我正在尝试从firebase检索数据。操作看起来成功，但在我登录/注册时正在崩溃。我认为这可能是阵列适配器的问题。我已经清理、重建并查看了清单文件(顺便说一下，我正在使用一个模拟器）
我是android studio+firebase+stack overflow的新手，
控制台运行输出
reported: 147798919; UID 10154; state: ENABLED
I/OpenGLRenderer: Davey! duration=701ms; Flags=0, IntendedVsync=28127383579304, Vsync=28127400245970, OldestInputEvent=9223372036854775807, NewestInputEvent=0, HandleInputStart=28127409815200, AnimationStart=28127409867900, PerformTraversalsStart=28127410700500, DrawStart=28127411258900, SyncQueued=28127414225700, SyncStart=28127422917600, IssueDrawCommandsStart=28127422979700, SwapBuffers=28127823242800, FrameCompleted=28128093957100, DequeueBufferDuration=478000, QueueBufferDuration=266940200, GpuCompleted=0,
I/AssistStructure: Flattened final assist data: 1576 bytes, containing 1 windows, 9 views
W/System: Ignoring header X-Firebase-Locale because its value was null.
W/System: Ignoring header X-Firebase-Locale because its value was null.
W/System: Ignoring header X-Firebase-Locale because its value was null.
D/FirebaseAuth: Notifying id token listeners about user ( ZHeNAZbKDUQbUSF5u9ilCXmlycv1 ).
D/AndroidRuntime: Shutting down VM
Process: com.example.bearnecetties4, PID: 18765
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.bearnecetties4/com.example.bearnecetties4.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3365)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:173)
at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:174)
at android.content.Context.obtainStyledAttributes(Context.java:744)
at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:839)
at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:806)
at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:630)
at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:223)
at com.example.bearnecetties4.MainActivity.<init>(MainActivity.java:28)
at java.lang.Class.newInstance(Native Method)
at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
at android.app.Instrumentation.newActivity(Instrumentation.java:1253)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3353)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
I/Process: Sending signal. PID: 18765 SIG: 9主活动.java
我认为问题出在代码的这一部分
package com.example.bearnecetties4;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import com.google.firebase.auth.FirebaseAuth;
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 java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
private Button logout = findViewById(R.id.logout);
private ListView listView = findViewById(R.id.listVie
w);
private Button add = findViewById(R.id.add);
private EditText edit = findViewById(R.id.edit);
private TextView label =findViewById(R.id.label);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
logout.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
FirebaseAuth.getInstance().signOut();
Toast.makeText(MainActivity.this, "logged Out", Toast.LENGTH_SHORT).show();
startActivity(new Intent(new Intent(MainActivity.this, StartActivity.class)));
}
});
add.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
String txt_name = edit.getText().toString();
if (txt_name.isEmpty())
Toast.makeText(MainActivity.this,"Logged Out",Toast.LENGTH_SHORT).show();
else {
FirebaseDatabase.getInstance().getReference().child("Test").push().child("Name").setValue(txt_name);
}
}
**});
final ArrayList<String> list= new ArrayList<>();
final ArrayAdapter adapter = new ArrayAdapter<String>(this,R.layout.list_item,list);
listView.setAdapter(adapter);
DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
list.clear();
for (DataSnapshot snapshot : dataSnapshot.getChildren()){
list.add(snapshot.getValue().toString());
}
adapter.notifyDataSetChanged();
}
@Override
public void onCancelled(@NonNull DatabaseError error) {
}
});
}
}清单文件
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.bearnecetties4">
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="BearNecessities"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/Theme.BearNecetties4">
<activity android:name=".MainActivity"/>
<activity android:name=".LoginActivity2" />
<activity android:name=".RegisterActivity2" />
<activity android:name=".StartActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest/>
暂无答案！
目前还没有任何答案，快来回答吧！