Ошибка активности Android 5

Question

Хороший день для всех гуру в развитии здесь, прежде всего, извините за мой плохой английский, но у меня есть ошибка в приложении для Android, которое я разрабатываю, и я не мог его исправить, и я google и не найдешь ответа.

LogCat

09-28 13:21:59.360 2085-2085/com.colpsic.domain.colpsic_app I/art﹕ Not late-enabling -Xcheck:jni (already on) 
09-28 13:21:59.360 2085-2085/com.colpsic.domain.colpsic_app I/art﹕ Late-enabling JIT 
09-28 13:21:59.362 2085-2085/com.colpsic.domain.colpsic_app I/art﹕ JIT created with code_cache_capacity=2MB compile_threshold=1000 
09-28 13:21:59.384 2085-2085/com.colpsic.domain.colpsic_app W/System﹕ ClassLoader referenced unknown path: /data/app/com.colpsic.domain.colpsic_app-2/lib/x86 
09-28 13:21:59.387 2085-2085/com.colpsic.domain.colpsic_app D/AndroidRuntime﹕ Shutting down VM 
09-28 13:21:59.387 2085-2085/com.colpsic.domain.colpsic_app E/AndroidRuntime﹕ FATAL EXCEPTION: main 
    Process: com.colpsic.domain.colpsic_app, PID: 2085 
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.colpsic.domain.colpsic_app/com.colpsic.domain.colpsic_app.PrincipalActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference 
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327) 
      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
      at android.app.ActivityThread.-wrap11(ActivityThread.java) 
      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
      at android.os.Handler.dispatchMessage(Handler.java:102) 
      at android.os.Looper.loop(Looper.java:148) 
      at android.app.ActivityThread.main(ActivityThread.java:5417) 
      at java.lang.reflect.Method.invoke(Native Method) 
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference 
      at android.app.Activity.findViewById(Activity.java:2090) 
      at com.colpsic.domain.colpsic_app.PrincipalActivity.<init>(PrincipalActivity.java:22) 
      at java.lang.Class.newInstance(Native Method) 
      at android.app.Instrumentation.newActivity(Instrumentation.java:1067) 
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317) 
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
            at android.app.ActivityThread.-wrap11(ActivityThread.java) 
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
            at android.os.Handler.dispatchMessage(Handler.java:102) 
            at android.os.Looper.loop(Looper.java:148) 
            at android.app.ActivityThread.main(ActivityThread.java:5417) 
            at java.lang.reflect.Method.invoke(Native Method) 
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
09-28 13:22:01.785 2085-2085/? I/Process﹕ Sending signal. PID: 2085 SIG: 9 

PrincipalActivity.java

package com.colpsic.domain.colpsic_app; 

import android.content.Intent; 
import android.os.StrictMode; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.TextView; 
import android.widget.Toast; 

import java.sql.Connection; 
import java.sql.DriverManager; 
import java.sql.ResultSet; 
import java.sql.ResultSetMetaData; 
import java.sql.Statement; 

public class PrincipalActivity extends AppCompatActivity { 
    EditText EdtxtCedula=(EditText)findViewById(R.id.lblCedula); 

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

     Button btnAceptar=(Button)findViewById(R.id.BtnAceptar); 

     btnAceptar.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       boolean existeDocumento; 
       existeDocumento = conection(); 
       validacionDocumento(existeDocumento); 
      } 


     }); 
    } 

    private void validacionDocumento(boolean validar) { 
     if (validar==true){ 
      Intent intent = new Intent(PrincipalActivity.this, ProfesionalActivity.class); 
      Bundle b = new Bundle(); 
      b.putInt("CEDULA", Integer.parseInt(EdtxtCedula.getText().toString())); 
      intent.putExtras(b); 
      startActivity(intent); 
     }else{ 
      EdtxtCedula.setText(""); 
     } 
    } 

    private boolean conection() { 
     final String url = "jdbc:mysql://"; 
     final String user = ""; 
     final String pass = ""; 
     boolean resultadoConexion = false; 
     TextView lblCambio=(TextView)findViewById(R.id.lblBienvenido); 
     try{ 

      StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build(); 
      StrictMode.setThreadPolicy(policy); 

      Class.forName("com.mysql.jdbc.Driver").newInstance(); 
      Connection con = DriverManager.getConnection(url, user, pass); 
      Statement st = con.createStatement(); 
      ResultSet rs = st.executeQuery("select * from usuarios where id="+EdtxtCedula.getText()); 
      //ResultSetMetaData rsmd = rs.getMetaData(); 
      //rs.next(); 
      //lblCambio.setText(rs.getString(1)); 
      while (rs.next()){ 
       if (rs.getRow() == 0) 
       { 
        //es un result set vacío 
        Toast toast = Toast.makeText(getApplicationContext(), "La cedula no existe", Toast.LENGTH_SHORT); 
        toast.show(); 
        resultadoConexion = false; 

       }else{ 
        //el result set tiene datos 
         //Toast toast = Toast.makeText(getApplicationContext(), "Conexion exitosa", Toast.LENGTH_SHORT); 
         //toast.show(); 
         lblCambio.setText(rs.getString(2)); 
         resultadoConexion = true; 
       } 
      } 
      con.close(); 

     } catch (Exception e) 
     { 
      e.printStackTrace(); 
     } 
     return resultadoConexion; 
    } 


} 

activity_principal.xml

<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:paddingLeft="@dimen/activity_horizontal_margin" 
    android:id="@+id/layContenedor" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".PrincipalActivity" 
    android:gravity="center"> 

    <ImageView android:id="@+id/imgLogo" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:src="@drawable/colpsic_logo" 
     android:layout_alignParentBottom="true" 
     android:layout_centerHorizontal="true" 
     android:layout_marginBottom="354dp" 
     android:contentDescription="@string/logo_descripcion"> 
    </ImageView> 

    <RelativeLayout android:id="@+id/layTexto" 
     android:orientation="vertical" 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:layout_alignTop="@+id/imgLogo" 
     android:layout_alignParentLeft="true" 
     android:layout_alignParentStart="true" 
     android:layout_marginTop="134dp"> 

     <TextView android:id="@+id/lblBienvenido" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:textAppearance="?android:attr/textAppearanceLarge" 
      android:text="@string/bienvenido" 
      android:layout_gravity="center_horizontal" 
      android:textSize="32sp" 
      android:textColor="#0107ff" 
      android:layout_alignParentTop="true" 
      android:layout_centerHorizontal="true" /> 

     <TextView android:id="@+id/lblMensaje_Bienvenida" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:textAppearance="?android:attr/textAppearanceMedium" 
      android:text="@string/mensaje" 
      android:layout_gravity="center_horizontal" 
      android:textColor="#2514ff" 
      android:layout_below="@+id/lblBienvenido" 
      android:layout_alignParentLeft="true" 
      android:layout_alignParentStart="true" 
      android:layout_marginTop="39dp" /> 

     <EditText android:id="@+id/lblCedula" 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" 
      android:hint="@string/cedula" 
      android:textColorHint="#CFCFCF" 
      android:inputType="number" 
      android:layout_below="@+id/lblMensaje_Bienvenida" 
      android:layout_alignParentLeft="true" 
      android:layout_alignParentStart="true" 
      android:layout_marginTop="49dp" /> 
    </RelativeLayout> 

    <LinearLayout 
     android:id="@+id/BarraBotones" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:orientation="horizontal" 
     android:layout_alignParentBottom="true" 
     style="?android:attr/buttonBarStyle"> 

     <Button android:id="@+id/BtnAceptar" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_weight="1" 
      android:text="@string/Aceptar" 
      style="?android:attr/buttonBarButtonStyle" /> 

     <Button android:id="@+id/BtnCancelar" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_weight="1" 
      android:text="@string/salir" 
      style="?android:attr/buttonBarButtonStyle" /> 

    </LinearLayout> 

</RelativeLayout> 

AndroidManifiest.xml

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="com.colpsic.domain.colpsic_app" > 

    <uses-permission android:name="android.permission.INTERNET" /> 

    <application 
     android:allowBackup="true" 
     android:icon="@mipmap/ic_launcher" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme" > 
     <activity 
      android:name=".PrincipalActivity" 
      android:label="@string/app_name" > 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
     <activity 
      android:name=".ProfesionalActivity" 
      android:label="Profesional" > 
     </activity> 
    </application> 

</manifest> 

Answer 1

Следующая строка должна идти внутри метода. (В данном случае, onCreate)

EditText EdtxtCedula=(EditText)findViewById(R.id.lblCedula); 

Он падает, потому что к тому времени эта линия называется, setContentView не был вызван для деятельности, поэтому он не знает, где найти свой EditText

Put это с вашим другим видом, например,

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

    Button btnAceptar=(Button)findViewById(R.id.BtnAceptar); 
    EditText EdtxtCedula=(EditText)findViewById(R.id.lblCedula); 

    btnAceptar.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      boolean existeDocumento; 
      existeDocumento = conection(); 
      validacionDocumento(existeDocumento); 
     } 


    }); 
} 

Answer 2

удалите этот EditText EdtxtCedula=(EditText)findViewById(R.id.lblCedula); из PrincipalActivity и поместить его в onCreate метод

public class PrincipalActivity extends AppCompatActivity { 


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

     Button btnAceptar=(Button)findViewById(R.id.BtnAceptar); 
     EditText EdtxtCedula=(EditText)findViewById(R.id.lblCedula);