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所以我正在开发一个应用程序，我刚刚开始学习适用于 android 的 SQLite，显然我在一个问题上被困了 3 天。每当我尝试从月份等于特定月份的表中对 SUM Up 字段运行查询时，都会抛出 NullPointer。

package com.example.droid;
import java.text.SimpleDateFormat;
import java.util.Calendar;

import com.example.droid.SqDb;

import android.accounts.Account;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.text.format.DateFormat;
import android.util.Log;


public class DbCon {

    private static SQLiteDatabase database;
    private SqDb SqHelper;
    private String[] UserColumns = 
        {
            SqDb.ACCOUNT_ID,
            SqDb.ACCOUNT_NAME,
            SqDb.ACCOUNT_USERNAME,
            SqDb.ACCOUNT_PASSWORD,
            SqDb.ACCOUNT_AGE,
            SqDb.ACCOUNT_CITY,
            SqDb.ACCOUNT_COUNTRY
        };
    private String [] GuestColumns = 
        {
            SqDb.GUEST_ID,
            SqDb.GUEST_NAME
        };
    private String [] TransColumns =
        {
            SqDb.TRAN_ID,
            SqDb.TRAN_DESC,
            SqDb.TRAN_TYPE,
            SqDb.TRAN_TIME,
            SqDb.TRAN_DAY,
            SqDb.TRAN_MON,
            SqDb.TRAN_YEAR,
            SqDb.TRAN_CAT,
            SqDb.TRAN_VAL
        };

    private static DbCon myDCon;

    DbCon(Context context)
    {
        SqHelper = SqDb.getInstance(context);
    }

    public static DbCon getInstance(Context context)
    {
        if(myDCon == null)
            {
            myDCon = new DbCon(context.getApplicationContext());
            }
        return myDCon;
    }

    public void open() throws SQLException
    {
        database = SqHelper.getWritableDatabase();
    }

    public void close()
    {
        SqHelper.close();
    }

    public void createUser(String username, String password, String name, String Age, String City, String Country)
    {
        ContentValues values = new ContentValues();
        values.put(SqDb.ACCOUNT_USERNAME, username);
        values.put(SqDb.ACCOUNT_PASSWORD, password);
        values.put(SqDb.ACCOUNT_NAME, name);
        values.put(SqDb.ACCOUNT_AGE, Age);
        values.put(SqDb.ACCOUNT_CITY, City);
        values.put(SqDb.ACCOUNT_COUNTRY, Country);
        database.insert(SqDb.ACCOUNT, null, values);
    }

    public void createGuest(String name)
    {
        ContentValues values = new ContentValues();
        values.put(SqDb.GUEST_NAME, name);
        database.insert(SqDb.GUEST, null, values);
        }

    public void AddTask(String desc, String type, String cat, double Value)
    {
        ContentValues values = new ContentValues();
        values.put(SqDb.TRAN_DESC, desc);
        values.put(SqDb.TRAN_TYPE, type);
        values.put(SqDb.TRAN_CAT, cat);
        values.put(SqDb.TRAN_VAL, Value);
        SimpleDateFormat df = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        Calendar cal = Calendar.getInstance();
        String timedata = df.format(cal.getTime());
        String[] whens = timedata.split(" ");
        String time = whens[1];
        String[] dates = whens[0].split("/");
        values.put(SqDb.TRAN_TIME, time);
        values.put(SqDb.TRAN_DAY, dates[2]);
        values.put(SqDb.TRAN_MON, dates[1]);
        values.put(SqDb.TRAN_YEAR, dates[0]);
        database.insert(SqDb.TRAN, null, values);
    }
    Calendar cal = Calendar.getInstance();
    public int getMonthInt(){
        int month = cal.get(Calendar.MONTH);
        return month;
    }
    public double CountMonthExp()
    {
        double din = 0;
        this.open();
        Cursor c = database.rawQuery("SELECT sum("+SqDb.TRAN_VAL+") as"+SqDb.TRAN_VAL+" FROM "+SqDb.TRAN+" WHERE "+SqDb.TRAN_TYPE+"=EXPENDITURE and "+SqDb.TRAN_MON+"=3", null);
        if(c.moveToFirst()){
            din = c.getDouble(0);
        }
        else{
            din = 0;
        }
        return din;
    }


}

有什么建议么？是的，该表创建得很好并且工作正常，我测试插入记录工作正常。

这是错误：

03-19 00:18:38.119: E/AndroidRuntime(19822): 致命异常: main 03-19 00:18:38.119: E/AndroidRuntime(19822): java.lang.RuntimeException: 无法启动活动 ComponentInfo{com. example.droid/com.example.droid.Hist_act}：android.database.sqlite.SQLiteException：没有这样的列：EXPENDITURE：，编译时：SELECT sum(tran_val) astran_val FROM tran WHERE tran_type=EXPENDITURE and tran_mon=3 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 android.app.ActivityThread .handleLaunchActivity(ActivityThread.java:1667) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 android.app.ActivityThread.access$1500(ActivityThread.java:117) 03-19 00:18:38.119: E/AndroidRuntime(19822)：在 android.app。ActivityThread$H.handleMessage(ActivityThread.java:935) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 android.os.Handler.dispatchMessage(Handler.java:99) 03-19 00:18: 38.119: E/AndroidRuntime(19822): 在 android.os.Looper.loop(Looper.java:130) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 android.app.ActivityThread.main(ActivityThread .java:3687) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 java.lang.reflect.Method.invokeNative(Native Method) 03-19 00:18:38.119: E/AndroidRuntime(19822) : 在 java.lang.reflect.Method.invoke(Method.java:507) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit .java:867) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625) 03-19 00:18:38.119:E/AndroidRuntime(19822): at dalvik.system.NativeStart.main(Native Method) 03-19 00:18:38.119: E/AndroidRuntime(19822): Caused by: android.database.sqlite.SQLiteException: no such column: EXPENDITURE：，编译时：SELECT sum(tran_val) astran_val FROM tran WHERE tran_type=EXPENDITURE and tran_mon=3 03-19 00:18:38.119: E/AndroidRuntime(19822): at android.database.sqlite.SQLiteCompiledSql.native_compile(Native方法) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 android.database.sqlite.SQLiteCompiledSql.compile(SQLiteCompiledSql.java:92) 03-19 00:18:38.119: E/AndroidRuntime(19822) : 在 android.database.sqlite.SQLiteCompiledSql.(SQLiteCompiledSql.java:65) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 android.database.sqlite.SQLiteProgram.(SQLiteProgram.java:83) 03 -19 00:18:38.119：E/AndroidRuntime（19822）：在 android.database.sqlite.SQLiteQuery.(SQLiteQuery.java:49) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:42) 03 -19 00:18:38.119: E/AndroidRuntime(19822): 在 android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1356) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 android .database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1324) 03-19 00:18:38.119: E/AndroidRuntime(19822): at com.example.droid.DbCon.CountMonthExp(DbCon.java:122) 03- 19 00:18:38.119: E/AndroidRuntime(19822): 在 com.example.droid.Hist_act.onCreate(Hist_act.java:42) 03-19 00:18:38.119: E/AndroidRuntime(19822): 在 android。 app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 03-19 00:18:38.119:E/AndroidRuntime(19822): 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615) 03-19 00:18:38.119: E/AndroidRuntime(19822): ... 11 更多

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1 回答 1

1

我想说这里至少有两个问题：

SELECT sum(tran_val) astran_val FROM tran WHERE tran_type=EXPENDITURE and tran_mon=3

我怀疑你的意思是：

SELECT sum(tran_val) as tran_val FROM tran WHERE tran_type='EXPENDITURE' and tran_mon=3

我相信您将能够自己更改代码以实现这些调整。

于 2013-03-19T00:24:56.200 回答