我正在登录活动中的应用程序中使用google登录方法来执行使用google的登录。 现在，每当我单击导航到登录活动的按钮时，我都会出错。 请帮忙！ 只是想知道我的代码内部正在发生什么！
这是：
LoginActivity：
package com.raicsit.wardha;
import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.common.api.ApiException;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthCredential;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.auth.GoogleAuthProvider;
public class LoginActivity extends AppCompatActivity{
//a constant for detecting the login intent result
private static final int RC_SIGN_IN = 234;
//Tag for the logs optional
private static final String TAG = "simplifiedcoding";
//creating a GoogleSignInClient object
GoogleSignInClient mGoogleSignInClient;
//And also a Firebase Auth object
FirebaseAuth mAuth;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//first we intialized the FirebaseAuth object
mAuth = FirebaseAuth.getInstance();
//Then we need a GoogleSignInOptions object
//And we need to build it as below
GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
.requestIdToken(getString(R.string.default_web_client_id))
.requestEmail()
.build();
//Then we will get the GoogleSignInClient object from GoogleSignIn class
mGoogleSignInClient = GoogleSignIn.getClient(this, gso);
//Now we will attach a click listener to the sign_in_button
//and inside onClick() method we are calling the signIn() method that will open
//google sign in intent
findViewById(R.id.sign_in_button).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
signIn();
}
});
}
@Override
protected void onStart() {
super.onStart();
//if the user is already signed in
//we will close this activity
//and take the user to profile activity
if (mAuth.getCurrentUser() != null) {
finish();
startActivity(new Intent(this, ProfileActivity.class));
}
}
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
//if the requestCode is the Google Sign In code that we defined at starting
if (requestCode == RC_SIGN_IN) {
//Getting the GoogleSignIn Task
Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
try {
//Google Sign In was successful, authenticate with Firebase
GoogleSignInAccount account = task.getResult(ApiException.class);
//authenticating with firebase
firebaseAuthWithGoogle(account);
} catch (ApiException e) {
Toast.makeText(LoginActivity.this, e.getMessage(), Toast.LENGTH_SHORT).show();
}
}
}
private void firebaseAuthWithGoogle(GoogleSignInAccount acct) {
Log.d(TAG, "firebaseAuthWithGoogle:" + acct.getId());
//getting the auth credential
AuthCredential credential = GoogleAuthProvider.getCredential(acct.getIdToken(), null);
//Now using firebase we are signing in the user here
mAuth.signInWithCredential(credential)
.addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
@Override
public void onComplete(@NonNull Task<AuthResult> task) {
if (task.isSuccessful()) {
Log.d(TAG, "signInWithCredential:success");
FirebaseUser user = mAuth.getCurrentUser();
Toast.makeText(LoginActivity.this, "User Signed In", Toast.LENGTH_SHORT).show();
} else {
// If sign in fails, display a message to the user.
Log.w(TAG, "signInWithCredential:failure", task.getException());
Toast.makeText(LoginActivity.this, "Authentication failed.",
Toast.LENGTH_SHORT).show();
}
// ...
}
});
}
//this method is called on click
private void signIn() {
//getting the google signin intent
Intent signInIntent = mGoogleSignInClient.getSignInIntent();
//starting the activity for result
startActivityForResult(signInIntent, RC_SIGN_IN);
}
}
activitylogin.xml：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.google.android.gms.common.SignInButton
android:id="@+id/sign_in_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true" />
</RelativeLayout>
我的启动器活动是MainActivity。有一个导航到LoginActivity的按钮，单击“主活动”中的“按钮”后，出现以下错误：
09-17 05:18:55.468 26265-26265/com.raicsit.wardha E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.raicsit.wardha, PID: 26265
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.raicsit.wardha/com.raicsit.wardha.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3194)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3302)
at android.app.ActivityThread.-wrap12(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1891)
at android.os.Handler.dispatchMessage(Handler.java:108)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7425)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
at com.raicsit.wardha.LoginActivity.onCreate(LoginActivity.java:59)
at android.app.Activity.performCreate(Activity.java:7372)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1218)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3147)
如果需要，这是MainActivity：
package com.raicsit.wardha;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void loginbtn(View view)
{
Intent intent = new Intent(MainActivity.this,LoginActivity.class);
startActivity(intent);
}
}