Question

我试图使用 HashMap 从数据库中读取数据，但每次我在模拟器中运行该程序时都会受到攻击。我尝试使用带有** BasicNameValuePair *的Arraylist来检索数据，但这也没有用完。这是我读取数据的代码。

DatabaseHandler databaseHandler = new DatabaseHandler(
        getApplicationContext());
HashMap<String, String> user = new HashMap<String, String>();
user = databaseHandler.userDetails();

email = user.get("email").toString();
password = user.get("password").toString();

这是我的userDetails（）方法

   public HashMap<String, String> userDetails() {

        HashMap<String, String> user = new HashMap<String, String>();
        String query = "SELECT * FROM login";
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(query, null);
        // move to first row
        cursor.moveToFirst();

        if (cursor.getCount() > 0) {
            user.put("email", cursor.getString(1));
            user.put("password", cursor.getString(2));
        }
        cursor.close();
        db.close();
        return user;

    }

logcat显示错误

07-16 17:13:23.272: E/AndroidRuntime(1396):     at com.ved_main.mainpage.VerifyMainActivity.onCreate(VerifyMainActivity.java:56)
07-16 17:54:10.332: E/AndroidRuntime(1501): FATAL EXCEPTION: main
07-16 17:54:10.332: E/AndroidRuntime(1501): Process: com.ved_main.mainpage, PID: 1501
07-16 17:54:10.332: E/AndroidRuntime(1501): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ved_main.mainpage/com.ved_main.mainpage.VerifyMainActivity}: java.lang.NullPointerException
07-16 17:54:10.332: E/AndroidRuntime(1501):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at android.os.Handler.dispatchMessage(Handler.java:102)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at android.os.Looper.loop(Looper.java:136)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at android.app.ActivityThread.main(ActivityThread.java:5017)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at java.lang.reflect.Method.invokeNative(Native Method)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at java.lang.reflect.Method.invoke(Method.java:515)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at dalvik.system.NativeStart.main(Native Method)
07-16 17:54:10.332: E/AndroidRuntime(1501): Caused by: java.lang.NullPointerException
07-16 17:54:10.332: E/AndroidRuntime(1501):     at com.ved_main.mainpage.VerifyMainActivity.onCreate(VerifyMainActivity.java:54)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at android.app.Activity.performCreate(Activity.java:5231)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
07-16 17:54:10.332: E/AndroidRuntime(1501):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
07-16 17:54:10.332: E/AndroidRuntime(1501):     ... 11 more

Answer 1

该表没有任何行，因此email对象中没有user条目。

使用游标从数据库中检索数据。

1 个答案: