为什么我得到空指针异常？当添加值与静态int

请帮助我差不多完成我的代码，但是当我运行它时，我得到nullpointerexception .. 我想增加一个静态int变量上的按钮单击，他们是五个活动。在每次活动他们是一个问题，如果回答正确到达最后一页时，静态INT必须由1递增。我显示总..为什么我得到空指针异常？当添加值与静态int

package com.example.kei; 

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

public class MainActivity extends Activity { 


    RadioButton correctChoice1; 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     correctChoice1.findViewById(R.id.correct1); 
     correctChoice1.setOnClickListener(new OnClickListener() { 

      @Override 
      public void onClick(View v) { 
       AppSingleton.score++; 
       Intent intent = new Intent(MainActivity.this, Page_two.class); 
       startActivity(intent); 
      } 
     }); 
    } 

    public static class AppSingleton { 

     public static int score= 0; 
    } 

    public void choice_a(View view){ 
     Intent intent = new Intent(this, Page_two.class); 
     startActivity(intent); 
    } 



    public void choice_c(View view){ 
     Intent intent = new Intent(this, Page_two.class); 
     startActivity(intent); 
    } 

}

代码 choice_a和 choice_c

是错误的答案。我尝试用onlicklistener为单选按钮增加正确答案。为什么不能执行代码并给出空指针异常？请帮助..我不知道现在该做什么..

的logcat：

03-25 05:21:04.811: D/dalvikvm(1052): Late-enabling CheckJNI 
03-25 05:21:04.827: E/Trace(1052): error opening trace file: No such file or directory (2) 
03-25 05:21:04.863: D/AndroidRuntime(1052): Shutting down VM 
03-25 05:21:04.863: W/dalvikvm(1052): threadid=1: thread exiting with uncaught exception (group=0xa6246288) 
03-25 05:21:04.867: E/AndroidRuntime(1052): FATAL EXCEPTION: main 
03-25 05:21:04.867: E/AndroidRuntime(1052): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.kei/com.example.kei.MainActivity}: java.lang.NullPointerException 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at android.app.ActivityThread.access$600(ActivityThread.java:130) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at android.os.Handler.dispatchMessage(Handler.java:99) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at android.os.Looper.loop(Looper.java:137) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at android.app.ActivityThread.main(ActivityThread.java:4745) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at java.lang.reflect.Method.invokeNative(Native Method) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at java.lang.reflect.Method.invoke(Method.java:511) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at dalvik.system.NativeStart.main(Native Method) 
03-25 05:21:04.867: E/AndroidRuntime(1052): Caused by: java.lang.NullPointerException 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at com.example.kei.MainActivity.onCreate(MainActivity.java:18) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at android.app.Activity.performCreate(Activity.java:5008) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023) 
03-25 05:21:04.867: E/AndroidRuntime(1052):  ... 11 more 
03-25 05:33:23.686: E/Trace(1694): error opening trace file: No such file or directory (2) 
03-25 05:33:23.718: D/AndroidRuntime(1694): Shutting down VM 
03-25 05:33:23.718: W/dalvikvm(1694): threadid=1: thread exiting with uncaught exception (group=0xa6246288) 
03-25 05:33:23.722: E/AndroidRuntime(1694): FATAL EXCEPTION: main 
03-25 05:33:23.722: E/AndroidRuntime(1694): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.kei/com.example.kei.MainActivity}: java.lang.NullPointerException 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at android.app.ActivityThread.access$600(ActivityThread.java:130) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at android.os.Handler.dispatchMessage(Handler.java:99) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at android.os.Looper.loop(Looper.java:137) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at android.app.ActivityThread.main(ActivityThread.java:4745) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at java.lang.reflect.Method.invokeNative(Native Method) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at java.lang.reflect.Method.invoke(Method.java:511) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at dalvik.system.NativeStart.main(Native Method) 
03-25 05:33:23.722: E/AndroidRuntime(1694): Caused by: java.lang.NullPointerException 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at com.example.kei.MainActivity.onCreate(MainActivity.java:23) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at android.app.Activity.performCreate(Activity.java:5008) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023) 
03-25 05:33:23.722: E/AndroidRuntime(1694):  ... 11 more

来源

2014-03-25 Jose Perez

只需从'AppSingleton'类中移除静态。简单地创建类并仅将其变量设置为静态。 – GrIsHu

'correctChoice1'未初始化。用'correctChoice1 =（RadioButton）findViewById（R.id.correct1）'替换'correctChoice1.findViewById（R.id.correct1）;'' – JoelFernandes

Radiobutton TypeCasting错误。 –

尝试初始化你RadioButton如下：

correctChoice1= (RadioButton)findViewById(R.id.correct1); 
    correctChoice1.setOnClickListener(new OnClickListener() { 

     @Override 
     public void onClick(View v) { 
      if(AppSingleton.score <=5) 
      AppSingleton.score++; 
      Intent intent = new Intent(MainActivity.this, Page_two.class); 
      startActivity(intent); 
     } 
    });

来源

2014-03-25 05:43:19 GrIsHu

更换correctChoice1.findViewById(R.id.correct1);与

correctChoice1 = (RadioButton)findViewById(R.id.correct1);

希望这有助于。

来源

2014-03-25 05:42:12

你的单选按钮声明是错误的：

做这样的;

RadioButton correctChoice1; 

correctChoice1 = (RadioButton).findViewById(R.id.correct1);

来源

2014-03-25 05:43:37 Lokesh

为什么我得到空指针异常？当添加值与静态int

回答

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