Ein Fehler zu Intent Android

Question

mit dem Gehen

package com.lazerg.apptask; 


import android.content.Intent; 
import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.view.View; 
import android.widget.Button; 

public class tasks extends AppCompatActivity { 
    Button APlusBButton = (Button) findViewById(R.id.aplusbgoto); 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_tasks); 

     APlusBButton.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       APlubBGotoIntent(); 
      } 
     }); 
    } 

    void APlubBGotoIntent(){ 
     Intent i = new Intent(getApplicationContext(),APlusBClass.class); 
     startActivity(i); 
    } 
} 

Dies ist mein Code Wenn ich andere bin versucht Absicht Sein

09-01 17:49:22.109 9259-9259/com.lazerg.apptask E/AndroidRuntime: FATAL EXCEPTION: main 
     Process: com.lazerg.apptask, PID: 9259 
     java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.lazerg.apptask/com.lazerg.apptask.tasks}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference 
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2989) 
      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3260) 
      at android.app.ActivityThread.access$1000(ActivityThread.java:218) 
      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1734) 
      at android.os.Handler.dispatchMessage(Handler.java:102) 
      at android.os.Looper.loop(Looper.java:145) 
      at android.app.ActivityThread.main(ActivityThread.java:6934) 
      at java.lang.reflect.Method.invoke(Native Method) 
      at java.lang.reflect.Method.invoke(Method.java:372) 
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1404) 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1199) 

Answer 1

Mit out

setContentView(R.layout.activity_tasks); 

Wie Sie

Button APlusBButton = (Button) findViewById(R.id.aplusbgoto); 

erklären können Sie sollten Taste nach InhaltAlle erklären, weil mit Blick wie Sie Widget für diese Ansicht verwenden können.

Answer 2

Verschieben Button APlusBButton = (Button) findViewById(R.id.aplusbgoto); innen onCreate sagen zu bewegen, bevor Sie die clicklistener eingestellt.

diesen Code Versuchen Sie,

public class tasks extends AppCompatActivity { 

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

     // Move this line inside onCreate 
     Button APlusBButton = (Button) findViewById(R.id.aplusbgoto); 

     APlusBButton.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       APlubBGotoIntent(); 
      } 
     }); 
    } 

    void APlubBGotoIntent(){ 
     Intent i = new Intent(getApplicationContext(),APlusBClass.class); 
     startActivity(i); 
    } 
} 

Answer 3

Definieren Sie den Knopf APlusBButton unten/nach dem setContentView() Verfahren.

public class tasks extends AppCompatActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_tasks); 
    Button APlusBButton = (Button) findViewById(R.id.aplusbgoto); 

    APlusBButton.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      APlubBGotoIntent(); 
     } 
    }); 
} 

void APlubBGotoIntent(){ 
    Intent i = new Intent(getApplicationContext(),APlusBClass.class); 
    startActivity(i); 
} 
} 

Answer 4

Wechsel von:

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

    APlusBButton.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      APlubBGotoIntent(); 
     } 
    }); 
} 

An:

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_tasks); 
    APlusBButton = (Button) findViewById(R.id.aplusbgoto); 
    APlusBButton.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      APlubBGotoIntent(); 
     } 
    }); 
} 

findViewById sollte einmal die setContentView genannt wird aufgerufen werden.