空指针创建SQLite数据库

Question

Why do these two lines of code throw a NPE?

SQLiteDatabase db;
db = openOrCreateDatabase("TestingData.db", SQLiteDatabase.CREATE_IF_NECESSARY, null);

Stacktrace:

08-23 10:33:14.285: ERROR/AndroidRuntime(1001): Caused by: java.lang.NullPointerException
08-23 10:33:14.285: ERROR/AndroidRuntime(1001):     at android.content.ContextWrapper.openOrCreateDatabase(ContextWrapper.java:203)
08-23 10:33:14.285: ERROR/AndroidRuntime(1001):     at org.*****.android.CopyOfSQLLite.data(CopyOfSQLLite.java:14)
08-23 10:33:14.285: ERROR/AndroidRuntime(1001):     at org.******.android.*****.****(****.java:200)
08-23 10:33:14.285: ERROR/AndroidRuntime(1001):     at org.********.android.****.onCreate(DashboardPage.java:25)
08-23 10:33:14.285: ERROR/AndroidRuntime(1001):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-23 10:33:14.285: ERROR/AndroidRuntime(1001):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)

Answer 1

Your ContextWrapper does not have a base Context. Most likely you are not calling this method at the correct place, but I cannot say more without a little more code.

Answer 2

The nice thing about Android is that it is open source . So we can see that openOrCreateDatabase() is implemented like:

public SQLiteDatabase openOrCreateDatabase(String name, int mode, CursorFactory factory) {
    return mBase.openOrCreateDatabase(name, mode, factory);
}

The only way I can see this code throwing a NPE is if mBase is null. From your calling convention I assume your class is derived from android.content.ContextWrapper ? If so, are you ensuring that the base context ( mBase ) is set when your class is instantiated? If you aren't, then that would be what's causing the problem.