实施Firebase

Question

我们尝试将Firebase数据库实现到我们的项目中，但是它一开始直接崩溃。另一个问题是我们对数据库的了解不强，但我希望我们可以解决该问题。

这是一开始就出现的例外情况

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.myapplicationteeeeeeeeeest, PID: 19187
    java.lang.NoSuchMethodError: No virtual method setTokenProvider(Lcom/google/firebase/internal/InternalTokenProvider;)V in class Lcom/google/firebase/FirebaseApp; or its super classes (declaration of 'com.google.firebase.FirebaseApp' appears in /data/app/com.example.myapplicationteeeeeeeeeest-N3UsgThAADh1hlowT55AfA==/base.apk)
        at com.google.firebase.auth.zzp.create(Unknown Source:4)
        at com.google.firebase.components.ComponentRuntime.lambda$new$0(com.google.firebase:firebase-common@@19.0.0:66)
        at com.google.firebase.components.ComponentRuntime$$Lambda$1.get(Unknown Source:4)
        at com.google.firebase.components.Lazy.get(com.google.firebase:firebase-common@@19.0.0:55)
        at com.google.firebase.components.ComponentRuntime.initializeEagerComponents(com.google.firebase:firebase-common@@19.0.0:155)
        at com.google.firebase.FirebaseApp.initializeAllApis(com.google.firebase:firebase-common@@19.0.0:553)
        at com.google.firebase.FirebaseApp.initializeApp(com.google.firebase:firebase-common@@19.0.0:300)
        at com.google.firebase.FirebaseApp.initializeApp(com.google.firebase:firebase-common@@19.0.0:264)
        at com.google.firebase.FirebaseApp.initializeApp(com.google.firebase:firebase-common@@19.0.0:249)
        at com.google.firebase.provider.FirebaseInitProvider.onCreate(com.google.firebase:firebase-common@@19.0.0:51)
        at android.content.ContentProvider.attachInfo(ContentProvider.java:2092)
        at android.content.ContentProvider.attachInfo(ContentProvider.java:2066)
        at com.google.firebase.provider.FirebaseInitProvider.attachInfo(com.google.firebase:firebase-common@@19.0.0:45)
        at android.app.ActivityThread.installProvider(ActivityThread.java:6983)
        at android.app.ActivityThread.installContentProviders(ActivityThread.java:6528)
        at android.app.ActivityThread.handleBindApplication(ActivityThread.java:6445)
        at android.app.ActivityThread.access$1300(ActivityThread.java:219)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1859)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
W/DynamiteModule: Local module descriptor class for com.google.firebase.auth not found.
I/FirebaseAuth: [FirebaseAuth:] Loading module via FirebaseOptions.
I/FirebaseAuth: [FirebaseAuth:] Preparing to create service connection to gms implementation
Disconnected from the target VM, address: 'localhost:8604', transport: 'socket'

这是我们用于下载和查看数据的数据库类

   package com.example.myapplicationteeeeeeeeeest;

    import android.os.Bundle;
    import android.util.Log;
    import android.widget.ArrayAdapter;
    import android.widget.ListView;
    import android.widget.Toast;
    import com.google.firebase.FirebaseApp;

    import androidx.annotation.NonNull;
    import androidx.annotation.Nullable;
    import androidx.appcompat.app.AppCompatActivity;

    import com.example.myapplicationteeeeeeeeeest.R;
    import com.example.myapplicationteeeeeeeeeest.recipe;
    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 java.util.ArrayList;

    public class ViewDatabase extends AppCompatActivity {
        private static final String TAG = "ViewDatabase";

        //add Firebase Database stuff
        private DatabaseReference mFirebaseDatabase;
        private FirebaseAuth mAuth;
        private FirebaseAuth.AuthStateListener mAuthListener;
        private DatabaseReference myRef;
        private String recipes;

        private ListView listView_test;

        @Override
        protected void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.view_database_layout);


            //declare the database reference object. This is what we use to access the database.
            //NOTE: Unless you are signed in, this will not be useable.
            mAuth = FirebaseAuth.getInstance();
            mFirebaseDatabase = FirebaseDatabase.getInstance().getReference().child("testrecipe");
            FirebaseUser user = mAuth.getCurrentUser();
            recipes = user.getUid();



            myRef.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    showData(dataSnapshot);
                }

                @Override
                public void onCancelled(@NonNull DatabaseError databaseError) {

                }
            });

        }


        private void showData(DataSnapshot dataSnapshot){
            for (DataSnapshot ds : dataSnapshot.getChildren()){
                recipe recipe = new recipe();
                recipe.setNameOfRecipe(ds.child(recipes).getValue(com.example.myapplicationteeeeeeeeeest.recipe.class).getNameOfRecipe());



                ArrayList<String> array = new ArrayList<>();
                array.add(recipe.getNameOfRecipe());
                ArrayAdapter adapter = new ArrayAdapter(this, R.layout.shopping_list_item, array);
                listView_test.setAdapter(adapter);
            }
        }

        @Override
        public void onStart() {
            super.onStart();
            mAuth.addAuthStateListener(mAuthListener);
        }

        @Override
        public void onStop() {
            super.onStop();
            if (mAuthListener != null) {
                mAuth.removeAuthStateListener(mAuthListener);
            }
        }


        /**
         * customizable toast
         * @param message
         */
        private void toastMessage(String message){
            Toast.makeText(this,message,Toast.LENGTH_SHORT).show();
        }
    }

以及我们想要通过单击按钮显示信息的片段

package com.example.myapplicationteeeeeeeeeest.ui.AHome;

import android.content.Intent;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;

import androidx.annotation.Nullable;
import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProviders;

import com.example.myapplicationteeeeeeeeeest.MainActivity;
import com.example.myapplicationteeeeeeeeeest.R;
import com.example.myapplicationteeeeeeeeeest.ViewDatabase;
import com.google.firebase.FirebaseApp;



public class HomeFragment extends Fragment {

    private HomeViewModel homeViewModel;
    private Button categorie1;
    private Button categorie2;
    private Button categorie3;
    private Button categorie4;
    private Button database_button;


    public View onCreateView(@NonNull LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        homeViewModel =
                ViewModelProviders.of( this ).get( HomeViewModel.class );

        View root = inflater.inflate( R.layout.fragment_home, container, false );
        categorie1 = (Button) root.findViewById(R.id.button_category_1);
        categorie2 = (Button) root.findViewById(R.id.button_category_2);
        categorie3 = (Button) root.findViewById(R.id.button_category_3);
        categorie4 = (Button) root.findViewById(R.id.button_category_4);
        database_button = (Button) root.findViewById(R.id.button_database);
        initButtons();

        final TextView textView = root.findViewById( R.id.text_home );
        homeViewModel.getText().observe( this, new Observer<String>() {
            @Override
            public void onChanged(@Nullable String s) {
                textView.setText( s );
            }
        } );
        return root;
    }

    public void initButtons(){
        categorie1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

            }
        });

        categorie2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

            }
        });

        categorie3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

            }
        });

        categorie4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

            }
        });

        database_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(getActivity(), ViewDatabase.class);
                startActivity(intent);
            }
        });
    }
}

修复第一个问题后，单击主页片段上的按钮，我们得到了一个新的问题。

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.myapplicationteeeeeeeeeest, PID: 20309
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplicationteeeeeeeeeest/com.example.myapplicationteeeeeeeeeest.ViewDatabase}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.google.firebase.auth.FirebaseUser.getUid()' on a null object reference
        at com.example.myapplicationteeeeeeeeeest.ViewDatabase.onCreate(ViewDatabase.java:49)
        at android.app.Activity.performCreate(Activity.java:7802)
        at android.app.Activity.performCreate(Activity.java:7791)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:214) 
        at android.app.ActivityThread.main(ActivityThread.java:7356) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
I/Process: Sending signal. PID: 20309 SIG: 9
Disconnected from the target VM, address: 'localhost:8604', transport: 'socket'

Answer 1

我猜您缺少Firebase身份验证库，因此请尝试添加

implementation 'com.google.firebase:firebase-auth:19.0.0'

在您的app/build.gradle中。

我之前遇到过同样的错误，并添加了Firebase Auth为我修复了该错误。我在某处读到，如果您在应用程序中使用Firestore，则还需要添加Firebase身份验证库。

Answer 2

首先初始化Firebase

FirebaseApp.initializeApp(getApplicationContext());