Android 内容提供者的实现

接着上文《Android 内容提供者简介》进一步实现内容提供者。

每个Content Provider类都使用URI（Universal Resource Identifier，通用资源标识符）作为独立的标识，格式如：content://com.example.app.provider/table1。其他应用程序通过不同的uri访问不同的内容提供者，并获取/操作里面的数据。

例如在本项目中对应如下URI：

content://com.wuyudong.db.personprovider/insert 添加的操作
content://com.wuyudong.db.personprovider/delete 删除的操作
content://com.wuyudong.db.personprovider/update 更新的操作
content://com.wuyudong.db.personprovider/query 查询的操作

在PersonDBProvider.java中添加代码：

package com.wuyudong.db;

import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;

public class PersonDBProvider extends ContentProvider {

    // 定义一个URI的匹配器用于匹配uri， 如果路径不满足条件 返回-1
    private static UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
    private static final int INSERT = 1;
    private static final int DELETE = 2;
    private static final int UPDATE = 3;
    private static final int QUERY = 4;
    private PersonSQLiteOpenHelper helper; 

    static {
        // 添加一组匹配规则 com.wuyudong.db.personprovider
        matcher.addURI("com.wuyudong.db.personprovider", "insert",
                INSERT);
        matcher.addURI("com.wuyudong.db.personprovider", "delete",
                DELETE);
        matcher.addURI("com.wuyudong.db.personprovider", "update",
                UPDATE);
        matcher.addURI("com.wuyudong.db.personprovider", "query", QUERY);
    }

    @Override
    public boolean onCreate() {

        helper = new PersonSQLiteOpenHelper(getContext());
        return false;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder) {
        if (matcher.match(uri) == QUERY) {
            // 返回查询的结果集
            SQLiteDatabase db = helper.getReadableDatabase();
            Cursor cursor = db.query("person", projection, selection, selectionArgs, null, null, sortOrder);
            return cursor;
        } else {
            throw new IllegalArgumentException("路径不匹配，不能执行查询操作");
        }
    }

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

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
            String[] selectionArgs) {
        // TODO Auto-generated method stub
        return 0;
    }

}

新建一个名为other的项目，布局如下：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <Button
        android:onClick="click"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="读取DB的数据" />

</RelativeLayout>

点击下图的按钮，kill掉 com.wuyudong.db进程

点击Button按钮后，com.wuyudong.db进程重新运行，而且打印数据库中person表中的数据

进一步完善其他操作，修改布局

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <Button
        android:onClick="click"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="读取DB的数据" />
     <Button
        android:onClick="delete"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="删除DB的数据" />
      <Button
        android:onClick="update"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="修改DB的数据" />
       <Button
        android:onClick="insert"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="添加DB的数据" />

</LinearLayout>

接下来实现PersonDBProvider中的其他方法

package com.wuyudong.db;

import android.content.ContentProvider;
import android.content.ContentValues;
import android.content.UriMatcher;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;

public class PersonDBProvider extends ContentProvider {

    // 定义一个URI的匹配器用于匹配uri， 如果路径不满足条件 返回-1
    private static UriMatcher matcher = new UriMatcher(UriMatcher.NO_MATCH);
    private static final int INSERT = 1;
    private static final int DELETE = 2;
    private static final int UPDATE = 3;
    private static final int QUERY = 4;
    private PersonSQLiteOpenHelper helper;

    static {
        // 添加一组匹配规则 com.wuyudong.db.personprovider
        matcher.addURI("com.wuyudong.db.personprovider", "insert", INSERT);
        matcher.addURI("com.wuyudong.db.personprovider", "delete", DELETE);
        matcher.addURI("com.wuyudong.db.personprovider", "update", UPDATE);
        matcher.addURI("com.wuyudong.db.personprovider", "query", QUERY);
    }

    @Override
    public boolean onCreate() {

        helper = new PersonSQLiteOpenHelper(getContext());
        return false;
    }

    @Override
    public Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder) {
        if (matcher.match(uri) == QUERY) {
            // 返回查询的结果集
            SQLiteDatabase db = helper.getReadableDatabase();
            Cursor cursor = db.query("person", projection, selection,
                    selectionArgs, null, null, sortOrder);
            return cursor;
        } else {
            throw new IllegalArgumentException("路径不匹配，不能执行查询操作");
        }
    }

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

    @Override
    public Uri insert(Uri uri, ContentValues values) {
        if (matcher.match(uri) == INSERT) {
            // 返回查询的结果集
            SQLiteDatabase db = helper.getWritableDatabase();
            db.insert("person", null, values);
        } else {
            throw new IllegalArgumentException("路径不匹配，不能执行插入操作");
        }
        return null;
    }

    @Override
    public int delete(Uri uri, String selection, String[] selectionArgs) {
        if (matcher.match(uri) == DELETE) {
            // 返回查询的结果集
            SQLiteDatabase db = helper.getWritableDatabase();
            db.delete("person", selection, selectionArgs);
        } else {
            throw new IllegalArgumentException("路径不匹配，不能执行删除操作");
        }
        return 0;
    }

    @Override
    public int update(Uri uri, ContentValues values, String selection,
            String[] selectionArgs) {
        if (matcher.match(uri) == UPDATE) {
            // 返回查询的结果集
            SQLiteDatabase db = helper.getWritableDatabase();
            db.update("person", values, selection, selectionArgs);
        } else {
            throw new IllegalArgumentException("路径不匹配，不能执行修改操作");
        }
        return 0;
    }

}