
import com.nadav.weddingcalc.R;
import com.squareup.picasso.Picasso;
public class ActivityBest extends AppCompatActivity {
static ListView lv;
private AdapterActivityBest adapterActivityBest;
DatabaseReference mDatabase;
FirebaseUser user;
static private FirebaseAuth auth;
DatabaseReference myRef;
static AdView mAdView;
public String numOfRows;
MenuItem it;
Menu men;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_activity_place);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
final ProgressBar pBar = (ProgressBar) findViewById(R.id.progresbar);
mAdView = (AdView) findViewById(R.id.adView);
AdRequest adRequest = new AdRequest.Builder().
addTestDevice(getString(R.string.ad_test_device_nexus5x))
.addTestDevice("0E9830DF43C4EB440157B8C079727CF9")
.build();
mAdView.loadAd(adRequest);
auth = FirebaseAuth.getInstance();
mDatabase = FirebaseDatabase.getInstance().getReference();
user = auth.getCurrentUser();
lv = (ListView) findViewById(R.id.lv);
adapterActivityBest = new AdapterActivityBest(getApplicationContext() ,lv, this);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setVisibility(View.INVISIBLE);
lv.setAdapter(adapterActivityBest);
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
FirebaseDatabase database = FirebaseDatabase.getInstance();
FirebaseUser user = auth.getCurrentUser();
myRef = database.getReference("users");
myRef.child(user.getUid()).child("list Best").orderByChild("orderNum").addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot snapshot) {
adapterActivityBest.removeAllll();
adapterActivityBest.notifyDataSetChanged();
if (!snapshot.hasChildren()) {
auth = FirebaseAuth.getInstance();
mDatabase = FirebaseDatabase.getInstance().getReference();
FirebaseUser user = auth.getCurrentUser();
String[] temp = getResources().getStringArray(R.array.Best_list);
int[] arrDividers = {0,5,10,18,24,31,37,46};
int[] arrSectors = {1,4,6,7,8,9,11,12,13,14,15,17,19,23,25,27,29,39,43,49,50,51,52};
for(int i=0; i<=55 ; i++){
boolean flag = false;
for(int j=0; j<=22; j++) {
if (i == arrSectors[j]) {
ObjectActivityBest ob = new ObjectActivityBest("false", temp[i], i, "sector");
mDatabase.child("users").child(user.getUid()).child("list Best").child(ob.name+"").setValue(ob);
flag = true;
}
}
for(int j=0; j<=7; j++) {
if (i == arrDividers[j]) {
ObjectActivityBest ob = new ObjectActivityBest("false", temp[i], i, "divider");
mDatabase.child("users").child(user.getUid()).child("list Best").child(ob.name+"").setValue(ob);
flag = true;
}
}
if(!flag){
ObjectActivityBest ob = new ObjectActivityBest("false", temp[i], (i), "item");
mDatabase.child("users").child(user.getUid()).child("list Best").child(ob.name+"").setValue(ob);
}
}
} else {
int countchecks=0;
FirebaseDatabase database = FirebaseDatabase.getInstance();
FirebaseUser user = auth.getCurrentUser();
myRef = database.getReference("users");
for (DataSnapshot messageSnapshot : snapshot.getChildren()) {
String name = (String) messageSnapshot.child("name").getValue();
String check = (String) messageSnapshot.child("check").getValue();
int orderNum = ((Long) messageSnapshot.child("orderNum").getValue()).intValue();
String sector = (String) messageSnapshot.child("sector").getValue();
ObjectActivityBest e = new ObjectActivityBest(check, name, orderNum, sector);
switch(e.sector){
case "sector":
switch(e.name){
case "צלם":
e.name = "בחירת צלם";
mDatabase.child("users").child(user.getUid()).child("list Best").child(e.orderNum+"").setValue(e);
break;
case "קייטרינג":
e.name = "בחירת קייטרינג";
mDatabase.child("users").child(user.getUid()).child("list Best").child(e.orderNum+"").setValue(e);
break;
case "דיגיי":
e.name = "בחירת תקליטן";
mDatabase.child("users").child(user.getUid()).child("list Best").child(e.orderNum+"").setValue(e);
break;
}
adapterActivityBest.addSectionHeaderItem(e);
break;
case "divider":
adapterActivityBest.addDividerHeaderItem(e);
break;
default:
adapterActivityBest.addItem(e);
break;
}
if(e.check.equals("true")){
if(e.name.equals("בחירת אולם")){
countchecks= countchecks+20;
}else{
if((e.orderNum>0&&e.orderNum<=9)){
countchecks+=5;
}else if(e.orderNum>=11 && e.orderNum<=15){
countchecks+=2;
}else{
countchecks++;
}
}
}
}
setIconPercent(countchecks);
}
pBar.setVisibility(View.INVISIBLE);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
// launchAutomaticHint();
}
}, 0);
}
private void setIconPercent(int countchecks) {
TypedArray imgs = getResources().obtainTypedArray(R.array.random_imgs);
it = men.findItem(R.id.action_check);
it.setIcon(ContextCompat.getDrawable(getApplicationContext(), imgs.getResourceId(countchecks/5, -1)));
imgs.recycle();
if(countchecks%5==0){
it = men.findItem(R.id.action_text);
it.setVisible(false);
it = men.findItem(R.id.action_check);
it.setVisible(true);
}else{
it = men.findItem(R.id.action_check);
it.setVisible(false);
it = men.findItem(R.id.action_text);
it.setVisible(true);
it.setTitle(countchecks+"%");
}
}
public void makeTextLong(String s){
Context context = getApplicationContext();
Toast.makeText(context,s,Toast.LENGTH_LONG).show();
}
public Menu getMen() {
return men;
}
public MenuItem getIt() {
return it;
}
public String getNumOfRows() {
return numOfRows;
}
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
// If the nav drawer is open, hide action items related to the content view
getMenuInflater().inflate(R.menu.percentage_menu, menu);
men = menu;
return super.onPrepareOptionsMenu(menu);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(com.nadav.weddingcalc.R.menu.percentage_menu, menu);
men = 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();
android.app.Fragment fragment = null;
//noinspection SimplifiableIfStatement
switch (id) {
case android.R.id.home:
NavUtils.navigateUpFromSameTask(this);
// try{
// this.finish();
// }catch(Exception e){
// makeTextLong("crash");
// }
return true;
default:
return super.onOptionsItemSelected(item);
}
}
}
最佳答案
您得到这个空指针是因为您没有为 fragment 维护堆栈。 当您恢复 Activity 时， fragment 的实例会被破坏并且不会重新初始化。 所以需要维护fragment stack并检查fragment stack是否为null
关于java - 恢复应用程序时尝试写入空对象引用上的字段 'int android.app.Fragment.mNextAnim'，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/42581127/