I'm creating a mobile application for android and I have a problem when after the download connection by Google
the application crashes. Could someone give me a reason and how to attach it?
Main activities within reach.
public class MainActivity extends AppCompatActivity {
GoogleSignInClient mGoogleSignInClient;
private int RC_SIGN_IN = 3;
SignInButton signInButton;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
signInButton = findViewById(R.id.sign_in_button);
signInButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
switch (view.getId()) {
case R.id.sign_in_button:
signIn();
break;
// ...
}
}
});
GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
.requestEmail()
.build();
mGoogleSignInClient = GoogleSignIn.getClient(this, gso);
}
private void signIn() {
Intent signInIntent = mGoogleSignInClient.getSignInIntent();
startActivityForResult(signInIntent, RC_SIGN_IN);
}
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
// Result returned from launching the Intent from GoogleSignInClient.getSignInIntent(...);
if (requestCode == RC_SIGN_IN) {
// The Task returned from this call is always completed, no need to attach
// a listener.
Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
handleSignInResult(task);
}
}
private void handleSignInResult(Task<GoogleSignInAccount> completedTask) {
try {
GoogleSignInAccount account = completedTask.getResult(ApiException.class);
Intent intent = new Intent(MainActivity.this, MenuActivity.class);
startActivity(intent);
} catch (ApiException e) {
// The ApiException status code indicates the detailed failure reason.
// Please refer to the GoogleSignInStatusCodes class reference for more information.
Log.w("TAG", "signInResult:failed code=" + e.getStatusCode());
// updateUI(null);
}
}
}
Target activity after logging in:
public class MenuActivity extends AppCompatActivity {
GoogleSignInClient mGoogleSignInClient;
Button logoutBtn;
TextView userName;
ImageView profileImage;
private GoogleSignInOptions gso;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
.requestEmail()
.build();
mGoogleSignInClient = GoogleSignIn.getClient(this, gso);
logoutBtn=(Button)findViewById(R.id.button_wyl);
profileImage=(ImageView)findViewById(R.id.profileImage);
userName = findViewById(R.id.name);
logoutBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
switch (view.getId()) {
// ...
case R.id.button_wyl:
signOut();
break;
// ...
}
}
});
GoogleSignInAccount acct = GoogleSignIn.getLastSignedInAccount(this);
if (acct != null) {
String personName = acct.getDisplayName();
Uri personPhoto = acct.getPhotoUrl();
userName.setText(personName);
Glide.with(this).load(String.valueOf(personPhoto)).into(profileImage);
}
}
private void signOut() {
mGoogleSignInClient.signOut()
.addOnCompleteListener(this, new OnCompleteListener<Void>() {
@Override
public void onComplete(@NonNull Task<Void> task) {
Toast.makeText(MenuActivity.this, "Signed out Successfully", Toast.LENGTH_LONG).show();
finish();
}
});
}
}
Exception:
E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.goodmath, PID: 1780 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.goodmath/com.example.goodmath.MenuActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:193) at android.app.A ctivityThread.main(ActivityThread.java:6669) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at com.example.goodmath.MenuActivity.onCreate(MenuActivity.java:46) at android.app.Activity.performCreate(Activity.java:7136) at android.app.Activity.performCreate(Activity.java:7127) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) at android.app.servertransaction.TransactionExecutor.executeCa llbacks(TransactionExecutor.java:108) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:193) at android.app.ActivityThread.main(ActivityThread.java:6669) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) I/Process: Sending signal. PID: 1780 SIG: 9
You do not call setContentView()
in onCreate()
of MenuActivity
, so your findViewById()
lookups will fail. As a result, logoutBtn
is null
, so you crash with a NullPointerException
when you try calling a method on it.
The actual error is:
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.Button.setOnClickListener(android.view.View$OnClickListener)'
on a null object
So findViewById fails.
Do setContentView(R.layout.activity_menu)
directly after super.onCreate()
And if that doesn't work, are you sure that the view you are referencing is within the activity_menu layout file?
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