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我正在做一個博客的應用程序，但是當我運行它，我有崩潰的這段代碼：NullPointerException異常與火力地堡認證
了java.lang.RuntimeException：無法啓動活動ComponentInfo {com.fgvelectro。 f/com.fgvelectro.f.MainActivity}：java.lang.NullPointerException：嘗試調用空對象引用虛擬方法'java.lang.String com.google.firebase.auth.FirebaseUser.getUid（）'
我在網上搜索了幾天，沒有成功。我看到其他討論這個問題的線索，但沒有解決。這是我的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();
}
}
我知道這是很難（消磨時間和）來解決這個問題，但如果你能幫助我，謝謝，謝謝，謝謝。
faby
現在我的代碼如下所示：
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();
}
}
我該怎麼辦？可以嗎？
[新編輯]
嗨，謝謝，但沒有任何工作。現在火力支持，幫助我，我會得到你知道，如果事情會工作
的【什麼是一個NullPointerException，如何解決呢？（可能的複製https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do- i-fix-it） –
* mAuth.getCurrentUser（）*很可能是零，這就是getUid（）拋出錯誤的原因。您的Firebase可能未正確初始化，並且/或者用戶未通過身份驗證。通過代碼進行一些基本的故障排除和步驟可能會揭示原因。 – Jay