小编Mar*_*nho的帖子

我正在攻读我的数据库系统考试(明天),我在练习中遇到麻烦,我被要求编写查询.这是一个例子:

我被要求写一个查询来回答以下问题:年龄最低的作者中,谁写的书最多？

问题是我的老师禁止我在FROM子句中使用子查询,并使用TOP.

我写了一个答案,但我知道的是不正确的:

SELECT W.AName, COUNT(W.ID_B) AS NBooks
FROM Write W, Author A1
WHERE (A1.AName = W.AName) AND
      (A1.AAge = (SELECT MIN(A2.Age)
                  FROM Author A2))
GROUP BY W.AName
ORDER BY NBooks DESC

这个给所有年龄较低的作者,以及他们各自的书籍数量(我希望......).正确的答案应该只是这一行的第一行.

让我说清楚一下:

Table Author
AName    | AAge
---------------
John     | 25
Rick     | 30
Sean     | 26
Lena     | 25

Table Writes
AName    | ID_B
---------------
John     | 2
Lena     | 1
John     | 3
Lena     | 4
Rick     | 5
Rick     | 6
Lena …

大约1小时后,在相关主题中寻找我的问题的解决方案,我决定公开我的案例.这是:我每次尝试打开PreferenceActivity时都会出现InflateException.

日志

E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: lineo.smarteam, PID: 5087
                  Theme: themes:{}
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{lineo.smarteam/lineo.smarteam.activity.SettingsActivity}: android.view.InflateException: Binary XML file line #5: Error inflating class lineo.smarteam.preference.MyEditTextPreference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2450)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2510)
                      at android.app.ActivityThread.-wrap11(ActivityThread.java)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1363)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:148)
                      at android.app.ActivityThread.main(ActivityThread.java:5461)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                   Caused by: android.view.InflateException: Binary XML file line #5: Error inflating class lineo.smarteam.preference.MyEditTextPreference
                      at android.preference.GenericInflater.createItem(GenericInflater.java:388)
                      at android.preference.GenericInflater.createItemFromTag(GenericInflater.java:432)
                      at android.preference.GenericInflater.rInflate(GenericInflater.java:483)
                      at android.preference.GenericInflater.rInflate(GenericInflater.java:495)
                      at android.preference.GenericInflater.inflate(GenericInflater.java:327)
                      at android.preference.GenericInflater.inflate(GenericInflater.java:264)
                      at android.preference.PreferenceManager.inflateFromResource(PreferenceManager.java:273)
                      at android.preference.PreferenceFragment.addPreferencesFromResource(PreferenceFragment.java:304)
                      at lineo.smarteam.activity.SettingsActivity$SettingsFragment.onCreate(SettingsActivity.java:57)
                      at …

我在Matlab编辑器中编写了一些代码,它有大约30个数字.因此,当我发布它时,它会打开30个数字窗口,这很烦人.如何防止它打开窗户,但将数字保留在已发布的窗口中？

我试过了close(figure),但随后数字没有显示在已发布的窗口上.

提前致谢

当加载更多数据并附加到状态时，我遇到了经典的无限滚动问题。

我有一个页面，其中显示了自定义的无限滚动城市列表。
这些城市是从外部库中获取的。

import { City, Country, CitiesQuery } from "an-external-library";

export const CountryComponent: FC<Props> = ({ country: Country }) => {
  const [cities, setCities] = useState<City[]>([]);
  const [citiesQuery, setCitiesQuery] = useState<CitiesQuery>();

  const loadMoreCities = useCallback(() => {
    console.log("loadMoreCities", "cities", cities);

    citiesQuery
      ?.load((newCities) => {
        console.log("loadMoreCities", "newCities", newCities);
        const updatedCities = [...cities, ...newCities];
        console.log("loadMoreCities", "updatedCities", updatedCities);
        setCities(updatedCities);
      })
      .then(() => setCitiesQuery(citiesQuery))
      .catch(console.error)
  }, [cities]); // I've tried adding more dependencies here

  useEffect(() => {
    const query = country.createCitiesQuery()
    query.limit = …

我已经读过几个关于此的问题,但我对答案不满意,所以我决定问一下我的具体例子.

我正在开发和Android应用程序,它有一个带有一些可配置整数参数的设置屏幕.所有这些参数都具有最大值和最小值.因此,每次用户为这些参数设置新值时,我都想验证它们.如果新值超出定义的范围,我想显示Toast通知用户出了什么问题.

另一方面,因为在我的应用程序的某些情况下,用户可以"垃圾"一个可能显示Toast的按钮,为了避免Toast显示重复一段时间,我创建了一个带有静态Toast的Application类,每次我想要祝酒:

public class MyApplication extends Application {
    private static Toast toast;
    public static void showToast(Context context, String string){
       //(...)
    }
}

回到"设置"页面,这是我实现它的方式:

public class SettingsActivity extends PreferenceActivity {
    private Context context;
    static SharedPreferences sharedPreferences;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        context = this;
        sharedPreferences = PreferenceManager.getDefaultSharedPreferences(context);
        getFragmentManager().beginTransaction().replace(android.R.id.content, new SettingsFragment()).commit();
    }

    public static class SettingsFragment extends PreferenceFragment implements SharedPreferences.OnSharedPreferenceChangeListener {
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            addPreferencesFromResource(R.xml.preferences);
            setListeners();
        }

        public void setListeners() {
            setListenerA();
            //(other listeners to …