我该如何解决NullPointerException？

-1

07-28 11:36:48.010: W/dalvikvm(31346): threadid=1: thread exiting with uncaught exception (group=0x41daf960) 
07-28 11:36:48.020: E/AndroidRuntime(31346): FATAL EXCEPTION: main 
07-28 11:36:48.020: E/AndroidRuntime(31346): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example/com.example.MainActivity}: java.lang.NullPointerException 
07-28 11:36:48.020: E/AndroidRuntime(31346): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2255) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2309) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at android.app.ActivityThread.access$700(ActivityThread.java:157) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1289) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at android.os.Handler.dispatchMessage(Handler.java:99) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at android.os.Looper.loop(Looper.java:176) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at android.app.ActivityThread.main(ActivityThread.java:5317) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at java.lang.reflect.Method.invokeNative(Native Method) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at java.lang.reflect.Method.invoke(Method.java:511) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at dalvik.system.NativeStart.main(Native Method) 
07-28 11:36:48.020: E/AndroidRuntime(31346): Caused by: java.lang.NullPointerException 
07-28 11:36:48.020: E/AndroidRuntime(31346): at com.example.MainActivity.onCreate(MainActivity.java:18) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at android.app.Activity.performCreate(Activity.java:5326) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1097) 
07-28 11:36:48.020: E/AndroidRuntime(31346): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2218) 
07-28 11:36:48.020: E/AndroidRuntime(31346): ... 11 more 
07-28 11:36:49.612: I/Process(31346): Sending signal. PID: 31346 SIG: 9

package com.example;我该如何解决NullPointerException？

import android.os.Bundle; 
import android.app.Activity; 
import android.content.Intent; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.EditText; 

public class MainActivity extends Activity { 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     // TODO Auto-generated method stub 
     super.onCreate(savedInstanceState); 
     final EditText txt =(EditText) findViewById(R.id.editText1); 
     Button btn =(Button) findViewById(R.id.button1); 
     btn.setOnClickListener(new OnClickListener() 
     { 
      @Override 
      public void onClick(View v) { 
       Intent m = new Intent(MainActivity.this,Main2.class); 
       m.putExtra("a",txt.getText().toString()); 
      } 
     }); 

    } 

}

来源

2015-07-28 A.T

E/AndroidRuntime（31346）：显示java.lang.NullPointerException 11月7日至28日：由造成36：48.020：此行是你的实际的错误和在它旁边发生。 –

在这一行中，您将得到异常'com.example.MainActivity.onCreate（MainActivity.java:18）'：引起：java.lang.NullPointerException –

错误是因为您指的是控件而没有将视图设置为活动。使用'setcontentview（）'方法指向你的xml布局，你的控件实际上是 –

您错过了设置您的内容视图。

后super.onCreate(savedInstanceState);

setContentView(R.layout.your_layout_name);

来源

2015-07-28 07:23:35 dhuma1981

非常感谢。我这样做，但还没有工作。 –

当我按下按钮“不幸已停止”发生。我必须做什么？ –

'公共类MAIN2延伸活动{ @覆盖保护无效的onCreate（捆绑savedInstanceState）{ \t // TODO自动生成方法存根 \t super.onCreate（savedInstanceState）; \t setContentView（R.layout.main2）; \t EditText a =（EditText）findViewById（R.id.textView1）; （）。getText（）。getExtras（）。getString（“a”））; \t \t \t } }' –

你没有设置你的活动布局引用添加下面的线。这就是为什么您需要在onCreate方法中的super.onCreate(savedInstanceState);之后添加setContentView(R.layout.yourXMLFile);。希望它能帮助

来源

2015-07-28 07:25:56

只需设置setContentView(R.layout.xxxxxx);

@Override 
    protected void onCreate(Bundle savedInstanceState) 
    { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.xxxxxx); 
     final EditText txt =(EditText) findViewById(R.id.editText1); 
     Button btn =(Button) findViewById(R.id.button1); 
     btn.setOnClickListener(new OnClickListener() 
     { 
      @Override 
      public void onClick(View v) { 
       Intent m = new Intent(getApplicationContext(),Main2.class); 
       m.putExtra("a",txt.getText().toString()); 

       startActivity(intent); 
      } 
     }); 

    } 

}

来源

2015-07-28 07:29:07

我该如何解决NullPointerException？

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