Question

我正在尝试按照本教程https://examples.javacodegeeks.com/android/core/database/android-database-example/创建数据库应用程序

在我的AndroidDatabaseExample类中，代码如下：

package com.example.database;


import java.util.ArrayList;
import java.util.List;

import android.app.ListActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;

public class AndroidDatabaseExample extends ListActivity implements OnItemClickListener {
JCGSQLiteHelper db = new JCGSQLiteHelper(this);
List list;
ArrayAdapter myAdapter;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);

    // drop this database if already exists
    db.onUpgrade(db.getWritableDatabase(), 1, 2);

    db.createBook(new Book("The Great Gatsby", "F. Scott Fitzgerald"));
    db.createBook(new Book("Anna Karenina", "Leo Tolstoy"));
    db.createBook(new Book("The Grapes of Wrath", "John Steinbeck"));
    db.createBook(new Book("Invisible Man", "Ralph Ellison"));
    db.createBook(new Book("Gone with the Wind", "Margaret Mitchell"));
    db.createBook(new Book("Pride and Prejudice", "Jane Austen"));
    db.createBook(new Book("Sense and Sensibility", "Jane Austen"));
    db.createBook(new Book("Mansfield Park", "Jane Austen"));
    db.createBook(new Book("The Color Purple", "Alice Walker"));
    db.createBook(new Book("The Temple of My Familiar", "Alice Walker"));
    db.createBook(new Book("The waves", "Virginia Woolf"));
    db.createBook(new Book("Mrs Dalloway", "Virginia Woolf"));
    db.createBook(new Book("War and Peace", "Leo Tolstoy"));

    // get all books
    list = db.getAllBooks();
    List listTitle = new ArrayList();

    for (int i = 0; i < list.size(); i++) {
        listTitle.add(i, list.get(i).getTitle());
    }

    myAdapter = new ArrayAdapter(this, R.layout.row_layout, R.id.listText, listTitle);
    getListView().setOnItemClickListener(this);
    setListAdapter(myAdapter);
}

@Override
public void onItemClick(AdapterView arg0, View arg1, int arg2, long arg3) {
    // start BookActivity with extras the book id
    Intent intent = new Intent(this, BookActivity.class);
    intent.putExtra("book", list.get(arg2).getId());
    startActivityForResult(intent, 1);
}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    // get all books again, because something changed
    list = db.getAllBooks();

    List listTitle = new ArrayList();

    for (int i = 0; i < list.size(); i++) {
        listTitle.add(i, list.get(i).getTitle());
    }

    myAdapter = new ArrayAdapter(this, R.layout.row_layout, R.id.listText, listTitle);
    getListView().setOnItemClickListener(this);
    setListAdapter(myAdapter);
}
}

它为getTitle，row_layout，listText和getId提供了“无法解决”错误。

这些内容都是在一个名为“Book.java”的单独类中定义和实现的，如教程指示的那样：

package com.example.database;

public class Book {

private int id;
private String title;
private String author;

public Book(){}

public Book(String title, String author) {
    super();
    this.title = title;
    this.author = author;
}

public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public String getTitle() {
    return title;
}
public void setTitle(String title) {
    this.title = title;
}
public String getAuthor() {
    return author;
}
public void setAuthor(String author) {
    this.author = author;
}

@Override
public String toString() {
    return "com.example.database.Book [id=" + id + ", title=" + title + ", author=" + author
            + "]";
}
}

所以应该认识到这些事情，但事实并非如此。我该如何解决这个问题？

Answer 1

您错误地定义了变量

List listTitle = new ArrayList();

请使用正确的

进行更改

List<String> listTitle = new Arraylist<>();

因此，当您尝试使用列表中的某个项目时，它将是预订POJO

的实例

然后您可以使用getId，getTitle以及您在图书模型中定义的其他方法

我的Android Studio应用程序中出现错误

1 个答案: