Erreur de référence d'objet nulle lors de la tentative d'ouverture d'une nouvelle activité sur Android?

Question

Ceci est mon code pour l'activité XML, le code pour ouvrir une nouvelle activité déclenche une erreur d'exception nulle sur ce projet mais quand j'essaye le même code sur un autre projet cela fonctionne et s'exécute bien sur l'émulateur ? L'erreur produite dans le journal des erreurs est:

java.lang.RuntimeException: Impossible de démarrer l'activité ComposantInfo {com.swaziprocurement.sppraapp/com.swaziprocurement.sppraapp.Main2Activity}: java.lang.NullPointerException : Tentative d'invoquer la méthode virtuelle 'vide android.widget.Button.setOnClickListener (android.view.View $ OnClickListener)' sur une référence d'objet nul

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    tools:context="com.swaziprocurement.sppraapp.MainActivity"> 

    <TextView 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:text="User Registration Form" 
     android:textSize="20dp" 
     android:textStyle="bold" 
     android:id="@+id/textView" 
     android:layout_centerHorizontal="true" 
     android:gravity="center"/> 

    <EditText 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/EditTextFullName" 
     android:layout_below="@+id/textView" 
     android:layout_marginTop="20dp" 
     android:hint="Enter Your Full Name" 
     android:gravity="center"/> 

    <EditText 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/EditTextEmail" 
     android:layout_below="@+id/EditTextFullName" 
     android:layout_marginTop="20dp" 
     android:inputType="textEmailAddress" 
     android:hint="Enter Your Email" 
     android:gravity="center"/> 

    <EditText 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/EditTextPassword" 
     android:layout_below="@+id/EditTextEmail" 
     android:layout_marginTop="20dp" 
     android:inputType="textPassword" 
     android:hint="Enter Your Password" 
     android:gravity="center"/> 

    <Button 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:text="Click Here To Register" 
     android:layout_below="@+id/EditTextPassword" 
     android:id="@+id/ButtonRegister" 
     android:layout_marginTop="20dp"/> 

    <Button 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Login Menu" 
     android:id="@+id/button2" 
     android:layout_below="@+id/ButtonRegister" 
     android:layout_alignParentStart="true" 
     android:layout_alignParentEnd="true" /> 

</RelativeLayout> 

code Java:

package com.swaziprocurement.sppraapp; 

import android.app.ProgressDialog; 
import android.content.Intent; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.text.TextUtils; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.Toast; 

import com.android.volley.Request; 
import com.android.volley.RequestQueue; 
import com.android.volley.Response; 
import com.android.volley.VolleyError; 
import com.android.volley.toolbox.StringRequest; 
import com.android.volley.toolbox.Volley; 

import java.util.HashMap; 
import java.util.Map; 

public class MainActivity extends AppCompatActivity { 
Button Register,buttonOpen; 
EditText FullName,Email,Password; 

    RequestQueue requestQueue; 

    String NameHolder,PasswordHolder,EmailHolder; 

    ProgressDialog progressDialog; 
    String HttpUrl="https://android-examples.000webhostapp.com/User-Registration.php"; 

    Boolean CheckEditText; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     FullName=(EditText)findViewById(R.id.EditTextFullName); 
     Email=(EditText)findViewById(R.id.EditTextEmail); 
     Password=(EditText)findViewById(R.id.EditTextPassword); 

     Register=(Button)findViewById(R.id.ButtonRegister); 
     buttonOpen=(Button)findViewById(R.id.button2); 




     requestQueue= Volley.newRequestQueue(MainActivity.this); 

     progressDialog=new ProgressDialog(this); 




     Register.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       CheckEditTextIsEmptyOrNot(); 
       if (CheckEditText) 
        UserRegistration(); 
       else{ 
        Toast.makeText(MainActivity.this,"Please fill all form fields",Toast.LENGTH_SHORT).show(); 
       } 

      } 
     }); 

     buttonOpen.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       openAct(); 

      } 
     }); 


    } 
    public void UserRegistration(){ 

     // Showing progress dialog at user registration time. 
     progressDialog.setMessage("Please Wait, We are Inserting Your Data on Server"); 
     progressDialog.show(); 

     // Creating string request with post method. 
     StringRequest stringRequest = new StringRequest(Request.Method.POST, HttpUrl, 
       new Response.Listener<String>() { 
        @Override 
        public void onResponse(String ServerResponse) { 

         // Hiding the progress dialog after all task complete. 
         progressDialog.dismiss(); 

         // Showing Echo Response Message Coming From Server. 
         Toast.makeText(MainActivity.this, ServerResponse, Toast.LENGTH_LONG).show(); 
        } 
       }, 
       new Response.ErrorListener() { 
        @Override 
        public void onErrorResponse(VolleyError volleyError) { 

         // Hiding the progress dialog after all task complete. 
         progressDialog.dismiss(); 

         // Showing error message if something goes wrong. 
         Toast.makeText(MainActivity.this, volleyError.toString(), Toast.LENGTH_LONG).show(); 
        } 
       }) { 
      @Override 
      protected Map<String, String> getParams() { 

       // Creating Map String Params. 
       Map<String, String> params = new HashMap<String, String>(); 

       // Adding All values to Params. 
       // The firs argument should be same sa your MySQL database table columns. 
       params.put("User_Email", EmailHolder); 
       params.put("User_Password", PasswordHolder); 
       params.put("User_Full_Name", NameHolder); 

       return params; 
      } 

     }; 

     // Creating RequestQueue. 
     RequestQueue requestQueue = Volley.newRequestQueue(MainActivity.this); 

     // Adding the StringRequest object into requestQueue. 
     requestQueue.add(stringRequest); 

    } 
    public void CheckEditTextIsEmptyOrNot(){ 

     // Getting values from EditText. 
     NameHolder = FullName.getText().toString().trim(); 
     EmailHolder = Email.getText().toString().trim(); 
     PasswordHolder = Password.getText().toString().trim(); 

     // Checking whether EditText value is empty or not. 
     if(TextUtils.isEmpty(NameHolder) || TextUtils.isEmpty(EmailHolder) || TextUtils.isEmpty(PasswordHolder)) 
     { 

      // If any of EditText is empty then set variable value as False. 
      CheckEditText = false; 

     } 
     else { 

      // If any of EditText is filled then set variable value as True. 
      CheckEditText = true ; 
     } 
    } 

    public void openAct(){ 

     startActivity(new Intent(MainActivity.this,Main2Activity.class)); 
    } 
    } 

Ceci est la deuxième activité

package com.swaziprocurement.sppraapp; 

import android.app.ProgressDialog; 
import android.content.Intent; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.text.TextUtils; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.Toast; 

import com.android.volley.Request; 
import com.android.volley.RequestQueue; 
import com.android.volley.Response; 
import com.android.volley.VolleyError; 
import com.android.volley.toolbox.StringRequest; 
import com.android.volley.toolbox.Volley; 

import java.util.HashMap; 
import java.util.Map; 

public class Main2Activity extends AppCompatActivity { 
    Button button,LoginButton; 
    EditText Email,Password; 

    Boolean CheckEditText; 

    RequestQueue requestQueue; 

    String EmailHolder,PasswordHolder; 

    ProgressDialog progressDialog; 

    String HttpUrl = "https://android-examples.000webhostapp.com/user_login.php"; 



    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main2); 
     button =(Button)findViewById(R.id.button); 
     progressDialog=new ProgressDialog(this); 

     LoginButton.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       CheckEditTextIsEmptyOrNot(); 

       if (CheckEditText) { 

        UserLogin(); 

       } else { 

        Toast.makeText(Main2Activity.this, "Please fill all form fields.", Toast.LENGTH_LONG).show(); 

       } 

      } 
     }); 

     button.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       Intent intent =new Intent(Main2Activity.this,MainActivity.class); 
       startActivity(intent); 
      } 
     }); 
    } 

    public void CheckEditTextIsEmptyOrNot() { 

     // Getting values from EditText. 
     EmailHolder = Email.getText().toString().trim(); 
     PasswordHolder = Password.getText().toString().trim(); 

     // Checking whether EditText value is empty or not. 
     if (TextUtils.isEmpty(EmailHolder) || TextUtils.isEmpty(PasswordHolder)) { 

      // If any of EditText is empty then set variable value as False. 
      CheckEditText = false; 

     } else { 

      // If any of EditText is filled then set variable value as True. 
      CheckEditText = true; 
     } 
    } 

    public void UserLogin() { 

     // Showing progress dialog at user registration time. 
     progressDialog.setMessage("Please Wait"); 
     progressDialog.show(); 

     // Creating string request with post method. 
     StringRequest stringRequest = new StringRequest(Request.Method.POST, HttpUrl, 
       new Response.Listener<String>() { 
        @Override 
        public void onResponse(String ServerResponse) { 

         // Hiding the progress dialog after all task complete. 
         progressDialog.dismiss(); 

         // Matching server responce message to our text. 
         if(ServerResponse.equalsIgnoreCase("Data Matched")) { 

          // If response matched then show the toast. 
          Toast.makeText(Main2Activity.this, "Logged In Successfully", Toast.LENGTH_LONG).show(); 

          // Finish the current Login activity. 
          finish(); 

          // Opening the user profile activity using intent. 
          Intent intent = new Intent(Main2Activity.this, Main3Activity.class); 

          // Sending User Email to another activity using intent. 
          intent.putExtra("UserEmailTAG", EmailHolder); 

          startActivity(intent); 
         } 
         else { 

          // Showing Echo Response Message Coming From Server. 
          Toast.makeText(Main2Activity.this, ServerResponse, Toast.LENGTH_LONG).show(); 

         } 


        } 
       }, 
       new Response.ErrorListener() { 
        @Override 
        public void onErrorResponse(VolleyError volleyError) { 

         // Hiding the progress dialog after all task complete. 
         progressDialog.dismiss(); 

         // Showing error message if something goes wrong. 
         Toast.makeText(Main2Activity.this, volleyError.toString(), Toast.LENGTH_LONG).show(); 
        } 
       }) { 
      @Override 
      protected Map<String, String> getParams() { 

       // Creating Map String Params. 
       Map<String, String> params = new HashMap<String, String>(); 

       // Adding All values to Params. 
       // The firs argument should be same sa your MySQL database table columns. 
       params.put("User_Email", EmailHolder); 
       params.put("User_Password", PasswordHolder); 

       return params; 
      } 

     }; 
     // Creating RequestQueue. 
     RequestQueue requestQueue = Volley.newRequestQueue(Main2Activity.this); 

     // Adding the StringRequest object into requestQueue. 
     requestQueue.add(stringRequest); 


    } 
} 

Le XML pour la deuxième activité

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    tools:context="com.swaziprocurement.sppraapp.Main2Activity"> 
    <TextView 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/textView" 
     android:textSize="20dp" 
     android:textStyle="bold" 
     android:text="Volley User Login System" 
     android:gravity="center" 
     android:layout_marginTop="20dp"/> 

    <EditText 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:hint="Enter Your Email" 
     android:gravity="center" 
     android:id="@+id/editText_Email" 
     android:layout_below="@+id/textView" 
     android:layout_marginTop="20dp"/> 

    <EditText 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:hint="Enter Your Email" 
     android:gravity="center" 
     android:id="@+id/editText_Password" 
     android:inputType="textPassword" 
     android:layout_below="@+id/editText_Email" 
     android:layout_marginTop="20dp"/> 

    <Button 
     android:layout_width="fill_parent" 
     android:layout_height="wrap_content" 
     android:text="CLICK HERE TO LOGIN" 
     android:id="@+id/button_login" 
     android:layout_below="@id/editText_Password" 
     android:layout_marginTop="20dp"/> 

    <Button 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Registration Menu" 
     android:id="@+id/button" 
     android:layout_below="@+id/button_login" 
     android:layout_alignParentStart="true" 
     android:layout_alignParentEnd="true" /> 
</RelativeLayout> 

Answer 1

Vous devez initialiser votre bouton, vous appelez OnClickListener sur référence null

LoginButton =(Button)findViewById(R.id.button_login); 

B Avant d'appeler le LoginButton.setOnClickListener(), initialisez votre bouton de connexion.

Answer 2

initialiser votre LoginButton,

LoginButton =(Button)findViewById(R.id.button_login); 

que d'utiliser

LoginButton.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View view) { 
       CheckEditTextIsEmptyOrNot(); 

       if (CheckEditText) { 

        UserLogin(); 

       } else { 

        Toast.makeText(Main2Activity.this, "Please fill all form fields.", Toast.LENGTH_LONG).show(); 

       } 

      } 
     });