Android:使用 SimpleCursorAdapter 从数据库获取数据到 ListView [英] Android: Using SimpleCursorAdapter to get Data from Database to ListView
问题描述
我正在编写一个 android 应用程序，它应该使用数据库来存储数据并从中读取数据.使用 本教程(在archive.org 上) 我有应用程序来创建一个数据库，我能够创建新条目，但是，我不知道，如何读取数据库以获取 ListView 中存储的数据.我知道这个网站上有很多类似的问题，但似乎没有一个适用于教程中的数据库有效的方式.
I am programming an android app that should use a database to store data and read from it. Using this tutorial (on archive.org) I got the app to create a database and I'm able to create new entries, however, I don't know, how to read the database to get the stored data in a ListView. I know there are many similar questions on this website but it seems none of them apply to the way, the database from the tutorial works.
代码:
import java.util.Calendar;
import maturarbeit.nicola_pfister.studenttools.database.DBAdapter;
import android.app.AlertDialog.Builder;
import android.app.ListActivity;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.database.Cursor;
import android.os.Bundle;
import android.support.v4.widget.SimpleCursorAdapter;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.ListView;
public class Marks extends ListActivity {
DBAdapter db = new DBAdapter(this);
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.marks);
}
@Override
protected void onPause() {
super.onPause();
db.close();
}
@Override
protected void onResume() {
super.onResume();
db.open();
getData();
}
@SuppressWarnings("deprecation")
private void getData() {
SimpleCursorAdapter adapter = new SimpleCursorAdapter(this,
android.R.layout.simple_list_item_1,
db.getAllMarks(),
new String[] { "value" },
new int[] { android.R.id.text1 });
ListView listView = (ListView) findViewById(R.id.marks_list);
listView.setAdapter(adapter);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.marks, menu);
return true;
}
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.menu_add:
Calendar cal = Calendar.getInstance();
int day = cal.get(Calendar.DAY_OF_MONTH);
int month = cal.get(Calendar.MONTH);
final String date = day + "." + month;
Builder builder = new Builder(this);
builder
.setTitle(R.string.dialog_addmarks)
.setItems(R.array.markslist, new OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
@SuppressWarnings("unused")
long id;
String selection = getResources().getStringArray(R.array.markslist)[which];
id = db.insertMark(date, "Default", selection);
}
})
.show();
getData();
break;
case R.id.menu_delete:
//Deleting function yet to be implemented.
break;
}
return super.onOptionsItemSelected(item);
}
}
ListView ID 错误，因为它必须是 android:list.
The ListView ID was wrong since it had to be android:list.
推荐答案
使用你链接的教程中的数据库格式，每一行都有一个_id，isbn、title 和 publisher.现在让我们假设您想在 ListView 中显示每个标题:
Using the database format in the tutorial that you linked to, every row has an _id, isbn, title, and publisher. Now let's assume that you want to display every title in a ListView:
db = new DBAdapter(this);
SimpleCursorAdapter adapter = new SimpleCursorAdapter(this,
android.R.layout.simple_list_item_1,
db.getAllTitles(),
new String[] { "title" },
new int[] { android.R.id.text1 });
ListView listView = (ListView) findViewById(R.id.list);
listView.setAdapter(adapter);
(您不需要自己遍历 Cursor，适配器可以为您完成这项工作！)
(You don't need to loop through the Cursor yourself, an adapter does this work for you!)
您缺少 SimpleCursorAdapter 构造函数中的最后两个参数.它们是from"和to"参数:
The last two parameters in your SimpleCursorAdapter constructor are what you are missing. They are the "from" and "to" parameters:
- 我们想要获取存储在列名
title中的每本书的名称，这是我们从"获取信息的地方. - 接下来我们需要告诉它去"哪里:
android.R.id.text1是android.R.layout.simple_list_item_1布局中的 TextView.(您可以浏览您的 SDK 并自己查看 simple_list_item_1.xml 文件，或者暂时相信我.)
- We want to get the name of each book which is stored in the column name
title, this is where we get the information "from". - Next we need to tell it where "to" go:
android.R.id.text1is a TextView in theandroid.R.layout.simple_list_item_1layout. (You can dig through your SDK and see the simple_list_item_1.xml file yourself or just trust me for the moment.)
现在from"和to"参数都是数组，因为我们可以传递不止一列信息，也试试这个适配器:
Now both the "from" and "to" parameters are arrays because we can pass more than one column of information, try this adapter as well:
SimpleCursorAdapter adapter = new SimpleCursorAdapter(this,
android.R.layout.simple_list_item_2,
db.getAllTitles(),
new String[] { "title", "publisher" },
new int[] { android.R.id.text1, android.R.id.text2 });
使用此适配器，他们数据库中的图书将按书名显示，然后是出版商.我们所要做的就是使用一个布局 android.R.layout.simple_list_item_2，它接受两个字段并定义哪些列转到哪些 TextView.
With this adapter the books in their database will displayed by title, then publisher. All we had to do is use a layout android.R.layout.simple_list_item_2 that takes two fields and define which columns go to which TextViews.
希望对你有所帮助.还有很多东西需要学习，但也许这会给你一些基础知识.
I hope that helps a little. There's plenty more to learn but maybe this will give you some basics.
最后评论
在我的脑海里，在添加新数据后刷新 ListView 试试这个:
Off the top of my head, to refresh the ListView after adding new data try this:
public void onClick(DialogInterface dialog, int which) {
String selection = getResources().getStringArray(R.array.markslist)[which];
db.insertMark(date, "Default", selection);
cursor.requery();
adapter.notifyDataSetChanged();
}
您必须定义 adapter 并为 cursor 创建一个变量，但这很简单:
You'll have to define adapter and create a variable for cursor but that's simple:
public class Marks extends ListActivity {
SimpleCursorAdapter adapter;
Cursor cursor;
DBAdapter db = new DBAdapter(this);
...
并相应地更改 getData():
And change getData() accordingly:
private void getData() {
cursor = db.getAllMarks();
adapter = new SimpleCursorAdapter(this,
android.R.layout.simple_list_item_1,
cursor,
new String[] { "value" },
new int[] { android.R.id.text1 });
...
}
祝你好运！
这篇关于Android:使用 SimpleCursorAdapter 从数据库获取数据到 ListView的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
