Android的 - 版本

Question

我已經創建了一個應用程序，並測試了它的Android API16和API19和它的作品，但是當我測試API18在啓動

03-13 11:17:25.884: E/AndroidRuntime(2678): FATAL EXCEPTION: main 
03-13 11:17:25.884: E/AndroidRuntime(2678): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.arr_app/com.arr_app.MainActivity}: java.lang.NullPointerException 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2137) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at android.app.ActivityThread.access$600(ActivityThread.java:141) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at android.os.Handler.dispatchMessage(Handler.java:99) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at android.os.Looper.loop(Looper.java:137) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at android.app.ActivityThread.main(ActivityThread.java:5103) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at java.lang.reflect.Method.invokeNative(Native Method) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at java.lang.reflect.Method.invoke(Method.java:525) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at dalvik.system.NativeStart.main(Native Method) 
03-13 11:17:25.884: E/AndroidRuntime(2678): Caused by: java.lang.NullPointerException 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at  android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:146) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at com.arr_app.DBHelper.<init>(DBHelper.java:31) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at com.arr_app.MainActivity.<init>(MainActivity.java:44) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at java.lang.Class.newInstanceImpl(Native Method) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at java.lang.Class.newInstance(Class.java:1130) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at android.app.Instrumentation.newActivity(Instrumentation.java:1061) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2128) 
03-13 11:17:25.884: E/AndroidRuntime(2678):  ... 11 more 

項目有Minimum Required SDK: API8和Target SDK: API18

Answer 1

給錯誤在onCreate()之前，在構造函數/成員變量初始化階段，您過早使用MainActivity作爲Context。

將DBHelper初始化爲onCreate()。