Android：Sqlite Exception没有这样的表？

概述我已经决定讨厌SQL,并且为此目的,我试图创建一个可以反复使用的辅助类,而不必再次对其进行混乱,但是它无法正常工作！这是我现在所拥有的：DBAssistant.javapublicclassDBAssistant{SQLiteDatabasedb=null;publicDBAssistant(){

我已经决定讨厌sql,并且为此目的,我试图创建一个可以反复使用的辅助类,而不必再次对其进行混乱,但是它无法正常工作！

这是我现在所拥有的：

DBAssistant.java

    public class DBAssistant {            sqliteDatabase db = null;        public DBAssistant (){              }        /** Opens database **/        public voID openDB(Context context, String name){            db = new DBOpenHelper(context, name, DB_VERSION);        }        /** Creates the table "tablename" with the columns contained in "cols" **/        public voID createtable(String tablename, String[] cols){            String table = "CREATE table IF NOT EXISTS " + tablename + " (";            int numOfColums = cols.length;            columnnames = cols;            for (int i = 0; i < (numOfColums - 1); i++){                table += cols[i] + " VARCHAR, ";            }            table += cols[numOfColums - 1] + " VARCHAR);";            try{            db.execsql("" + table);            System.out.println("Execsql:" + table);            } catch(Exception e){                System.out.println(e);            }            System.out.println("Column names: ");            for (String c : getColnames(tablename)){                System.out.print(c + " ");            }        }        /** Inserts "data" into new row **/        public voID insertRow(String tablename, String[] data){            int cols = getCols(tablename);            System.out.println("if ((data.length) = " + (data.length) + ") ==" +                    " (getCols(tablename) = " +  getCols(tablename) + ")?");            if (data.length == cols){                System.out.println("InsIDe if loop");                String cmd = "INSERT INTO " + tablename + " (";                for (int i = 0; i < cols - 1; i++){                    cmd += getColnames(tablename)[i] + ", ";                }                cmd += getColnames(tablename)[cols - 1] + ") VALUES ('";                for (int k = 0; k < data.length - 1; k++){                    cmd += data[k] + "', '";                }                cmd += "');";                System.out.println(cmd);                db.execsql(cmd);            }            else{                System.out.println("InsIDe else loop");                String dat = "";                String sCols = "";                for (String d : data)                    dat += "'" + d + "'";                for (String c : getColnames(tablename))                    sCols += "'" + c + "'";                System.out.println("-------------------");                System.out.println("[insertRow] ERROR: Number of elements in data[" + dat + "]");                System.out.println("doesnt match the number of columns [" + cols + "] in " + tablename);                System.out.println("-------------------");            }                   }        /** Return String[] containing the column names in tablename **/        public String[] getColnames(String tablename){            Cursor c = db.rawquery("SELECT * FROM " + tablename , null);            return c.getColumnnames();        }        /** Returns the number of rows in tablename **/        public int getCols(String tablename){            return getColnames(tablename).length;        }    /***  Other methods that have no relevance here .... ***/private static class DBOpenHelper extends sqliteOpenHelper {    DBOpenHelper(Context context, String dbname, int dbVersion) {       super(context, dbname, null, dbVersion);    }    @OverrIDe    public voID onCreate(sqliteDatabase arg0) {        // Do nothing    }    @OverrIDe    public voID onUpgrade(sqliteDatabase arg0, int arg1, int arg2) {        // Do nothing    } }}

我提供了一些System.out.println()语句来帮助我调试代码并查找问题,因此请忽略它们. PrintDB是我编写的另一项测试,用于确保一切正常.现在,这就是我为确保一切正常而写的内容.

DBAssistant db = new DBAssistant();String dbname = "testing";String tablename = "test";String[] cols = {"_num", "num_eng", "num_span"};String[] row1 = {"1", "one", "uno"};String[] row2 = {"2", "two", "dos"};String[] row3 = {"3", "three", "tres"};String[] row4 = {"4", "four", "quatro"};String[] row5 = {"5", "five", "cinco"};TextVIEw databaseVIEw = (TextVIEw)findVIEwByID(R.ID.databaseVIEw);db.openDB(this, dbname);db.createtable(tablename, cols);db.insertRow(tablename, row1);db.insertRow(tablename, row2);db.insertRow(tablename, row3);db.insertRow(tablename, row4);db.insertRow(tablename, row5);databaseVIEw.setText(db.printtable(tablename));

运行此代码,一切都会顺利进行,所有System.out.println()语句中都包含正确的信息,直到到达databaseVIEw.setText(db.printtable(tablename));为止.
部分并引发异常

ERROR/AndroIDRuntime(3440): androID.database.sqlite.sqliteException: no such table: test: , while compiling: SELECT * FROM test

指向printtable()方法中的行：

Cursor c = dbr.rawquery("SELECT * FROM " + tablename , null);

这让我感到困惑,因为在此之前多次调用getColnames()方法中使用了同一行代码,并且没有问题.另外,如果该表不存在,当我调用insertRow()时会不会引发异常？我连续五次调用该方法,没有抛出任何异常！这是怎么回事

编辑：

Implement onCreate() in your DBOpenHelper. Put there content of the createtable() method.

为什么需要在onCreate()方法中创建表？如果要执行此 *** 作,是否可以使用现有方法来执行此 *** 作,而仅从该方法中调用它？

And the second why you don’t use content provIDers and uri >concept which is already sqlless?

哇…？我不知道.请解释一下这是什么,或者给我留下某种教程的链接.

解决方法:

在您的DBOpenHelper中实现onCreate().将createtable()方法的内容放在此处.

参考Dev Guide.

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