Question

我正在构建一个搜索界面。数据库使用全文搜索来查询数据库。

我有一个电子书表 - 列是

title | author | publisher | edition content

“内容”列包含有关该书的说明。在用户界面中，我有一个输入edittext框。在此框中，我输入一个单词或短语，单词或短语与列内容匹配（使用MATCH查询）。如果找到匹配项，则显示详细信息（即标题，作者，出版商，版本）。我有一个主类和一个数据库类。但每次我都被例外：

java.lang.illegalstateexception: could not execute method of the activity

我提供的两个代码。

MAIN CLASS

package com.search.wordfinder;
import java.util.ArrayList;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
public class Main extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

public void onClickChange(View v){
    EditText searchText = (EditText)findViewById(R.id.edit_message);
    String searchId = searchText.getText().toString();
            setContentView(R.layout.nextpage);
    ListView list=(ListView)findViewById(R.id.list);
    DatabaseCreation dc = new DatabaseCreation(this);
    ArrayList<String> rslt = dc.queryDatabase(searchId);

    ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1, rslt);

    list.setAdapter(adapter);
            dc.close();

}   

public void onClickBack(View v){
    setContentView(R.layout.main);

}
}

数据库类

package com.search.wordfinder;
import java.util.ArrayList;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.content.ContentValues;
import android.util.*;

public class DatabaseCreation extends SQLiteOpenHelper {

String sString;
SQLiteDatabase mDatabase;
String query;

public static final String DATABASE_NAME = "wor.db";
public static final int DATABASE_VERSION = 1;

public static final String TABLE_NAME = "cpy";

private static String DATABASE_CREATE =  "CREATE VIRTUAL TABLE " + TABLE_NAME + " USING   FTS3" + "(" + "title TEXT," + "author TEXT," + "publisher TEXT," + "edition TEXT," + "content TEXT" + ")";

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

@Override
    public void onCreate(SQLiteDatabase db) {
             try{
        //db.delete(TABLE_NAME, null, null);
        db.execSQL(DATABASE_CREATE);

        insertData("Operating System", "PeterGalvin", "Willey", "Eight", "An operating System (OS) is a collection of software that manages computer hardware resources and provides common services for computer programs.");
        insertData("Database Management System", "Korth", "McGraw-Hill", "Fourth", "A DataBase Management System (DBMS) is a software system that manages execution of users applications to access and modify database."); 

         } catch (Exception e){ 
            e.printStackTrace();
            }       
}

@Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.w(DatabaseCreation.class.getName(),"Upgrading database from version" + 
        oldVersion + "to" + newVersion + ",which will destroy all old data");
        db.execSQL("Drop table if exists" + TABLE_NAME);
        onCreate(db);
}

public void insertData(String ttl, String athr, String pub, String ed, String cnt){
mDatabase = this.getWritableDatabase(); 
    ContentValues values = new ContentValues();
    values.put("title", ttl);
    values.put("author", athr);
    values.put("publisher", pub);
    values.put("edition", ed);
    values.put("content", cnt);
    mDatabase.insert(TABLE_NAME, null, values);

}
public ArrayList<String> queryDatabase(String id){
    sString=id;
    ArrayList<String> data = new ArrayList<String>();
           try{
    query = "SELECT title,author,publisher,edition FROM " + TABLE_NAME + " WHERE content MATCH '"+sString+"'";
    Cursor c = mDatabase.rawQuery(query, null);
        c.moveToFirst();
        while(c.isAfterLast()==false){
            String str = "Title: " + c.getString(0) +"\n"+ "Author: " + c.getString(1)+ "\n" + "Publisher: " + c.getString(2) + "\n" +
                    "Edition: " + c.getString(3);
            data.add(str);
            c.moveToNext();
        }   
    c.close();
            } catch (Exception e){ 
            e.printStackTrace();
            }
    return data; 
    }
}

Answer 1

堆栈跟踪说：

java.lang.NullPointerException
    at com.search.wordfinder.DatabaseCreation.insertData(DatabaseCreation.java:59)

鉴于此方法的内容，第59行必须是以下内容：

mDatabase.insert(TABLE_NAME, null, values);

如果此行发生NullPointerException，则表示mDatabase为空。因此，请检查此变量是否已在任何位置初始化。它不是：我没有看到像

这样的行

mDatabase = ...;

初始化此变量。

JAVA.LANG.ILLEGALSTATEEXCEPTION：无法执行活动的方法..！

1 个答案: