Question

我尝试在数据库助手类的构造函数中获取数据库路径，如下所示：

public DB_Nabege_helper(Context context) {
    super(context, DBname, null, 1);
    Nabege_context = context;
    DBpath=Nabege_context.getDatabasePath(DBname).getPath();
}

运行app：崩溃的应用

    10-15 16:41:37.164: E/AndroidRuntime(1420): FATAL EXCEPTION: main
10-15 16:41:37.164: E/AndroidRuntime(1420): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.nabproduct.nabege/com.nabproduct.nabege.Collection_List_Activity}: java.lang.NullPointerException
10-15 16:41:37.164: E/AndroidRuntime(1420):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at android.app.ActivityThread.access$600(ActivityThread.java:130)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at android.os.Handler.dispatchMessage(Handler.java:99)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at android.os.Looper.loop(Looper.java:137)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at android.app.ActivityThread.main(ActivityThread.java:4745)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at java.lang.reflect.Method.invokeNative(Native Method)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at java.lang.reflect.Method.invoke(Method.java:511)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at dalvik.system.NativeStart.main(Native Method)
10-15 16:41:37.164: E/AndroidRuntime(1420): Caused by: java.lang.NullPointerException
10-15 16:41:37.164: E/AndroidRuntime(1420):     at android.content.ContextWrapper.getDatabasePath(ContextWrapper.java:231)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at com.nabproduct.nabege.DB_Nabege_helper.<init>(DB_Nabege_helper.java:44)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at com.nabproduct.nabege.Collection_List_Activity.<init>(Collection_List_Activity.java:165)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at java.lang.Class.newInstanceImpl(Native Method)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at java.lang.Class.newInstance(Class.java:1319)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
10-15 16:41:37.164: E/AndroidRuntime(1420):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)

我添加了更多代码作为答案。

Answer 1

我从堆栈跟踪中看到，您可能在活动构造函数或字段初始化程序中创建了数据库帮助程序。在这两种情况下，活动尚未初始化（此外，在大多数情况下，您不需要覆盖活动构造函数）。在活动onCreate()方法中移动数据库帮助程序分配。

哪里获取数据库中的数据库路径打开帮手？

1 个答案: