所以我正在尝试使用 Android Studio 创建一个简单的 android 应用程序，当我构建时它看起来很好但是当我运行应用程序时崩溃所以我被告知检查 Logcat 并且它说 FirebaseApp 未初始化在我的主要 Activity 中。所以我添加了

FirebaseApp.initializeApp(this);

到 onCreate() 并且它无法解析符号 FirebaseApp 那么我该怎么做才能解决这个问题？

这是我的 Github:

https://github.com/radekkrowicki/Cv4

还有我的主要 Activity :

import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;

import com.firebase.ui.auth.AuthUI;
import com.firebase.ui.database.FirebaseListAdapter;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.database.FirebaseDatabase;

public class MainActivity extends AppCompatActivity {
private static final int SIGN_IN_REQUEST_CODE = 111;
private FirebaseListAdapter<ChatMessage> adapter;
private ListView listView;
private String loggedInUserName = "";
private FirebaseAuth mAuth;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    FirebaseApp.initializeApp(this);

    //find views by Ids
    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    final EditText input = (EditText) findViewById(R.id.input);
    listView = (ListView) findViewById(R.id.list);

    if (FirebaseAuth.getInstance().getCurrentUser() == null) {
        // Start sign in/sign up activity
        startActivityForResult(AuthUI.getInstance()
                .createSignInIntentBuilder()
                .build(), SIGN_IN_REQUEST_CODE);
    } else {
        // User is already signed in, show list of messages
        showAllOldMessages();
    }

    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            if (input.getText().toString().trim().equals("")) {
                Toast.makeText(MainActivity.this, "Please enter some texts!", Toast.LENGTH_SHORT).show();
            } else {
                FirebaseDatabase.getInstance()
                        .getReference()
                        .push()
                        .setValue(new ChatMessage(input.getText().toString(),
                                FirebaseAuth.getInstance().getCurrentUser().getDisplayName(),
                                FirebaseAuth.getInstance().getCurrentUser().getUid())
                        );
                input.setText("");
            }
        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    if (item.getItemId() == R.id.menu_sign_out) {
        AuthUI.getInstance().signOut(this)
                .addOnCompleteListener(new OnCompleteListener<Void>() {
                    @Override
                    public void onComplete(@NonNull Task<Void> task) {
                        Toast.makeText(MainActivity.this, "You have logged out!", Toast.LENGTH_SHORT).show();
                        finish();
                    }
                });
    }
    return true;
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if (requestCode == SIGN_IN_REQUEST_CODE) {
        if (resultCode == RESULT_OK) {
            Toast.makeText(this, "Signed in successful!", Toast.LENGTH_LONG).show();
            showAllOldMessages();
        } else {
            Toast.makeText(this, "Sign in failed, please try again later", Toast.LENGTH_LONG).show();

            // Close the app
            finish();
        }
    }
}

private void showAllOldMessages() {
    loggedInUserName = FirebaseAuth.getInstance().getCurrentUser().getUid();
    Log.d("Main", "user id: " + loggedInUserName);

    adapter = new MessageAdapter(this, ChatMessage.class, R.layout.item_in_message,
            FirebaseDatabase.getInstance().getReference());
    listView.setAdapter(adapter);
}

public String getLoggedInUserName() {
    return loggedInUserName;
}
}

提前感谢您的帮助。

最佳答案

这一定是同步问题，您正在正确初始化 Firebase:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    FirebaseApp.initializeApp(this);
    ...
    ...
}

请务必再次清理并构建您的项目。

还要确保 apply plugin: 'com.google.gms.google-services' 在 /app/build.grade 文件的末尾:

 dependencies {
    ...
    ...
}

apply plugin: 'com.google.gms.google-services'

关于java - "Make sure to call FirebaseApp.initializeApp(Context) first."如何解决这个错误？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/55521386/