안드로이드 페이지 이동 오류 봐주실 수 있으실까요?

Question

MainActivity.java package com.example.a1202prj; import androidx.annotation.NonNull; import androidx.annotation.Nullable; import androidx.appcompat.app.AppCompatActivity; import android.content.Intent; import android.os.Binder; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.TextView; import android.widget.Toast; 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; public class MainActivity extends AppCompatActivity { EditText edtId, edtPw; Button btnLogin ,btnReg; FirebaseDatabase db; DatabaseReference refUser; String id; &#64;Override protected void onActivityResult(int requestCode, int resultCode, &#64;Nullable Intent data) { super.onActivityResult(requestCode, resultCode, data); if(resultCode&#61;&#61;RESULT_OK){ id&#61;data.getStringExtra(&#34;id&#34;); edtId.setText(id); } } &#64;Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); edtId &#61; findViewById(R.id.edtID); edtPw &#61; findViewById(R.id.edtPW); btnLogin &#61; findViewById(R.id.btnLogin); btnReg &#61; findViewById(R.id.btnReg); db &#61; FirebaseDatabase.getInstance(); refUser &#61; db.getReference(&#34;user&#34;); btnReg.setOnClickListener(new View.OnClickListener() { &#64;Override public void onClick(View v) { Intent in &#61; new Intent(getApplicationContext(),RegisterActivity.class); startActivityForResult(in,0); } }); btnLogin.setOnClickListener(new View.OnClickListener() { &#64;Override public void onClick(View v) { refUser.addValueEventListener(new ValueEventListener() { &#64;Override public void onDataChange(&#64;NonNull DataSnapshot dataSnapshot) { if(dataSnapshot.child(edtId.getText().toString()).exists()){ User u &#61; dataSnapshot.child(edtId.getText().toString()).getValue(User.class); if(u.getPw().equals(edtPw.getText().toString())){ Toast.makeText(getApplicationContext(),&#34;로그인 성공&#34;,Toast.LENGTH_SHORT).show(); Intent i &#61; new Intent(getApplicationContext(),ProfileActivity.class); i.putExtra(&#34;id&#34;,edtId.getText().toString()); startActivity(i); edtId.setText(&#34;&#34;); edtPw.setText(&#34;&#34;); }else{Toast.makeText(getApplicationContext(),&#34;패스워드가 다릅니다.&#34;,Toast.LENGTH_SHORT).show();} }else {Toast.makeText(getApplicationContext(),&#34;가입되어 있지 않습니다.&#34;,Toast.LENGTH_SHORT).show();} } &#64;Override public void onCancelled(&#64;NonNull DatabaseError error) { } }); } }); } } RegisterActivity.javapackage com.example.a1202prj; import android.content.Intent; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.EditText; import android.widget.Toast; import androidx.annotation.Nullable; import androidx.appcompat.app.AppCompatActivity; import com.google.firebase.database.DatabaseReference; import com.google.firebase.database.FirebaseDatabase; public class RegisterActivity extends AppCompatActivity { EditText edtID, edtPW, edtName; Button btnReg, btnCancel; FirebaseDatabase db; DatabaseReference refUser; &#64;Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.reg); edtID&#61;findViewById(R.id.edtID); edtPW&#61;findViewById(R.id.edtPW); edtName&#61;findViewById(R.id.edtName); btnCancel&#61;findViewById(R.id.btnCanel); db&#61;FirebaseDatabase.getInstance(); refUser&#61;db.getReference(&#34;user&#34;); btnReg.setOnClickListener(new View.OnClickListener(){ &#64;Override public void onClick(View v) { String id &#61; edtID.getText().toString(); String pw &#61; edtPW.getText().toString(); String name &#61; edtName.getText().toString(); User user &#61; new User(id, pw, name); refUser.child(id).setValue(user); Toast.makeText(getApplicationContext(),&#34;가입 성공&#34;,Toast.LENGTH_SHORT).show(); Intent in &#61; new Intent(getApplicationContext(), MainActivity.class); in.putExtra(&#34;id&#34;,id); setResult(RESULT_OK, in); finish(); } }); btnCancel.setOnClickListener(new View.OnClickListener() { &#64;Override public void onClick(View v) { finish(); } }); } } 메인페이지에서 계정가입 페이지로 이동하는 버튼인 회원가입 버튼을 누르면 이동이 돼야 하는데 어플이 튕깁니다.. 온클릭리스너 메소드에서 경로도 잡아줬는데 무슨 문제일까요? 오류 코드는 널포인트 문제라는데 찾아봐도 모르겠습니다.. 오류 구문 E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.a1202prj, PID: 17767 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.a1202prj/com.example.a1202prj.RegisterActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) at android.app.ActivityThread$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$MethodAndArgsCaller.run(RuntimeInit.java:492) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setOnClickListener(android.view.View$OnClickListener)' on a null object reference at com.example.a1202prj.RegisterActivity.onCreate(RegisterActivity.java:36) 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)

RWB · Answer

RegisterActivity.java에 할당된 Button 객체가 없습니다.다른 버튼과 마찬가지로 findViewById를 사용하여 올바른 버튼을 할당해주세요.

완전초보ㅠ · Answer

감사합니다.. 이제 갓 시작해서 널포인트 오류가 무슨 소리인가 했네요.. 객체 생성이 기본인데 주의 해야겠네요 ㅎㅎ 다시 한 번 감사드립니다!

안드로이드 페이지 이동 오류 봐주실 수 있으실까요?

2개의 답변

#activity 목록