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系出名门Android(9) - 数据库支持(SQLite), 内容提供器(ContentProvider)


作者： webabcd


介绍
在 Android 中使用 SQLite, ContentProvider 
  • 数据库支持(SQLite) - Android 开发平台提供了操作 SQLite 数据库的相关 API 
  • 内容提供器(ContentProvider) - 当数据需要在应用程序之间共享时，可以在某程序中使用 ContentProvider 定义 URI， 以使其它应用程序可以通过此 URI 访问指定的数据


1、SQLite 的 Demo
DatabaseHelper.java
package com.webabcd.SQLite;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.database.sqlite.SQLiteDatabase.CursorFactory;

// 数据库操作的 Helper 类
public class DatabaseHelper extends SQLiteOpenHelper {

        DatabaseHelper(Context context, String name, CursorFactory cursorFactory, int version) {
                 super(context, name, cursorFactory, version);
        }

        @Override
         public void onCreate(SQLiteDatabase db) {
                 // TODO 创建数据库后，对数据库的操作
        }

        @Override
         public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
                 // TODO 更改数据库版本的操作
        }

        @Override
         public void onOpen(SQLiteDatabase db) {
                 super.onOpen(db);
                
                 // TODO 每次成功打开数据库后首先被执行
        }
}
 
Main.java
package com.webabcd.SQLite;

import java.util.Random;

import android.app.Activity;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class Main extends Activity {

         private DatabaseHelper dbHelper;

         private static final String DATABASE_NAME = "db.db";
         private static final int DATABASE_VERSION = 1;
         private static final String TABLE_NAME = "employee";

        TextView txtMsg;

         /** Called when the activity is first created. */
        @Override
         public void onCreate(Bundle savedInstanceState) {
                 super.onCreate(savedInstanceState);
                setContentView(R.layout.main);

                dbHelper = new DatabaseHelper( this, DATABASE_NAME, null,
                                DATABASE_VERSION);

                txtMsg = (TextView) this.findViewById(R.id.txtMsg);

                Button btn1 = (Button) this.findViewById(R.id.btn1);
                btn1.setText( "创建表");
                btn1.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                CreateTable();
                        }
                });

                Button btn2 = (Button) this.findViewById(R.id.btn2);
                btn2.setText( "插入 3 条记录");
                btn2.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                insertItem();
                        }
                });

                Button btn3 = (Button) this.findViewById(R.id.btn3);
                btn3.setText( "删除全部记录");
                btn3.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                deleteItem();
                        }
                });

                Button btn4 = (Button) this.findViewById(R.id.btn4);
                btn4.setText( "更新指定数据");
                btn4.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                updateItem();
                        }
                });

                Button btn5 = (Button) this.findViewById(R.id.btn5);
                btn5.setText( "显示全部数据");
                btn5.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                showItems();
                        }
                });

                Button btn6 = (Button) this.findViewById(R.id.btn6);
                btn6.setText( "删除表");
                btn6.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                dropTable();
                        }
                });
        }

         // 创建数据表
         private void CreateTable() {
                SQLiteDatabase db = dbHelper.getWritableDatabase();
                String sql = "CREATE TABLE IF NOT EXISTS " + TABLE_NAME
                                + " (ID INTEGER PRIMARY KEY, Name VARCHAR, Age INTEGER);";
                 try {
                        db.execSQL(sql);
                        txtMsg.append( "数据表成功创建\n");
                } catch (SQLException ex) {
                        txtMsg.append( "数据表创建错误\n" + ex.toString() + "\n");
                }
        }

         // 插入数据
         private void insertItem() {
                SQLiteDatabase db = dbHelper.getWritableDatabase();
                
                 try {
                        Random random = new Random();
                         for ( int i = 0; i < 3; i++) {
                                String sql = "insert into " + TABLE_NAME
                                                + " (name, age) values ('name" + String.valueOf(i)
                                                + "', " + random.nextInt() + ")";
                                 // execSQL() - 执行指定的 sql
                                db.execSQL(sql);
                        }
                        txtMsg.append( "成功插入 3 条数据\n");
                } catch (SQLException ex) {
                        txtMsg.append( "插入数据失败\n" + ex.toString() + "\n");
                }
        }

         // 删除数据
         private void deleteItem() {
                 try {
                        SQLiteDatabase db = dbHelper.getWritableDatabase();
                        db.delete(TABLE_NAME, " id < 999999", null);
                        txtMsg.append( "成功删除数据\n");
                } catch (SQLException e) {
                        txtMsg.append( "删除数据失败\n");
                }
        }

         // 更新数据
         private void updateItem() {
                SQLiteDatabase db = dbHelper.getWritableDatabase();

                 try {
                        ContentValues values = new ContentValues();
                        values.put( "name", "批量更新后的名字");

                        db.update(TABLE_NAME, values, "id<?", new String[] { "3" });
                        txtMsg.append( "成功更新数据\n");
                } catch (SQLException e) {
                        txtMsg.append( "更新数据失败\n");
                }
        }

         // 查询数据
         private void showItems() {
                SQLiteDatabase db = dbHelper.getReadableDatabase();

                 try {
                        String[] column = { "id", "name", "age" };
                        Cursor cursor = db.query(TABLE_NAME, column, null, null, null,
                                         null, null);
                        Integer num = cursor.getCount();
                        txtMsg.append( "共 " + Integer.toString(num) + " 条记录\n");
                        cursor.moveToFirst();

                         while (cursor.getPosition() != cursor.getCount()) {
                                txtMsg.append(Integer.toString(cursor.getPosition()) + ","
                                                + String.valueOf(cursor.getString(0)) + ","
                                                + cursor.getString(1) + ","
                                                + String.valueOf(cursor.getString(2)) + "\n");
                                cursor.moveToNext();
                        }
                } catch (SQLException ex) {
                        txtMsg.append( "读取数据失败\n" + ex.toString() + "\n");
                }
        }

         // 删除数据表
         private void dropTable() {
                SQLiteDatabase db = dbHelper.getWritableDatabase();
                String sql = "DROP TABLE IF EXISTS " + TABLE_NAME;
                 try {
                        db.execSQL(sql);
                        txtMsg.append( "数据表删除成功\n");
                } catch (SQLException ex) {
                        txtMsg.append( "数据表删除错误\n" + ex.toString() + "\n");
                }
        }
}
 
 
2、ContentProvider 的 Demo
MyUser.java
package com.webabcd.contentprovider;

import android.net.Uri;
import android.provider.BaseColumns;

// 自定义 ContentProvider 所需的实体类
public class MyUser {

         // 必须要有 _id 字段。本例中 BaseColumn 类中已经包含了 _id 字段
         public static final class User implements BaseColumns {
                
                 // 定义 CONTENT_URI
                 public static final Uri CONTENT_URI = Uri.parse( "content://com.webabcd.MyContentProvider");

                // 表数据列
                public static final String USER_NAME = "USER_NAME";
        }
}
 
MyContentProvider.java
package com.webabcd.contentprovider;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

import org.apache.http.util.EncodingUtils;

import android.content.ContentProvider;
import android.content.ContentUris;
import android.content.ContentValues;
import android.database.Cursor;
import android.database.MatrixCursor;
import android.net.Uri;

// 继承 ContentProvider 以实现自定义的 ContentProvider（基于文件的信息存储）
public class MyContentProvider extends ContentProvider {

         private File file;
         private FileOutputStream out;
         private FileInputStream in;

         // ContentProvider 的删除数据接口
        @Override
         public int delete(Uri uri, String selection, String[] selectionArgs) {
                 // TODO Auto-generated method stub
                 return 0;
        }

        @Override
         public String getType(Uri uri) {
                 // TODO Auto-generated method stub
                 return null;
        }

         // ContentProvider 的插入数据接口    
        @Override
         public Uri insert(Uri uri, ContentValues values) {

                 try {
                        out = new FileOutputStream(file);
                        out.write(values.getAsString(MyUser.User.USER_NAME).getBytes());
                        out.close();

                         int rowId = 0;
                        Uri rowUri = ContentUris.appendId(
                                        MyUser.User.CONTENT_URI.buildUpon(), rowId).build();
                        getContext().getContentResolver().notifyChange(rowUri, null);

                         return rowUri;
                } catch (Exception e) {
                         return null;
                }
        }

         // 创建用于保存信息的文件
        @Override
         public boolean onCreate() {
                 try {
                         // 每个包中应用程序的私有目录为：/data/data/包名/
                         // SD 卡目录为：/sdcard
                        file = new File( "/data/data/com.webabcd.contentprovider/",
                                         "demo.txt");
                         if (!file.exists())
                                file.createNewFile();

                         return true;
                } catch (Exception ex) {
                         return false;
                }
        }

         // ContentProvider 的查询数据接口
        @Override
         public Cursor query(Uri uri, String[] projection, String selection,
                        String[] selectionArgs, String sortOrder) {
                
                String content;

                 try {
                        in = new FileInputStream(file);
                         int length = ( int) file.length();
                         byte[] buffer = new byte[length];
                        in.read(buffer, 0, length);
                        content = EncodingUtils.getString(buffer, "UTF-8");
                        in.close();

                        String[] columns = new String[] { MyUser.User._ID, MyUser.User.USER_NAME };
                        MatrixCursor cur = new MatrixCursor(columns);
                        String[] values = new String[] { "0", content };
                        cur.moveToFirst();
                        cur.addRow(values);

                         return cur;
                } catch (Exception e) {
                         return null;
                }
        }

         // ContentProvider 的更新数据接口
        @Override
         public int update(Uri uri, ContentValues values, String selection,
                        String[] selectionArgs) {
                 // TODO Auto-generated method stub
                 return 0;
        }
}
 
Main.java
package com.webabcd.contentprovider;

import java.util.Random;

import android.app.Activity;
import android.content.ContentUris;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.Contacts;
import android.provider.Contacts.People;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

/*
* 几个常用的系统内置的 ContentProvider 如下：    
* content://media/internal/p_w_picpaths    这个URI将返回设备上存储的所有图片
* content://contacts/people/ 这个URI将返回设备上的所有联系人信息
* content://contacts/people/45 这个URI返回单个结果（联系人信息中ID为45的联系人记录）
*/
public class Main extends Activity {
         /** Called when the activity is first created. */
        @Override
         public void onCreate(Bundle savedInstanceState) {
                 super.onCreate(savedInstanceState);
                setContentView(R.layout.main);

                Button btn1 = (Button) this.findViewById(R.id.btn1);
                btn1.setText( "新增联系人记录");
                btn1.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                Random random = new Random();
                                insertRecords( "name" + String.valueOf(random.nextInt()), String
                                                .valueOf(random.nextInt()));
                        }
                });

                Button btn2 = (Button) this.findViewById(R.id.btn2);
                btn2.setText( "查看联系人记录");
                btn2.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                displayRecords();
                        }
                });

                Button btn3 = (Button) this.findViewById(R.id.btn3);
                btn3.setText( "清除联系人记录");
                btn3.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                deleteRecords();
                        }
                });

                Button btn4 = (Button) this.findViewById(R.id.btn4);
                btn4.setText( "更新联系人记录");
                btn4.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                 // 此处只是演示，id 来自 People._ID ，可参见 displayRecords() 是如何获取 id 的
                                 int id = 0;
                                updateRecord(id, "修改后的name");
                        }
                });

                Button btn5 = (Button) this.findViewById(R.id.btn5);
                btn5.setText( "新增记录到 MyContentProvider");
                btn5.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                insertRecord2MyContentProvider( "webabcd");
                        }
                });

                Button btn6 = (Button) this.findViewById(R.id.btn6);
                btn6.setText( "获取记录从 MyContentProvider");
                btn6.setOnClickListener( new Button.OnClickListener() {
                         public void onClick(View v) {
                                displayRecord2MyContentProvider();
                        }
                });
        }

         // 调用 ContentProvider 的插入接口
         private void insertRecords(String name, String phoneNum) {
                ContentValues values = new ContentValues();
                values.put(People.NAME, name);
                Uri uri = getContentResolver().insert(People.CONTENT_URI, values);
                Log.d( "MyDebug", uri.toString());
                Uri numberUri = Uri.withAppendedPath(uri,
                                People.Phones.CONTENT_DIRECTORY);
                Log.d( "MyDebug", numberUri.toString());

                values.clear();
                values.put(Contacts.Phones.TYPE, People.Phones.TYPE_MOBILE);
                values.put(People.NUMBER, phoneNum);
                getContentResolver().insert(numberUri, values);
        }

         // 调用 ContentProvider 的查询接口
         private void displayRecords() {
                String[] columns = new String[] { People._ID, People.NAME,
                                People.NUMBER };
                Uri contacts = People.CONTENT_URI;
                Log.d( "MyDebug", contacts.toString());
                Cursor cur = managedQuery(contacts, columns, // 要返回的数据字段
                                 null, // WHERE子句
                                 null, // WHERE 子句的参数
                                 null // Order-by子句
                );

                 if (cur.moveToFirst()) {
                        String id = null;
                        String name = null;
                        String phoneNo = null;
                         while (cur.getPosition() != cur.getCount()) {
                                id = cur.getString(cur.getColumnIndex(People._ID));
                                name = cur.getString(cur.getColumnIndex(People.NAME));
                                phoneNo = cur.getString(cur.getColumnIndex(People.NUMBER));

                                Toast.makeText( this, id + " / " + name + " / " + phoneNo,
                                                Toast.LENGTH_SHORT).show();
                                cur.moveToNext();
                        }
                }
        }

         // 调用 ContentProvider 的删除接口
         private void deleteRecords() {
                Uri uri = People.CONTENT_URI;
                Log.d( "MyDebug", uri.toString());
                getContentResolver().delete(uri, null, null);
                 // getContentResolver().delete(uri, "NAME=" + "'name'", null);
        }

         // 调用 ContentProvider 的更新接口
         private void updateRecord( int recordNo, String name) {
                Uri uri = ContentUris.withAppendedId(People.CONTENT_URI, recordNo);
                Log.d( "MyDebug", uri.toString());
                ContentValues values = new ContentValues();
                values.put(People.NAME, name);
                getContentResolver().update(uri, values, null, null);
        }

        
         // 调用自定义 ContentProvider 的插入接口
         private void insertRecord2MyContentProvider(String name) {
                ContentValues values = new ContentValues();
                values.put(MyUser.User.USER_NAME, name);
                getContentResolver().insert(MyUser.User.CONTENT_URI, values);

        }

         // 调用自定义 ContentProvider 的查询接口
         private void displayRecord2MyContentProvider() {
                String[] columns = new String[] { MyUser.User.USER_NAME };
                Uri uri = MyUser.User.CONTENT_URI;
                Cursor cur = managedQuery(uri, columns, null, null, null);

                 while (cur.getPosition() != cur.getCount()) {
                        String id = cur.getString(cur.getColumnIndex(People._ID));
                        String name = cur.getString(cur.getColumnIndex(MyUser.User.USER_NAME));
                        Toast.makeText( this,
                                        id + " / " + name,
                                        Toast.LENGTH_SHORT).show();
                        cur.moveToNext();
                }
        }
}
 
AndroidManifest.xml
<? xml version ="1.0" encoding ="utf-8" ?>
< manifest xmlns:android ="http://schemas.android.com/apk/res/android"
             package ="com.webabcd.contentprovider"
             android:versionCode ="1"
             android:versionName ="1.0" >
         < application android:icon ="@drawable/icon" android:label ="@string/app_name" >
                 < activity android:name =".Main"
                                     android:label ="@string/app_name" >
                         < intent-filter >
                                 < action android:name ="android.intent.action.MAIN" />
                                 < category android:name ="android.intent.category.LAUNCHER" />
                         </ intent-filter >
                 </ activity >
                
                <!--
                        配置一个自定义的 ContentProvider"
                -->
                 < provider android:name ="MyContentProvider" android:authorities ="com.webabcd.MyContentProvider" />
         </ application >
         < uses-permission android:name ="android.permission.WRITE_CONTACTS" > </ uses-permission >
         < uses-permission android:name ="android.permission.READ_CONTACTS" > </ uses-permission >
         < uses-sdk android:minSdkVersion ="3" />
</ manifest >