java - 当我启动应用程序时尝试获取 Android_ID 崩溃

Question

这是获取AndroidID的代码:

String userID = Settings.Secure.getString(getApplicationContext()
.getContentResolver(), Settings.Secure.ANDROID_ID);

当我启动应用程序时，我收到以下 logcat 评论:

04-28 01:30:02.012 9328-9328/com.hubermoritz.beercounter.beercounter02 E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                     Process: com.hubermoritz.beercounter.beercounter02, PID: 9328
                                                                                     java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.hubermoritz.beercounter.beercounter02/com.hubermoritz.beercounter.beercounter02.MainActivity}: java.lang.NullPointerException
                                                                                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2305)
                                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2470)
                                                                                         at android.app.ActivityThread.access$900(ActivityThread.java:174)
                                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1307)
                                                                                         at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                         at android.os.Looper.loop(Looper.java:146)
                                                                                         at android.app.ActivityThread.main(ActivityThread.java:5593)
                                                                                         at java.lang.reflect.Method.invokeNative(Native Method)
                                                                                         at java.lang.reflect.Method.invoke(Method.java:515)
                                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283)
                                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
                                                                                         at dalvik.system.NativeStart.main(Native Method)
                                                                                      Caused by: java.lang.NullPointerException
                                                                                         at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:114)
                                                                                         at com.hubermoritz.beercounter.beercounter02.MainActivity.<init>(MainActivity.java:48)
                                                                                         at java.lang.Class.newInstanceImpl(Native Method)
                                                                                         at java.lang.Class.newInstance(Class.java:1208)
                                                                                         at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
                                                                                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2296)
                                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2470) 
                                                                                         at android.app.ActivityThread.access$900(ActivityThread.java:174) 
                                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1307) 
                                                                                         at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                                         at android.os.Looper.loop(Looper.java:146) 
                                                                                         at android.app.ActivityThread.main(ActivityThread.java:5593) 
                                                                                         at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                                         at java.lang.reflect.Method.invoke(Method.java:515) 
                                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1283) 
                                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099) 
                                                                                         at dalvik.system.NativeStart.main(Native Method) 

04

尝试过:

public String userID = Settings.Secure.getString(getContentResolver(), Settings.Secure.ANDROID_ID);

而且，也不起作用。顺便说一句，我很清楚这不是识别用户的完美方式，因为号码可能会因恢复出厂设置或更换手机以及其他几种方式而发生变化。

Answer 1

Caused by: java.lang.NullPointerException
  at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:114)
  at com.hubermoritz.beercounter.beercounter02.MainActivity.<init>(MainActivity.java:48)

您正尝试从字段初始值设定项调用从 Activity 继承的方法。不要这样做。一般来说，在 onCreate() 方法中调用 super.onCreate() 之前，不要调用 Activity 上的继承方法。欢迎您拥有一个字段，但不要在 super.onCreate() 之后初始化它。