java - 需要更改 android studio 数据库中的 SQL 查询以返回多个结果

Question

我的 android 应用程序中有一个功能正常的数据库，它返回一个结果查询。我正在尝试为 Wine 关键字返回多个结果，但每次我尝试运行应用程序时都会崩溃。我对 android 编码相当陌生，所以我可能会遗漏一些明显的东西。

第一个.java 是搜索功能。第二个是查询 Activity 。

package com.example.winedatabase;

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

public class DatabaseAccess {
    private SQLiteOpenHelper openHelper;
    private SQLiteDatabase db;
    private static DatabaseAccess instance;
    Cursor c = null;

    //private constructor so that object creation from outside is avoided
    private DatabaseAccess(Context context){
        this.openHelper = new DatabaseOpenHelper(context);

    }

    //to return the single instance of database
    public static DatabaseAccess getInstance(Context context){
        if(instance == null){
            instance= new DatabaseAccess(context);

        }
        return instance;
    }

    //to open the database
    public void open(){
        this.db = openHelper.getWritableDatabase();
    }
    //closing the database connection
    public void close(){
        if (db != null) {
            this.db.close();
        }
    }
    //method to query and return the result from the database
    public String getKeyword(String winename){
        c = db.rawQuery(" select WineName from Wine where WineName LIKE %'"+winename+"'%", new String[]{});
        StringBuffer buffer = new StringBuffer();
        while(c.moveToNext()){
            String description = c.getString(0);
            buffer.append(""+description);
        }
        return buffer.toString();
    }

}

package com.example.winedatabase;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class KeywordSearch extends AppCompatActivity {

    public EditText name;
    public Button query_button;
    public TextView result_address;

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

        name = findViewById(R.id.name);
        query_button = findViewById(R.id.query_button);
        result_address = findViewById(R.id.result);

        //set onClickListnener to query button

        query_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                //create the instance of database access class and open database connection

                DatabaseAccess databaseAccess = DatabaseAccess.getInstance(getApplicationContext());
                databaseAccess.open();

                //get string value of edittext

                String n = name.getText().toString();
                String description = databaseAccess.getKeyword(n);  //used the get address method to get address

                //set text to result field
                result_address.setText(description);
                databaseAccess.close();
                //database connection closed

            }
        });
    }
}

Answer 1

您的查询在语法上是错误的。通配符 %和参数 winename应该用单引号括起来，但也建议传递参数winename更安全在 rawQuery() 的第二个参数中.
改成这样:

c = db.rawQuery(
    "select WineName from Wine where WineName LIKE '%' || ? || '%'", 
    new String[]{winename}
);