尝试从 radioButton 获取值时出现 java.lang.NullPointerException (Android)

Question

我试图从 radioButton 获取字符串值，但是当我尝试时，它在 LogCat 上显示此错误。我似乎不知道如何修复它..这些是代码:

    protected void onCreate(Bundle konsumsi) {
        super.onCreate(konsumsi);
        radioAktivitasGroup = (RadioGroup) findViewById(R.id.radioAktivitasGroup);
        setContentView(R.layout.aktivitas_user);
        usernameP = Login.usernameP;
        System.out.println(usernameP);

        buttonDone();

    }
public void buttonDone() {
        selesai = (Button) findViewById(R.id.buttonProses);
        selesai.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                 int selectedId = radioAktivitasGroup.getCheckedRadioButtonId();     
                    radioAktivitasButton = (RadioButton) findViewById(selectedId);
                    String Aktivitas = radioAktivitasButton.getText().toString();
            }
        });
    }  

错误:

    05-20 07:01:07.858: E/AndroidRuntime(3179): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ta.nutrifact/com.ta.nutrifact.AktivitasUser}: java.lang.NullPointerException
05-20 07:01:07.858: E/AndroidRuntime(3179):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at android.os.Looper.loop(Looper.java:137)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at android.app.ActivityThread.main(ActivityThread.java:5103)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at java.lang.reflect.Method.invokeNative(Native Method)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at java.lang.reflect.Method.invoke(Method.java:525)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at dalvik.system.NativeStart.main(Native Method)
05-20 07:01:07.858: E/AndroidRuntime(3179): Caused by: java.lang.NullPointerException
05-20 07:01:07.858: E/AndroidRuntime(3179):     at com.ta.nutrifact.AktivitasUser.onCreate(AktivitasUser.java:71)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at android.app.Activity.performCreate(Activity.java:5133)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-20 07:01:07.858: E/AndroidRuntime(3179):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
05-20 07:01:07.858: E/AndroidRuntime(3179):     ... 11 more

我在另一门课上做了完全相同的事情，它有效，但在这门课上不起作用。任何帮助，将不胜感激。谢谢

Answer 1

颠倒陈述

 radioAktivitasGroup = (RadioGroup) findViewById(R.id.radioAktivitasGroup);
 setContentView(R.layout.aktivitas_user);

至

 setContentView(R.layout.aktivitas_user);
 radioAktivitasGroup = (RadioGroup) findViewById(R.id.radioAktivitasGroup);