【发布时间】：2021-05-16 05:55:58
【问题描述】：
我最近将我的代码从 android 更新到了 andoidx。现在，我的应用程序在我成功登录后崩溃。我在MainActivity.class 中使用 Viewpager 和 Tablayout。我正在使用MainActivityFragmentsAdapter.class 来获取片段。
经过大量研究，有人建议使用finishUpdate 方法，但我的应用仍然崩溃。
@Override public void finishUpdate(ViewGroup container) {
try{
super.finishUpdate(container);
}
catch (NullPointerException nullPointerException){
System.out.println("Catch the NullPointerException in MainActivityFragmentsAdapter.finishUpdate");
}
}
我也尝试将代码 tabLayout.setupWithViewPager(viewPager); 替换为下面的代码，但发生了同样的错误
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
//tabLayout.addOnTabSelectedListener(new TabLayout.ViewPagerOnTabSelectedListener(viewPager));
tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
@Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabUnselected(TabLayout.Tab tab) {
}
@Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
我在 logcat 上收到此错误：
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.material.tabs.TabLayout.setupWithViewPager(androidx.viewpager.widget.ViewPager)' on a null object reference
at com.fyp.selfzenapp.MainActivity.onCreate(MainActivity.java:44)
MainActivity.class
package com.fyp.selfzenapp;
import android.content.Intent;
import android.os.PersistableBundle;
import androidx.viewpager.widget.ViewPager;
import androidx.core.app.ActivityCompat;
import com.fyp.selfzenapp.adapters.MainFragmentAdapter;
import com.google.android.material.tabs.TabLayout;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mainActivityFragmentsAdapter = new MainActivityFragmentsAdapter(getSupportFragmentManager());
viewPager = findViewById(R.id.main_view_pager);
viewPager.setAdapter(mainActivityFragmentsAdapter);
if(savedInstanceState != null ) {
position = savedInstanceState.getInt(SAVE_INSTANCE_STATE_KEY);
viewPager.setCurrentItem(position);
}
final TabLayout tabLayout = findViewById(R.id.main_tab_layout);
tabLayout.setupWithViewPager(viewPager); // ERROR LINE
viewPager.setOffscreenPageLimit(4);
setTabIcons(tabLayout);
ActivityCompat.requestPermissions(MainActivity.this, new String[]
{android.Manifest.permission.ACCESS_FINE_LOCATION, android.Manifest.permission.ACCESS_COARSE_LOCATION}, 100);
}
int position;
@Override
protected void onPause() {
super.onPause();
position = viewPager.getCurrentItem();
}
@Override
protected void onResume() {
super.onResume();
viewPager.setCurrentItem(position);
}
public void setTabIcons(TabLayout tabLayout) {
int icons[]= {
R.drawable.ic_calendar,
R.drawable.ic_task_complete,
R.drawable.ic_alarm_clock,
R.drawable.ic_man_user
};
for(int i = 0; i < icons.length; i++) {
tabLayout.getTabAt(i).setIcon(icons[i]);
}
}
@Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
Log.d("MAIN ACTIVITY", "Saving instance state");
outState.putInt(SAVE_INSTANCE_STATE_KEY, viewPager.getCurrentItem());
}
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
}
MainActivityFragmentsAdapter.class
public class MainActivityFragmentsAdapter extends FragmentStatePagerAdapter {
int FRAGMENT_COUNT = 4;
public MainActivityFragmentsAdapter(FragmentManager fm) {
super(fm, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
}
@NonNull
@Override
public Fragment getItem(int i) {
AlarmFragment fragment = null;
Bundle args = new Bundle();
switch (i) {
case 0: ScheduleFragment.getInstance(); break;
case 1: new TaskFragment(); break;
case 2: new AlarmFragment(); break;
case 3: new UserFragment(); break;
default: new UserFragment(); break;
}
// The object is just an integer
return fragment;
}
public int getCount() {
return FRAGMENT_COUNT;
}
@Override
public CharSequence getPageTitle(int position) {
String titles[] = {
"SCHED",
"TASK",
"ALARM",
"USER"
};
return titles[position];
}
@Override
public void finishUpdate(ViewGroup container) { //I try this method to fix this error but nothing changes
try{
super.finishUpdate(container);
} catch (NullPointerException nullPointerException){
System.out.println("Catch the NullPointerException in FragmentPagerAdapter.finishUpdate");
}
}
}
build.gradle（应用程序）
apply plugin: 'com.android.application'
android {
signingConfigs {
config {
keyAlias 'androiddebugkey'
keyPassword 'android'
storeFile file('debug.keystore')
storePassword 'android'
}
}
compileSdkVersion 29
buildToolsVersion "29.0.3"
defaultConfig {
applicationId "com.fyp.selfzenapp"
minSdkVersion 21
targetSdkVersion 29
versionCode 1
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
}
debug {
signingConfig signingConfigs.config
}
}
compileOptions {
targetCompatibility = "8"
sourceCompatibility = "8"
} // No static method metafactory
}
apply plugin: 'com.android.application'
dependencies {
implementation fileTree(include: ['*.jar'], dir: 'libs')
implementation 'androidx.appcompat:appcompat:1.2.0'
implementation 'com.android.support.constraint:constraint-layout:2.0.4'
implementation 'androidx.legacy:legacy-support-v4:1.0.0'
implementation 'com.google.firebase:firebase-firestore:23.0.0'
implementation 'com.google.firebase:firebase-storage:20.0.0'
implementation 'com.google.firebase:firebase-functions:20.0.0'
implementation 'com.google.firebase:firebase-core:19.0.0'
implementation 'com.google.firebase:firebase-auth:21.0.1'
implementation 'com.google.firebase:firebase-database:20.0.0'
implementation 'com.google.firebase:firebase-iid:21.1.0'
implementation 'com.google.firebase:firebase-messaging:20.2.3'
testImplementation 'junit:junit:4.13.2'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
implementation 'com.google.android.gms:play-services-auth:19.0.0'
implementation 'com.google.code.gson:gson:2.8.6'
implementation 'com.pes.materialcolorpicker:library:1.2.0'
implementation 'com.google.android.gms:play-services-location:18.0.0'
implementation 'com.google.android.gms:play-services-maps:17.0.1'
implementation 'com.google.android.material:material:1.4.0-beta01'
// Import the Firebase BoM
implementation platform('com.google.firebase:firebase-bom:27.1.0')
// Add the dependency for the Firebase SDK for Google Analytics
// When using the BoM, don't specify versions in Firebase dependencies
implementation 'com.google.firebase:firebase-analytics'
}
apply plugin: 'com.google.firebase.crashlytics'
apply plugin: 'com.google.gms.google-services'
【问题讨论】：
标签： java android-studio android-viewpager android-tablayout