我非常抱歉要求这个简单的疑问。我刚开始学习android,现在正在研究android中的数据库部分。
我创建了一个名为“books”且表名为“titles”的数据库。
然后我将数据库拖放到项目的资产部分。
现在我想从数据库中获取一个值(五列中的任何值)并显示在文本视图中。任何人都可以帮我解决这个问题。
以下是我用来读取数据库的代码。
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
public class DBAdapter {
public static final String KEY_ROWID = "_id";
public static final String KEY_ISBN = "isbn";
public static final String KEY_TITLE = "title";
public static final String KEY_PUBLISHER = "publisher";
private static final String TAG = "DBAdapter";
private static final String DATABASE_NAME = "books";
private static final String DATABASE_TABLE = "titles";
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_CREATE =
"create table titles (_id integer primary key autoincrement, "
+ "isbn text not null, title text not null, "
+ "publisher text not null);";
private final Context context;
private DatabaseHelper DBHelper;
private SQLiteDatabase db;
public DBAdapter(Context ctx)
{
this.context = ctx;
DBHelper = new DatabaseHelper(context);
}
private static class DatabaseHelper extends SQLiteOpenHelper
{
DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db)
{
db.execSQL(DATABASE_CREATE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion,
int newVersion)
{
Log.w(TAG, "Upgrading database from version " + oldVersion
+ " to "
+ newVersion + ", which will destroy all old data");
db.execSQL("DROP TABLE IF EXISTS titles");
onCreate(db);
}
}
//---opens the database---
public DBAdapter open() throws SQLException
{
db = DBHelper.getWritableDatabase();
return this;
}
//---closes the database---
public void close()
{
DBHelper.close();
}
//---insert a title into the database---
public long insertTitle(String isbn, String title, String publisher)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_ISBN, isbn);
initialValues.put(KEY_TITLE, title);
initialValues.put(KEY_PUBLISHER, publisher);
return db.insert(DATABASE_TABLE, null, initialValues);
}
//---deletes a particular title---
public boolean deleteTitle(long rowId)
{
return db.delete(DATABASE_TABLE, KEY_ROWID +
"=" + rowId, null) > 0;
}
//---retrieves all the titles---
public Cursor getAllTitles()
{
return db.query(DATABASE_TABLE, new String[] {
KEY_ROWID,
KEY_ISBN,
KEY_TITLE,
KEY_PUBLISHER},
null,
null,
null,
null,
null);
}
//---retrieves a particular title---
public Cursor getTitle(long rowId) throws SQLException
{
Cursor mCursor =
db.query(true, DATABASE_TABLE, new String[] {
KEY_ROWID,
KEY_ISBN,
KEY_TITLE,
KEY_PUBLISHER
},
KEY_ROWID + "=" + rowId,
null,
null,
null,
null,
null);
if (mCursor != null) {
mCursor.moveToFirst();
}
return mCursor;
}
//---updates a title---
public boolean updateTitle(long rowId, String isbn,
String title, String publisher)
{
ContentValues args = new ContentValues();
args.put(KEY_ISBN, isbn);
args.put(KEY_TITLE, title);
args.put(KEY_PUBLISHER, publisher);
return db.update(DATABASE_TABLE, args,
KEY_ROWID + "=" + rowId, null) > 0;
}
}
main.xml中
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello" />
</LinearLayout>
DatabaseActivity.java
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);
}
}
希望得到你的帮助。谢谢。
答案 0 :(得分:3)
创建类并使用contentProvider扩展它并像这样使用它
public class XyzDB extends ContentProvider {
static Context context;
private SQLiteOpenHelper mOpenHelper;
public XyzDB() {}
public XyzDB(Context context)
{
XyzDB.context = context;
mOpenHelper = new DatabaseHelper(context);
mOpenHelper.getWritableDatabase();
}
并在XyzDB中创建一个类
private static class DatabaseHelper extends SQLiteOpenHelper
{
//create table here
}
然后放入以下方法
您必须从数据库帮助程序类中的游标获取数据。你必须创建这样的方法并返回游标值。
public Cursor fetchData()
{
SQLiteDatabase mDB = mOpenHelper.getWritableDatabase();
Cursor mCursor;
mCursor = mDB.rawQuery("Select * from table, null);
return mCursor;
}
并在您的活动中创建Database helper类对象并调用此方法并从游标中获取数据
Cursor c = jDB.fetchDataByID(id);
if(c.moveToFirst())
{
do
{
id = c.getInt(0);
}while(c.moveToNext());
}
c.close();
并在文本视图中设置id或任何值。
并点击此链接
答案 1 :(得分:3)
我将在你的帮助下给你一个例子,你可以很容易地理解我们如何在textview上显示数据库中的数据。 下面是testdata是具有用户表的数据库名称的代码,其中存在2列。我在2 diff上显示这两列的数据。 textviews。
public class high_score extends Activity{
SQLiteDatabase mydatabase=null;
String Data="";
String Data1="";
String TableName="users";
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.high_score);
RelativeLayout main=(RelativeLayout)findViewById(R.id.main);
try
{
mydatabase=this.openOrCreateDatabase("testdata", MODE_PRIVATE, null);
Cursor c=mydatabase.rawQuery("SELECT DISTINCT name,score FROM "+TableName+" , null);
int column1=c.getColumnIndex("name");
int column2=c.getColumnIndex("max_score");
c.moveToFirst();
if(c!=null)
{
do
{
String Name=c.getString(column1);
int Score=c.getInt(column2);
Data=Data+Name+"\n";
Data1=Data1+Score+"\n";
System.out.println("name"+Name+" score"+Score);
}while(c.moveToNext());
TextView tv=(TextView)findViewById(R.id.tv);
TextView points=(TextView)findViewById(R.id.points);
tv.setText(Data);
points.setText(Data1);
setContentView(main);
}
/*TextView tv=(TextView)findViewById(R.id.tv);
tv.setText(Data);
setContentView(tv);*/
}catch(Exception ex)
{
Log.e("ERROR","ERROR" ,ex);
}
finally
{
if(mydatabase!=null)
mydatabase.close();
}
您可以轻松访问此类数据