Android中ContentProvider和ContentResolver详解

android中contentprovider和contentresolver详解

在android中，我们的应用有的时候需要对外提供数据接口，可以有如下几种方法：

1）aidl 2）broadcast 3）contentprovider。

使用aidl需要我们编写aidl接口以及实现，而且对方也要有相应的接口描述，有点麻烦；使用broadcast，我们不需要任何接口描述，只要协议文档就可以了，但是有点不好就是，这种方式不直接而且是异步的；使用contentprovider我们不需要接口描述，只需要知道协议，同时这种方式是同步的，使用方便。

下面是contentprovider实现：

package com.backgroundservice;

import android.content.contentprovider;
import android.content.contentvalues;
import android.content.urimatcher;
import android.database.cursor;
import android.database.sqlite.sqlitedatabase;
import android.database.sqlite.sqlitequerybuilder;
import android.net.uri;
import android.util.log;

/**
 * todo
 * 
 * @author zengpeng
 * @version 1.0 create at : 2010-3-18 下午02:52:40
 */
public class testcontentprovider extends contentprovider {
  private sqlitedatabase mdb;
  private databasehelper mdbhelper = null;
  private static final string database_name = "rssitems.db";
  private static final string database_table_name = "rssitems";
  private static final int db_version = 1;
  private static final int all_messages = 1;
  private static final int specific_message = 2;

  // set up our url matchers to help us determine what an
  // incoming uri parameter is.
  private static final urimatcher uri_matcher;
  static {
    uri_matcher = new urimatcher(urimatcher.no_match);
    uri_matcher.adduri("test", "item", all_messages);
    uri_matcher.adduri("test", "item/#", specific_message);
  }

  // here's the public uri used to query for rss items.
  public static final uri content_uri = uri
      .parse("content://test/item");

  // here are our column name constants, used to query for field values. 

    public static final string id = "_id";
    public static final string name = "name";
    public static final string value = "value";
    public static final string default_sort_order = id + " desc";

  private static class databasehelper extends abstractdatabasehelper {

    @override
    protected string[] createdbtables() {
      // todo auto-generated method stub
      string sql = "create table " + database_table_name + "(" + id
          + " integer primary key autoincrement, " + name + " text,"
          + value + " text);";
      return new string[] { sql };
    }

    @override
    protected string[] dropdbtables() {
      // todo auto-generated method stub
      return null;
    }

    @override
    protected string getdatabasename() {
      // todo auto-generated method stub
      return database_name;
    }

    @override
    protected int getdatabaseversion() {
      // todo auto-generated method stub
      return db_version;
    }

    @override
    protected string gettag() {
      // todo auto-generated method stub
      return testcontentprovider.class.getsimplename();    }

  }

  /**
   * 
   */
  public testcontentprovider() {
    // todo auto-generated constructor stub
    
  }

  /*
   * (non-javadoc)
   * 
   * @see android.content.contentprovider#delete(android.net.uri,
   * java.lang.string, java.lang.string[])
   */
  @override
  public int delete(uri uri, string selection, string[] selectionargs) {
    // note argument checking code omitted. check your parameters!
    int rowcount = mdb.delete(database_table_name, selection, selectionargs);

    // notify any listeners and return the deleted row count.
    getcontext().getcontentresolver().notifychange(uri, null);
    return rowcount;
  }

  /*
   * (non-javadoc)
   * 
   * @see android.content.contentprovider#gettype(android.net.uri)
   */
  @override
  public string gettype(uri uri) {
    switch (uri_matcher.match(uri)) {
    case all_messages:
      return "vnd.android.cursor.dir/rssitem"; // list of items.
    case specific_message:
      return "vnd.android.cursor.item/rssitem"; // specific item.
    default:
      return null;
    }
  }

  /*
   * (non-javadoc)
   * 
   * @see android.content.contentprovider#insert(android.net.uri,
   * android.content.contentvalues)
   */
  @override
  public uri insert(uri uri, contentvalues values) {
    // note argument checking code omitted. check your parameters! check that
    // your row addition request succeeded!
    long rowid = -1;
    rowid = mdb.insert(database_table_name, name, values);
    uri newuri = uri.withappendedpath(content_uri, ""+rowid);
    log.i("testcontentprovider", "saved a record " + rowid + " " + newuri);
    // notify any listeners and return the uri of the new row.
    getcontext().getcontentresolver().notifychange(content_uri, null);
    return newuri;
  }

  /*
   * (non-javadoc)
   * 
   * @see android.content.contentprovider#oncreate()
   */
  @override
  public boolean oncreate() {
    // todo auto-generated method stub
    try
    {
      mdbhelper = new databasehelper();
      mdbhelper.open(getcontext());
      mdb = mdbhelper.getmdb();
    }catch(exception e){
      e.printstacktrace();
    }
    return true;
  }

  /*
   * (non-javadoc)
   * 
   * @see android.content.contentprovider#query(android.net.uri,
   * java.lang.string[], java.lang.string, java.lang.string[],
   * java.lang.string)
   */
  public cursor query(uri uri, string[] projection, string selection,
      string[] selectionargs, string sortorder) {
    // we won't bother checking the validity of params here, but you should!

    // sqlitequerybuilder is the helper class that creates the
    // proper sql syntax for us.
    sqlitequerybuilder qbuilder = new sqlitequerybuilder();

    // set the table we're querying.
    qbuilder.settables(database_table_name);

    // if the query ends in a specific record number, we're
    // being asked for a specific record, so set the   

    // where clause in our query.
    if((uri_matcher.match(uri)) == specific_message){
      qbuilder.appendwhere("_id=" + uri.getlastpathsegment());
      log.i("testcontentprovider", "_id=" + uri.getlastpathsegment());
    }


    // make the query.
    cursor c = qbuilder.query(mdb,
        projection,
        selection,
        selectionargs,
        null,
        null,
        sortorder);
    log.i("testcontentprovider", "get records");
    c.setnotificationuri(getcontext().getcontentresolver(), uri);
    return c;
  }

  /*
   * (non-javadoc)
   * 
   * @see android.content.contentprovider#update(android.net.uri,
   * android.content.contentvalues, java.lang.string, java.lang.string[])
   */
  @override
  public int update(uri uri, contentvalues values, string selection,
      string[] selectionargs) {
    // note argument checking code omitted. check your parameters!
    int updatecount = mdb.update(database_table_name, values, selection, selectionargs);

    // notify any listeners and return the updated row count.
    getcontext().getcontentresolver().notifychange(uri, null);
    return updatecount;
  }

}

配文件如下：  

 <provider android:name="testcontentprovider"
      android:authorities="test">
    </provider>

在客户端中可以使用如下方法进行调用：

 contentvalues values = new contentvalues();
        values.put(testcontentprovider.name, "testname1");
        values.put(testcontentprovider.value, "testvalu1e");
        uri newadduri = testactivity.this.getcontentresolver().insert(testcontentprovider.content_uri, values);
        cursor c = testactivity.this.managedquery(newadduri, new string[]{testcontentprovider.name}, null, null, null);
        log.i("testactivity", "" + c.getcount());
        if(c.movetonext())
        {
          log.i("testactivity", c.getstring(0));
        }

上面的代码是先进行插入，然后进行查询并打印。就是如此简单，所有的应用如果需要都可以对外方便的提供数据接口，同时其他应用也可以很方便的进行调用。

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