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我正在做一个博客的应用程序，但是当我运行它，我有崩溃的这段代码：NullPointerException异常与火力地堡认证
了java.lang.RuntimeException：无法启动活动ComponentInfo {com.fgvelectro。 f/com.fgvelectro.f.MainActivity}：java.lang.NullPointerException：尝试调用空对象引用虚拟方法'java.lang.String com.google.firebase.auth.FirebaseUser.getUid（）'
我在网上搜索了几天，没有成功。我看到其他讨论这个问题的线索，但没有解决。这是我的MainActivity：
import com.firebase.ui.database.FirebaseRecyclerAdapter;
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 com.squareup.picasso.Picasso;
public class MainActivity extends AppCompatActivity {
private RecyclerView mBlogList;
private DatabaseReference mDatabase;
private DatabaseReference mDatabaseUsers;
private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthListener;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mAuth = FirebaseAuth.getInstance();
mAuthListener = new FirebaseAuth.AuthStateListener() {
@Override
public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
if(firebaseAuth.getCurrentUser() == null){
Intent loginIntent = new Intent(MainActivity.this, LoginActivity.class);
loginIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(loginIntent);
}
}
};
mDatabase = FirebaseDatabase.getInstance().getReference().child("Blog");
mDatabaseUsers = FirebaseDatabase.getInstance().getReference().child("Users");
mDatabaseUsers.keepSynced(true);
mDatabase.keepSynced(true);
mBlogList = (RecyclerView) findViewById(R.id.blog_list);
LinearLayoutManager layoutManager = new LinearLayoutManager(this);
layoutManager.setReverseLayout(true);
layoutManager.setStackFromEnd(true);
mBlogList.setHasFixedSize(true);
mBlogList.setLayoutManager(new LinearLayoutManager(this));
}
@Override
protected void onStart() {
super.onStart();
checkUserExist();
mAuth.addAuthStateListener(mAuthListener);
FirebaseRecyclerAdapter<Blog, BlogViewHolder> firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<Blog, BlogViewHolder>(
Blog.class,
R.layout.blog_row,
BlogViewHolder.class,
mDatabase
) {
@Override
protected void populateViewHolder(BlogViewHolder viewHolder, Blog model, int position) {
viewHolder.setTitle(model.getTitle());
viewHolder.setDesc(model.getDesc());
viewHolder.setImage(getApplicationContext(), model.getImage());
}
};
mBlogList.setAdapter(firebaseRecyclerAdapter);
}
private void checkUserExist() {
final String user_id = mAuth.getCurrentUser().getUid();
mDatabaseUsers.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(!dataSnapshot.hasChild(user_id)){
Intent setupIntent = new Intent(MainActivity.this, SetupActivity.class);
setupIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(setupIntent);
}
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
public static class BlogViewHolder extends RecyclerView.ViewHolder{
View mView;
public BlogViewHolder(View itemView) {
super(itemView);
mView = itemView;
}
public void setTitle(String title){
TextView post_title = (TextView) mView.findViewById(R.id.post_title);
post_title.setText(title);
}
public void setDesc(String desc){
TextView post_desc = (TextView) mView.findViewById(R.id.post_desc);
post_desc.setText(desc);
}
public void setImage(Context ctx, String image){
ImageView post_image = (ImageView) mView.findViewById(R.id.post_image);
Picasso.with(ctx).load(image).into(post_image);
}
}
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main_menu, menu);
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
if(item.getItemId() == R.id.action_add){
startActivity(new Intent(MainActivity.this, PostActivity.class));
}
if (item.getItemId() == R.id.action_logout){
logout();
}
return super.onOptionsItemSelected(item);
}
private void logout() {
mAuth.signOut();
}
}
我知道这是很难（消磨时间和）来解决这个问题，但如果你能帮助我，谢谢，谢谢，谢谢。
faby
现在我的代码如下所示：
private void checkUserExist() {
final String user_id = mAuth.getCurrentUser().getUid();
mDatabaseUsers.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(!dataSnapshot.hasChild(user_id)){
Intent setupIntent = new Intent(MainActivity.this, SetupActivity.class);
setupIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(setupIntent);
}
if (FirebaseAuth.getInstance().getCurrentUser() == null) {Intent loginIntent = new Intent(MainActivity.this, LoginActivity.class);
loginIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(loginIntent);
}
else{
String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
}
}
我该怎么办？可以吗？
[新编辑]
嗨，谢谢，但没有任何工作。现在火力支持，帮助我，我会得到你知道，如果事情会工作
的【什么是一个NullPointerException，如何解决呢？（可能的复制https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do- i-fix-it） –
* mAuth.getCurrentUser（）*很可能是零，这就是getUid（）抛出错误的原因。您的Firebase可能未正确初始化，并且/或者用户未通过身份验证。通过代码进行一些基本的故障排除和步骤可能会揭示原因。 – Jay