使用数据库
现在你已经可以利用创建的辅助类来使用数据库了，在DatabaseActivity.java文件中，创建一个DBAdapter类的实例：
package net.learn2develop.Database;
import android.app.Activity;
import android.os.Bundle;
public class DatabaseActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
}
}
import android.app.Activity;
import android.os.Bundle;
public class DatabaseActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
}
}
增加一个标题
如果想在titles表中增加一个标题，可以使用DBAdapter类的insertTitle()方法：
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
//---add 2 titles---
db.open();
long id;
id = db.insertTitle(
"0470285818",
"C# 2008 Programmer's Reference",
"Wrox");
id = db.insertTitle(
"047017661X",
"Professional Windows Vista Gadgets Programming",
"Wrox");
db.close();
}
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
//---add 2 titles---
db.open();
long id;
id = db.insertTitle(
"0470285818",
"C# 2008 Programmer's Reference",
"Wrox");
id = db.insertTitle(
"047017661X",
"Professional Windows Vista Gadgets Programming",
"Wrox");
db.close();
}
insertTitle()方法返回插入行的ID，如果在添加过程中遇到错误，它就返回-1。
如果你分析Android设备/模拟器的文件系统，你可以看到book数据库创建在database文件夹下，如图3所示。
图3 database文件夹
检索所有标题
想要检索titles表中的所有标题，可以使用DBAdapter类的getAllTitles()方法，如清单5所示。
清单5 使用DBAdapter类的getAllTitles()方法检索titles表中的所有标题
package net.learn2develop.Database;
import android.app.Activity;
import android.database.Cursor;
import android.os.Bundle;
import android.widget.Toast;
public class DatabaseActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
//---获取所有标题---
db.open();
Cursor c = db.getAllTitles();
if (c.moveToFirst())
{
do {
DisplayTitle(c);
} while (c.moveToNext());
}
db.close();
}
}
import android.app.Activity;
import android.database.Cursor;
import android.os.Bundle;
import android.widget.Toast;
public class DatabaseActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
DBAdapter db = new DBAdapter(this);
//---获取所有标题---
db.open();
Cursor c = db.getAllTitles();
if (c.moveToFirst())
{
do {
DisplayTitle(c);
} while (c.moveToNext());
}
db.close();
}
}
返回的结果是一个Cursor对象，如果要显示所有标题，你首先应该调用Cursor对象的moveToFirst()方法，如果它成功(意味着至少有一行有效)，使用DisplayTitle()方法显示详细的标题，要移动到下一个标题，可以调用Cursor对象的moveToNext()方法，下面是DisplayTitle()方法的定义：
public void DisplayTitle(Cursor c)
{
Toast.makeText(this,
"id: " + c.getString(0) + "\n" +
"ISBN: " + c.getString(1) + "\n" +
"TITLE: " + c.getString(2) + "\n" +
"PUBLISHER: " + c.getString(3),
Toast.LENGTH_LONG).show();
}
{
Toast.makeText(this,
"id: " + c.getString(0) + "\n" +
"ISBN: " + c.getString(1) + "\n" +
"TITLE: " + c.getString(2) + "\n" +
"PUBLISHER: " + c.getString(3),
Toast.LENGTH_LONG).show();
}
图4显示Toast类，它从数据库中检索并显示一个标题。
图4 Toast类
