游标如何在Android中工作 [英] How does Cursor work in android

问题描述

我很难在程序中准确显示光标功能。我有点理解，但是有人能详细解释它的功能吗？

I'm having a hard time exactly visualizing 'Cursor' functionality in my program. I kind of get the jist of it, but can anyone explain it's functionality in detail?

通过光标，我的意思是 Cursor 界面。
我不能简单地理解它在任何事物中的作用。

By Cursor, I mean the Cursor interface. I can't simply understand the role it plays with anything.

http://developer.android.com/reference/android/database/Cursor.html

推荐答案

在SQLite数据库上的查询返回了Cursor对象。
它将返回查询返回的所有行。

A Cursor object is returned from a query on a SQLite database. It will return all rows that the query returns.

假设您有一个名为 names 的表您的数据库数据库配置如下：

Say you have a table called names in your database database configured as such:

_id     _name
1       Space Ghost
2       Zorak
3       Moltar
4       Brak

如果要从此表中获取所有数据并使用它，您将执行
这样的操作：

If you want to get all data from this table and use it, you would do something like this:

public HashMap<Integer, String> getNames(){

 HashMap<Integer, String> data = new HashMap<Integer, String>();

 try{
  SQLiteOpenHelper helper = new MyOpenDbHelper(context);
  SQLiteDatabase db = helper.getReadableDatabase();
  String selectQuery = "SELECT  * FROM names";
  Cursor cursor = db.rawQuery(selectQuery, null);
  if (cursor != null && cursor.moveToFirst()){ //make sure you got results, and move to first row
    do{
        int mID = cursor.getInt(0); //column 0 for the current row
        String mName = cursor.getString(1); //column 1 for the current row
        data.put(mID, mName);

      } while (cursor.moveToNext()); //move to next row in the query result

  }

 } catch (Exception ex) {
    Log.e("MyApp", ex.getMessage());
 } finally
 {
    if (cursor != null) {
       cursor.close();

    }
    if (db != null) {
        db.close();
    }

 }

return data;
}

通常，您将创建自己的类来扩展SQLiteOpenHelper，例如：

Usually you will create your own class to extend SQLiteOpenHelper, as such:

public class MyOpenDbHelper extends SQLiteOpenHelper {
     //........
}

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