原创 Android之自定义 ContentProvider

 2021-9-2 15:01  2044 10 10 分类: 软件与OS 文集: android studio

在学习了ContentProvider 的几个常用类和如何创建一个内容提供者的方法之后，下面我们用一个实例来进一步加深理解。通过一个完整的实例来展示如何用ContentProvider类进行数据库操作。将通过创建 100条模拟数据，用ListView 展示出来。

在进行具体的数据库操作之前，先建立一个Java 实体类 User类，再通过这个实体类进行数据的封装。User类中包括 userId、name、age三个属性，具体代码如下∶

package com.rfstar.sqlitetest2;
public class User {
private int userId;
private String name;
private int age;
public int getUserId()
{
return userId;
}
public void setUserId(int userId)
{
this.userId=userId;
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name=name;
}
public int getAge()
{
return age;
}
public void setAge(int age)
{
this.age=age;
}
}

完成Java实体类的创建之后，通过继承SQLiteOpenHelper来实现数据库辅助类，并实现其中的onCeate()方法和onUpgrate()方法。在onCreate()方法中创建表并使表中的字段与User类的属性相一致。同时实现onUpgrate()方法，以更新数据库。

package com.rfstar.sqlitetest2;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class OpenHelper extends SQLiteOpenHelper {
private static final String name="test.db";
private static final int version=1;
public OpenHelper(Context context)
{
super(context,name,null,version);
}
@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {
sqLiteDatabase.execSQL("CREATE TABLE IF NOT EXISTS "+
"user (person_id INTEGER PRIMARY KEY AUTOINCREMENT,"+
"name varchar(32),age INTEGER)");
}
@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int oldVersion, int newVersion) {
if(newVersion>oldVersion)
{
sqLiteDatabase.execSQL("ALTER TABLE user ADD phone VARCHAR(11)");
}
}
}

接下来创建UserDao类，并在该类中实现对User的增、删、改、查操作，代码如下：

package com.rfstar.sqlitetest2;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import java.util.ArrayList;
import java.util.List;
public class UserDao {
private SQLiteDatabase database;
public UserDao(SQLiteDatabase sqLiteDatabase) {
this.database = sqLiteDatabase;
}
public boolean insert(User user) {
ContentValues contentValues = new ContentValues();
contentValues.put("name", user.getName());
contentValues.put("age", user.getAge());
long insertResult = database.insert("user", null, contentValues);
if (insertResult == -1) {
return false;
}
return true;
}
public boolean delete(User user) {
int deleteResult = database.delete("user", "user_id+?", new String[]{user.getUserId() + ""});
if (deleteResult == 0){
return false;
}
return true;
}
public boolean update(User user)
{
ContentValues contentValues=new ContentValues();
contentValues.put("name",user.getName());
contentValues.put("age",user.getAge());
int updateResult=database.update("user",contentValues,"user_id=?",new String[]{user.getUserId()+""});
if(updateResult==0)
{
return false;
}
return true;
}
public User queryOne(User user)
{
Cursor cursor=database.query("user",null,"name=?",new String[]
{user.getName()},null,null,null);
while (cursor.moveToNext())
{
user.setUserId(cursor.getInt(0));
user.setAge(cursor.getInt(2));
}
return user;
}
public List<User> queryAll()
{
List<User> userList=new ArrayList<>();
Cursor cursor=database.query("user",null,null,null,null,null,null);
while (cursor.moveToNext())
{
User user=new User();
user.setUserId(cursor.getInt(0));
user.setName(cursor.getString(1));
user.setAge(cursor.getInt(2));
userList.add(user);
}
return userList;
}
}

当完成上述3个类之后，接下来就可以使用Activity进行各项操作了（1）创建数据

创建一个MainActivity,并在MainActivity中创建一个循环生成100条数据的方法，代码如下：

package com.rfstar.sqlitetest2;
import androidx.appcompat.app.AppCompatActivity;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.util.Log;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class MainActivity extends AppCompatActivity {
private OpenHelper openHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
openHelper=new OpenHelper(this);
initData();
}
private void initData()
{
SQLiteDatabase sqLiteDatabase=openHelper.getReadableDatabase();
UserDao userDao=new UserDao(sqLiteDatabase);
sqLiteDatabase.beginTransaction();
try
{
User user=new User();
for(int i=0;i<100;i++)
{
user.setName("大鸟科创空间"+i);
user.setAge(6);
userDao.insert(user);
}
sqLiteDatabase.setTransactionSuccessful();
}catch (Exception e)
{
Log.e("user Transaction",e.toString());
}finally {
sqLiteDatabase.endTransaction();
sqLiteDatabase.close();
}
}
}

我们在这个应用中增加一个ContentProvider,再创建一个新的应用，在应用中去操作这个ContentProvider的数据。

首先创建UserProvider类，并让UserProvider类继承ContentProvider类，并实现onCreate()等方法。这些方法主要是对数据库进行操作，代码如下：

package com.rfstar.sqlitetest;
import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import java.util.regex.Matcher;
public class UserProvider extends ContentProvider {
private OpenHelper openHelper;
//若不匹配采用UriMatcher.NO_MATCH(-1)返回
private static final UriMatcher MATCHER=new UriMatcher(UriMatcher.NO_MATCH);
//匹配码
private static final int USER=1;
private static final int USER_ID=2;
static
{
//匹配返回USER,不匹配返回-1
MATCHER.addURI("com.rfstar.sqlitetest.userProvider","user",USER);
//匹配返回USER_ID,不匹配返回-1
MATCHER.addURI("com.rfstar.sqlitetest.userProvider","user/#",USER_ID);
}
@Override
public boolean onCreate()
{
openHelper=new OpenHelper(this.getContext());
return true;
}
/**
* 外部应用向本应用插入数据
*/
@Override
public Uri insert(Uri uri, ContentValues values)
{
SQLiteDatabase db=openHelper.getWritableDatabase();
switch (MATCHER.match(uri))
{
case USER:
long id=db.insert("user","name",values);
Uri insertUri= ContentUris.withAppendedId(uri,id);
return insertUri;
default:
throw new IllegalArgumentException("this is unknown uri:"+uri);
}
}
/**
* 外部应用向本应用删除数据
*/
@Override
public int delete(Uri uri,String selection,String[] selectionArgs)
{
SQLiteDatabase db=openHelper.getWritableDatabase();
switch (MATCHER.match(uri))
{
case USER:
return db.delete("user",selection,selectionArgs);//删除所有记录
case USER_ID:
long id=ContentUris.parseId(uri);//取得跟在Uri后面的数字
String where="user_id="+id;
if(null!=selection&&!"".equals(selection.trim()))
{
where+="and"+selection;
}
return db.delete("user",where,selectionArgs);
default:
throw new IllegalArgumentException("this is unknown uri:"+uri);
}
}
/**
* 外部应用向本应用更新数据
*/
@Override
public int update(Uri uri,ContentValues values,String selection,String[] selectionArgs)
{
SQLiteDatabase db=openHelper.getWritableDatabase();
switch (MATCHER.match(uri))
{
case USER:
return db.update("user",values,selection,selectionArgs);//更新所有记录
case USER_ID:
long id=ContentUris.parseId(uri);//取得跟在Uri后面的数字
String where="user_id="+id;
if(null!=selection&&!"".equals(selection.trim()))
{
where+="and"+selection;
}
return db.update("user",values,where,selectionArgs);
default:
throw new IllegalArgumentException("this is unknown uri:"+uri);
}
}
/**
* 如果是单条记录，应该返回以vnd.android.cursor.item/为首的字符串
* 如果是多条记录，应该返回以vnd.android.cursor.dir/为首的字符串
*/
@Override
public String getType(Uri uri)
{
switch(MATCHER.match(uri))
{
case USER:
return "vnd.android.cursor.dir/user";
case USER_ID:
return "vnd.android.cursor.item/user";
default:
throw new IllegalArgumentException("this is unknown uri:"+uri);
}
}
@Override
public Cursor query(Uri uri,String[] projection,String selection,String[]selectionArgs,String sortOrder)
{
SQLiteDatabase db=openHelper.getReadableDatabase();
switch (MATCHER.match(uri))
{
case USER:
return db.query("user",projection,selection,selectionArgs,null,null,sortOrder);
case USER_ID:
long id=ContentUris.parseId(uri);
String where="user_id="+id;
if(null!=selection&&!"".equals(selection.trim()))
{
where+="and"+selection;
}
return db.query("user",projection,where,selectionArgs,null,null,sortOrder);
default:
throw new IllegalArgumentException("this is unknown uri:"+uri);
}
}
}