Android的ListView的数据库异常 [英] Android ListView Database Exception

问题描述

我一直是个顽皮的男孩，我已经复制从Android开发者官方网站的记事本应用程序的方法，这是我的类：

I have been a naughty boy and I've copied a method from official Notepad application from android developer site, this is my class :

package com.example.prva;

import android.app.ListActivity;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.widget.SimpleCursorAdapter;


public class ListView extends ListActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.listview);
        fillData();
        }

    private void fillData() {
        // Get all of the notes from the database and create the item list
        Cursor c = DatabaseManager.getAllData();
        startManagingCursor(c);

        String[] from = new String[] { DatabaseManager.TABLE_COLUMN_ONE };
        int[] to = new int[] { R.id.text1 };

        // Now create an array adapter and set it to display using our row
        SimpleCursorAdapter notes =
            new SimpleCursorAdapter(this, R.layout.notes_row, c, from, to);
        setListAdapter(notes);
    }
    }

当我尝试运行这个ListActivity我得到这个错误：

When I try to run this ListActivity I get this error :

01-31 02:39:14.259: E/AndroidRuntime(1845): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.prva/com.example.prva.ListView}: java.lang.IllegalArgumentException: column '_id' does not exist

现在我明白了这一点，因为它的真实，我没有_id列在我的数据库（记事本应用程序数据库中有它，使用它，但我有我自己的数据库），我只是不明白的地方是提到，色谱柱在我的ListActivity类？它在哪里被从那么它给人的错误叫什么名字？

Now I understand this because its true, I do not have the _id column in my database (the notepad application database has it and used it but I have my own database), I just don't understand where is that column mentioned in my ListActivity class? Where is it being called from so it gives the error?

推荐答案

查看文档的的CursorAdapter ：

光标必须包含一个指定的列_id或本级将无法正常工作。

The Cursor must include a column named _id or this class will not work.

在你的code，使用SimpleCursorAdapter，这是一个派生类，所以会出现这种说法适用。

In your code, you use the SimpleCursorAdapter, which is a derived class, so it appears this statement applies.

光标是像迭代器和指针，它们仅仅包含了一种机制，横切数据，它们不包含列本身。

Cursors are like iterators or pointers, they contain nothing but a mechanism for transversing the data, they contain no columns themselves.

从另一个文档，你可以了解上述更好的语句：

From another documentation, you can understand the statement above better:

内容处理URI标识

按照惯例，供应商提供访问单个行表中的由   接受内容的URI与该行的ID值时的结束   URI。同样按照约定，供应商ID值表的匹配   _ID列，并执行对符合该行的请求的访问。

By convention, providers offer access to a single row in a table by accepting a content URI with an ID value for the row at the end of the URI. Also by convention, providers match the ID value to the table's _ID column, and perform the requested access against the row that matches.

该公约有利于一个常见的​​设计模式的应用程序访问   的提供者。该应用程序做了查询，对供应商并显示   导致光标在使用CursorAdapter的一个ListView。定义   的CursorAdapter的要求在光标的一列是_ID。

This convention facilitates a common design pattern for apps accessing a provider. The app does a query against the provider and displays the resulting Cursor in a ListView using a CursorAdapter. The definition of CursorAdapter requires one of the columns in the Cursor to be _ID.

多种方式可以解决这个问题：

Several ways for you to fix the problem:

1. 添加列_id在表中。

1. Add a column "_id" in your table.

使用别名来获得curosr。例如：

Using alias to get the curosr. For example:

选择someid为_id，姓名，FROM表1号;

SELECT someid as _id, name, number FROM TABLE1;

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