java - 在 WebView 中使用来自 sqlite 数据库的 URL

Question

我正在尝试构建一个根据主要 Activity 传递的 Intent 数据从数据库中提取 url 的应用

我已经实现了代码，但应用程序一直崩溃/强制关闭。

这是我的 DBHelper 类

package com.snplabs.learncpp;

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

public class DBHelper extends SQLiteOpenHelper {

final protected static String DATABASE_NAME="cppreference";
public DBHelper(Context context) {
super(context, DATABASE_NAME, null,2);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
if (oldVersion >= newVersion) return;
db.execSQL("DROP DATABASE IF EXISTS " + DATABASE_NAME +";");
onCreate(db);
}
@Override
public void onCreate(SQLiteDatabase db) {

//here is the database definition
db.execSQL("CREATE TABLE cppref " +
"(_id INTEGER PRIMARY KEY, link TEXT);");
//insert pre-configured records
db.execSQL("INSERT INTO cppref (_id, link) VALUES(1,'URL_HERE');");
db.execSQL("INSERT INTO cppref (_id, link) VALUES(2,'URL_HERE');");
db.execSQL("INSERT INTO cppref (_id, link) VALUES(3,'URL_HERE');");
db.execSQL("INSERT INTO cppref (_id, link) VALUES(4,'URL_HERE');");
db.execSQL("INSERT INTO cppref (_id, link) VALUES(5,'URL_HERE');");
  }


}

下面是使用 DBHelper 获取 url 的类:

package com.snplabs.learncpp;

import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.TextView;

public class ViewItem extends Activity{
private DBHelper dbhelper=new DBHelper(this);
private SQLiteDatabase db;
private String pgurl;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.setContentView(R.layout.item_view);

    db = dbhelper.getReadableDatabase();

    TextView txtProduct = (TextView) findViewById(R.id.product_label);

    Intent i = getIntent();
    // getting attached intent data
    String product = i.getStringExtra("product");
    int data=Integer.parseInt(product.substring(4));
    // displaying selected product name

    txtProduct.setText(product);

    Cursor quer=db.rawQuery("SELECT link FROM cppref "+"WHERE _id='"+data+"';", null);
            //-fetch record
            if(quer.getCount()!=0){
            quer.moveToFirst();//go to first row
            pgurl=quer.getString(1).toString();
            }
            else{
            //display some notice here saying no data found
            txtProduct.setText("Error");
            }

    WebView myWebView = (WebView) findViewById(R.id.webview);
    myWebView.setWebViewClient(new WebViewClient());
    myWebView.loadUrl(pgurl);
}

Answer 1

首先更正这个移动这个

 DBHelper dbhelper=new DBHelper(this);

在 setContentView(.....) 之后的 onCreate(......)