Android Studio 没有显示未关闭光标的警告，我是否仍应关闭它？

Question

我在 class DatabaseHelper extends SQLiteAssetHelper 中有一个 private Cursor c;，它全局处理我的应用程序的所有数据库操作。此游标在整个 class 中使用，在多个方法中用于从 private static SQLiteDatabase mydb; 获取数据。我既没有关闭任何地方的游标，也没有关闭数据库，但我没有看到任何警告。我有一个案例，我被警告从方法内部关闭本地游标（我解决了）。我必须关闭这个游标吗？（假设我不必关闭静态数据库）

这里是全部class，以防万一：

    class DatabaseHelper extends SQLiteAssetHelper {

    static final String AUTHORITY = "com.example.attendance.provider";
    static final String ACCOUNT_TYPE = "example.com";
    static final String ACCOUNT = "Lazim";
    static final String WIFI_ERROR = "Please enter your office premises";
    static final boolean DEBUG = true;
    private static final String DATE_FORMAT = "d-M-yyyy";
    private static final String TIME_FORMAT = "hh:mm:ss a";
    private static final String DB_NAME = "attendance.db";
    private static final int DB_VERSION = 1;
    private static SQLiteDatabase mydb;
    private Cursor c;
    private Context context;

    DatabaseHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
        this.context = context;
        mydb = getWritableDatabase();
    }

    boolean insertTable(int u_id, String name, String username, String password) {
        boolean b;
        try {
            c = mydb.rawQuery("select * from login where u_id=" + u_id + ";", null);
            if (!c.moveToFirst()) {
                mydb.execSQL("insert into login (u_id,name,username,password) values(" + u_id + ",'" + name + "','" + username + "','" + password + "');");
                b = true;
            } else {
                mydb.execSQL("update login set name='" + name + "',username='" + username + "',password='" + password + "' where u_id=" + u_id + ";");
                mydb.execSQL("delete from records where u_id=" + u_id + ";");
                b = true;
            }
        } catch (Exception e) {
            e.printStackTrace();
            b = false;
        }
        return b;
    }

    boolean insertTable(int id, String name, String date, String checkin, int flag) {
        boolean b = false;
        try {
            c = mydb.rawQuery("select * from records where u_id=" + id + " and date='" + date + "' and checkin='" + checkin + "';", null);
            if (!c.moveToFirst()) {
                mydb.execSQL("insert into records (u_id,name,date,checkin,checkout,flag) values(" + id + ",'" + name + "','" + date + "','" + checkin + "',''," + flag + ");");
                b = true;
            }
        } catch (SQLiteException e) {
            e.printStackTrace();
        }
        return b;
    }

    Boolean deleteRecords(String username) {
        Boolean b = null;
        try {
            c = mydb.rawQuery("select u_id from login where username='" + username + "';", null);
            if (c.moveToFirst()) {
                int u_id = c.getInt(0);
                Cursor cursor = mydb.rawQuery("select * from records where u_id=" + u_id + ";", null);
                if (cursor.moveToFirst())
                    mydb.execSQL("delete from records where u_id=" + u_id + ";", null);
                cursor.close();
                mydb.execSQL("delete from login where username='" + username + "';");
                b = true;
            } else
                b = false;
        } catch (SQLiteException e) {
            e.printStackTrace();
        }
        return b;
    }

    boolean insertOnLogin(int u_id, String name, String username, String password) {
        boolean b = false;
        try {
            c = mydb.rawQuery("select * from login where u_id=" + u_id + ";", null);
            if (!c.moveToFirst())
                mydb.execSQL("insert into login (u_id,name,username,password) values(" + u_id + ",'" + name + "','" + username + "','" + password + "');");
            else
                mydb.execSQL("update login set name='" + name + "',username='" + username + "',password='" + password + "' where u_id=" + u_id + ";");
            b = true;
        } catch (SQLiteException e) {
            e.printStackTrace();
        }
        return b;
    }

    boolean updateTable(int id, String name, String checkout, String date, int flag) {
        boolean b = false;
        int s_id, f;
        try {
            c = mydb.rawQuery("select s_id,flag from records where u_id=" + id + " and date='" + date + "' and checkin='" + getCheckin() + "';", null);
            if (c.moveToFirst()) {
                s_id = c.getInt(0);
                f = c.getInt(1);
                if (f == 0)
                    flag = 0;
                mydb.execSQL("update records set flag=" + flag + ",checkout='" + checkout + "' where s_id=" + s_id + ";");
                b = true;
            } else {
                mydb.execSQL("insert into records (u_id,name,date,checkin,checkout,flag) values(" + id + ",'" + name + "','" + date + "','','" + checkout + "'," + flag + ");");
                b = true;
            }
        } catch (SQLiteException e) {
            e.printStackTrace();
        }
        return b;
    }

    void updateFlags(Cursor c) {
        if (c.moveToFirst()) {
            do {
                try {
                    mydb.execSQL("update records set flag=1 where u_id=" + c.getInt(0) + " and date='" + c.getString(2) + "' and checkin='" + c.getString(3) + "' and checkout='" + c.getString(4) + "';");
                    if (DEBUG) Log.i("#####", "###FLAGS UPDATED");
                } catch (SQLiteException e) {
                    e.printStackTrace();
                }
            } while (c.moveToNext());
        }
    }

    long getMinDate(int u_id) {
        long minDate = -1;
        long tempDate;
        try {
            c = mydb.rawQuery("select distinct(date) from records where u_id=" + u_id + ";", null);
            if (c.moveToFirst()) {
                minDate = getLongDateTime(c.getString(0), DATE_FORMAT);
                while (c.moveToNext()) {
                    tempDate = getLongDateTime(c.getString(0), DATE_FORMAT);
                    if (tempDate < minDate)
                        minDate = tempDate;
                }
            }
        } catch (SQLiteException e) {
            e.printStackTrace();
        }
        return minDate;
    }

    private String getMaxDate(int u_id, String check) {
        long longDate;
        long tempDate;
        String maxDate = null;
        try {
            if ("checkout".equals(check))
                c = mydb.rawQuery("select distinct(date) from records where u_id=" + u_id + " and checkout!='';", null);
            else
                c = mydb.rawQuery("select distinct(date) from records where u_id=" + u_id + ";", null);
            if (c.moveToFirst()) {
                maxDate = c.getString(0);
                longDate = getLongDateTime(maxDate, DATE_FORMAT);
                while (c.moveToNext()) {
                    tempDate = getLongDateTime(c.getString(0), DATE_FORMAT);
                    if (tempDate > longDate) {
                        longDate = tempDate;
                        maxDate = c.getString(0);
                    }
                }
            }
        } catch (SQLiteException e) {
            e.printStackTrace();
        }
        return maxDate;
    }

    private long getLongDateTime(String datetime, String format) {
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(format, Locale.US);
        Date newDate;
        long longDate = -1;
        try {
            newDate = simpleDateFormat.parse(datetime);
            longDate = newDate.getTime();
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return longDate;
    }

    POJO urlConnector(String con) {
        POJO pojo = new POJO();
        int u_id;
        String response;
        try {
            URL url = new URL(con);
            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            httpURLConnection.setConnectTimeout(10000);
            httpURLConnection.setReadTimeout(10000);
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader((InputStream) httpURLConnection.getContent()));
            response = bufferedReader.readLine();
            httpURLConnection.disconnect();
            JSONObject object = new JSONObject(response);
            response = object.getString("response");
            pojo.setResponse(response);
            if ("success".equals(response)) {
                u_id = object.getInt("u_id");
                pojo.setU_id(u_id);
            }
        } catch (SocketTimeoutException e) {
            e.printStackTrace();
            pojo.setResponse("Connection timed out");
        } catch (IOException e) {
            e.printStackTrace();
            pojo.setResponse("Network unavailable");
        } catch (JSONException e) {
            e.printStackTrace();
            pojo.setResponse("Data unavailable");
        }
        return pojo;
    }

    POJO jsonReceiver(String con) {
        POJO pojo = new POJO();
        String name = "", response;
        int u_id = -1;
        try {
            URL url = new URL(con);
            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
            httpURLConnection.setConnectTimeout(10000);
            httpURLConnection.setReadTimeout(10000);
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader((InputStream) httpURLConnection.getContent()));
            String result = bufferedReader.readLine();
            httpURLConnection.disconnect();
            JSONObject object = new JSONObject(result);
            response = object.getString("response");
            pojo.setResponse(response);
            if ("success".equals(response)) {
                u_id = object.getInt("u_id");
                name = object.getString("name");
                pojo.setU_id(u_id);
                pojo.setNamePojo(name);
            }
            if (object.has("jsonarray")) {
                JSONArray jsonArray = object.getJSONArray("jsonarray");
                if (DEBUG) Log.i("#####", "JSONARRAY: " + jsonArray.toString());
                for (int i = 0; i < jsonArray.length(); i++) {
                    JSONObject jsonObject = jsonArray.getJSONObject(i);
                    if (DEBUG) Log.i("###########", "#####" + jsonObject);
                    String date = jsonObject.getString("date");
                    String checkin = jsonObject.getString("checkin");
                    String checkout = jsonObject.getString("checkout");
                    try {
                        c = mydb.rawQuery("select * from records where u_id=" + u_id + " and date='" + date + "' and checkin='" + checkin + "';", null);
                        if (!c.moveToFirst())
                            mydb.execSQL("insert into records (u_id,name,date,checkin,checkout) values (" + u_id + ",'" + name + "','" + date + "','" + checkin + "','" + checkout + "');");
                    } catch (SQLiteException e) {
                        e.printStackTrace();
                    }
                }
            } else if (DEBUG) Log.i("#####", "###NO JSON ARRAY");
        } catch (SocketTimeoutException e) {
            e.printStackTrace();
            pojo.setResponse("Connection timed out");
        } catch (IOException e) {
            e.printStackTrace();
            pojo.setResponse("Network unavailable");
        } catch (JSONException e) {
            e.printStackTrace();
            pojo.setResponse("Data unavailable");
        }
        return pojo;
    }

    String uploadData(String con) {
        String result;
        try {
            URL url = new URL(con);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setConnectTimeout(10000);
            connection.setReadTimeout(10000);
            BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            result = reader.readLine();
            connection.disconnect();
        } catch (SocketTimeoutException e) {
            e.printStackTrace();
            result = "Connection timed out";
        } catch (IOException e) {
            e.printStackTrace();
            result = "Network unavailable";
        }
        return result;
    }

    void setCheckin(String checkin) {
        SharedPreferences preferences = context.getSharedPreferences("checkin", MODE_PRIVATE);
        SharedPreferences.Editor editor = preferences.edit();
        editor.putString("last_checkin", checkin);
        editor.apply();
    }

    String getCheckin() {
        SharedPreferences preferences = context.getSharedPreferences("checkin", MODE_PRIVATE);
        return preferences.getString("last_checkin", null);
    }


    Cursor getFileQueue() {
        try {
            c = mydb.rawQuery("select u_id,name,date,checkin,checkout from records where flag=0 order by s_id", null);
            return c;
        } catch (Exception e) {
            e.printStackTrace();
            return null;
        }
    }

    private Cursor getSessionLogAM(String date, int u_id) {
        Cursor mergeCursorAM = null;
        try {
            c = mydb.rawQuery("select checkin,checkout from records where u_id=" + u_id + " and date='" + date + "' and checkin like '12%AM' order by checkin;", null);
            mergeCursorAM = mydb.rawQuery("select checkin,checkout from records where u_id=" + u_id + " and date='" + date + "' and checkin like '%AM' and checkin not like '12%' order by checkin;", null);
            if (c.moveToFirst()) {
                if (mergeCursorAM.moveToFirst())
                    mergeCursorAM = new MergeCursor(new Cursor[]{c, mergeCursorAM});
                else
                    mergeCursorAM = c;
            }
        } catch (SQLiteException e) {
            e.printStackTrace();
        }
        return mergeCursorAM;
    }

    private Cursor getSessionLogPM(String date, int u_id) {
        Cursor mergeCursorPM = null;
        try {
            c = mydb.rawQuery("select checkin,checkout from records where u_id=" + u_id + " and date='" + date + "' and checkin like '12%PM' order by checkin;", null);
            mergeCursorPM = mydb.rawQuery("select checkin,checkout from records where u_id=" + u_id + " and date='" + date + "' and checkin like '%PM' and checkin not like '12%' order by checkin;", null);
            if (c.moveToFirst()) {
                if (mergeCursorPM.moveToFirst())
                    mergeCursorPM = new MergeCursor(new Cursor[]{c, mergeCursorPM});
                else
                    mergeCursorPM = c;
            }
        } catch (SQLiteException e) {
            e.printStackTrace();
        }
        return mergeCursorPM;
    }

    Cursor getMergedLog(String date, int u_id) {
        Cursor AM = getSessionLogAM(date, u_id), PM = getSessionLogPM(date, u_id);
        if (AM.moveToFirst()) {
            if (PM.moveToFirst())
                return new MergeCursor(new Cursor[]{AM, PM});
            else return AM;
        } else if (PM.moveToFirst())
            return PM;
        else return null;
    }

    String enString(String s) {
        try {
            return URLEncoder.encode(s, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            return null;
        }
    }

    String getName(String username) {
        String name = "";
        try {
            c = mydb.rawQuery("select name from login where username='" + username + "';", null);
            if (c.moveToFirst()) {
                do {
                    name = c.getString(0);
                } while (c.moveToNext());
            }
        } catch (SQLiteException e) {
            e.printStackTrace();
        }
        return name;
    }

    int getID(String username) {
        int id = -1;
        try {
            c = mydb.rawQuery("select u_id from login where username='" + username + "';", null);
            if (c.moveToFirst()) {
                do {
                    id = c.getInt(0);
                } while (c.moveToNext());
            }
        } catch (SQLiteException e) {
            e.printStackTrace();
        }
        return id;
    }

    String getLastLogin(int id) {
        String maxTime;
        String maxDate;
        maxDate = getMaxDate(id, null);
        if (maxDate != null) {
            maxTime = getMaxTime(id, maxDate, "checkin");
            if (maxTime != null)
                return (maxTime + "  " + maxDate);
        }
        return "N/A";
    }


    String getLastLogout(int id) {
        String maxTime;
        String maxDate;
        maxDate = getMaxDate(id, "checkout");
        if (maxDate != null) {
            maxTime = getMaxTime(id, maxDate, "checkout");
            if (maxTime != null)
                return (maxTime + "  " + maxDate);
        }
        return "N/A";
    }

    private String getMaxTime(int u_id, String date, String check) {
        long time, tempTime;
        String maxTime = null;
        try {
            c = mydb.rawQuery("select distinct(" + check + ") from records where u_id=" + u_id + " and date='" + date + "';", null);
            if (c.moveToFirst()) {
                maxTime = c.getString(0);
                time = getLongDateTime(maxTime, TIME_FORMAT);
                while (c.moveToNext()) {
                    tempTime = getLongDateTime(c.getString(0), TIME_FORMAT);
                    if (tempTime > time) {
                        time = tempTime;
                        maxTime = c.getString(0);
                    }
                }
            }
        } catch (SQLiteException e) {
            e.printStackTrace();
        }
        return maxTime;
    }


    boolean checkWifi() {
        boolean b = false;
        WifiManager wifiManager = (WifiManager) context.getApplicationContext().getSystemService(Context.WIFI_SERVICE);
        if (wifiManager.startScan()) {
            List<ScanResult> scanResults = wifiManager.getScanResults();
            if (scanResults != null)
                for (int i = 0; i < scanResults.size(); i++) {
                    ScanResult result = scanResults.get(i);
                    if ("6c:72:20:fa:0b:6c".equals(result.BSSID) || "d8:fe:e3:17:93:0c".equals(result.BSSID))
                        if (result.level >= -67) {
                            b = true;
                            break;
                        }
                }
        }
        return b;
    }

    void setLoggedIn(String username) {
        SharedPreferences sharedPreferences = context.getSharedPreferences("logged_in", MODE_PRIVATE);
        SharedPreferences.Editor editor = sharedPreferences.edit();
        editor.putBoolean("login", true);
        editor.putBoolean("login_received", true);
        editor.putBoolean("logout_received", false);
        editor.putString("username", username);
        editor.apply();
    }

    void setLoggedOut() {
        SharedPreferences sharedPreferences = context.getSharedPreferences("logged_in", MODE_PRIVATE);
        SharedPreferences.Editor editor = sharedPreferences.edit();
        editor.putBoolean("login", false);
        editor.putBoolean("logout_received", true);
        editor.putBoolean("login_received", false);
        editor.apply();
    }

    void setCheckBox(boolean b, String username, String password) {
        SharedPreferences preferences = context.getSharedPreferences("checkbox", MODE_PRIVATE);
        SharedPreferences.Editor editor = preferences.edit();
        editor.putBoolean("remember", b);
        if (b) {
            editor.putString("username", username);
            editor.putString("password", password);
        } else {
            if (preferences.getString("username", null) != null)
                editor.remove("username");
            if (preferences.getString("password", null) != null)
                editor.remove("password");
        }
        editor.apply();
    }

}

Answer 1

您没有收到警告的原因是 c 被声明为 class 成员。

AndroidStudio 假定如果您在方法范围之外声明 Cursor，那么它也会与其他方法共享。使用此声明范围，您有效地声明了 "I know what I'm doing and will close the Cursor once I'm done with it".

通常Cursor管理有以下三种方法：

在方法范围内声明 Cursor 并在 finally 块中关闭它
在具有生命周期的 class 范围内声明 Cursor，并作为特定生命周期事件的结果关闭它（例如，当 Activity 停止时关闭游标）
在实现Closable接口的class范围内声明Cursor，当包含class的close()方法时关闭它正在呼叫

通过快速查看您的代码，似乎没有必要 Cursor 在使用它的方法 return 之后保持打开状态，因此您应该考虑重构代码接近#1.

Android Studio 没有显示未关闭光标的警告，我是否仍应关闭它？

Android Studio doesn't show warning for not closing cursor, should I still close it?

sqlite

android

android-cursor