Question

我一直在学习使用SQLite对数据库进行基本读/写的教程。

在AddWord.java（Activity）中的loaddata操作中程序冻结。我不确定调试器哪条线路出现故障。该计划分为以下三个类别：

DBHandler.Java：

package com.AH.memorisethai;

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.content.ContentValues;
import android.content.Context;

public class DBHandler extends SQLiteOpenHelper {

    private static final String KEY_ID = "id";
    private static final String KEY_ENGLISH = "english";
    private static final String KEY_THAI = "thai";
    private static final String KEY_WORDTYPE = "wordtype";
    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "wordsmanager";
    private static final String TABLE_WORDS = "words";
    private static final String TABLE_CREATE = "CREATE TABLE " + TABLE_WORDS
                                + "(" + KEY_ID + " AUTOINCREMENT," + KEY_ENGLISH + " TEXT NOT NULL," + KEY_THAI + " TEXT NOT NULL" + ");";

    public DBHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub
        db.execSQL(TABLE_CREATE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub
        db.execSQL("DROP TABLE IF EXISTS" + TABLE_WORDS);
        onCreate(db);
    }

    public void addEntry(Entry entry) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_ENGLISH, entry.getEnglishword()); // Contact Name
        values.put(KEY_THAI, entry.getThaiword()); // Contact Phone Number

        // Inserting Row
        db.insert(TABLE_WORDS, null, values);
        db.close(); // Closing database connection
    }

    // Getting contacts Count
    public int getContactsCount() {
        String countQuery = "SELECT  * FROM " + TABLE_WORDS;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        cursor.close();
        // return count
        return cursor.getCount();
    }
}

Entry.Java：

package com.AH.memorisethai;

public class Entry {

    private long id;
    private String englishword;
    private String thaiword;

    public Entry(){
    }

    public Entry(int id, String englishword, String thaiword){
        this.id = id;
        this.englishword = englishword;
        this.thaiword = thaiword;
    }

    // constructor
    public Entry(String englishword, String thaiword){
        this.englishword = englishword;
        this.thaiword = thaiword;
    }

    public long getId(){
        return id;
    }

    public String getEnglishword(){
        return englishword;
    }

    public String getThaiword(){
        return thaiword;
    }

    public void setId(long id){
        this.id=id;
    }

    public void setEnglishword(String englishword){
        this.englishword=englishword;
    }

    public void setThaiword(String thaiword){
        this.thaiword=thaiword;
    }
}

在活动中：

public int getContactsCount() {
    String countQuery = "SELECT COUNT(*) FROM " + TABLE_WORDS;
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(countQuery, null);
    int count = -1;
    if (cursor.moveToFirst()) {
        count = cursor.getInt(0);
    }
    cursor.close();
    return count;
}

由于目前没有数据ed应该返回值0 - 我认为这是确保DBHandler代码有效的最简单的测试。

Answer 1

这里有多个问题。

首先，SQL语法问题在这里：

private static final String TABLE_CREATE = "CREATE TABLE" + TABLE_WORDS
                                + "(" + KEY_ID + "AUTOINCREMENT," + KEY_ENGLISH + "TEXT NOT NULL," + KEY_THAI + "TEXT NOT NULL" + ");";

您需要在关键字和标识符之间添加空格，如下所示：

private static final String TABLE_CREATE = "CREATE TABLE " + TABLE_WORDS
                                + "(" + KEY_ID + " AUTOINCREMENT," + KEY_ENGLISH + " TEXT NOT NULL," + KEY_THAI + " TEXT NOT NULL" + ");";

AUTOINCREMENT要求它为INTEGER PRIMARY KEY AUTOINCREMENT。最后的分号;是可选的。

DROP TABLE中还需要空格：

db.execSQL("DROP TABLE IF EXISTS " + TABLE_WORDS)
//                         here ^

在getContactsCount()：

public int getContactsCount() {
    String countQuery = "SELECT  * FROM " + TABLE_WORDS;
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(countQuery, null);
    cursor.close();
    // return count
    return cursor.getCount();
}

...你关闭后正在访问光标。此外，由于您只在计数中进行了交互，因此您可以要求数据库引擎为您计算行数：

public int getContactsCount() {
    String countQuery = "SELECT COUNT(*) FROM " + TABLE_WORDS;
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(countQuery, null);
    int count = -1;
    if (cursor.moveToFirst()) {
        count = cursor.getInt(0);
    }
    cursor.close();
    return count;
}

在db helper onCreate()中编辑数据库模式后，请确保重新创建数据库。实现这一目标的最简单方法是卸载应用程序，以便删除包括数据库文件在内的数据文件。

Android SQLite数据库处理程序实现错误

1 个答案: