找不到NullPointerException的原因；安卓

Question

我在 LogCat 堆栈中收到 NullPointerExcpetion，但我似乎不明白为什么。我只是希望外界的目光能帮助我找到问题所在。

这是来自 LogCat 的堆栈：

    10-28 02:04:55.998: ERROR/AndroidRuntime(524): FATAL EXCEPTION: main
    10-28 02:04:55.998: ERROR/AndroidRuntime(524): java.lang.NullPointerException
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at vt.nhw.android.easyringertoggle.ScheduleDbAdapter.createSchedule(ScheduleDbAdapter.java:77)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at vt.nhw.android.easyringertoggle.ScheduleEditActivity.saveState(ScheduleEditActivity.java:195)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at vt.nhw.android.easyringertoggle.ScheduleEditActivity.access$3(ScheduleEditActivity.java:189)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at vt.nhw.android.easyringertoggle.ScheduleEditActivity$5.onClick(ScheduleEditActivity.java:135)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at android.view.View.performClick(View.java:2408)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at  android.view.View$PerformClick.run(View.java:8816)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at android.os.Handler.handleCallback(Handler.java:587)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at android.os.Handler.dispatchMessage(Handler.java:92)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at android.os.Looper.loop(Looper.java:123)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at android.app.ActivityThread.main(ActivityThread.java:4627)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at java.lang.reflect.Method.invokeNative(Native Method)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at java.lang.reflect.Method.invoke(Method.java:521)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
    10-28 02:04:55.998: ERROR/AndroidRuntime(524):     at dalvik.system.NativeStart.main(Native Method)

该堆栈似乎指向 saveState() 方法和 createSchedule() 方法。相关行已加双星号。

saveState():

private void saveState() {
    String title = mTitleText.getText().toString();
    SimpleDateFormat dateTimeFormat = new SimpleDateFormat(DATE_TIME_FORMAT);
    String scheduleDateTime = dateTimeFormat.format(mCalendar.getTime());

    if (mRowId == null) {
        **long id = mDbHelper.createSchedule(title, scheduleDateTime);**
        if(id > 0) {
            mRowId = id;
        }
    } else {
        mDbHelper.updateSchedule(mRowId, title, scheduleDateTime);
    }
}

createSchedule()：

public long createSchedule(String title, String scheduleDateTime) {
    ContentValues initialValues = new ContentValues();
    initialValues.put(KEY_TITLE, title);
    initialValues.put(KEY_DATE_TIME, scheduleDateTime);
    **return mDb.insert(DATABASE_TABLE, null, initialValues);**
}

如果我需要发布任何其他代码，请告诉我。感谢您能给我的任何帮助。

问候， 贾森

Answer 1

mDb 似乎为 NULL，因为这是唯一的全局变量。